Second Symposium on the Geology of the Southeastern Coastal Plain : proceedings

PROCEEDINGS

SECOND SYMPOSIUM

on the GEOLOGY
of the SOUTHEASTERN COASTAL PLAIN

Edited by Daniel D. Arden, Barry F. Beck, and Eleanore Morrow
Sponsored and hosted by Earth Science Department Georgia Southwestern College
Americus, Georgia March 5-6, 1979
Published by Department of Natural Resources Environmental Protection Division
Georgia Geologic Survey
53 INFORMATION CIRCULAR

~ ,
The papers prese nted in this Information Ci rcul ar represe nt the opinions of the respective authors. No manuscripts were revie wed by the manageme nt of t he Georgia Geologic Survey for technical accuracy. The Georgia Geologic Survey does wish to stress that the petroleum potential for those strata underlying the veneer of Coastal Plai n deposits is not addressed in this volume.

PROCEEDINGS

SECOND SYMPOSIUM

on the GEOLOGY
of the SOUTHEASTERN COASTAL PLAIN

Edited by Daniel D. Arden, Barry F. Beck, and Eleanore Morrow

Atlanta 1982

Sponsored and hosted by Earth Science Department Georgia Southwestern College
Americus, Georgia March 5-6, 1979
Published by Department of Natural Resources
Joe D. Tanner, Commissioner Environmental Protection Division
J. Leonard Ledbetter, Director Georgia Geologic Survey
William H. Mclemore, State Geologist
53 INFORMATION CIRCULAR

SYMPOSIUM COMMITTEES
Daniel D. Arden, General Chairman
Technical Program : Barry F. Beck Harland E. Cofer
Publicity and Printing : Barry F. Beck Richard Little
Housing A. Richard Henderson Frank B. Jones
Local Arrangements: J. Philip Manker Walter K. Mathews James W. Russell
Smoker: A. Richard Henderson William Tietjen
Registration ; Dowe P. Ca rter Jack C. Carter 0. Jay Cliett Max T. McKinney

TABLE OF CONTENTS
Page
I. STRATIGRAPHY AND PALEONTOLOGY
Kevnote Paper Biostratigraphy, sea level fluctuations, subsidence rates, and petroleum potential of the Southeast
Georgia Embayment. C. Wylie Poag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Palynostratigraphy of the basal Cretaceous un1ts of the eastern Gulf and southern Atlantic
Coastal Plains. . Raymond A. Christopher. .. .. . . . . . . . . . . .. .. . ... . .. . . . .......... . . .. .. . ..... 10 Paleoenvironment and age of kaolin deposits in Andersonville , Georgia, district.
Harland E. Cofer, Jr. and Norman Frederiksen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
o. Late Mesozoic and Paleocene geology of the Georgia Coastal Plain. Howard R. Cramer and D. Arden . . 38
Sedimentology and paleoenvironmental analysis of the Upper Cretaceous Tuscaloosa and Eutaw Formations in western Georgia. William J. Frazier .. .. . .. . . .. .......... . .. . . . ..... . ... . . . ..... 39
Paleocene to Middle Eocene depositional cycles in eastern Alabama and western Georgia. Thomas G. Gibson ....... .... . ..... . . . . . . .. ....... . ....... ... .... . .... .. ..... ... . . . . .. . . 53
A stratigraphic framework for Cretaceous and Paleogene margins along the South Carolina and Georgia coastal sediments , G.S. Gohn, L.M. Bybe/1, R.A. Christopher, J.P. Owens, and C.C. Smith ... 64
Upper Eocene stratigraphy of eastern Georgia. Paul F. Huddlestun and John Hetrick . . .... .. . . . . . .... 7 5 Upper Jurassic Smackover petroleum geology of southwest Alabama.
Ernest A. Mancini ........ ..... . .. . ... . . . . . . . . ..... . ..... .. . .. . . ..... . . . ... . .. . .. .. ... ... 76 Structural control of Jurassic sedimentation in Alabama and Florida. James A. Miller . . . . . ............. 88 Foraminiferal biostratigraphy and paleoecology of the marls associated with the Tuscahoma Sand
(Paleocene/Eocene) of southwest Alabama. Gary E.' Oliver . . . .. .... . . .. . .... . .. .. . .. .. ..... . . . 88 Lithofacies and depositional cycles in Upper Cretaceous rocks, central Georgia to eastern Alabama .
Juergen Reinhardt .. .. . . . .. . . . . .. . .. . ... . .................... .. . . .. . . .. . ... . . .. .. .. .... . 89 Micropaleontology ~f the Twiggs Clay, Georgia Coastal Plain .
Walter Schmidt and S. W. Wise, Jr. ................... . . . ... . ...... . ..... . . . ...... . ... . . . . .. 97 Sedimentological tools for identifying depositional environments . William F. Tanner ............. . . .. .114 Environmental implications of palygorskite (attapulgite) in Miocene of the southeastern United States,
Charles E. Weaver and Kevin C. Beck . .. . . . ...... ... ... . ... .... . .... . ...... . ... ... ... . . .. . .118 Depositional environments in the Jurassic Norphlet Formation in south.
Alabama. Richard P. Wilkerson ... ..... .... . ... . ... . ... . . .. ..... . . .. . . . ... ... . .. . ..........126
(continued)
iii

Page
II. HYDROLOGY AND ENVIRONMENTAL GEOLOGY
Keynote Paper Ground water from the Coastal Plain for the future. Philip E. LaMoreaux .... . .... . .. . ...... .. ... ... 132 Hydrochemical processes in Coastal Plain aquifers. William Back, Mary Jo Baedecker, and
Warren Wood ....................... ; ... ... . ..... ..... ........... .... ...... .. . ..... . . . 136 Environmental geologic mapping in Florida. Ernest W. Bishop and Walter Schmidt . . ........ . . ...... . 137 Development and implementation of water resource investigations utilizing surface resistivity geophysi-
cal techniques in the Suwannee River Water Management District, Florida. David W. Fisk ......... 138 Hazardous waste disposal in the southeastern United States-an imminent problem .
Richard C. Fountain and Arthur W. Hayes .................................. .. . . . ..... . .... 139 The geohydrology of the Gulf Trough-a preliminary investigation. CarolS. Gelbaum and
Ju)ian Howell ..... .. .. . .... ..... ... ....... .. ........ .. . . .. . ............ .... ...... .. . . . 140 Geological evaluation of potential pipeline corridor sites along the Georgia coast. Vernon J. Henry, .. Robert T. Giles, and James L. Harding .. . . ... . ....... . ...... . .. . ........... . ... . . .... ..... 154 Relict fresh ground water of the U .S. Atlantic contintental shelf: and unevaluated buffer in
present-day saltwater encroachment. Francis A. Kohout .................................... I 70 Altitude of the Floridian aquifer in Northwest Florida. Tom Kwader ... ............... . ..... .. .. .... 177 Long-term hydrologic stability of Gulf Coast salt domes and mines.
Joseph D. Martinez and Madhurendu B. Kumar ............. .. . .... . .... . ........ . ......... . 177 The stratigraphy of the Florida-Hatteras shelf and slope and its relationship to the offshore extension
of the principal artesian aquifEH. Charles K. Paull and William P. Dillon ............. .. .. ... . .... 178 Geologic hazards and constraints to petroleum exploration and development on the southeastern U.S.
Continental Shelf, slope, and Blake plateau . Peter Popenoe .................................. 182 Geological investigations for dredging operations, FBM Submarine Support Base, Kings Bay, Georgia .
Earl R. Titcomb . ..................................................................... 182 Aquifer potential of the shallow sediments of the coastal area of Georgia, Thomas W. Watson . ......... 183
Ill. STRUCTURE, TECTONICS, AND GEOPHYSICS
Pre-Cretaceous rocks beneath the Georgia Coastal Plain. Timothy M. Chowns .... .. ..... ........... 196 Drainage patterns, buried volcanic necks, and plate tectonics in the south Georgia Coastal Plain.
James E. Clark, Jr. ......................................................... . ........... 196 Heat flow and the geothermal resource potential in the eastern United States. John K. Costain ........ 196 Summary of development of the continental margin off Georgia based on multichannel and single-
channel seismic-reflection profiling and stratigraphic well data. William P. Dillon and Charles Paull .197 Geochemistry of pre-Cretaceous rocks beneath the Coastal Plain of Georgia and South Carolina.
David Gottfried and Michael W. Higgins ................................................... 201 Joints and minor faults in the Georgia Coastal Plain . Michael W. Higgins and
Sam M. Pickering, Jr. .................................. ..... ................ . ........... 201 Seismicity in Georgia. Leland Timothy Long ................................................... 202 Hydrochemistry of formation fluids in onshore and offshore strata in the Southeast Georgia Embayment:
Frank T. Manheim and Charles K. Paul/ ... .. ......... ..... ..... . .... .. . ....... .. .. ........ 211 The effects of Cretaceous and younger faulting on Coastal Plain rocks around Augusta, Georgia.
David C. Prowell ... ... .... .. . ...... . . . .................. . . . ... . ....... . ....... ......... 219
iv

INTRODUCTION
Five years ago, the Earth Science Department at Georgia Southwestern College sponsored a "Symposium on the Petroleum Geology of the Georgia Coastal Plain." The symposium was well attended and the proceedings volume , which was published by the Georgia Geological Survey as Bulletin 87, was so well received that it quickly sold out and has been out-of-print for several years.
Enco uraged by th at success and spurred by the initiation of offshore drillin g In ttle Southeast Georgia Embayment, we decided that 1979 was a g o o d tl me. tp re vi ew o ur kn o wl edge of A tlantic and Gulf Coastal Plain geology. Recent exp loratory dri lling and seis mic prospecting have provided much new data wit h 'w hich to in terp ret t he comp licated picture of subsurface coastal plain stratigraphy and basement structure.
The increasing population and industrial expansion of the Atlantic and Gulf Coastal Plains, however, have als o p laced ne w st ra in s o n the geoh ydrologic system and created a multiplicity o f prob lems in env ironme ntal g eo logy which were only anticipated five year s ago. Thu s, the 1979 sym posiurn was not confined to petroleum geology, but was expa nded by the add iti on of a larg e, well-attended session on environmental geology and hydrology.
Geologic investigations in the Southeast are continuing at a high level of activity , and new Info rmat ion is constantly developing which indicates that our past con ce pts of t he stratigraphy and structure of this region may have been greatly o versimplifi ed . We predict that the next symposium will have even greater sc op e th an t he 1979 session.
Daniel D. Arden, Barry F. Beck , and Eleanore Morrow -
The Editors

I. STRATIGRAPHY AND PALEONTOLOGY
2

Keynote Paper
BIOSTRATIGRAPHY, SEA LEVEL FLUCTUATIONS, SUBSIDENCE RATES, AND PETROLEUM POTENTIAL OF THE SOUTHEAST GEORGIA EMBAYMENT
C. Wylie Poag U.S. Geological Survey Woods Hole, Massachusetts

ABSTRACT
The foraminiferal record in the COST GE-1 well, Southeast Georgia Embayment, permits the recognition of discrete biozones, paleoenvironments, and depositional hiatuses, and thereby provides a basis for estimating the magnitude of sea-level fluctuations, sediment accumulation rates, and subsidence rates of the Georgia-Florida continental shelf. The age of sedimentary rocks in the GE-1 well ranges from Early Cretaceous (Valanginian?) to Pleistocene, and a variety of paleoenvironments are represented (e .g., terrestrial, continental shelf, upper continental slope). Eight major hiatuses represent intervals of erosion and nondeposition and are correlative with low stands of global sea level. Conversely, the deepest water paleoenvironments correspond to high stands of global sea level. Generally, the rates of sediment accumulation fluctuated in unison with changing paleoenvironments. For example, accumulation was most rapid (5 .0 to 6.4 cm / 1000 yrs) in terrestrial or shallow marine biotopes that developed during the Early Cretaceous, the middle and late Eocene , and the middle Miocene. Accumulation rates were slowest (1.3 to 2.5 cm/1000 yrs) in deep marine environments during the Late Cretaceous, early Oligocene and Pleistocene. Two complementary methods of calculating subsidence rates at the GE-1 well site indicate the significant effect of sediment loading. Periods of most rapid subsidence correspond to periods of rapid sediment accumulation, whereas periods of uplift of the shelf correspond to episodes of erosion or nondeposition. Subsidence was greatest during the Cretaceous and early Tertiary, and uplift has been dominant since the middle Oligocene. A poor potential for significant petroleum production in the Southeast Georgia Embayment is attributed to the low geothermal gradient coupled with the shallow burial of potential source beds that resulted from the numerous intervals of erosion and nondeposition during Cenozoic time.
INTRODUCTION
The first deep stratigraphic test well (COST G E-1) in the Southeast Georgia Embayment was drilled by the Ocean Production Co. between February 22 and May 31, 1977. The well site (fig, 1) is located approximately 74 nautical miles east of Jacksonville, Fla., at lat. 30 37'08" N and long . 80 17'59" W near the edge of the continental shelf (water depth,41.5 m;

total depth of well,3966 m). Two preliminary reports concerning the structure, stratigraphy, petrography, organic chemistry and petroleum potential of the GE-1 well have been published by the U.S. Geological Survey (Amato and Bebout, 1978; Scholle , 1979) . The purpose of this report is to review the stratigraphic sequence penetrated by the GE-1 well, to present paleoenvironmental interpretations, to relate these results to global sea-level cycles and to basin subsidence, and to comment briefly on the petroleum potential of the Southeast Georgia Embayment.
GEOLOGIC SETTING
The COST GE-1 well was drilled on the western side of a narrow basement ridge that separates the Triassic rocks of the Southeast Georgia Embayment from Triassic and Jurassic rocks in the Blake Plateau Basin (Dillon and others, 1979, and this volume ; my figs. 1, 2). However, the Cretaceous and Cenozoic rocks penetrated by the GE-1 well are structurally continuous with their equivalents in the Blake Plateau Basin. Seismic profiles show that the 3279 m of Cretaceous and Cenozoic rocks penetrated by the G E-1 well are part of a flat-lying, structureless sequence of evenly bedded rocks that crosses the basement ridge without perturbation and thins gradually landward and basinward from the GE-1 well (Dillon and others, 1979, and this volume; my fig. 2) . The basement ridge was penetrated a total of 687 m and consists of metamorphosed sedimentary and igneous rocks interbedded with volcanic rocks. Radiometric dating of this metamorphic basement yielded an average date of 355 3 m.y . (Late Devonian; Simonis, 1979) .
The COST GE-1 well, located in the east central part of the Southeast Georgia Embayment, is the only offshore drill hole in the embayment that has penetrated pre-Cretaceous rocks. Cenozoic rocks, however, have been sampled in three additional core holes located toward the northern, western, and southern margins of the embayment (AMCOR 6002, JOIDES 1, and JOIDES 2; my fig. 2; Schlee, 1977; Poag and Hall, 1979).

3

Figure 1.
Location of drill holes and major geologic structures superimposed on bathymetric map of the Georgia-Florida continental margin.
(COST = Continental Offshore Stratigraphic
Test; AMCOR = Atlantic Margin Coring Project; J = JOIDES= Joint Oceanographic Institutions for Deep Earth Sampling) .

1------- ~25 Km - - - -- - - i

w

E

GE-l

Figure 2.
Schematic stratigraphic section based on a seismic reflection profile through the COST GE-1 well.

SOUTHEAST GEORGIA
EMBAYMENT

BLAKE

~

PLATEAU .._____)"

BASIN

-- -----

4

STRATIGRAPHY
The stratigraphic record of the COST GE-1, AMCRO 6002, JOIDES 1 and JOIDES 2 bore holes has been described on the basis of micropaleontology, lithology, and petrography (Amato and Bebout, 1978; Poag and Hall, 1979; Valentine, 1979; Rhodehamel, 1979; Halley, 1979). The sedimentary section at COST GE-1 consists of 1000 m of Cenozoic rocks resting disconformably on 700 m of Upper Cretaceous rocks, which in turn lie disconformably on 1600 m of Lower Cretaceous rocks (fig . 3). Two thirds of the Cenozoic section is Eocene in age; at least six regional hiatuses represent interruptions in the deposition of the remaining Cenozoic strata (fig. 3) and can be traced regionally in the other core holes

and by means of seismic reflection profiles (Pauli and Dillon, 1979; Poag and Hall, 1979). All of the Upper Cretaceous stages except the Cenomanian are represented in the COST GE-1 well . However, an erosional interval in the early Paleocene apparently removed the upper Maestrichtian; the lower Coniacian and upper Turonian rocks also are missing . Microfossils as old as Aptian in age have been identified in the GE-1 well (Amato and Bebout, 1978; Poag and Hall , 1979; Valentine, 1979) . 1have extrapolated sedimentation rates in order to estimate Barremian through Valanginian ages for the lowest Cretaceous rocks. These estimates agree with the seismic interpretation that Jurassic rocks are not present at this well site (Dillon and others, 1979) .

AGE

LITHOLOGY

L :I:MES'lO>IE
white, tan, dolomitic,
cherty

CU\.YS"'':M: ,

foUDS'IONE'

(f)

(CHALK? )

w0:::

gray

Iw -

~

~

SANilS'IIl'lE' LIMES"'UUE

OOI.CMITE,

z

E.Vl\PORITE

0

I-

gray

<!

0:::

Iawzw.-.

SHIUE, SI\NlJS'ICNE

red, brown, occas iona I evaporites,
COd I

LATE DEVONIAN

METASEDIMfNJ'S &
VOlCANICS

Figure 3. Generalized stratigraphic column for COST GE-1 well displaying thickness, age, lithology, and organic carbon content of sediments.
5

In general terms, the Oligocene through Pleistocene rocks are unconsolidate gray, calcareous, quartzose sands, claystones, and limestones. The underlying thick Eocene rocks are chiefly white and tan dolomitic, cherty limestone. The Paleocene lithology is similar, but includes more clay. A major lithologic change occurs across the disconformable Cenozoic-Cretaceous boundary. Upper Cretaceous rocks are dark-gray calcareous mudstones and claystones with chalky intercalations.
Albian rocks are gray sandstones, limestones and dolomites, with thin evaporite beds. Aptian and older rocks encompass arkosic sandstones, red and brown shales, and occasional evaporite beds and coal seams. The basal Cretaceous rocks are coarse conglomerates (see Rhodehamel, 1979).
PALEOENVIRONMENTS
The rocks penetrated by the COST GE-1 well were deposited in a variety of sedimentary environments (fig. 4B), ranging from terrestrial conditions during the Early Cretaceous to upper continental slope conditions(~ 500 m water depth) during the Late Cretaceous, middle Oligocene, and middle Miocene (Poag and Hall, 1979). Two major depositional cycles can be distinguished from the Cretaceous part of the paleobathymetric curve. The earliest depositional cycle was initiated with chiefly nonmarine accumulation, but during the Aptian, marine conditions developed and transgression culminated in middle shelf deposition ( rv 100 m depth) during Albian time.
After a Cenomanian regression, the second major cycle began with the return of shallow shelf conditions; gradually deepening water culminated in upper slope conditions(~ 500 m) during Campanian and earliest Maestrichtian time.
These paleobathymetric fluctuations correlate remarkably well with the cycles of global sea-level change presented by Vail and others (1977; my fig. 4A). The deep water intervals represent high stands of sea level, and the nonmarine and hiatal intervals correspond to low stands of sea level. Supercycles Ka and Kb of Vail and others (1977) are clearly defined by the paleobathymetric curve.
The cyclical pattern is not as well displayed in the Cenozoic part of the paleobathymetric curve because of the frequent interruption of the section at COST GE-1 by hiatuses. But it can be readily observed that in the Cenozoic, too, the hiatuses correspond to low sea-level stands, and the deepest water intervals (middle 0 Iigocene, middle Miocene, upper Pliocene) correspond to high sea-level stands (fig. 4A, B). Similar records of depositional cycles are present in the AMCOR 6002, JOIDES 1, and JOIDES 2 core holes (Poag and Hall, 1979) .

SEDIMENT ACCUMULATION RATES
The record of sediment accumulation rates in the COST G E-1 well reflects clearly the paleobathymetric fluctuations (presuming that accumulation rate varies inversely with distance from the sediment sources; (fig. 4C) . For example, highest rates (rv 6 .5 cm/1000 yrs) were maintained during the Early Cretaceous phase of terrestrial deposition. Lowest rates (1.3 cm/1000 yrs) , in turn, developed during the deep-water Campanian-Maestrichtian interval. However, two pulses of high sedimentation rate do not reflect the paleobathymetry. The first of these two exceptional pulses took place during the middle and late Eocene. During this time, the paleodepth increased from middle shelf (rv 100m) to outer shelf depths (rv 200m), presumably moving the shoreline farther from the GE-1 well site. However, the embayment at this time was the site of high productivity among the carbonate-secreting organisms and the thick accumulation of biogenic carbonate created a wide, rapidly prograding carbonate shelf. The second Cenozoic pulse of unusually rapid sediment accumulation took place during the middle Miocene, when upper slope paleodepths existed at COST GE-1. Apparently, major climatic changes during the Miocene, as indicated by the cool-water diatom and radiolarian assemblages (Abbott, 1979), allowed rapid erosion of the continent; a great thickness of middle Miocene terrigenous sediments, rich in biogenic silica, accumulated all along the Atlantic margin of the U.S. (Poag, 1978; Poag and Hall, 1979). The Pleistocene sedimentation rates are also somewhat anomalous, for although water depths were moderate and the shoreline was often near the well site, erosion during the glacial low stands of sea level removed most of what had accumulated during the interglacial intervals.
SUBSIDENCE OF THE BASIN
Poag and Hall (1979) have shown that subsidence of the basement beneath the Southeast Georgia Embayment can be calculated in two ways. The first calculation yields an average " uncorrected rate of subsidence" of the basement (uRs; it is "uncorrected" because the rate was not corrected for short~ ening of the sedimentary column that resulted from compaction; fig . 4D). This average curve is based on the average subsidence rate of the major series and stage boundaries from the time of original deposition to the present. The second method of calculating subsidence rates yields an incremental "uncorrected rate of subsidence" of the basement. This incremental curve is based on the subsidence rate of each major stage and series boundary from the time of original deposition to the end of the respective age or epoch and is also uncorrected for compaction (fig. 4D).

6

TIME I~ (M.Y.) <t

RELATIVE CHANGE OF

GLOBAL SEA LEVEL

- - Risl119

LO

Q5

PALEOBATHYMETRY

SEDIMENT ACCUMULATION RATE

SUBSIDENCE OR UPLIFT RATE

(em 11000 yrs)

(cm/1000 yn)

0

2

4

8 ~R~~'j ~ -1 0 I 2 3 4 5 ~~d~Q9-;

:::::::::

Tc
~

----, . I
,\ _,_________,____

r

, _____ _
I

L-

,---------

1

\

-....PRESENT SEA LEVEL , Kb
-.....1

~

,,,-_, _-__-___-__-_-_-_-_--_--_--_1_l

'-----------

Ko

~

Average u R s -

!lft:nlfMnltJI uRs

A

8

c

D

Figure 4.

A-Curve of relative change of sea level for Late Jurassic through Holocene time (after Vail and others, 1977). B-Paleobathymetric curve for COST GE-1 well based on analysis of foraminiferal assemblages and lithology. C-Sediment accumulation rate curve for COST GE-1 well. D-Average and Incremental subsidence rate curves for the COST GE-1 well.

The average curve shows that the basement of the Southeast Georgia Embayment subsided at a moderate rate of rv 2 cm / 1000 yrs from the beginning of Lower Cretaceous deposition to the middle Eocene. During the middle Eocene, the subsidence rate began to diminish (this also was approximately the time that initial outbuilding of the present continental shelf took place; see Pauli and Dillon, 1979) . Stasis was reached during the early Oligocene and, since that time, the relative motion of the basement and the shelf has been upward at a steadily increasing rate . The Pleistocene average rate upward was 2.5 cm/ 1000 yrs .
The calculated incremental values (solid part of incremental curve; fig. 4D) are consistently higher rates of basement subsidence than the values of the average curve, except for the Cretaceous-Cenozoic boundary interval (fig. 4D) . Because the sum of all the incremental rates theoretically should equal the average rate, we must infer that during the time represented by the hiatuses (when the shelf was freed of its load of water, and when erosion removed the upper rock layers) , the basement rebounded , and relative movement was upward .This rebound is indicated by the dashed lines in the incremental curve (fig. 4D). The inference that uplift accompanied shelf unloading is consistent with the work of Steckler and Watts (1978) who showed that the chief cause of basement subsidence in the Baltimore Canyon Trough (a strucural feature analogous to the Southeast Georgia Embayment) is sediment loading.
It should be pointed out that the values used for sea-level height and paleodepth used in the subsidence calculations are gross estimates derived from Vail and others (1977) and from Poag and Hall (1979). I assume that further refinement of these estimates (for example, Pitman, 1978; Watts and Steckler, 1979) will alter the magnitude of the calculated subsidence rates . But it seems clear that the rate of basement subsidence increased when sediment accumulation rates on the shelf increased (Pitman, 1978; Watts and Steckler, 1979). Conversely, the subsidence rate of the basement decreased (or changed to uplift) when shelf sedimentation decelerated or ceased, or when the shelf was eroded.
PETROLEUM POTENTIAL
Analyses of total pyrolytic hydrocarbon yield, total extractable hydrocarbon, and total organic carbon in the GE-1 well indicate that only the Upper Cretaceous rocks can be considered as potential source rocks (Miller and others, 1979). Unfortunately, though, the present geothermal gradient is low (16 .2 C/ km; Robbins, 1979) and apparently was not significantly higher at any time since the Late Cretaceous. Seismic reflection profiles indicate that

the Upper Cretaceous rocks of the Southeast Georgia Embayment have never been buried significantly deeper than their present depth (Dillon and others, 1979). As a result of these conditions, the organic carbon of the Upper Cretaceous rocks has not been sufficiently heated to produce liquid hydrocarbons .
The number and magnitude of the hiatus present in the Cenozoic section of the GE-1 well are indicative of the shallow burial of the Upper Cretaceous strata and their resulting thermal immaturity. The total time span represented by the Cenozoic hiatuses is 34 m.y., which is more than half that era. Thus, I conclude that the petroleum potential for the Southeast Georgia Embayment is minimal.
SUMMARY
The Southeast Georgia Embayment at the COST GE-1 well site contains rv1000 m of Cenozoic rocks, rv 700 m of Upper Cretaceous rocks, and rv 1600 m of Lower Cretaceous rocks that lie unconformably on metamorphosed Upper Devonian basement. The sedimentary record is incomplete, however, for eight hiatuses representing 45 m.y. of geologic time have been recognized.
Paleobathymetric cycles in the Cretaceous section correlate closely with the global sea-level cycles postulated by Vail and others (1977), suggesting direct cause and effect. The Cenozoic cycles are obscured by numerous hiatuses, but even so, it is obvious that the deepest water intervals correlate with high sea-level stands, and the hiatuses correspond to low sea-level stands. Sediment accumulation rates fluctuated in general unison with the paleobathymetric and eustatic cycles. Exceptions occur in the middle and late Eocene and middle Miocene when high biogenic carbonate production and rapid terrestrial erosion, respectively, created unusually high rates of deposition. Thus, the Southeast Georgia Embayment appears to be an excellent place to test and refine the hypothesis of global sea-level cycles. Petroleum potential of the basin is minimized by the low geothermal gradient and the shallow burial of the Upper Cretaceous rocks, which contain the only potential petroleum source beds.
REFERENCES CITED
Abbott, W.H., 1979, Analysis of diatom assemblages and stratigraphically significant silicoflagellates from the United States Geological Survey Atlantic Margin Coring Program and other Atlantic margin sites : Micropaleontology, in press.

8

Amato, R.V., and Bebout, J.W., eds., 1978, Geological and operational summary, COST No. GE-1 well, Southeast Georgia Embayment area, South Atlantic OCS: U.S. Geol. Survey Openfile Rept. 78-668, 122 p.
Dillon, W.P., Pauli, C.K., Dahl, A.G., and Patterson, W.C., 1976, Structure of the continental margin near the COST No. GE-1 drill site from a common depth-point seismic-reflection profile: U.S. Geol. Survey Circ. 800, p. 97-107.
Halley, R.B., 1979, Petrographic summary: U.S. Geol. Survey Circ. 800, p. 42-47.
Miller, R.E., Schultz, D.M., Claypool, G.E., Smith, M.A., Lerch, H.E., Ligon, D., Gary, C., and Owings, O.K., 1979, Organic geochemistry: U.S. Geol. Survey Circ. 800, p. 74-92.
Pauli, C.K., and Dillon, W.P., 1979, The subsurface geology of the Florida-Hatteras Shelf, Slope, and Inner Blake Plateau: U.S. Geol. Survey Open-file Rept. 79-448, 94 p.
Pitman, W.C., Ill, 1978, Relationship between eustasy and stratigraphic sequences of passive margins: Geol. Soc. America Bull., v. 89, p. 1389-1403.
Poag, C.W., 1978, Stratigraphy of the Atantic Continental Shelf and Slope of the United States: Ann. Rev. Earth and Planetary Sci., v. 6, p. 251-280.
Poag, C.W., and Hall, R.E ., 1979, Foraminiferal biostratigraphy, paleoecology, and sediment accumulation rates: U.S. Geol. Survey Circ. 800, p. 49-63.
Rhodehamel, E.G., 1979, Lithologic descriptions: U.S. Geol. Survey Circ. 800, p. 24-36.
Robbins, E.l., 1979, Geothermal gradients: U.S. Geol. Survey Circ. 800, p. 72-73.
Schlee, J.S., 1977, Stratigraphy and Tertiary development of the continental margin east of Florida: U.S. Geol. Survey Prof. Paper 581-F, 25 p.
Scholle, P.A ., ed ., 1979, Geological studies of the COST GE-1 well, United States South Atlantic Outer Continental Shelf Area: U.S. Geol. Survey Ci rc. 800, 114 p.
Simonis, E.K., 1979, Radiometric age determinations: U.S. Geol. Survey Circ. 800, p. 71.
Steckler, M.S., and Watts, A.B., 1978, Subsidence of the Atlantic-type continental margin off New York: Earth and Planetary Sci. Lett., v. 41, p. 1-13.
Vail, P.R., Mitchum, R.M., Jr., and Thompson, S. Ill, 1977, Global cycles of relative changes of sea level: Am. Assoc. Petroleum Geol., Mem. 26, p. 83-97.
Valentine, P.C., 1979, Calcareous nannofossil biostratigraphy and paleoenvironmental interpretation: U.S. Geol. Survey Circ. 800, p. 64-70.
Watts, A.B., and Steckler, M.S., 1979, Subsidence and eustasy of the continental margin of eastern North America: Am. Geophys. Union special Pub., in press..
9

PALYNOSTRATIGRAPHY OF THE BASAL CRETACEOUS UNITS OF THE
EASTERN GULF AND SOUTHERN ATLANTIC COASTAL PLAINS
Raymond A. Christopher U.S. Geological Survey
Reston, Virginia

ABSTRACT
Palynologic examination of samples from the Tuscaloosa Group (or Formation) of Alabama and extreme western Georgia, the subsurface Atkinson Formation of coastal South Carolina and Georgia, and the updip equivalents of Unit Fin northern North Carolina suggests that they are biostratigraphically equivalent, and all can be placed in pollen zone IV of late Cenomanian (middle Eaglefordian) Age. Likewise, the Eutaw Formation of Alabama and extreme western Georgia, the Cape Fear, Middendorf, and basal part of the Black Creek Formations of the Carolinas, some of the units mapped as Tuscaloosa in central and eastern Georgia, and the subsurface unit described as "beds of Austin age" in coastal South Carolina and Georgia are biostr~tigraphic equivalents, and can be placed in pollen zone Vol latest Coniacian and (or) Santonian (early and middle Austinian) Age Palynologic characteristics of zones IV and Vas they occur in the eastern Gulf and southern Atlantic Coastal Plains are discussed The two biostratigraphic units recognized are separated by a hiatus representing the Turonian and all but possibly the latest Coniacian (late Eaglefordian and earliest Austinian).
In the updip section, zone IV occurs in outcrop from Alabama into extreme western Georgia. From this point eastward and northward, deposits of zone IV age pinch out and are overlain by lithologic units of zone V age. Only in northernmost North Carolina do lithologies of zone IV age again o ccur in the updip section. Zone IV does occur in the subsurface of coastal Georgia and all but the northernmost part of South Carolina. Drill cuttings from the traditional Lower Cretaceous section of extreme southwestern Georgia also contain assemblages of zone IV age. The updip and subsurface studies suggest that the landward limit of zone IV occurs somewhere between the outcropping Cretaceous units and coastal South Carolina and Georgia.
INTRODUCTION
Palynologic studies of numerous samples of the outcropping basal Coastal Plain units between Alabama and North Carolina and the basal subsurface units of coastal Georgia and South Carolina permit a biostratigraphic evaluation to be made of the relationships among them (localities 1-23, fig. 1). The lithostratigraphic units examined are: the outcropping Tuscaloosa Group (or Formation) and Eutaw Formation of Alabama and extreme western Gear-

gia; the Cape Fear Formation, the Middendorf Formation, the basal part of the Black Creek Formation and other units formerly mapped as Tuscaloosa in Georgia and the Carolinas; the subsurface Atkinson Formation; Unit F of Brown and others (1972); and the "beds of Austin age" as described by Applin and Applin (1967). According to results of these examinations, the lithostratigraphic units listed here can all be included in one of two existing pollen zones established for the Cretaceous System of the middle Atlantic states. Specifically, assemblages characteristic of pollen zone IV of late Cenomanian (middle Eaglefordian) Age occur in:
1. the Tuscaloosa Group (or Formation) of Alabama and extreme western Georgia;
2. the subsurface Atkinson Formation; 3. Unit F of Brown and others (1972).
Assemblages characteristic of pollen zone V of latest Coniacian and (or) Santonian (early and middle Austinian) Age occur in:
1. the Eutaw Formation of Alabama and western Georgia;
2. the Cape Fear, Middendorf, and the basal part of the Black Creek Formations of the Carolinas;
3. much of the units formerly mapped as Tuscaloosa in Georgia and the Carolinas; and
4. "beds of Austin age."
Ages assigned to these zones suggest that the Turonian and all but possibly the uppermost part of the Coniacian (upper part of the Eaglefordian and basal part of the Austinian) are absent in the eastern Gulf and southern Atlantic Coastal Plains. The purpose of this paper is to informally describe the palynologic assemblages by which these biostratigraphic zones are recognized and to illustrate the relationships between the basal biostratigraphic and lithostratigraphic units of the Alabama, Georgia, South Carolina, and North Carolina Coastal Plains.
STRATIGRAPHIC PALYNOLOGY
Ten pollen zones have been recognized in the Cretaceous System of the middle Atlantic states (fig. 2). The Upper Cretaceous zones IV and Vestablished by Doyle (1969a) and Sirkin (1974), respec-

10

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e OUTCROP SAMPLES
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DELINEATES THE CRETACEOUS SYSTEM

Figure 1.

Outcrop pattern of the Cretaceous System of the eastern Gulf and southern Atlantic Coastal Plains Lithostratigraphic units sampled include the Tuscaloosa Group (or Formation) of Alabama and extreme western Georgia (localities 1, 2, 4), the Eutaw Formation of Alabama and extreme western Georgia (localities 3 and 4), units mapped as Tuscaloosa in central and eastern Georgia (localities 5-9), the Middendorf Formation (localities 11 and 12), the Cape Fear Formation (locality 13), the basal part of the Black Creek Formation (locality 13), Unit F of Brown and others (1972; locality 14), the Atkinson Formation (localities 15-22), "beds of Austin age" as described by Applin and Applin (1967; localities 15-22), and beds correlative with the Lower Cretaceous as described by Applin and Applin (1964, 1965; locality 23).

tively, for the Raritan and Magothy Formations of New Jersey have been modified by Doyle and Robbins (1977) and Christopher (1977a, in press) . The following two sections describe the characteristics of zones IV and V in the eastern Gulf and southern Atlantic Coastal Plains. These characterizations are based on:
1. Fourteen outcrop samples of the Tuscaloosa, Eutaw, Cape Fear, Middendorf, and Black Creek Formations of the southeastern United

States, and the "Tuscaloosa" Formation of central and eastern Georgia.
2. Thirty-four cuttings samples from wells that penetrated the Atkinson Formation and "beds of Austin age" in coastal South Carolina and Georgia (localities 18 through 22, fig . 1).
3. One hundred fifty-seven core samples from boreholes of the Tuscaloosa and Eutaw Formations and Unit F of Brown and others (1972) in Alabama, Georgia, and North Carolina .

11

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Figure 2. Palynological zonation of the Cretaceous System of the middle Atlantic states.

Palynological characteristics of zone IV in the Coastal Plain of the southeastern United States
In general, assemblages from pollen zone IV in both outcrop and subsurface samples contain an abundance of moderately to well-preserved palynomorphs, consisting of a wide variety of pteridophyte spores, gymnosperm pollen, angiosperm pollen, and in samples from Alabama, a few dinoflagellate cysts and acritarchs.
Many of these forms range into younger zones and are not considered biostratigraphically useful. The forms discussed below were not all found together in every assemblage examined from zone IV, but all have been found useful guides to the zone at more than one locality. The biostratigraphically significant palynomorphs from zone IV of the eastern Gulf and southern Atlantic Coastal Plains are:

Nevesisporites sp. (pl. 1, fig. 1). This species is characterized by a narrow cingulum, laesurae that bifurcate at their ends, and thin, closely spaced cicatricose striae on the proximal surface that are oriented obliquely to the rays of the laesurae. Nevesisporites sp. occurs with a low relative frequency in all samples in which it has been observed, but its distinctive morphology and consistent occurrence make it a potentially useful guide to zone IV.
Equisetosporites spp. and Welwitschiapites sp. (pl. 1, figs. 2-7). Although only a few specimens of Equisetosporites (pl. 1, figs . 2-5) have been observed in samples from zone V, polyplicates, represented by these two genera, are more diverse and generally more abundant in zone IV than in the overlying zones. In addition, Welwitschiapites sp. (pl. 1, figs. 6, 7), with its numerous thin ribs ornamenting its outer exinal layer, appears to be restricted to zone IV, especially in samples from the outcropping Tuscaloosa Group (or Formation).
Carolina torosus (Reissinger) Klaus 1960 emend. Cornet and Traverse 1975 (pl. 1, fig. 8). This species is consistently present in samples from zone IV. In the stratigraphically higher zones, however, Carolina is rarely found, and where present, the genus is represented by a morphotype that is one-half to three-quarters of the diameter of those from zone IV.
Fraxinoipollenites rotundus sensu Phillips &Felix 1971 (pl. 1, fig. 9), "Retitricolpites" geranioides Couper sensu Brenner 1963, (pl.1, figs. 10, 11), and Tricolpites wilsonii Kimyai 1966 (pl. 1, fig. 12). These forms are among the more commonly occurring and morphologically distinctive tricolpate and tricolporates pollen types that are restricted to zone IV.
?Ajatipol/is tetraedralis (Bolchovitina) Krutzsch 1970 (pl. 1, fig. 13). A species of small permanent tetrad with poroid apertures arranged according to "Garsides Law" appears to be restricted to zone IV and therefore serves as a guide to that zone. The species closely resembles the form described as Ajatipol/is tetraedralis (Bolchovitina) Krutzsch 1970, which has been referred to as cf. Ajatipollis tetraedralis by Doyle and Robbins (1977).
Atlantopol/is verrucosa (Groot & Groot) Goczan, Groot, Krutzsch & Pacltova 1967 (pl. 1, fig. 14) and Complexiopol/is spp. (pl. 1, figs. 15-21). The most characteristic microfloral elements of zone IV are the distinctive Normapolles forms referred to the general Complexiopollis and Atlantopol/is. Atlantopollis is represented by a single species. A verrucosa (Groot & Groot) Goczan, Groot, Krutzsch & Pacltova 1967 (pl. 1, fig. 14). This species has not

12

been recorded from zone V. Most of the species of Complexiopo/lis from zone IV are as yet undescribed, the single exception being C. funiculus Tschudy 1973 {pl. 1, fig. 16). Although the genus Complexiopollis occurs throughout zones IV and V, most species from the two units can be clearly differentiated on the combined basis of two morphologic characteristics. First, the majority of Complexiopo/lis species from zone IV exhibit some type of low sculptural elements (pl. 1, figs. 15, 18, 19); typically, this type of sculpturing is absent in species from stratigraphically higher zones (see pl. 2, figs. 23-27). Second, the exine of most species from zone IV possess a discernible columellate layer, at least in the region of the exogerminal (.pl. 1, figs. 15-21 ), if not around the entire grain. This columellate layer, if present, is not visible with light microscopy in species from zone V.
The only species of Complexiopo/'lis from zone IV that has been observed in zone Vis C. funiculus (pl. 1, fig. 16). although it is not known if the species ranges throughout the zone.
Palynological characteristics of zone V in the Coastal Plain of the southeastern United States
Pteridophyte spores and gymnosperm pollen are found infrequently or sporadically in zone V, thereby limiting their biostratigraphic utility. Angiosperm pollen is much more diverse and has a higher relative frequency in zone V than in zone IV. As a result of these two factors, I have based my palynological characterization of zone V exclusively on angiosperm pollen; more specifically, it is characterized by the occurrence of several morphologically d isti net tricol pates, tricol porates, tri porates, and Normapolles:
Nyssapo/lenites sp. (pl. 2, figs. 1, 2). The species is characterized by its tetrahedral shape, subtriangular amb, micropunctate surface, and nexine that thins abruptly at the colpi margins to produce a distinctive "border" surrounding the colpi. Doyle (1969a, fig. 5h, i) illustrated a similar form from the "Cliffwood beds" of the Magothy Formation of New Jersey, which he referred to as "Tricolporate type 5."
Porocolpopollenites spp. (pl. 2, figs . 3-6) . At least two species of Poroco/popollenites can be delineated in zone V. Both forms are characterized by their oblate shape, circular amb, brevitricolporate apertures, scabrate surface, and a weJI-developed "postvestibulum" at each aperture. P. sp. A (pl. 2,

figs. 5, 6) is the smaller of the two morphotypes, has an equatorial diameter that ranges from 20 to 30J.J.m, and an exine that is 1.5 J.J.m thick. The equatorial diameter of P. sp. B (pl. 2, figs, 3, 4) ranges from 30to 45 11m, and its thinner exine measures 1 Jlm. Porocolpopollenites sp. A and P. sp. B have previously been reported from the Eutaw Formation of western Alabama by Leopold and Pakiser (1964) as Porocolpopollenites orbiformis Thomson & Pflug 1953, and Porocolpopollenites Thomson & Pflug 1953 (some unnamed species), respectively. Doyle (1969a) and Doyle and Robbins (1977) illustrated a form similar to Porocolpopo/lenites sp. B from the South Amboy Fire Clay Member of the Raritan Formation of New Jersey.
Tricolporate type 34 (pl. 2, figs. 7, 8). A wide range of morphologic variation is displayed by the forms referred to here as Tricolporate type 34. All are oblate, and have a triangular amb and reticulate ornamentation. The equatorial diameter of most forms is relatively uniform, ranging from 18 to 23 J1m. However, the nature of the reticulum varies considerably . The lumina may be small and circular, or large with irregular or polygonal shapes; the muri may be thick or thin, low or high. At present, I do not know if it would be advantageous to treat the morphotypes as a single species or as a series of closely related species because sufficient stratigraphic work has yet to be carried out. Forms similar to Tricolporate type 34 were reported by Leopold and Pakiser (1964, pl. 8, figs. 73-77) from the Eutaw Formation of western Alabama as Pollenites kruschi (R. Potonie) "asp. pseudolaesus" (R. Potonie) Thomson & Pflug 1~53. Doyle (1969a, fig. 5j, k) also illustrated a similar form from the Magothy Formation of New Jersey, which he referred to as "Tricolporate type 6."
Cupuliferoidaepol/enites sp. (pl. 2, fig. 9). This species, with its unsculptured exine is characterized by its sexine, which is thickest in the mesocolpia and thins toward the colpi margins. Cupuliferoidaepollenites sp. is generally a rare element of the zone V microflora.
Tricolpites sp. (pl. 2, figs. 10, 11). This species, with its finely reticulate sexine, shows a nexine that is thickest in the mesocolpia, thinning toward the colpi margins. The species is common to abundant in assemblages from zone V.
Myrtacidites sp. (pl. 2, figs. 12, 13). This species lacks surface ornamentation, and characteristically shows a separation of nexine and sexine in the vicinity of the pore. Myrtacidites sp. is present in most samples from zone V, but whereas it is a common element in samples from the basal part of the zone, it is rare in samples from the upper part.

13

Tricolporate type 69 (pl. 2, figs. 14, 15). Like Myrtacidites sp., this species exhibits a distinctive exinal structure, with a relatively thick nexine separated from a thin sexine by a distinct columellate layer. In most specimens, the columellate layer is thickest near the aperture margins. Tricolporate type 69 is common in samples from the basal part of zone V. but is rare in the upper part of the zone.
Holkopol/enites spp. (pl. 2, figs. 16-22). I have recognized several morphotypes of this genus in
zone V, the most commonly occurring of which is a
large (25to 30J.Lm) form with a thick nexine in which the channeling of the nexine is more random than in typical representative of the genus (for example, the type species. Holkopollenites chemardensis Fairchild in Stover, Elsik & Fairchild, 1966). This species closely resembles the morphotype referred to by Wolfe (1976) as CP3E-1 from the Campanian-aged Merchantville, Woodbury, Englishtown, Marshalltown,, Wenonah, and Mount Laurel Formations of the middle Atlantic states. Although the forms from zone V of the southeastern Coastal Plain may eventually prove to be conspecific with those of Wolfe, the amb of the specimens from zone V appear to be more triangular than those described by Wolfe. Other, less commonly occurring forms of Holkopollenites include smaller oblate forms with a triangular amb (pl. 2, figs. 20-22). All species of Holkopollenites occur throughout zone V.
Triporate and Normapolles forms (pl . 2, figs. 2327; pi. 3, figs. 1-23). The most dramatic difference between the palynological composition of zones IV and Vis seen in the triporate and Normapolles elements of the microflora. These pollen types are more abundant and more diverse in zone V than in zone IV, with only one species occurring in both zones [Complexiopo//is funiculus Tschudy 1973 (pl. 1' fig.16)].
The genus Complexiopollis is the most commonly occurring Normapolles in zone V. and is represented by a wide variety of forms (pl. 2. figs. 23-27). Most of these species can be differentiated from those in zone IV by their reduced or lack of ornamentation, and by the absence of a discernible columellate layer. Many of these forms range into higher biostratigraphic zones; with the exception of Complexiopo//is abditus Tschudy 1973 {pi 2. fig . 24) and C. sp. D (pl. 2, fig. 25); however, none have as high a relative frequency as they do in zone V. Leopold and Pakiser (1964) illustrated several of these Complexiopollis species from the Eutaw Formation of western Alabama (their pl. 8, figs. 21-44, 47-52); Doyle (1969a) illustrated three forms from the South Amboy Fire Clay Member of the Raritan Formation and from the Magothy Formation of New Jersey (his fig. 4a, c, d); Doyle and Robbins (1977) illustrated two forms from the South Amboy Fi1e Clay of New Jersey (their pi 7, figs. 21, 23-25).

In addition to Complexiopo//is, a number of other Normapolles and triporate forms are commonly found in zone V, but are absent in zone IV. Among these are Pseudoplicapollis spp. {pl. 3, figs. 1-4), Minorpo//is spp. (pl. 3, figs. 5-7), Santalacites sp . (pi 3, fig. 8), Momipites spp. (pl. 3, figs. 9-12), and several representatives of an undescribed genus characterized by its convexly triangular amb, small, weakly developed annuli, and a narrow interloculum or "Schichtfuge" (pl. 3, figs. 13, 14). Other Normapolles that occur as very rare elements in zone V include Plicapo//is spp . (pl. 3, figs. 15, 16), Praecursipo//is plebius Tschudy 1975 (pl. 3, figs. 17, 18), Labrapollis spp. {pl. 3, figs. 19-21 ), Trudopo//is sp. (pl. 3, fig. 22), and Osculapo//is sp. (pl. 3, fig. 23).
Age of pollen zones IV and V
In all respects, the basal palynologic zone recognized in the eastern Gulf and southern Atlantic Coastal Plains fits the criteria for inclusion in pollen zone IV (fig. 2) of Doyle (1969a; Doyle and Robbins, 1977). This zone has also been referred to as the Complexiopo//is Zone by Habib (1977) and the Complex iopol lis-A tlantopo/1 is A sse m b Iage-Zone by Christopher (in press).
Pollen zone IV has been considered as old as middle Cenomanian (Wolfe and Pakiser, 1971; Christopher, 1977b), and as young as early Turonian (Doyle, 1969b; Doyle and Robbins, 1977) . However, recent unpublished palynological investigations of the Eagle Ford Group of Texas suggest that zone IV is present within its Britton Formation, and corresponds to the Eaglefordian part of the Rotalipora cushmani-greenhornensis subzone (foraminifers) of Pessagno (1969). Pessagno considered the R. cushmani-greenhornensis subzone to be late Cenomanian in age, and it follows that pollen zone IV is also late Cenomanian.
A comparison of the microfloral assemblages from zone V with those described by Leopold and Pakiser (1964) from the McShan and Eutaw Formations of western Alabama suggests a strong biostratigraphic correlation between these units. I conclude, therefore, that there is very little, if any, age difference between the McShan and Eutaw Formations at their type localities in western Alabama and zone V reported on here.
Leopold and Pakiser (1964) considered the Eutaw Formation to be pre-Senonian in age, on the basis of the absence of structurally advanced Normapolles that typify the Senonian of Europe. They suggested that the McShan and Eutaw Formations, together with the underlying Tuscaloosa Group, are of preSenonian (latest Cenomanian and Turonian) Age, and (or) of Coniacian Age.

14

In terms of its microfloral composition and relative frequencies of occurrence of the biostratigraphically significant pollen types, zone V of the eastern Gulf and southern Atlantic Coastal Plains bears some similarity to pollen subzone V-A (fig. 2) as described by Christopher (1977a, b; in press) . On the basis of the concurrent ranges of selected Normapolles genera in New Jersey and Europe, Christopher considered subzone V-A to be late Turonian in age, which would indicate a similar age for zone V described in this report. However, recent unpublished investigations of the Cretaceous System of Texas suggest that biostratigraphic equivalents of the Eutaw Formation (that is, zone V reported on here) occur in the Austin Group of Coniacian and Santonian Age, rather than in the Eagle Ford Shale of late Cenomanian and Turonian Age. On the basis of studies of calcareous nannofossils, Charles C. Smith (personal commun., 1978) supported an Aus~ tinian equivalency of the Eutaw Formation, and further suggested that the Eutaw Formation of eastern Alabama and western Georgia may be early to middle Santonian in age.
In summary, the basal or older biostratigraphic zone described in this report can be correlated with pollen xone IV of late Cenomanian (middle Eaglefordian) Age, and the upper or younger zone with subzone V-A of early to middle Santonian (early to middle Au~tinian) Age. In the eastern Gulf and southern Atlantic Coastal Plains, these zones appear to be separated by a hiatus representing the Turonian and all but possibly the uppermost part of the Coniacian (upper part of the Eaglefordian and basal part of the Austinian).
THE RELATIONSHIP OF ZONES IV AND V TO THE BASAL OUTCROPPING AND
SUBSURFACE LITHOLOGIC UNITS OF THE EASTERN GULF AND
SOUTHERN ATLANTIC COASTAL PLAINS
The updip section
Palynologic examination of a number of samples from near the fall line between Alabama and North Carolina (that is, sample localities 1-14, fig. 1) reveals the following about the relationship between pollen zones IV and V and the basal outcropping lithologic units of the area:
1. Zone IV occurs in the outcropping Tuscaloosa Group (or Formation) between Alabama (localities 1 and 2) and extreme western Georgia (locality 4), whereas the Eutaw Formation of this region can be placed in zone V (locality 3; data from Leopold and Pakiser, 1964) .

2. Throughout central and eastern Georgia (localities 5-9), outcropping units mapped as Tuscaloosa contain assemblages that can be assigned to zone V. Even in the shallow subsurface of the Savannah River area, as revealed in samples from a core drilled on the Savannah River Nuclear Power Plant (locality 10), the basal Coastal Plain deposits can be placed in zone V.
3. The Cape Fear (locality 13), the Middendorf (localities 11 and 12), and the basal part of the Black Creek Formations of the Carolinas (locality 13) all contain zone V pollen assemblages.
4. Only in northernmost North Carolina are zone IV assemblages again found in the updip section. The assemblages were found in a shallow core drilled in Halifax County, North Carolina (locality 14); they occur in a lithology that Brown and others (1972) assigned to their Unit F, which they regarded as Fredericksburgian to Washitan in age.
It is not surprising that two distinct pollen zones can be recognized in the Tuscaloosa Group (or Formation) and Eutaw Formation of Alabama and extreme western Georgia, as lithologic and other nonpalynologic paleontologic differences between the marginal or nonmarine Tuscaloosa and the marine Eutaw suggest two disconformable periods of deposition (Eargle, 1946, 1948; Monroe and others, 1946; Applin and Applin, 1947; Conant, 1967; Brett, 1967; Drennen, 1953; Stephenson, 1956; Sohl, 1964, and others). However, throughout central and eastern Georgia, the basal outcropping Coastal Plain units are nonmarine in origin, and for this reason they have been traditionally mapped as, and correlated with, the Tuscaloosa of Alabama. Recent palynologic investigations (Scrudato and Bond, 1972;Cousminer,1973, Cousminer and Terris, 1973; Tschudy and Patterson, 1975; this study) suggest that the "Tuscaloosa" of central and eastern Georgia includes lithologies that range in age from Santonian (i.e., zone V of this report) to middle Eocene. No zone IV assemblages have been reported from this unit, and biostratigraphic correlation of the "Tuscaloosa" of central and eastern Georgia and the Tuscaloosa of Alabama does not appear to be demonstrable. Rather, the oldest "Tuscaloosa" of central and eastern Georgia appears to be biostratigraphically correlative with the Eutaw Formation of Alabama.
Throughout the Carolinas, where the basal outcropping Coastal Plain units have also been mapped as Tuscaloosa (Cooke, 1936; Stephenson and others, 1942; Spangler and Peterson, 1950; Conley, 1962; and others), the names Cape Fear, Middendorf, and Black Creek Formations are now

15

commonly applied to the basal Coastal Plain units (Heron, 1960; Heron and Wheeler, 1959, 1964; Heron and others , 1968; Swift and Heron, 1969; and others). Except for the upper part of the Black Creek Formation , which has yet to be studied in detail, all these units can be assigned to zone V.
I do not mean to imply that all the lithologic units in which zone V assemblages occur are facies of one another and are not superimposed , because additional work may result in a subdivision of zone V that will allow detection of time stratigraphic differences among them. At present, however, palynologic evidence suggests that deposition of the Eutaw, Cape Fear, Middendorf, and basal part of the Black Creek Formations , and some of the units mapped as "Tuscaloosa" in central and eastern Georgia are not far removed from one another in time .
The reappearance of zone IV assemblages in northern North Carolina (locality 14, fig. 1) is somewhat anomalous. As discussed above, zone IV has not been detected elsewhere in the updip section of central gnd eastern Georgia, South Carolina, or Notth Carolina . In addition, studies in Virginia suggest that only Lower Cretaceous desposits are present in outcrop in the southern part of the State. Detailed lithostratigraphic and biostratigraphic studies of this area are apparently needed for a better understanding of how the northern North Carolina units relate to Coastal Plain deposits to the north, south, and downdip.

The downdip section
Although zone IV does not occur in the updip section of South Carolina and most of Georgia, it does occur in a number of coastal wells in these states (localities 15-22, fig. 1). (A more complete discussion of the lithostratigraphic and biostratigraphic relationships among these and other wells is presented by Gohn and others, this volume). A palynologic correlation of the Cretaceous rocks from these eight wells is presented in figure 3.
Figure 3 indicates that a thin, unfossiliferous sand occurs at the base of the sectior1. The sand pfnches out both to the north and south, leaving deposits of zone IV age resting directly on basement rocks. If any lower Cretaceous rocks occur in the coastal areas of South Carolina and Georgia, they are represented by this thin sand .
Zone IV thins from south to north and apparently pinches out in northern South Carolina (between localities 15 and 16). A second barren interval, represented by a series of oxidized sands and clays, overlies deposits of zone IV age throughout all but the southernmost part of the section . Here, the oxidized sands and clays are absent, leaving dep(9sits of zone V age resting directly on those of zone IV age. Lithologically, desposits of zone IV age and the upper barren interval correspond to both the lower and upper members of the Atkinson Formation of Applin and Applin (1967).

22

21 20

s.cJN .o.

17

16

15

POST-ZONE V UPPER CRETACEOUS

TO
-1381

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50
BOkm 0 0 40

Figure 3

Biostratigraphic cross section of the subsurface Cretaceous System of coastal South Carolina and Georgia. The section extends from basement to the Cretaceous- Tertiary boundary. Locality 15 = Calabash Well, Brunswick County, North Carolina; locality 16 =Myrtle Beach-10th Avenue Well, Horry County, South Carolina; locality 17 = Penny Royal Well, Georgetown County, South Carolina;locality 18 = U.S .G .S. Clubhouse Crossroads Core No.1 . Dorchester County, South Carolina;locality 19 = Fripp Island Well, Beaufort County, South Carolina; locality 20 = Pan American-Union Camp Paper No.1 Well, Glynn County, Georgia, locality 21 = Humble-Union Bag Camp Paper ST No. 1 Well, Glynn County, Georgia; Locality 22 = Pan American-Union Camp B-1 Well, Camden County, Georgia.

16

Deposits of zone V age are continuous and maintain a fairly uniform thickness throughout the section. Lithologically, deposits of zone V age correspond to the unit described by Applin and Applin (1967) as "beds of Austin age." In all wells examined, rocks of zone V age are overlain by Cretaceous deposits of Campanian to middle Maestrichtian Age.
SUMMARY AND CONCLUSIONS
To summarize the updip relationship between pollen zones IV and V, we note that apparently zone IV occurs in the outcropping Tuscaloosa Group (or Formation) of Alabama and extreme western Georgia. Deposits of zone IV age plnch out and are overridden by younger lithologic units of zone V age somewhere in extreme western Georgia, and zone

IV does not reappear in the updip section until it reaches the northernmost part of North Carolina. This relationship indicates that the basal outcropping Coastal Plain units of most of Georgia and the Carolinas are of Santonian or younger age and are not biostratigraphically correlative with the Cenomanian-aged Tuscaloosa of Alabama.
However, inasmuch as zone IV does occur throughout most of the coastal areas of South Carolina and Georgia, its landward limit must be somewhere between the outcropping Cretaceous units and the coastal regions of Georgia and South Carolina as depicted in figure 4. I cannot determine at this time if this line represents the depositional extent of sediments of zone IV age, or if deposits of zone IV age once extended farther inland and were eroded during the hiatus between zones IV and V (that is, the Turonian and Coniacian).

,J

_I VA
~ - liNI.l -,-;;c-c-

f' "'

r

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,. )

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EXPLANATION

N

1

~

DELINEATES CRETACEOUS

THE SYSTEM

APPROXIMATE LANDWARD
EXTENT OF POLLEN ZONE IV IN THE SUBSURFACE
OF GEORGIA AND THE CAROLINAS

Figure 4 . out c rop pattern of the Cretaceous System of the eastern Gulf and southern Atlanti c Coastal Plain showing the position of the pinch out of pollen zone IV in the subsurface of Georgia and the C arolina s.

17

The results of a palynologic examination of a well located in extreme southwestern Georgia (locality 23, fig . 1) deserve mention at this time, although the well has yet to be tied into either the updi p or coastal subsurface sections. This well, located in the Southwest Georgia Embayment, penetrated 2163 m of Coastal Plain sediments before bottoming in Paleozoic rocks. Lithologic correlation with nearby wells suggests that lithologies below 1030 m can be assigned to the Lower Cretaceous as described by Applin and Applin (1964, 1965). However, four cutting samples from depths between 1666and 1945 m contain several guide fossils to zone IV. No forms known to be restricted to the Lower Cretaceous were observed. If we assume down-hole contamination is not the reason for the occurrence of zone IV palynomorphs at these depths, the Lower Cretaceous is apparently either absent or restricted to the basal 213m of the well . If the Lower Cretaceous is absent in southwestern Georgia, as it apparently is along the coast, then it raises the question of whether most, if not all, of the subsurface units in Georgia mapped as Lower Cretaceous are in reality of zone IV (late Cenomanian) age.
REFERENCES CITED
Applin, E.R., and Applin, P.L., 1964, Logs of selected wells in the Coastal Plains of Georgia: Georgia Geol. Survey Bull. 74, 229p.
Applin, P.L., and Applin, E.R ., 1947, Regional subsurface stratigraphy, structure, and correlation of middle and early Upper Cretaceous rocks in Alabama, Georgia and north Florida: U.S. Geol. Survey Oil and Gas lnv. Prelim. Chart 26.
_ _,1965, The Comanche Series and associated rocks in the subsurface in central and south Florida: U.S. Geol. Survey Prof. Paper 447, 84 p.
__,1967, The Gulf Series in the subsurface in northern Florida and southern Georgia: U .S. Geol. Survey Prof. Paper 524-G, 34 p.
Brenner, G.J., 1963, The spores and pollen of the Potomac Group of Maryland: Maryland Dept. Mines, Water Res. Bull. 27, 215p.
Brett, C.E., 1967, Upper Cretaceous equivalents in Georgia and the Carolinas, in Jones, D. E., ed., Geology of the Coastal Plain of Alabama: A guidebook for the 80th Ann. Mtg., Geol. Soc. America, New Orleans, La., p. 18-25.
Brown, P.M., Miller, J .A., and Swain, F.M ., 1972, Structural and stratigraphic framework, and spatial distribution of permeability of the Atlantic Coastal Plain, North Carolina to New York: U .S. Geol. Survey Prof . Paper 796, 79p.
Christopher, R.A ., 1977a, The stratigraphic distribution of Normapolles and triporate pollen in zones IV, V, and VII of the Raritan and Magothy Formations (Upper Cretaceous) of New Jersery (abs.): Am. Assoc. Strat. Palynologists 10th Ann. Mtg ., Abs . with Program, p. 7-8.

__,1977b, Selected Normapolles pollen genera and the age of the Raritan and Magothy Formations (Upper Cretaceous) of northern New Jersey, in Owens, J.P ., Soh!, N.F., and Minard, J .P., eds., A field guide to Cretaceous and Lower Tertiary beds of the Raritan and Salisbury embayments, New Jersey, Delaware, and Maryland: Guidebook prepared for Ann. AAPG/SEPM Convention, Washington, D.C., June 12-16, 1977, p. 58-69.
_ _,Normipolles and triporate pollen assemb-
lages from the Raritan and Magothy Formations (Upper Cretaceous) of New Jersey: Paly-
nology, v. 3, in press .
Conant , L.C., 1967, The pre-Selma Cretaceous strata, in Jones, D.E. (ed .), Geology of the Coastal Plain of Alabama : A guidebook for 80th Ann . Mtg ., Geol. Soc . America, New Orleans, La., p. 4-11.
Conley, J.F., 1962, Geology and mineral resources of Moore County, North Carolina: North Carolina Div. Mineral Res. Bull. 76, 40 p.
Cooke, C.W., 1936, Geology of the Coastal Plain of South Carolina: U.S . Geol. Survey Bull. 867, p. 1-196.
Cornet, B., and Traverse, A ., 1975, Palynological contributions to the chronology and stratigraphy of the Hartford Basin in Connecticut and Massachusetts: Geoscience and Man, v. 11' p. 1-33.
Cousminer, H .L., 1973, Paleogene palynology of basal Coastal Plain sediments, Irwinton district, Georgia (abs.): Geol. Soc. America Abs. with Program, v. 5, no. 7, p. 584-585.
Cousminer, H.L., and Terris, L., 1973, Palynology of Paleocene clays from Georgia (abs.): Am. Assoc. Strat. Palynologists, 5th Ann . Mtg ., Abs. with Program, p. 72-73.
Doyle, J.A., 1969a, Angiosperm pollen evolution and biostratigraphy of the basal Cretaceous formations of Maryland, Delaware, and New Jersey (abs.): Geol. Soc. America, Abs. with Program, Part 7, p. 51 .
__,1969b, Cretaceous angiosperm pollen of the Atlantic Coastal Plain and its evolutionary significance: Arnold Arboretum Jour., v. 50, no. 1, p. 1-35.
Doyle, J.A., and Robbins, E.l. , 1977, Angiosperm pollen zonation of the continental Cretaceous of the Atlantic Coastal Plain and its application to deep wells in the Salisbury embayment : Palynology, v. 1, p. 43-78.
Drennen, C.W., 1953, Reclassification of outcropping Tuscaloosa Group in Alabama : Am . Assoc. Petrol. Geol. Bull., v. 37, p. 522-538.
Eargle, D.N ., 1946, Correlation of the pre-Selma Upper Cretaceous formations between Tuscaloosa County, Alabama, and Neshoba County, Mississippi: U .S. Geol. Survey Oil and Gas . lnv. Prelim . Chart 20.
__,1948, Correlation of pre-Selma Upper Cretaceous rocks in northeastern Mississippi and northwestern Alabama: U.S. Geol. Survey Oil and Gas lnv. Prelim. Chart 35.

18

Goczan, F., Groot, J.J . Krutzsch, W., and Pacltova, B., 1967, Die Gattungen des "Stemma Normapolles Pfl. 1953b" (Angiospermae) . Neubeschreibungen und Revision europaischen Formen (Oberkreid bis Eozan): Palaontol. Abhandl., v. 2, no. 3, p. 427-633.
Gohn, G.S., Bybell, L.M ., Christopher, R.A., Owens, J .P., and Smith, C.C., this volume, A stratigraphic framework for Cretaceous and Paleogene sediments along the South Carolina and Georgia coastal margins.
Habib, D., 1977, Compqrison of Lower and Middle Cretaceous palynostratigraphic zonations in the western North Atlantic, in Swain, F.M., ed ., Stratigraphic micropaleontology of Atlantic basin and borderlands : Elsevier Scientific Publ. Co., Amsterdam, The Netherlands, p. 341-367.
Heron , S.D. , Jr ., 1960, Clay minerals of the outcropping basal Cretaceous beds between the Cape Fear River, North -Carolina , and Lynches River, South Carolina, in Clays and Clay Minerals, 7th Nat'l. Conf .: New York, Pergamon Press, p. 148-161.
Heron, S.D., and Wheeler, W.H., 1959, Guidebook for Coastal Plain field trip featuring basal Cretaceous sediments of the Fayetteville area, North Carolina : Geol. Soc . America, Southeastern Section, 1959, 20p .
_ _ ,1964, The Cretaceous formations along the Cape Fear River. North Carolina: Atlantic Coastal Plain Geol. Assoc., 5th ann . field excursion, 53p .
Heron, S.D., Swift, D.J.P., and Dill, C.E., Jr., 1968, Graded rhythmic bedding in the Cape Fear Formation, Carolina Coastal Plain : Sedimentology, v. 11, p. 39-52.
Kimyai, A. , 1966, New plant microfossils from the Raritan formation (Cretaceous) in New Jersey: Micropaleontology, v. 12, no. 4, p. 461-476.
Klaus, W., 1960, Sporen der karnischen Stufe der ostalpinen Trias : Jahrb. Geol. Bundesanstalt (Wien) Sonderbd ., v. 5, p. 107-183.
Krutzsch, W., 1970, Zur Kenntnis fossiler disperser Tetraden-pollen: Palaontol. Abhandl., v. 38, p. 399-433.
Leopold, E.B ., and Pakiser, H . M ., 1964, A preliminary report on the pollen and spores of the pre-Selma Upper Cretaceous strata of western Alabama: U.S. Geol. Survey Bull. 1160-E, p. 71-95.
Monroe , H.W., Conant, L.C., and Eargle, D.N ., 1946, Pre-Selma Upper Cretaceous stratigraphy of western Alabama : Am . Assoc . Petrol. Geol. Bull., v. 30, p. 187-212.
Pessago, E.A., Jr., 1969, Upper Cretaceous stratigraphy of the western Gulf Coast area, Mexico , Tex as and Arkans as: Geol . Soc. America Mem . 111 , 139 p.
Phillips , P.P., and Felix . C.J ., 1971 , A study of Lower and Middle Cretaceous spores and pollen from

the southeastern United States. II. Pollen: Pollen et Spores, v. 13, no. 3, p. 439-473 .
Scrudato , R.J ., and Bond, T.A., 1972, CretaceousTertiary boundary of east-central Georgia and west-central South Carolina: Southeastern Geology, v. 14, no. 4, p. 233-239.
Sirkin, L.A., 1974, Palynology and stratigraphy of Cretaceous strata in Long Island, New York, and Block Island, Rhode Island: U.S. Geol. Survey Jour. Res., v. 2, no. 4, p. 431-440.
Sohl, N.F., 1964, Pre-Selma larger invertebrae fossils from well core samples in western Alabama: U.S. Geol. Survey Bull. 1160-C, p. 5564 .
Spangler, W.B., and Peterson, . J .J., 1950, Geology of Atlantic Coastal Plain in New Jersey, Delaware, Maryland and Virginia: Am. Assoc. Petrol. Geol. Bull., v. 34, no. 1, p. 1-99.
Stephenson, L.W., 1956, Fossils from the Eutaw formation, Chattahoochee River region , Alabama-Georgia: U.S. Geol. Survey Prof. Paper 274-J, p. 227-250.
Stephenson, L.W., King, P.B., Monroe, W.H., and Imlay, R.W., 1942, Correlations of the outcropping Cretaceous Formations of the Atlantic and Gulf Coastal Plain and Trans-Pecos, Texas: Geol. Soc. America 1 Bull., v. 53, no. 3, p. 435-448.
Stover, L.E., Elsik, W.C., and Fairchild, W.W., 1966, New genera and species of early Tertiary palynomorphs from the Gulf Coast: Univ. Kansas, P'aleontol. Contributions , Paper 5, p. 1-10.
Swift, D.J.P., and Heron, S.D., Jr., 1969, Stratigraphy of the Carolina Cretaceous: South-
eastern Geology, v. 10, p. 201-245. Thomson, P.W. , and Pflug, H.D., 1953, Pollen und
Sporen des Mitteleuropaischen Tertiars: Palaeontographica, Abt. B, v. 94, p. 1-138. Tschudy, R.H., 1973, Complexiopollis pollen lineage in Mississippi embayment rocks : U.S. Geol. Survey Prof. Paper 743-C, o. C1-C15.
_ _ , 1975, Normapolies -pollen from the MISSISsippi embayment: U.S. Geol. Survey Prof. Paper 865, 42 p.
Tschudy, R.H., and Patterson, S.H., 1975, Palynologic evidence for Late Cretaceous, Paleocene, and early and middle Eocene ages for strata in the kaolin belt, central Georgia: U.S. Geol. Survey Jour. Res., v. 3, no. 4, p. 437-445.
Wolfe, J.A., 1976, Stratigraphic distribution of some pollen types from the Campanian and lower Maestrichtian rocks (Upper Cretaceous) of the middle Atlantic States: U.S. Geol. Survey Prof. paper 977, 18 p.
Wolfe, J.A., and Pakiser, H.M ., 1971, Stratigraphic interpretations of some Cretaceous microfossil floras of the middle Atlantic states : U.S. Geol. Survey Prof. Paper 750-B, p. B35-B47.

19

EXPLANATION OF PLATE 1

Biostratigraphically important sporomorphs from pollen zon e IV in the eastern Gulf and southern Atlantic Coastal Plains .

Figure 1

Nevesisporit es sp.

Figures 2-5

Equisetosporites spp.

Figures 6, 7.

Welwitschiapites sp.

Figure 8.

Carolina torosus (Reissinger) Klaus 1960 emend. Cornet and Traverse 1975.

Figure 9

Fraxinoipoflenites rotundus sensu Phillips & Felix 1971 .

Figures 10. 11.

"Retitricolpites" geranioides Couper 1960 sensu Brenner 1963.

Figure 12.

Tricolpites wilsonii Kimyai 1966.

Figure13.

?Ajatipoflis tetraedralis (Bolchovit ina) Krutzsch 1970.

Figure 14.

At!antopol/is verrucosa (Groot & Groot) Goczan, Groot, Krutzsch & Pacltova 1967.

Figures 15, 17-22. Complexiopoflis spp.

Figure 16.

Complexiopoflis funiculus Tschudy 1973.

EXPLANATION OF PLATE 2

Biostratigraphically important sporomorphs from pollen zone V in the eastern Gulf and southern Atlantic Coastal Plains.

Figures 1, 2.

Nyssapoflenites sp .

Figures 12. 13.

Myrtacidites sp.

Figures 3, 4

Porocolpopo/lenites sp, B

Figures 14, 15.

Tricolporate type 69.

Figures 5, 6.

Porocolpopol/enites sp. A

Figures 16-22.

Holkopoflenites spp.

Figures 7, 8.

Tricolporate type 34.

Figures 23. 26, 27 . Complexiopoflis spp.

Figure 9

Cupuliferoidaepol/enites sp .

Figure 24.

Complexiopof!is abditus Tschudy 1973.

Figures 10. 11.

Tricolpites sp .

Figure 25

Complexiopollis sp . D.

EXPLANATION OF PLATE 3

f3iostratigraphically important sporomorphs from pollen zone V in the eastern Gulf and southern Atlantic Coastal Plains.

Figures 1-4.

Pseudoplicapoflis spp.

Figures 5-7.

Minorpol/is spp

Figure 8.

Santalacites sp

Figures 9-12. Momipites spp.

Figures 13, 14 Representatives of an undescribed genus characterized by its convexly triangular amb, small weakly developed anuli, and narrow interloculum or "Schichtfuge."

Figures 15, 16 Plicapol/is spp .

Figures 17, 18 Praecursipollis plebius Tschudy 1975.

Figures 19-21 Labrapoflis spp .

Figure 22

Trudopoflis spp.

Figure 23.

Osculapo!lis sp .

20

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8

3 2
,
4

PLATE 1
5

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16

17

19

20

18

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21

21

PLATE 2


10

11

13

14

15

16

17

18

19

20

21

24

25

23 ----20um

22

PLATE 3

2

5

7

9

10

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..
15

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19

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23



17

18



PALEOENVIRONMENT AND AGE OF KAOLIN DEPOSITS IN THE ANDERSONVILLE DISTRICT, GEORGIA
Harland E. Cofer, Jr. Georgia Southwestern College
Americus, Georgia and
Norman Frederiksen U.S. Geological Survey
Reston, Virginia

ABSTRACT
The kaolin deposits of the Andersonville district of Georgia are thick and relatively pure; they grade laterally and vertically into sandy kaolin and sand. The sedimentological and mineralogical character of the clay and the enclosing sand suggests deposition in a marine shallowwater to estuarine environment. Palynomorph and invertebrate fossil assemblages from strata adjacent to the kaolin beds support the suggested depositional environment of the kaolin and the subsequent subaerial formation of bauxite. Movement on the Andersonville and related faults probably influenced basinal topography and served to maintain a restricted circulation in the basin . Sporomorph biostratigraphy limits the accumulation of kaolin and the formation of the bauxite deposts to early Wilcox (late Paleocene) time.
INTRODUCTION
The objective of this paper is to summarize the sedimentological, mineralogical, structural, and paleontological evidence observed in the sediments

of the Andersonville district and to fit this evidence into a paleoenvironmental framework. The ultimate objective is to explain the sequence of events leading to the formation of the kaolin-bauxite deposits within the time frame provided by palynological data. The authors make no attempt to cite the voluminous literature pertaining to the origin of kaolin deposits of the region or of the Andersonville area. Concepts and ideas contained within this literature have been freely used .
LOCATION AND GEOLOGIC SETTING
The Andersonville, Ga ., kaolin-bau xite district is about 40 km south of the Fall Line which separates the largely unconsolidated sediments of Mesozoic and Cenozoic age from the older crystalline rocks of the Piedmont. The district marks the westernmost extent in Georgia of commercial kaolin deposits that occupy the narrow outcrop belt of Upper Cretaceous and lower Tertiary rocks trending northeastward across the State (fig. 1). Bauxite is asso-

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CRlTACIOUS & lARlY HRTIARY ROCKS

---, I
\_,
Figure 1. Location of the Andersonville district and major faults of the area.
24

ciated with other deposits in the kaolin belt but is of mineable quality only in this district. At the present time. bauxite and kaolin are mined and processed for the manufacture of refractories and commercial alum near Andersonville.
GENERAL STRATIGRAPHY
The formation names used in the report are those adopted by Zapp (1965) for lithologically distinct units in the district (fig. 2). The stratigraphy was based in part on paleontologic evidence and in part on lithostratigraphic similarity of strata to beds of known age in eastern Alabama. The present authors include the thin, freshwater to brackish-water lateral equivalents of the marine Tuscahoma as part of that formation; Zapp apparently included these sediments in the Nanafalia in the central part of the district.
The Providence Sand of Late Cretaceous age is the oldest outcropping unit in the district. As exposed, it consists of about 6 m of nonmarine, coarse-grained, cross bedded arkosic sand containing clay clasts. In the subsurface, the arkosic sand grades rapidly downward into lignitic, pyritic sand and thence to marine sand.
The Providence is overlain by the Clayton Formation of the Midway group (lower Paleocene). The Clayton Formation consists of about 19 m of calcareous, gray clayey sand and sandy clay which contain thin limestone beds and abundant oyster biostromes and detrital shell lenses. Overlying the biostromal sand and clay is a variable thickness of dark greenish-gray, micaceous, glauconitic, phosphatic, silty montmorillonitic clay, which contains a planktic foraminiferal assemblage but no bottomdwelling fauna.
Unconformably overlying the Clayton is a thick section (18 m) of micaceous, kaolinitic sand that locally grades laterally and vertically through sandy kaolin into relatively pure lenticular beds of clay. These kaolin beds may in turn enclose thin lenses of bauxite and bauxite clay . In the subsurface to the west and south, the kaolinitic sand of the Nanafalia is represented by dark-gray, lignitic sand and silt containing scattered thin light-colored kaolin lenses as much as a meter thick. This unit lacks calcareous fossils but has been correlated with the Nanafalia Formation of Alabama because of its lithologic character and stratigraphic position (Zapp, 1965). The Nanafalia Formation is difficult to distinguish from the overlying Tuscahoma Formation by using sporomorphs, and some strata assigned to the Nanafalia in the Andersonville district may possibly be correlative with part of the Tuscahoma to the west. The Nanafalia represents the lowermost part of the Wilcox Group (upper Paleocene).

Conformably overlying the Nanafalia is the Tuscahoma Formation which is also in the lower part of the Wilcox. It consists of laminated sands and silts which may vary in character laterally within 100m from a fossiliferous, glauconitic, silty marine sand to a lignitic, pyritic, silty kaolinitic clay. The formation ranges in thickness from 0 to 10m.
Crossbedded deltaic and fluvial sands, which become progressively more marine in character toward the top, unconformably overlie the Tuscahoma Formation. The uppermost sand layers are weakly cross bedded to cross laminated, are bioturbated, and locally are calcareous and contain a microfauna typical of the Claiborne Group (middle Eocene) (Grumbles, 1957). The maximum thickness of the unit is about 18m south of Sweetwater Creek.
The uppermost Tertiary unit in the district is a silty, clayey sand, which is locally cherty and is presumably derived from the weathering of calcareous sediments of Claiborne and Jackson age that crop out south and east of the area.
A veneer of Quaternary alluvium covers two broad terraces at elevations of 91 m and 103 m adjacent to the Flint River, which bounds the district on the east.
STRUCTURE
The dominant structural feature of the area is the slightly arcuate west-trending Andersonville fault (fig. 1). The fault plane is nearly vertical, and the maximum displacement of 30m has been measured on the top of the Clayton Formation. The southern (seaward) block has moved upward relative to the northern (shoreward) block. A seismic profile along the Flint River and gravity profiles across the fault indicate that it extends to depth (Rountree and others, 1978).
The regional northeast strike and gentle (4 m/km) southeastward dip of the strata as determined on the Clayton surface are interrupted by the Andersonville fault (fig. 3). In a broad area north and south of the fault, the strike of the formation is east-west and dip varies from horizontal to about 2.5 m/ km. Farther south the dip steepens to 15 m/km. In the immediate vicinity of the fault, the dip is reversed and, in places, is as steep as 60. In the vicinity of Mountain Creek, abrupt changes exist in dip of the formations; a seismic profile, gravity data, vertical escarpments in alluvium, and conspicuous lineaments also indicate the presence of faulting .
In part, the structural relief of the Clayton surface is a result of post-Paleocene movement on the Andersonville fault; however, lithologic variation in the sediments of the Nanafalia and Tuscahoma suggests intermittent movement during early Wilcox time. We believe that the basinal topography at

25

GROilP FORMATION CH PHIC LO C

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51

11

R0 CK DESCRI PT I 0 N
r1RE.E.fliSH KAOLINITIC AND MONTMOR I LLON IT I C RICH SHALE
RED TO REDDISH BROWN CROSS-BEDDE~ QUARTZOSE SANDSTONE, CROSS-BEDDING POORLY DEVELOPED IN UPPER PORTION BECOMING WELL DEVELOPED IN MIDDLE PORTION, BIOTURBATION PRESENT IN MIDDLE AND UPPER PORTIONS.
WEAKLY TO STRONGLY LAMINATED CLAYEY SANDY SILTSTONE OCCASIONALLY BECOMING GLAUCONITIC AND FOSS ILl FEROUS, BASAL PORT I ON IS r.;RAY PYRITIC AND CARBONACEOUS COARSE GRAINED, LOCALLY CHANNELED SANDSTONE CONTAINING CLAYBALL CONGLOMERATE,
MEDIUM TO COARSE GRAINED KAOLINITIC MICACEOUS SANDSTONE ENCLOS lNG LOCAL ACCIIMULATIONS OF KAOLIN CONTAINING BAUXITIC MASSES
DARK GRAY MARINE SHALE CONTAINING Q.S.IR.EA Cl!li.t!I! U t!MiG l.dli.I/.1 OCCASIONALLY r,RADES LATERALLY TO AN ARGILLACEOUS LIMESTONE OR A GRAY ARENACEOUS SHALE CONTAINING PELECYPOD FRAGMENTS,

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Figure 2. Stratigraphic column of the Andersonville district.
26

SCALE
It I LDM [ llRS

- _EXPLANATION .... Faults
~ State Roads

~

Structural Contours

ij) THKJO Location of Samples Referred to in Text

Contour Interval 10 ft (3.05 m)

Figure 3. Structural contour map of the top of the Clayton Formation and location of samples cited in text.

the onset of deposition of the Nanafalia was similar to that of the subsurface map of the top of the Clayton (fig. 3) with the downdropped block of the Andersonville fault restored to the level of the adjacent surface.
Rountree and others ( 1978) proposed a major
fault extending west -northwest from 3 km south of
Mountain Creek on the Flint River to near Concord Community, Sumter County. The present authors believe the trend of the proposed fault is more nearly west-southwest and that it extends from this point on the Flint River to the vicinity of Plains, Ga. (figs. 1, 3).

SEDIMENTOLOGY OF ROCKS OF EARLY WILCOX AGE
Coarse, angular, micaceous sand overlies the marine clays of the Clayton Formation. Clasts of montmorillonitic clay derived from the Clayton commonly are present in the lower few centimeters of the sand overlying this formation. Where the lowermost part of the Nanafalia is clayey and plastic , clasts appear as ovoid or irregular patches of dark-colored montmorillonitic clay embedded in sandy kaolinitic clay. In a few localities, a dark-gray , lignitic, clayey sand overlies the Clayton and grades upward into kaolin.

27

A slightly modified computer-generated isopach map of nearly pure kaolin (< 15 percent sand and silt) indicates a gross northwest trend in clay-body distribution (fig . 4) The trend becomes more nearly east-west in the vicinity of the Andersonville fault. Thick kaolin accumulations are present where the slope of the Clayton surface is relatively flat and become thinner over steeper slopes (fig. 3) . At clay depocenters, kaolin and sandy kaolin occupy almost the entire section. Scattered incursions of sand and silt into the clay and the spreading of clay into sand depositional areas result in a lateral interfingering of clay and sand, accentuating the lenticular shape of the deposits. In the south and southwest part of the district, suspended clay appears to have moved down the steep basinal slope and to have become intercalated with the sands. Deposition of clays as gravity slides or turbidity currents probably producecfthe non bedded and poorly sorted character of the sandy clay lenses associated with the more marine facies of the Nanafalia in this part of the studv area.

Kaolin varies from massively bedded, uniformly colored, gray-white clay composed of nearly pure kaolinite to finely or coarsely laminated clay in which the bedding is marked by concentrations of silt-size and fine sand-size mica and quartz. The bedding may be accentuated by deposition of iron oxides, sulfides, or carbonates by percolating ground water.
Locally, carbonized and mineralized plant remains in the form of rootlike structures, twig-size fragments, and grass-bladelike impressions several centimeters long and a few millimeters across are present in otherwise pure kaolin (fig. 5A). Commonly associated with these plant remains are clay casts or molds that have been termed by others as bryozoan casts or filled burrows (Buie, 1978). These reach several centimeters in length and may be branching, curved, straight, or anastomosing (fig. 58) . The plant remains and casts both are present at multiple horizons and are widely distributed in the district. Casts, particularly the branching and anas-

---Andersonville Fault ~ State Roads ~ Streams
Isopac Interval 10 ft ( 3. 05 m)

SCALE
~-~S=====I MI LES
1- .J IILOM[T15

Figure 4. Modified computer generated isopach map of kaolin containing 15 percent or less coarse clastics .
28

B
Figure 5A. Carbonized root structures in otherwise massive kaolin . Figure 58 . Branching of clay-filled burrows in massive kaolin . Figure 5C. Contact between kaolin and fresh-water swamp deposits in mine face. Figure 50. Mud cracks in kaolin infilled with overlying marine-to-brackish water deposits of the Tuscahoma
Formation in mine face.
29

tomosing types, are always present in clays that contain root structures; similar features are found in the absence of identifiable plant debris, however. In a few localities, a kaolin lens may contain a layer a meter or more thick that is rich in organic matter. Typically, relatively pure or slightly sandy kaolin changes within a few centimeters into a highly lignitic clay (fig. SC). This clay is typically sandy and silty and contains small rip-up clasts of white kaolin well above the base. The top part of the layer rich in organic matter is fine grained and grades into the overlying kaolin by increase of clay relative to plant debris and some interlamination in the final few centimeters . The deposits tend to be elongated, to be somewhat sinuous, to cover less than a hectare in area, and to grade laterally into intertonguing clayey sand surrounding the kaolin lens. No large wood fragments. stumps, or roots were observed in the deposits and no root or rootlike structures extend into the underlying kaolin.
In most cores and mine exposures. the top of the kaolin beds contain cracks that extend downward for a few centimeters and are infilled by material from the overlying Tuscahoma sediments. The dimensions, shape, and distribution of the filled cracks, both in cross section and plan view, resemble those of mud cracks (fig. 50). Near the top of the kaolin beds that are overlain by nonmarine Tuscahoma sediments, large, infilled, chambered burrows most probably made by insects extend 10 or more centimeters into the clay (fig. 6A).
Bauxite and bauxitic clays are typically composed of pisolitic-structured intergrowths of kaolinite and gibbsite (fig. 6B), but a few bauxite samples are nonpisolitic. The "structureless bauxite'' is a fine-grained micro-oolitic intergrowth of the two minerals. Bauxitic materials form tabular bodies a few centimeters to a few meters thick within kaolin lenses and grade into kaolin laterally and vertically. Multiple lenses of bauxite are present within a single kaolin deposit.
Bauxite and bauxitic clay "horizons" appear to parallel the dip of the Nanafalia only generally. Their elevations in adjacent kaolin lenses may or may not be equivalent. Bauxite is not present in all lenses and is generally absent in southern parts of the district, where the enclosing sands have a more marine character.
The Tuscahoma Formation conformably overlies the sand and clay of the Nanafalia. It is composed of fine- or medium-grained sand which becomes interlaminated with silt toward the upper part of the formation . In the subsurface, glauconitic, fossiliferous sands and silts reach a maximum thickness of 9 min the southern part of the district, but they thin rapidly

across the structural high south of the Andersonville fault and become nonmarine. The formation pinches out over part of the Andersonvill~ uplift and is absent in the northern and northeastern part of the district. A marine incursion of Tuscahoma on the downdropped block of the Andersonville fault indicates that the formation was deposited near sea level. The lateral transition from a glauconitic sandy silt to a black kaolinitic silt containing abundant carbonized wood fragments takes place within 100 min the Wilburn Mine north of Sweetwater Creek at location WL 1 (fig. 3). In this exposure, a channel originating in the Tuscahoma and filled by Tuscahoma sediments cuts well into the underlying Nanafalia. Sporomorph (spore and pollen) assemblages from the sediments of the transition zone (WL 1) and the channel (WL 1C) suggest different source areas for the pollen (table 1). The assemblage from the channel is more diverse than that of the adjacent sediments, suggesting that the channel drained a broad area supporting several plant communities. Furthermore, the transition-zone assemblage contains a much higher proportion of marine to brackish-water microplankton (dinoflagellates and acritarchs), whereas the channel assemblage contains a higher proportion of presumably terrigenous fungal spores (table 1). In general, the channels are most abundant in the vicinity of the Andersonville fault, and the drainage patterns of the channels are directed toward the downdropped block of the fault and are marginal to the marine sediment facies.
MINERALOGY OF ROCKS OF EARLY WILCOX AGE
The principal clay mineral of the Nanafalia Formation is kaolinite, but montmorillonite, illite, gibbsite, and chamosite are present in many kaolin deposits. The crystallinity of the kaolinite is variable. According to Hinckley's (1963) indexing method, it varies from moderately good to poor (1.4 to 0.04) . The lower parts of all kaolin lenses are somewhat less well crystallized than the top parts (fig. 6C). Kaolin having the highest crystallinity usually is present in interstices of pisolitic bauxite and in-transition (bauxitic) clay horizons (Flock, 1966). Kaolin crystallinity is also high in the upper-middle parts of lenses containing no significant gibbsite enrichment . In most deposits where the Tuscahoma is absent and Claiborne sands overlie the kaolin, the crystallinity of the upper few decimeters of kaolin is also moderatlely good. Books and stacks of kaolin are small; vermicular books are almost totally lacking except in those areas of highest crystallinity (fig. 60).
Montmorillonite content of the kaolin varies from 1 percent to 30 percent and montmorillonite is most abundant in the topmost meter of many deposits

30

Figure 6A Large chambered (insect?) burrow in kaolin infilled with brackish water deposit of Tuscahoma Formation.
Figure 6B. Photomicrograph of pisolitic and oolitic bauxite composed of about 85 percent gibbsite and 15 percent kaolin. x25
Figure 6C. SEM photograph of kaolin of low c rystallinity index with "swirl" pattern . x3000
Figure 6D . SEM photograp11 of "moderately w ell crystallized" kaolin with small kaolin book . x5000
31

TABL 1 -- SPOROMORPH ASSEMBLAGES

FJELD NO.

wu wuc AX72 FVl LS95 58B

THJ24 FNl

PALYNOLOGY NO,

Rl492D Rl531 R1702D R1702F R1532 R1702C R1492C R1702B

ELEVATION IN FEET 280

380 430

323

315 290

262.5 317-322

AsCULIIOITES ClRCYMS!RIATIIS <FAJRcH.l ELs.
AIUUII:UfiiES AFF, A. IIEJIIi:t..l WODEH, (2)

X X

AatlfiiE:i SPP,

X XX X XX X X

RAsopoLLI s pascuaocpstATA TscHUDY (2)

lluw...!. INFREQUENS STAHL,

8oMR.ACACIP!TFS NACIMJENTOENSlS (AND,) ELS,

X

Bwi1At6,HHU:S REIII;UL.6IUS KRurzscH

X

X

~ SPP, (29 ~H (2)

X X X

C65UA81HUUIU SPP,

X XX

XX X X

CuoANOPQLL&N ues nu.c rpuLys TscHUDY (1)

EfiwiM :ll1l.liiA STAHL, li.oLo (3)

X

Hr;u.~aecLLtH In AFF. ll. tl:iE&BDEH:iU FAIRCH, ltH86I81Pil8(;U:~DWtUIS PU.I:-!IEBAE GRuAs-CAv,

X X

lHI86I81 PPBPPPL LEU IIE:i PSEUQ IHSIBII,IUS M.AI i1I.J...El1B.Iu tWWIA i<RUTZSCH

X X X

~ CQAYIQIQES, WODEH.

~EJ..lW:i.FRED. (3)

X

~ tii,BQEgli:EPI.AIUS (STANL,) NICH.

X X

X

~llB.J.'-lllli.fRED, & CHRIST, (3)

X

X

X

~ TENUIPQLUS GROUP

X

t'iuppem I IS EKQANGULAIA (PFLUG) PFLUG (3)

X

f'4UDOPQLL I$ TERM I NAU s (PFLUG & THOMS , ) PFLUG

X

X

X X

~spp,

X

pucATQPP'I IS TRlAADIATA {NICH,) FRED, & CHRIST

X X

X

Paa,u;;pl..fQPQII EIHIES ~IBiiHIEHSIS FRED, .S.L (2?)
Poa,u:a:u.eoeawttJu;s sP. (BACULATE)

X X X

Puun01 AEsarauts ~ (PoT,) FRED , (2)

X

~S~U.DDeLitAfDLLU CF ~. ~tt.u~useu TscHuDv

X

~SEUPQPLICAQLLIS UJlliAIA FRED.

X

PSUQQPliCAPQLl!S WE& TSCHUDY (1)

i!IUA.a86DL.L.EUII~:i ~ Srov. <2?,3?) REIIIB~SCQI liES AUGYLQLYMIN0$11$ (AND,) fRED,
~~FRED ,

X

l(

X X

Se&BIIAUIAtU!~eal L.CUII~:. sP. (2) Sp!NAEPQLus ~(PoT.) KRuTzscH (2)

X X

I'IB6tDI eaaoeowu 1I's sPP. THQ!!SQNIPQLl!S tloWIJm (PFLUG) i<RUTZSCH :;., L.

X X

lBIAIBIPPPLL~HII~~ I.Yllli..lliU:i <P~LUG) FRED . !RI CQLP liES oUfill FRED ,

X XX X X

lAICQLIIIIi:i ~FRED. (2)

X

X X

lBI,DLfiiE~ BEII6tiU5 FRED.
IBieDBoeoll ~UIIES cF. I. ~AND,

Iaungem I 1:i fi.tiA TSCHUDY

X

X

PERCENTAGE OF :
SPORES + POLLEN DINOFLAGELLATES + ACRITARCHS
FUNGAL SPORES
PRESERVATION OF SPOROMORPHS

21

23

100

88

34 77

79

31

76

76

65

19

69

1

12

14

FAIR FAIR GOOD GOOD GOOD GOOD GOOD FAIR

UBSERVED RANGE BASES AND TOPS IN THE GULF COAST AND SOUTH CAROLINA: (1) RANGE TOP - ToP oF PoRTERS CREEK CLAY (2) RANGE BASE BASE OF NANAFAliA FORMATION (3) RANGE TOP TOP OF PALEOCENE

32

that directly underlie marine Tuscahoma sediments. It is also relatively abundant toward the bottom of kaolin lenses that have small "patches" of dark montmorillonite clay that probably originated as clasts derived from the underlying Clayton. The mineral is uniformly distributed in lenses of kaolin in the subsurface in the southern part of the district, where the sediments are more marine in character.
Illite content of the kaolin varies from 0 to 20 percent and illite is most abundant in the downdip (southern) kaolin. It is generally more abundant in the lower part of most kaolin beds. Commonly, the kaolin contains illite; ragged, partially decomposed, silt-size muscovite; and fresh, compact, sand- to silt-size books of muscovite and biotite.
Gibbsite in small quantities is present in many clay lenses, and gibbsite and kaolinite are the principal minerals of the bauxite and bauxitic clay of the district. Gibbsite may constitute almost 100 percent of some pisolites, but generally pisolites, oolites, and micro-oolites are mixtures of kaolin and gibbsite, both of which are relatively coarsely crystalline .
Chamosite (berthierine) is present in kaolin and bauxitic material in a wide particle size range. Pellets vary from 5 mm to 0.5 mm in diameter and also are present as clay-size particles. Pelletal chamosite is usually associated with siderite, which commonly fully or partially replaces it.
Goethite, hematite, siderite, pyrite, and marcasite are common secondary minerals resulting from diagenetic or postdiagenetic processes. Gibbsite and anatase should perhaps also be classified as secondary minerals because evidence suggests postdiagenetic enrichment in these minerals. The detrital heavy-mineral suite includes muscovite, ilmenite, tourmaline, staurolite, zircon, kyanite, biotite, and sillimanite, in that order of relative abundance.
The Tuscahoma Formation consists of two thin lithologic units: a lower sandy unit and an upper silty unit. In the subsurface, especially in the southern and western part of the district, illite and montmorillonite are the dominant clay minerals of both units. Kaolinite is more abundant in the upper silty unit, where it may make up 30 percent of the clay minerals. In the lower part of the sand unit, it is present as clasts and clay balls which apparently were derived from the underlying Nanafalia.
In mine exposures, kaolinite is the dominant clay mineral of both units, although illite may vary in abundance from 10 percent to 40 percent. Quartz, glauconite, and muscovite are the most abundant

minerals in sand-size particles. Glauconite (mixedlayer illite/montmorillonite) is present in both pelletal and fragmental form. Pellets appeared to be replacements of fecal matter and casts of microfauna. The heavy-mineral suite is similar to that of the Nanafalia except for variations in the relative abundance of the minerals.
PALEONTOLOGY AND PALEOENVIRONMENT
Midway Group
Biostromal and detrital accumulations of the large oyster, Ostrea crenulimarginata (Gabb), are present throughout most of the Clayton section. Dark-gray montmorillonitic clay that interfingers with the biostromal sand and silt becomes dominant in the upper part of the section. It is sparsely glauconitic, is phosphatic, and locally contains gypsum. At most localities, the upper clay contains fish teeth, a few echinoid spines, and a planktic foraminiferal assemblage but does not contain much evidence of bottom-dwelling organisms. The thin, persistent limestone in the middle part of the section contains a diversified Midway fauna, including Hercoglossa ulrichi (White) and Venericardia spp. The presence of the sporomorphs Choanopollenites discipulus and Pseudoplicapollis serena in two samples (AX72 and FV1, table 1) collected from the upper part of the clay unit indicates a Midway age.
On the basis of lithologic and faunal variations, the Clayton appears to have been deposited in a bay or estuary that alternated between open and restricted circulation. The circulation tended to become restricted and hypersaline toward the end of the depositional period. The biostromal sand and the limestone are compatible with an estuarine environment subject to tidal influence and having a low sill. The carbonaceous, montmorillonitic clay containing phosphate and gypsum suggests hypersalinity resulting from restricted circulation and low freshwater inflow. We interpret the scarcity of benthic organisms and the abundance of organic matter in the upper clay to mean that the sea floor was eutrophic during deposition of these clays; the planktic foraminifers and at least some of the dinoflagellates (samples AX72 and FV1, table 1) in the upper clays apparently were washed from the open sea over a sill into the bay or estuary.
Lower part of the Wilcox Group
The Nanafalia Formation, in contrast to the Clayton, contains no identifiable marine calcareous fossils; however, small fragments of shells are present in carbonaceous sands in the southwestern part of the district. In the areas of thick kaolin accumula-

33

tion, the Nanafalia locally contains carbonized and mineralized plant material and lignitic clay beds. Few sporomorphs occur in association with the carbonized root structures and fine debris in massive kaolin. Whether the plant remains represent relics of a paleosoil or roots and debris of marine plants or salt-tolerant plants of tidal marshes and estuarine swamps is not clear. Preservation of cell structure is poor, but the roots are composed primarily of fibrous tissue and their size and distribution suggests that they are grasses. However, according to palynological evidence, true grasses (Family Gramineae) did not exist on the Gulf Coast until late in Claiborne time (Frederiksen, in press). The sandy and silty lignitic clay layers within the kaolin at locations LS95 and 588 (fig. 3) contain palynomorph assemblages of early Wilcox age that are suggestive of a freshwater environment of deposition (table 1); this environmental interpretation is based on the presence of Ovoidites (probably either a pollen grain or a freshwater plankter, according to Krutzsch, 1961) in LS95, the high relative abundance of fungal spores in 588, and the lack of marine to brackish-water dinoflagellates and acritarchs in both these samples.
The distribution of clay bodies in relationship to the slope of the underlying Clayton surface, the large size and tabular form of the clay, and the limited interlamination of clay and sand in the kaolin depositional areas indicate a low-energy environment such as a bay or lagoon protected from even moderate tidal currents. Although small, relatively pure kaolin lenses are present at different elevations in the section, in the principal depocenters, kaolin and sandy kaolin occupy almost the entire section. Kaolin bodies peripheral to the main depocenters tend to be sinuous or irregular in outline and are thin and discontinuous. The southeastward trend of the kaolin deposits and their accumulation in areas of low basinal floor slope suggest that the clays might have been deposited by lateral subaqueous spreading from a coherent sediment-laden current derived from a stream discharging into a shallow bay or lagoon.
The mineralogy of the kaolin suggests that the environment varied from marine to freshwater to subaerial and back to marine during the depositional period. Montmorillonite is the second most abundant clay mineral of the upper part of most kaolin lenses. It is as abundant as kaolin at some horizons within kaolin lenses in the south and southwestern part of the district such as locations P34, RHJ26, and THK30 (fig. 3). Muscovite of sand, silt, and clay size is more abundant in the southern part of the district and in the lower part of lenses in the central part of the district where it may compose as much as 20 percent of the clay. Although clay-

mineral distribution and relative abundance in sediments do not provide conclusive information as to the depositional environment, they may indicate something about the provenance of the sediments. The clay-mineral composition and distribution in the Nanafalia are compatible with those observed in modern estuaries of the southeastern United States (Mead, 1972; Hathaway, 1972; Ezwald and O'Melia, 1975).
Pelitic and pelletal chamosite is present at several horizons within kaolin beds at locations WLF8, FN1, 12-29 (fig. 3). This mineral is associated with fragmental and bedded bauxite at location WLF8, sandfree kaolin at location FN 1, and sandy montmorillonitic kaolin at location 12-29. Its occurrence as an authigenic mineral indicates a marine environment of deposition of the clay in these areas (Porrenga, 1967; Rohrlich and others, 1969).
Indications in the kaolin of at least two periods of bauxite formation and the presence of interbedded kaolin and freshwater swamp debris along with multiple horizons of root zones and burrows suggest that the deposits were above sea level two or more times. Sporomorph assemblages associated with the Nanafalia swamp deposits within the kaolin (sample numbers 588 and LS95, table 1) were of low species diversity, contained mainly specimens of Arecipites spp. (produced mostly or entirely by Palmae), and had a small admixture of Sapotaceae pollen (Tetracolporopol/enites spp.); such assem blages would now be found mainly in outer coastal plain swamp forests and hammocks in the southeastern States. The mud-cracked upper surface of the Nanafalia is infilled by glauconite-bearing fossiliferous Tuscahoma sands. These marine sands, which contain small clasts and mud balls of kaolin and grade into brackish water, channeled, sandy clays and silts, suggest a marine encroachment across a dessicated mud flat.
Samples of Tuscahoma sediments collected within a meter of the contact with the Nanafalia at locations THJ24 and FN1 (fig. 3) were examined for palynomorphs. Both samples were glauconitic and contained foraminifers as well as abundant dinoflagellates and rather diverse sporomorph assemblages that are typical of some brackish-water and nearshore marine sediments.
The foregoing discussion assumes that the kaolin was deposited as clayey sediment. However, diagenetic and postdiagenetic changes probably modified the original sediment considerably. Some of the evidence for changes in the character of the clay is as follows.
1. Some fine-grained mica has been kaolinized .

34

2. Sparse but widely distributed roots, plant debris, and burrows indicate that more carbonaceous material probably was present at the time of deposition.
3. Grossly tabular shape and irregular lower surfaces of bauxite bodies suggest that the bauxite formed in place. If bauxite formed in place, then the potential exists for dramatic compositional change in previously deposited material.
4. Some quartz grains appear to have been chemically attacked in the kaolins where kaolinite crystallinity is good.
5. Secondary pyrite and marcasite appear to have originated near the top of the kaolin and penetrated d9wnward to form dark-gray swirls in clay, and coarsely crystalline pyrite replaces woody material or fills veins in bauxite.
6. Siderite fully or partially replaces chamosite pellets, occurs in small nodules of uncertain origin and is pr'esent as euhedral crystals containing sand-grain inclusions.
7. Siderite and pyrite are locally oxidized to hematite or goethite. The transportation by ground water and dep6sition of finely divided hematite in more per.meable layers has accentuated bedding caused by grain-size variation in the kaolin bodies.
Evidence against extensive alteration of original materials after deposition is as follows:
1. The heavy-mineral suite of the kaolin is the same as that of the surrounding sediments and is typical of most sediments in the region derived from a metamorphic terrain. The siltsize grains, which are commonly well-formed crystals having sharp face edges and terminations or cleavage fragments, show no evidence of chemical attack.
2. Abundant sand- and silt-size muscovite and sparse bioHte books show little evidence of alteration and are associated with ragged and partially kaolinized mica. Thus, the micas may have had different provenances.
3. The surfaces of most silt- and sand-size quartz grains in clayey sediments show little evidence of chemical attack.
4. The preservation of delicate root structures and plant debris in life position and the preservation of the interface between clay-filled burrow casts and the enclosing clay would seem to preclude any significant volume change accompanying neomineralization.
5. Some kaolin lenses in the subsurface probably have not been subjected to subaerial weathering or elevated above the water table since deposition.

6. In general, the distribution of clay minerals within the district appears to reflect the depositional environment of the enclosing sediments.
SUMMARY AND CONCLUSIONS
Sedimentological, structural, mineralogical, and paleontological evidence indicates a complex history for the formation of kaolin and bauxite deposits of the region. Palynology of samples from the district indicates that the deposits are restricted to sediments of the lower part of the Wilcox Group (upper Paleocene). A possible sequence of events is suggested below for the formation of the deposits in light of the evidence presented elsewhere in this paper.
In the area of what is now the Andersonville district, an estuarine environment prevailed during much of the Paleocene Epoch. The lower sediments of the Midway Group and their contained fauna are typical of an estuarine basin subject to moderate tidal influence and sediment supply. By middle Midway time, an off-shore barrier in the vicinity of the inferred Americus fault restricted circulation in the basin. The restricted circulation led to mildly hypersaline conditions which accompanied the deposition of the dark montmorillonitic clays of the upper part of the Clayton Formation . No sediments representing the upper part of the Midway are present, and the kaolin-bearing sediments of early Wilcox age were deposited on the irregular erosional surface formed on Midway rocks. Fresh or only slightly weathered clays of the Clayton underlie the sand and sandy kaolin of the Nanafalia. At the onset of Wilcox time, recurrent movement on the Americus fault may have resulted in sufficient uplift to deflect longshore currents and promote the formation and maintenance of a barrier island. This barrier limited tidal and longshore current influence and provided a restricted basin open to the southwest during much of early Wilcox time.
A turbid stream (or streams) containing a large suspended load of mixed clays dominated by kaolinite flowed into the bay. The increase in abundance of illite and montmorillonite in the seaward sediments and the predominance of kaolin shoreward are thought to be due to differential flocculation under saline conditions. The coarser fraction of the stream load was deposited in the channel areas. Clay was deposited primarily in the interchannel areas . The thick accumulation of clay that occupies almost the entire Nanafalia section was deposited in those areas where the slope of the basin floor (Clayton surface) is relatively flat; the clay thins where the slope steepens. Sand, which may contain thin discontinuous and sinuous clay lenses, occupies principally those parts of the basin where the slopes are relatively steep.

35

The depositional cycle was interrupted by an uplift, which exposed the newly deposited sediments in the northern and central parts of the district to weathering and erosion. Relief was slight; freshwater swamps occupied parts of the exposed areas, and brackish or saltwater marshes probably occupied the seaward areas. Thick kaolin accumulations became the positive areas as the drainage pattern formed. The most easily eroded unconsolidated sands became the stream valleys. The upper parts of the kaolin subjected to subaerial weathering were bauxitized in some areas, fine micas were kaolinized, and coarsely crystalline particles of kaolin (books and stacks) were formed elsewhere; montmorillonite was destroyed. Locally, iron and titanium were mobilized to become concentrated in the pisolitic structures associated with bauxitization. Carbonaceous materials were oxidized. The mineralogy of the clays a few meters below the weathering surface was little changed. Siderite indicative of a mildly reducing environment formed nodules, crystals, and replacements of chamosite in the lower parts of the clays.
Sea level rose and the area was submerged. Wave action probably planed off the erosional surface, removing some of the weathering products. Redistribution of debris resulted in the formation of sediments rich in organic matter interbedded with kaolin, clastic kaolin, and rare, bedded, bauxitic materials. Silica in basinal waters reacted with gibbsite in the porous bauxite and reworked deposits to form kaolinite and produce the gradational upper contact between bauxite and transitional clay. The coarse particle size and higher crystallinity of kaolinite in bauxite, bauxitic clay, and kaolin occupying this general level within the deposits suggest that these characteristics are artifacts of weathering or products of resilication of gibbsite in the porous upper part of exposed clays and bauxite. Where reworked materials were high in iron, resilication in a saline environment resulted in the formation of chamosite at this horizon. Chamosite is present in the southern and southwestern (seaward) part of the district and on the downdropped block of the Andersonville fault. The presence of chamosite on this downdropped block suggests that the Andersonville fault was active during the deposition of the Nanafalia and that marine waters covered parts of this area.
Following submergence and reworking of surficial material, the deposition of sandy and clayey sediment was resumed. The drowned stream valleys became the channels and the sites of deposition of sandy sediments. The interchannel areas were again established as sites of kaolin accumulation; however, the clays deposited 1 contained considerably higher quantities of montmorillonite and less

mical ike clay. At the close of the kaolin depositional period, movement on the Andersonville fault resulted in the exposure of the areas immediately south of the fault to weathering. Pisolitic clays and low-grade bauxite are present in a limited area whereas elsewhere, the mud-cracked surface of the kaolin was covered by brackish-water and marine Tuscahoma sediments. The formation of commercial kaolin in the district came to a close with deposition of the marine and brackish-water Tuscahoma sediments.
Throughout the depositional period, climatic conditions probably were subtropical in the source area and the depositional basin. The kaolin-bearing sands were transported and deposited as clay and coarser detrital grains that were only slightly altered after deposition except in the areas of bauxite formation. The source for the sediment may have been the weathered Piedmont terrain 40 km to the north or kaolinitic sediments of the Coastal Plain itself.
Sandy kaolins and kaolinitic sands form a significant part of the Cretaceous sediments a few kilometers north of the district. The association of fresh and strongly altered, abraded and euhedral detrital mineral grains suggests more than one provenance for the mineral suites. Perhaps the kaolin-bearing sediments of early Wilcox age represent deposits derived from erosion of nearby kaolinitic sediments and a more remote Piedmont source.
ACKNOWLEDGEMENTS
This paper is an outgrowth of an evaluation of the kaolin and bauxite resources of the Andersonville district, Georgia, conducted under a grant from the U.S. Geological Survey. Operating companies in the district provided access to mine exposures and thousands of feet of core from exploration drill holes. Special thanks are extended to the exploration department personnel of A.P. Green and American Cyanamid Co. for providing drill-hole information and for allowing the senior author to select drill sites and cored intervals in critical areas . T.G. Gibson and R.H. Tschudy, U.S Geological Survey, reviewed the first draft of this paper and offered helpful suggestions for its improvement.
BIBLIOGRAPHY
Buie, B.F., 1978, The Huber Formation of eastern central Georgia, in Short contributions, 1978: Georgia Geol. Survey Bull. 93, p. 1-7.
Ezwald, J.K., and O'Melia, C.R., 1975, Clay distributions in recent estuarine sediments: Clay and Clay Minerals, v. 23, p. 39-44.

36

Flock, W.M., 1966, Mineralogy and petrology of the Andersonville, Georgia bauxite district: University Park, Pa., Pennsylvania State Univ., unpub. Ph.D. thesis, 214 p.
Frederiksen, N.O., Sporomorphs from the Jackson Group (upper Eocene) and adjacent strata of Mississippi and western Alabama: U.S. Geol. Survey Prof. Paper 1084, in press.
Grumbles, G.R., 1957, Stratigraphy and sedimentation of the Wilcox Formation in the Andersonville bauxite district of Georgia: Atlanta, Ga., Emory Univ. unpub. M.S. thesis, 114 p.
Hathaway, John, 1972, Regional clay mineral facies in estuaries and continental margins of the United States east coast: Geol. Soc. America Mem. 133, p. 293-316.
Hinckley, D.N., 1963, Variability in "crystallinity" values among the kaolin deposits of the Coastal Plain of Georgia and South Carolina, in Bradley, W.F., ed., Clays and clay mineralsProceedings of the Eleventh National Conferencece on Clays and Clay Minerals, Ottawa, Ontario, Canada, Aug. 13-17,1962: New York, Macmillian Co., p. 229-235.
Krutzsch, Wilfried, 1961, Beitrag zur Sporenpalaeontologie der praeoberoligozaenen kontinentalen und marinen Tertiaerablagerungen Brandenburgs: Berichte der Geologischen Gesellschaft in der Deutschen Demokratischen Republik, v. 5, p. 290-343.
Mead, R.H., 1972, Transport and deposition of sediments in estuaries: Geol. Soc. America Mem. 133, p. 91-120.
Porrenga, 1967, Glauconite and chamosite as depth indicators in the marine environment: Marine Geology, v. 5, p. 495-501.
Rohrlich, Vera, Price, N.B., and Calvert, S.E., 1969, Chamosite in recent sediments of Local Etive, Scotland: Jour. Sed. Petrology, v. 39, p. 624631.
Rountree, R.G., Jones, F.B., and Arden, D.O., 1978, Evidence for faulting in Sumter County, Georgia (abs.): Georgia Sci. Jour., v. 36, p. 94.
Zapp, A. D., 1965, Bauxite deposits of the Andersonville District, Georgia: U.S. Geol. Survey Bull. 1199-G, 37 p.
37

LATE MESOZOIC AND PALEOCENE GEOLOGY
OF THE GEORGIA COASTAL PLAIN
Howard R. Cramer Emory University Atlanta, Georgia
and Daniel D. Arden, Jr. Georgia Southwestern College Americus, Georgia

ABSTRACT

Following Triassic rifting and graben-filling, an invasion of southwestern Georgia from the Gulf of Mexico region began. Possibly Upper Jurassic. and certainly Lower Cretaceous (Coman che an) sedimentary rocks, predominantly clastic. were deposited as part of the filling of the Apalachicola (or Chattahoochee) Basin . Uplift. gentle warping. and erosion followed. Upper Cretaceous (Gulfian) rocks, which include the basal Atkinson Formation and its updip equivalent, the Tuscaloosa Formation, overlapped the Comanchean rocks . Post-Cretaceous uplift, including arching in southern Georgia and northern Florid a, preceded erosion, the Cretaceous rocks in the arch be1ng much thinned at the axis .
Midwayan (early Paleocene) overlap followed, at least in southwestern Georgia, after which further uplift. including faulting which pres erved the Midwayan rocks in the downdropped block. resulted in continued erosion of the Cretaceous rocks after the removal of the thin Midwayan rocks The Apalachicola (or Chattahoochee) Embayment is not identifiable in the record of the Georgia rocks after this event
Sabinian (late Paleocene and early Eocene) overlap followed, with thick carbonate sedimentation developing in southern Georgia: post-Sabinian uplift. including faulting in southern Georgia, was followed by another period of erosion . The Sabinian rocks, thicker in southern Georgia, and res ting on Gulfian rocks, are preserved in the downdropped blocks The updip Sabinian (called Wilcox

in literature) was extensively eroded, most of the carbonate rocks having been removed.
Claibornian (late early and middle Eocene) overlap followed, including the development of an evaporite sequence in southeastern Georgia where a basin developed on shore. Post-Claiborne sea withdrawal and erosion, but with no significant tectonism, followed.
Jacksonian (late Eocene) overlap followed, a basal clastic unit being overlain by an extensive shelfcarbonate blanket (the Ocala Formation) Post-Jackson uplift and sea withdrawal, including tectonism of uncertain dimensions, followed ,
These are overlain by Oligocene shelf-carbonate rocks, which are almost everywhere very thin, and are largely late Oligocene in age. but which include middle Oligocene rocks in some down dropped faulted areas and early Oligocene rocks immediately offshore . They reflect a reasonably certain, but unclear history of epieorogeny during Oligocene time. Post-Oligocene uplift and erosion is reflected in the sporadic distribution of the Oligocene rocks and the clastic nature of the overlying Miocene rocks .
Hydrocarbons, if present, would likely be in the older, deeper rocks which have been disturbed by the arching and faulting.

38

SEDIMENTOLOGY AND PALEOENVIRONMENTAL ANALYSIS OF THE UPPER CRETACEOUS TUSCALOOSA AND EUTAW FORMATIONS IN
WESTERN GEORGIA
William J. Frazier Earth Science Department
Columbus College Columbus, Georgia

ABSTRACT
Detrital sediments of the Upper Cretaceous Tuscaloosa and Eutaw Formations are well exposed in the Chattahoochee Valley region of western Georgia. The Tuscaloosa Formation lies nonconformably on Piedmont crystallines on top of which is developed a thin, lateritic paleosoil, present now primarily on the higher portions of the erosional surface The Tuscaloosa consists of two major lithologies, a crossbedded , conglomeratic, arkosic arenite and a mottled, silty mudstone, which occur stratigraphically in a series of fining-upward sequences separated by disconformities . These disconformity-bounded units contain a vertical succession of sedimentary structures characteristic of the point-bar model of fluvial deposition . Fossils in the Tuscaloosa include lignitized wood, well-preserved leaf molds, and vermicular burrows. Based on sedimentologic, paleontologic, and stratigraphic evidence, the Tuscaloosa is interpreted as being fluvial in origin Crossbedding dip directions imply a southerly flowing paleocurrent system.
The Eutaw Formation overlies the Tuscaloosa disconformably and is composed of four lithofacies Lithofacies I is a tabular and trough cross-stratified, Ophiomorphaburrowed, fine to medium, slightly feldspathic, quartzose sand with reactivation surfaces and mottled mudstone lenses . Lithofacies II is a trough cross-stratified. Ophiomorpha-burrowed, partially iron-cemented, medium to coarse quartzose sand with polymodal crossbed dip-directions . Lithofacies Ill is a horizontally stratified to hummocky cross-stratified, fossiliferous, micaceous, well-sorted. fine to very fine quartz arenite with carbonaceous laminae. Lithofacies IV is a pervasively bioturbated. fossiliferous. micaceous, carbonaceous, silty sand and sandy mudstone. The first three lithofacies are best developed in northern parts of the outcrop belt Diagenetic structures include penecontemporaneous deformation structures. calcareous septarianconcretions, and iron-oxide concretions. Eutaw strata in Georgia are interpreted to have been deposited in a barrier-island complex formed in a transgressive regime . Erosion during barr:er retreat removed subaerial barrier facies resulting in the deposition of a transgressive shoreface and transition zone sequence (Lithofacies II, Ill. and IV) on top of back-barrier tidal channel and abandoned channel deposits (Lithofacies I)
INTRODUCTION
Creta ceous strata in Georgia are of interest because th ey provide a link betwe en the stratigraphic frameworks of the Atlantic and Gulf Coastal

Plains. Further, because they represent primarily near-shore, basin-margin facies, they are important in the development of regional depositional models. The Tuscaloosa and Eutaw Formations are the oldest outcropping Cretaceous units in southwest Georgia and are exposed in an eastward- to northeastward-trending belt in Muscogee, Chattahoochee, Talbot, and Marion Counties (fig. 1). They are composed of a variety of detrital sediments that appear to have been formed in terrestrial and paralic environments. They rest with profound nonconformity on Piedmont crystalline "basement" and are overlain disconformably by the Blufftown Formation. Both units thin dramatically toward the east where they become increasingly difficult to differentiate from each other and from the rest of the Cretaceous section. Toward the west, they thicken and pass into facies with increasing evidence of marine influence.
History of Investigation
The Eutaw Formation was named in 1860 by Hilgard from exposures near Eutaw, Ala.; it included all strata from the base of the Coastal Plain up to his Tombigbee Sand Group. In 1887, Smith and Johnson defined the Tuscaloosa Formation as the basal unit of the Coastal Plain and redefined the Eutaw to include those strata from the top of the Tuscaloosa up to the Selma Chalk, i.e.,including all of the Tombig bee as a member of the Eutaw. This usage was applied to basal Cretaceous strata in Georgia by Spencer (1890). Langdon (1891) considered sands above Eutaw mudstones in western Georgia to represent the Ripley Formation, but Stephenson (1911) believed that the lower 120ft of sand in Langdon's Ripley was actually correlative with the Tombig bee Sand Member and so included it with the Eutaw . Stephenson (1911) considered the Tuscaloosa Formation to be Lower Cretaceous, but study of plant fossils led Berry (1923) to reinterpret it as Upper Cretaceous. Stephenson and Moore (1938), working in eastern Alabama, redefined the Eutaw to exclude the upper sands, putting them in the Blufftown Formation, a term proposed by Veatch in 1909. Cooke (1943) extended this usage to Georgia. Ray ( 1947, unpublished military maps) placed all sand below Eutaw mudstones into his Tuscaloosa Formation while including in the Eutaw all sands

39

I;<JSTREAM ALLUVIUM
D BLUFFTOWN FORMATION

I 2 3 4

1

1

1

1

I 1 I 11I

234567

li1'f'-41 EUTAW FORMATION

i l I ~

TUSCALOOSA FORMATION

~PIEDMONT

Figure 1. Geologic map of northern part of Coastal Plain in western Georgia (modified slightly from Eargle, 1955) . Dots indicate outcrops studied in preparation for this report.

below Blufftown mudstones. Drennen (1950) described the Piedmont-Coastal Plain contact in eastern Alabama and western Georgia. In his excellent discussion of the Cretaceous stratigraphy of Georgia, Eargle (1955) recognized the significance of unconformities in the section and used them to erect a more logical stratigraphic nomenclature. This usage is shown in figure 2 and will be followed without modification in this report. Stephenson (1957) described fossils from the Eutaw Formation in the Chattahoochee Valley region and, more recently, Marsalis and Friddell (1975) described several outcrops of Tuscaloosa and Eutaw Formations in their guide to Upper Cretaceous and lower Tertiary units of the Chattahoochee Valley.
TUSCALOOSA FORMATION
Stratigraphy
The Tuscaloosa Formation in the Chattahoochee Valley area consists of approximately 76 m of conglomeratic sandstone and sandy mudstone. It thins

rapidly toward the east, being approximately 15m thick in the Flint River area (Eargle, 1955). It thickens downdip (132m at Chattahoochee well #1 , Marsalis and Friddell, 1975) and toward the west into Alabama.
The Tuscaloosa lies nonconformably on Piedmont crystalline rocks, primarily gneisses and amphibolites, across a sharp, erosional contact (fig. 3A). Relief on this surface ranges up to approximately 15m within 0.8 km in northwestern Muscogee County. On upper parts of this erosional surface, especially in northern parts of the outcrop belt, Tuscaloosa sediments are separated from obvious gneissic saprolite by a 2 to 3m thick layer of residual, lateritic paleosoil. This material, referred to as "Pre-Tuscaloosa" by Drennen (1950}, consists of mottled red, orange, and tan, unsorted residuum with abundant maroon to yellow pisoliths, usually concentrated in a horizon about one-half meter beneath Tuscaloosa sediments. This residuum with its irregular mottling and well-formed pisoliths closely resembles the "massive vermiform laterites" and

40

0::
w aa....
::::>
Figure 2. Composite stratigraphic column of lower part of Upper Cretaceous Series in western Georgia
"spaced pisolithic laterites" of Uganda (McFarlane, 1976, plates 1, 2, and 3). Spaced pisoliths are usually indicative of residual soils (McFarlane, 1976) . The presence of unaltered quartz veins within the paleosoil which extend down into recognizable gneissic saprolite confirms this view . Some pisoliths are present in basal Tuscaloosa sediments.

The Tuscaloosa is overlain disconformably by the Eutaw Formation. The contact is sharp, appears to have relatively little relief, and is usually easy to recognize in the Chattahoochee Valley area, where Tuscaloosa maroon and greenish-gray mudstones are characteristically overlain by course, crossbedded, Ophiomorpha-burrowed sands of the Eutaw (fig. 3B) .
The Tuscaloosa Formation in southwest Georgia is equivalent to the upper part of the Tuscaloosa Group in Alabama, specifically correlative with the unnamed upper member of the Coker Formation and the overlying Gordo Formation (Drennen, 1953). To the east, the Tuscaloosa is correlated with the lower part of the Middendorf Formation in eastern Georgia and South Carolina and with the Potomac Group in Maryland. Based on palynological studies (Christopher , this volume) the Tuscaloosa has been correlated with the Britton Formation of the Eagle Ford Group in Texas and is therefore considered to be of late Cenomanian Age.
Lithologies
The Tuscaloosa Formation in southwest Georgia is composed of two distinct lithogies : a crossbedded, conglomeratic, arkosic arenite and a mottled, silty mudstone. In most exposures, mudstone overlies arenite across a continuous, gradational contact, forming a fining-upward sequence and separated from vertically adjacent finingupward sequences by local disconformities.
Crossbedded, conglomeratic, arkosic arenite
The most common Tuscaloosa lithology in the study area is mature to submature arkosic arenite . Mean grain size ranges from coarse to fine sand and sorting is generally poor to moderate; skewness is almost always positive. Graphs of cumulative grainsize frequency distributions plotted on probability paper show the dominance of both suspended and saltated loads (see other examples in Visher, 1972) . Quartz-grain shapes range from nearly equant to elongated and usually are very angular to subangular, the degree of roundness increasing proportionally with increasing grain size. This roundness trend continues into the gravel fraction , most of which is very well rounded to subrounded. Tuscaloosa gravels are composed mainly of metaquartzite clasts whose textures suggest at least partial derivation from metaquartzite exposures in the Pine Mountain area north of Muscogee County. An excellent example of this is the presence within the Tuscaloosa of rounded pebbles of itacolumite nearly identi c al to in situ exposures on Pine Mountain; since itacolumite is a relatively rare lithology, it provides a good indicator of sediment dispersal patterns and provenance. Feldspar grains were origi-

41

Figure 3

Features of the Tuscaloosa Formation. A, Nonconformity separating Tuscaloosa pebbly sand from gneissic saprolite . B, Disconformity between Eutaw sand and underlying Tuscaloosa mudstone. C, Fining-upward sequences: note sharp, irregular, erosional contract of coarse, crossbedded sand on structureless mudstone (arrow) . D, Multistory sand body; lower arrow indicates contact with underlying mudstone; upper arrow indicates local disconformity separating very coarse sand from fine to medium sand below.

nally subangular and generally coarse, but most have undergone chemical alteration and are now primarily kaolinite. In many areas, altered feldspar grains were deformed during compaction, being squeezed around adjacent quartz grains, resulting in a kaolinitic epimatrix. Only where early cementation prevented significant compaction can the original character of the feldspars be observed. Heavy minerals comprise from 0.2 to 1.4 percent of framework grains and consist of magnetite, zircon, kyanite, garnet, andalusite, ilmenite, and tourmaline (listed in order of abundance) . Sands range from almost unconsolidated to welllithified; cement type varies, being siliceous in some samples and ferruginous in others . The kaolinite epimatrix is responsible for moderate consolidation in many samples .

Primary sedimentary structures include largescale, high-angle tabular crossbeds, large-scale, high-angle trough (festoon) crossbeds, small-scale trough crossbeds (not observed in coarse sand), and horizontal bedding . These are usually arranged vertically within a fining-upward sequence with the large-scale tabular cross beds near the bottom, overlain by trough crossbedding whose scale decreases upward, coinciding with decreasing sediment grainsize (fig. 3C). Horizontal bedding, when observed, is usually associated with large-scale tabular crossbeds near the base of a fining-upward sequence . Penecontemporaneous slump structures, large dislocated mud blocks(up to one meter in diameter and usually associated with the coarsest sediment at the base of a fining-upward sequence), and smaller,

42

rounded mud-clasts are present in many exposures. Secondary structures include rare pyrite nodules and barite concretions (Eargle, 1955).
Over 300 determinations of crossbedding dip directions have been made of Tuscaloosa arenites. Distribution of dip directions from a given exposure are generally unimodal, but dispersion about the mean is high. Vector means for the various exposures studied range from southeasterly to westsouthwesterly, but the modal direction (and, significantly, the regional vector mean) is approximately southerly.
Mottled, silty mudstone.
Upper parts of Tuscaloosa fining-upward sequences typically consist of maroon and mediumgray mottled silty mudstone. The mean grain-size varies from coarse silt to fine silt, but sorting is usually poor and skewness is positive. Quartz dominates the mineralogy of the silt fracti'on.
Sedimentary structures are generally absent and vague compositional and color mottling is the most typical characteristic of the sediment. Even in those exposures where obvious mottling is absent, few depositional structures are present and deposits are typically massive. In several exposures, there are numerous, small, vermiform burrows with faint internal lamination. Penecontemporaneous slump structures are encountered in a few exposures. Of special note are siderite spherules about one millimeter in diameter which weather to red or brown spots of iron oxide (Eargle, 1955).
Mudstones contain the only fossils to be found within the Tuscaloosa in the study area. Especially interesting are well-preserved leaf imprints found in thick mudstones beneath the Eutaw contact in Upatoi Creek Valley. Many of these were described by Berry (1923) who cited them to champion the Late Cretaceous age of the Tuscaloosa Formation. Lignitic wood fragments and well-preserved palynomorphs are also present (see Christopher, this volume).
Stratigraphic relations of lithologies.
Silty mudstones ove'rlie arkosic arenites, making a conformable stratigraphic sequence in which grain size decreases vertically and in which sedimentary structures vary from tabular and trough crossbedding in the sands of the bottom to mottling and burrowing in the muds at the top. Each finingupward sequence is separated from those above and below by sharp, irregular, erosional disconformities (fig. 3C). Such fining-upward sequences are the hallmark of the Tuscaloosa Formation in western Georgia (fig. 4).

In some exposures, two fining-upward sequences contact each other without an intervening mudstone (fig. 30). The contact is recognized by the abrupt change in grain size and the presence of mud clasts directly above the erosional surface. Such an association of sandy fining-upward sequences without mudstone is termed a multistory sand body (Friedman and Sanders, 1978). Another exception to the usual fining-upward pattern is seen in lens-shaped mudstone bodies immediately adjacent to "normal" fining-upward sequences. Characteristically, the mudstone lenses contain coarse lag gravels overlain directly by structureless, sandy mudstone.
Paleoenvironmental Interpretation
Based on the evidence summarized below, the Tuscaloosa Formation in southwest Georgia is interpreted to have formed as alluvial deposits on a newly formed coastal plain. The evidence is taken from both the sedimentologic and paleontologic characteristics of the unit and is presented in summary fashion below.
1. The fining-upward sequences themselves constitute perhaps the best evidence of fluvial deposition because they are considered to represent the vertical succession of strata formed by the progradation of point bars and associated overbank envi ron ments over thalweg deposits during stream migration. Such fining-upward, pointbar sequences have been discussed by numerous authors (for example, McGowen and Garner, 1970; Visher, 1972; Friedman and Sanders, 1978) and are believed to typify fluvial deposition in a meandering stream environment.
2. Variations in point-bar sequences are also significant. Multistory sand bodies are formed where one stream eroded deeply into deposits of a previous fluvial cycle, removing muddy top stratum deposits (and, in the process, creating mud clasts by slumping of blocks off the cut bank and into the thalweg) and allowing the prograding point bar to deposit its sands directly on sands of the previous point bar. Mudstone lenses with basal lag-gravels probably represent "clay plugs" formed by the filling-in of river channels abandoned by stream migration, such as cut-off meanders and ox-bow lakes (Friedman and Sanders, 1978).
3. Festoon crossbedding (according to Visher, 1972) is indicative of confined, unidirectional flow and is therefore supportive (but not by itself conclusive) evidence of fluvial deposition.

43

A

en
0::::

(I)

w

1-
w

~

8
l
(2)
I
J

Figure 4. Fining-upward sequences with the Tuscaloosa Formation. Exposure A . is located on both sides of Lindsay Creek By-pass at the intersection with Macon Road. Exposure B is located on Wildcat Road just south of Buena Vista Road on the Fort Benning military reservation.

4. Crossbedding dip directions suggest a southward-flowing paleocurrent system moving down a regional paleoslope in the same manner as present streams. Sediment dispersal patterns agree with this conclusion, indicating a source area to the north. This may be seen not only in the itacolumite clasts of Tuscaloosa gravels, but also in the heavy mineral fraction of the sands. Their mineralogy suggests a high-rank metamorphic and plutonic igneous source, such as the Piedmont province.
5. Siderite, found in some Tuscaloosa top stratum muds, provides further evidence of alluvial origin. Siderite is only formed in freshwater environments characterized by strongly reducing chemical conditiot;~s such as might be

encountered in stagnant backswamp areas. It is not likely to be marine (Berner, 1971). 6. The presence of well-preserved terrestrial plant fossils, especially delicate leaves, suggests a non marine environment. Also, the complete lack of any marine fossils whatsoever supports the fluvial interpretation.
EUTAW FORMATION
Stratigraphy
The Eutaw Formation overlies the Tuscaloosa disconformably. In the Chattahoochee Valley area, it is approximately 38m thick but thins toward the east, being about 30.5 m thick in the Harmony Church area of Fort Benning and 26m thick east of

44

Fort Benning (Eargle, 1955). In the study area, the Eutaw consists of four lithofacies, three of which define a lower, crossbedded sandy member which is best developed in updip areas, especially in outliers on the tops of hills in southern and central Muscogee County, where it comprises most of the formation (being 26m thick in the Buena Vista Road area). This crossbedded sandy member thins to the south, being approximately 4.5 m thick on U.S. 27 just south of Upatoi Creek and absent altogether 4.8 km to the east in Ochillee Creek Valley. The fourth lithofacies is gray, bioturbated, fossiliferous, muddy sand and sandy mud which forms the majority of the Eutaw in most of its main outcrop belt in Upatoi Creek Valley. To the east, the lower sandy member thickens until it makes up the entire formation in the Flint River area. East of the Flint, the Eutaw is indistinguishable from overlying units (Eargle, 1955). The Eutaw is overlain disconformably by the Blufftown Formation.
Monroe (1947) considered the entire Eutaw in western Georgia to correlate with the Tombigbee Sand Member of the upper Eutaw in western Albama , but diagrams in Copeland's (1972) discussion of Alabama's Coastal Plain stratigraphy show correlation with the majority of the Eutaw in its type section. Stephenson (1957) considered the molluscan fauna of the Eutaw in the study area to be ancestral to that in the Snow Hill Member of the Black Creek Formation in North Carolina and to be correlative with the upper part of the Austin Chalk in Texas. Christopher (this volume) uses palynology to demonstrate correlation with the basal part of the Austin Group, suggesting a Coniacian or Santonian Age.
Eutaw Lithofacies
Lithologically, the Eutaw Formation in west Georgia is very complex. From eight to twelve different lithologies have been recognized , based on grain size, sedimentary structures, and fossils. I have grouped these into four lithologic associations, or lithofacies, which will be briefly described in the following paragraphs. Their stratigraphic relations are illustrated in figure 5.
Lithofacies I.
The lowermost Eutaw lithofacies, found only in northern parts of the outcrop belt, is characterized by fine to coarse, poorly to moderately sorted, unskewed to positively skewed , slightly feldspathic quartzose sand. As a general rule, grain size decreased upward within this unit. Heavy minerals make up less than one percent of the sand and include hematite, ilmenite, zircon, hornblende, magnetite, rutile, tourmaline (two different varie-

ties), and others (listed in order of abundance). Comparison with Tuscaloosa heavy-mineral suites s.uggests that Eutaw sands were at least partially derived from reworking of Tuscaloosa sands, revealed especially by the abundance of hematite in the Eutaw which occurs in the Tuscaloosa not as a detrital mineral but as a cementing agent. Quartz grains are generally sub-equant to prolate and roundness ranges from subangular to very angular. Feldspars are severely altered. This lithofacies typically is yellowish gray (5Y 2/6), very dusky red purple (5RP 2/2) and shades of bright orange not specifically on the rock color chart.
Primary sedimentary structures include welldeveloped, large-scale, wedge-shaped, tabular crossbedding, usually overlain by large-scale trough crossbedding (pi cross-stratification of Allen , 1963), followed by horizontal laminations (fig. 6A). "Herringbone" crossbedding is commonly observed above the horizontally laminated strata. Reactivation surfaces are encountered occasionally (fig. 6B) as well as other types of compound crossbedding. Well preserved, distinct Ophiomorpha burrows are sparsely distributed throughout this lithofacies. Polychaete burrows are also found occasionally. Thin, silty claystone lenses are interbedded with crossbedded medium to fine sand in the upper part of this lithofacies, sometimes as "clay drapes" between cross-laminations. Typically, thick clay lenses are overlain by crossbedded sand containing abundant clay clasts. Thin, discontinuous, peat beds are rarely found associated with bioturbated sand and thin clay lenses near the top of the unit; in one locality, a dislocated slump block of peat is found associated with large-scale, tabular crossbedding. Crossbed dip directions are usually bimodally distributed with modes approximately 180 apart, the dominant mode usually being directed southeasterly. Secondary sedimentary structures include thin iron-oxide hardpans and hollow ironoxide concretions ("Indian paint pots").
Paleoenvironmental Interpretation of Lithofacies I.
Lithofacies I is interpreted as representing deposition in tidal channels, perhaps associated with a tidal delta. Herringbone crossbedding, reactivation surfaces, and bimodally distributed crossbed dipdirections indicate reversing-flow conditions. The overall fining-upward character of the sediment and associated change in sedimentary structures from large-scale tabular and trough forms at the bottom to horizontal laminations and small-scale crossbedding at the top is similar to the stratigraphic sequence produced by the migration of tidal channels (Kumar and Sanders, 1974) . Bioturbated sands with clay lenses and peat beds at the top suggest

45

N
~
w
aw::
(.)

s
~
w
w
a::
(.)

LITHOFACIES :rsz:
D LITHOFACIES ][
1[
LITHOFACIES I

V.E.'" 80

0

2

KILOMETERS

Figure 5. Stratigraphic cross section and inferred correlations of Eutaw lithofacies in southern Muscogee and Chattahoochee Counties. Vertical lines indicate outcrop control of cross section.

channel abandonment and the development of a marsh environment. I have interpreted the strongly stained character of these upper sands and clays to be due to oxidation of dispersed organic materials and various divalent metal ions, originally deposited under the reducing conditions typically encountered in marsh environments. Abundant clay clasts were formed during storms which ripped up marsh deposits and the dislocated peat block mentioned above is believed to have slumped off the cut bank of a tidal channel during its migration. Ophiomorpha burrows indicate normal marine, shallow subtidal to low intertidal conditions (Weimer and Hoyt, 1964).
Lithofacies II
The second lithofacies lies disconformably on the first in northern parts of the study area (fig. 6C) and

constitutes the lowermost part of the Eutaw in its main outcrop belt, lying directly on the Tuscaloosa. It is characterized by medium to very coarse, moderately sorted, quartzose sand with iron oxide cement scattered through the unit as thick hardpans, irregular layers. and other masses. Grain size decreases upward within this unit but does not pass into a stained clay-lens and peat-bed aspect as in Lithofacies I. Rather, grain size decreases steadily, grading continuously into Lithofacies Ill. Heavy mineral suites contain tourmaline, rutile, and zircon, suggesting that ferromagnesian minerals seen in the first lithofacies have been removed by intrastratal solution possibly providing some of the material for iron-oxide cementation. Color ranges from moderate reddish brown (10R 4/6) to light brown (5YR 6/4) with little of the color variability of Lithofacies I.

46

Figure 6.

Features of the Eutaw Formation. A, Vertical section through tidal channel sequence in Lithofacies I, B, Reactivation surfaces within coarse sand in Lithofacies I (object at lower right is head of entrenching tool). C, Sharp, disconformable contact (arrow) of Lithofacies II overlying Lithofacies I. D, "Ball and pillow" structures in updip exposure of Lithofacies Ill. E, Hummocky crossbedding and burrowing in Lithofacies Ill interbedded with Lithofacies IV . F, Horizontal bedding and mud clast conglomerates in Lithofacies Ill.

47

This lithofacies is characterized by large-scale, trough crossbeds and less abundant tabular cross beds . Scale of crossbedding decreases upward in the unit, gradually being replaced by massive, unstructured sediments at the top. Ophiomorpha burrows are especially common at the base of the unit, where they may be so abundant that individual burrows are not distinguishable within a maze of burrows. The number of Ophiomorpha burrows decreases toward the top of the Iithofacies where they disappear altogether. Crossbed dip directions box the compass with no obvious modal direction.
The environmental interpretation of this lithofacies is drawn not only from its specific characteristics but also from the character and stratigraphic relations of the two overlying lithofacies, which form (with Lithofacies II) an essentially continuous, conformable "package" of strata. Consequently, discussion of paleoenvironments will be postponed until the remaining lithofacies have been described.
Lithofacies Ill.
The third lithofacies lies conformably on the second across a continuous, gradational contact in northern areas where it forms one to two-meterthick tabular layers. These layers are traceable over fairly large areas and can be shown to thin progressively toward the south wh ere they are intercalated with layers of the fourth lithofacies, usually with an abrupt, erosional, lower contact and a relatively sharp but mi xed, gradational, upper contact. Lithofacies Ill is characterized by fossi Iiferous, fine to very fine, moderately to well sorted, silty, micaceous, quartzose sand. Heavy minerals compose up to three percent of the sediment and consist of ilmenite, rutile, zircon, almandite, tourmaline, and rare glauconite. Fine, carbonaceous, plant debris is observed on bedding planes, especially in downdip areas where Lithofacies Ill is mainly represented by thin layers within Lithofacies IV . Color is generally light olive gray (5Y 6/ 1) but in places approaches very light gray (N8). Carbonaceous laminae are generally shades of brown.
In updip areas, the third lithofacies is typically massive or contains well-developed, large, "balland-pillow structures (fig. 60). In other areas, it contains horizontal laminations and very low-angle crossbedding of the type called "hummocky crossstratification" by Harms (1975). This type of bedding has the following characteristics: "(1) lower bounding surfaces of sets are erosional and commonly slope at angles less than 10 degrees ... , (2) laminae above these erosional set boundaries are parallel to that surface, or nearly so, (3) laminae can systematically thicken laterally in a set, so that their

traces on a vertical surface area are fan-like and dip diminishes regularly, and (4) the dip directions of erosional set boundaries and of the overlying laminae are scattered" (Harms, 1975, p. 87). In addition, bounding surfaces between sets are typically convex upward (Harms, 1975, fig. 5-5) . Figure 6E is a photograph of Lithofacies Ill showing these characteristics. Frequently associated with hummocky crossbedding are thin beds of intraformational conglomerate whos e clasts are sub-equant, subrounded "balls of medium dark-gray (N4) silty clay, similar to some clay beds in Lithofacies IV (fig. 6F) . Distinct burrowing is often observed, especially at the tops of layers and some can be recognized as the escape burrows of a callianassid-shrimplike organism (Ron Taylor, personal commun., 1979).
This lithology is frequently very fossiliferous with numerous molds and casts of bivalves (Cardium , Protarca, and Corbu/a, to name a few), gastropods, and cephalopods , along w ith rare sharks' teeth and fish scales. The fossils are typically found on bedding plane surfaces and are uniformly small (regardless of their genera), suggesting hydrodynamic sorting during transportation. The shells are generally unrounded, however, and thus have not been transported far.
Lithofacies IV.
The fourth lithofacies composes the bulk of th e Eutaw Formation in its main outcrop belt in Upatoi Creek Valley . It is intercalated with the third lithofacies, and individual beds thicken as Lithofacies Ill beds thin in the downdip direction. In most of the study area, Lithofacies IV is a fossiliferous, poorly sorted, silty, clayey, very fine to fine, micaceous, quartzose sand, but the average grain size decreases gradually downdip so that on the south side of Upatoi Creek the unit is composed of very fine sandy, clayey siltstone or even silty claystone . The primary texture of the sediment is speculative since the entire lithofacies is strongly and p ervasively bioturbated . What may have originally been alternating layers of very fine sand and silty clay are now layers that are completely intermixed and churned up. The sediment contains up to two percent muscovite mica, and heavy minerals include glauconite, rutile, almandite, ilmenite, tourmaline, hematite, zircon, and magnetite. Glauconite grains are generally fine to very fine sand size and have a
subrounded appearance. The sediment ranges in
color from medium light gray (N6) to dark gray (N3).
Notice has already been taken of the completely bioturbated character of the sediment which results in a distinctly to indistinctly mottled appearance. In some instances, individual trace fossils can be

48

observed and are dominantly horizontal in their orientation although they may be seen to move up and down through the strata along their horizontal course. Some of these burrows are recognizable because of the presence of clean, white sand within generally dark-gray mud, suggesting sand infilling of open burrows. Calcareous concretions, occasionally with septarian-type shrinkage cracks, occur in downdip areas, usually associated with very fossiliferous horizons. The septarian aspect of these concretions is taken to imply relatively low sedimentation rates because the shrinkage necessary to crack the sediment could not have occurred under high lithostatic (and hydrostatic) stress in the deeper subsurface.
This lithofacies is abundantly fossiliferous (see Stephenson, 1957) with numerous bivalves (especially Exogyra upatoiensis, Ostrea cretacea, Gryphaea wratheri, Anomia argentaria, Cardium sp. Nucula sp., etc .), gastropods, cephalopods (for example, Placenticeras, benningi), abundant sharks' teeth , fish vertebrae, and unidentified bone material. Unlike the fossils in Lithofacies Ill, those in Lithofacies IV range widely in size and some appear to be in life position. Carbonaceous plant debris and pieces of lignite (from small "twigs" up to half-meter long "logs") are found dispersed through the lithofacies, but lignitic pieces are "water-worn" in appearance and plan debris (like that in Lithofacies Ill) is composed of very small fragments with no recognizable leaf prints .
Paleoenvironmental interpretation of Lithofacies II, Ill, and IV.
The upper three lithofacies are considered together because they constitute a stratigraphically and genetically related unit. I interpret them as representing deposition in progressively deeper subenvironments of the shore zone, the record of a marine transgression.
Lithofacies II is considered to have been deposited on the low-tide terrace of the upper shoreface (or swash zone) just below mean low-water mark (Davis, 1978). The dominance of trough crossstratification implies megaripple migration (see relation of bed forms to shore geometry in Clifton, and others, 1971) and subordinate tabular crossstratification represents deposition from sand waves during slight fluctuations of hydraulic conditions, especially depth of flow. Strongly polymodal paleocurrent data suggest highly variable flow conditions of the wave-, tide-. and storm-influenced upper shoreface (Selley, 1968; see also the paleocurrent model for low-tide terrace deposits in figure 34, Davis, 1978). The abundance of Ophiomorpha burrows at the base of Lithofacies II coincides in this

model with the area just below low tide, the same area preferred today by Callianassa major, the most likely candidate for the "Ophiomorpha - animal" (Weimer and Hoyt, 1964) . Vertical change in grain size and in scale of cross stratification indicates progressively deepening water as sea level rose, increasing the distance from shore.
Lithofacies II grades upward into Lithofacies Ill, which is believed to represent deposition on the lower shoreface . Harms (1975, p. 87) characterizes lower shoreface sediments as consisting of "very fine to fine sandstone with tabular beds of nearly horizontal stratification or hummocky crossstratification. . .. The sandstone contains more mica and carbonaceous fragments than does the upper, swash zone facies." Hummocky crossstratification is believed by Harms (1975) to have been formed by strong storm-wave surges over the lower shoreface, a speculation supported in Eutaw deposits by the association of mud-clast intraformational conglomerates and hydrodynamically sorted bioclasts. Burrowing within Lithofacies Ill deposits provides supportive evidence for this model as does the presence of fine carbonaceous debris on bedding planes and as discrete laminae instead of dispersed through the sediment as might be expected if the source of the debris were nearby. The high degree of sorting of Lithofacies Ill sand and relatively high proportion of heavy minerals suggest constant winnowing and reworking of the sediment by waves . The constantly downdipthinning and continuous, tabular nature of Lithofacies Ill strata may also be considered as evidence for the proposed model, since the shoreface is a geographically continuous zone characterized by water-depth asymmetry away from land .
As water depth continued to increase during transgression, the lower shoreface was progressively less affected by wave agitation, passing gradually into the transition zone between the shoreface and the shallow shelf. The transition zone, represented in Eutaw strata by Lithofacies IV, is characterized by intensely bioturbated sandy, silty, clayey sediment (Harms, 1975) and a cosmopolitan marine faunal assemblage. Lithofacies IV fossil assemblages do not appear to have been transported any significant distance and are characterized by high diversity and moderate density, an ecological situation typical of open marine environments. The relatively large amount of carbonaceous debris is supportive evidence of the transition zone interpretation. Campbell (1971) reports that carbonaceous particles exceeded ten percent of total grains in some transition zones within the Gallup Sandstone. Such carbonaceous material was probably carried by ebbtidal currents or storm currents and allowed to settle out relatively far from land where wave

49

energy was less. The geometry of Lithofacies IV strata is also significant. They thicken in the downdip direction, implying that it was progressively better developed with increasing distance from land. The presence of thin intercalated layers of Lithofacies Ill-type sediment probably represents storm deposits, formed by waves of great length which scoured the bottom and momentarily initiated lower-shorefacelike conditions. Gradual decrease in grain size in the downdip direction implies gradual deepening of water and the change to a true graded shelf environment. Such true shelf deposits do not exist in surface exposures of the Eutaw Formation in Georgia; however, they are found in Alabama (Reinhardt, this volume).
Eutaw Paleogeography
It remains now to assemble the specific depositional environments discussed above into a coherent reconstruction of Eutaw paleogeography. I believe that the Eutaw Formation in western Georgia represents a barrier-island complex formed during rising sea level. However, all of the original barrier-complex facies have not been retained in the stratigraphic record. Subaerial facies were removed by erosion as the transgressing sea pushed the barrier complex landward, producing the disconformity between Lithofacies I and Lithofacies II. This barrier retreat and concomitant erosion resulted in the deposition of subtidal shore-zone sediments (Lithofacies II, Ill, and IV) directly over subtidal back-barrier sediments (Lithofacies I). This model presumes the former existence of more extensive back-barrier facies north of the present Eutaw outcrop belt. These deposits have been removed by post-Eutaw erosion, either during pre-Biufftown emergence or, more likely, during a more recent period of emergence.
Complete preservation of barrler-cornplex deposIts In transgress ive stra tig.raphi c sequences is rare, but l1as been reported {for examp le, Hobday and Tanl<ard, 1978). For s uch prese rva1io n to occur, however, there must bea r equilib rium between se diment influx and sea-level rise. Should rate of sediment influx exceed the rate of sediment dispersal by marine processes (longshore currents, tidal curre nts, etc.), t11en a prograding barrier would form, even i n~ transg ressive reg ime. On the ot l1 er hand, very low rates of sediment inf lu x may well result in the development o t a retr at lng barrier complex whose sediments are comp letely reworked by marine processes, leaving no record whatever of the barrier's existence. Selley (1978) shows that there is a complete continuum between total retention of a transgressive barrier sequence and zero retention. The Eutaw Formation of Georgia thus falls somewhere within that continuum.

At some point during Eutaw time, sea-level rise slowed or stopped. This may actually be responsible for preservation of the back-barrier environment in extreme northern parts of the outcrop belt. The tendency of the Eutaw to become increasingly sandy near the top of the unit (Eargle, 1955) is possibly due to the onset of barrier progradation late in Eutaw time as a result of this new marine regime. The disconformity separating the Eutaw and Blufftown Formations may be due to falling sea level and emergency following the cessation of sea-level rise.
CONCLUSIONS
The Tuscaloosa Formation is the lowermost unit of the outcropping Cretaceous System in Georgia. It was deposited over a relatively low erosional surface developed on Piedmont crystalline rocks, in places with a lateritic soil intervening between gneissic saprolite and Tuscaloosa sediment. The hallmark of Tuscaloosa strata in Georgia is the fining-upward stratigraphic sequence in which coarse to pebbly arkosic sand at the bottom is overlain by sediment of continuously decreasing grain size, grading finally into mottled silty mudstone at the top. The change in grain size is accompanied by a corresponding change in sedimentary structures from large-scale tabular cross beds below to smaller scale trough crossbeds and ripple bedding above. Each sequence is separated from vertically adjacent sequence by local disconformities. Considered to be the records of deposition on prograding point bars, these fining-upward sequences constitute the primary evidence for interpretation of Tuscaloosa sediments as being fluvial in origin. Supporting evidence includes the presence of "clay plugs" formed in abandoned channels, multistory sand bodies, well-preserved leaf fossils, and siderite spherules.
The overall impression about west Georgia paleogeography during Tuscaloosa time is of a forested alluvial plain adjacent to a very old Piedmont upland which supplied immature sediment whose mineralogy suggests that their source was an igneous and metamorphic complex. Climate was probably tropical to subtropical, but deposition was rapid enough to allow preservation of feldspars (albeit intrastratally altered) and other labile heavy minerals.
The Eutaw Formation represents the first marine incursion in west Georgia recorded in outcropping Cretaceous strata. The Tuscaloosa-Eutaw contact is disconformable, suggesting a period of erosion before Eutaw deposition. Eutaw strata are divided into four lithofacies based on grain size, sedimentary structures, and fossils. Lithofacies I is a tabular and trough crossbedded, slightly feldspathic, fine to medium quartzose sand with Ophiomorpha burrows, reactivation surfaces, herringbone crossbed-

50

ding, and lenses of mottled mudstone and peat. Lithofacies I is considered to be tidal-channel deposits, probably part of a tidal delta. Lithofacies II is a trough crossbedded , Ophiomorpha-burrowed , partially iron-cemented, medium to coarse quartzose sand with polymodal crossbed dip directions. It is believed to represent the upper shoreface environment. Lithofacies Ill is a horizontally bedded to hummocky, crossbedded, fossiliferous , micaceous, well-sorted fine to very fine quartzose sand with relatively high amounts of heavy minerals and carbonaceous laminae. It is believep to represent the lower shoreface . Lithofacies IV is a completely bioturbated, fossiliferous, micaceous, carbonaceous silty sand and sandy mudstone which is interpreted as the transition zone between shoreface and shelf . Taken together, these lithofacies are considered to have been deposited in a barrier-island complex formed during marine transgression very early in Eutaw time. As the transgression was apparently rapid, sediment influx to the area was unable to keep pace with rising sea level and the barrier complex was pushed back to the north with continuous erosion and reworking of barrier deposits so that few sediments were left to record the event other than a thin sheet of sand at the base of the Eutaw in downdip areas. With increasing water depth, a vertical succession of upper shoreface to lower shoreface to transition zone was deposited . Sometime later, sealevel rise slowed and then stopped , leaving unreworked back-barrier flood tidal-delta deposits overlain by the transgressive shoreface sequence, across a disconformity which represents the removal of subaerial-barrier faces . Responding to the new marine regime. the barrier complex prograded, resulting in an increasingly sandy aspect at the top of the Eutaw Formation .
ACKNOWLEDGEMENTS
Many people have offered help in the development of the above ideas, especially students in my sedimentology and stratigraphy courses who located outcrops, rotapped, pipetted , separated , weighed, and measured . Three among this cadre deserve special mention: Charles Willetts. who provided much information on the Tuscaloosa Formation in the area north of Juniper Creek; Howell Crenshaw, who was one of the most ambitious ?utcrop locators it has ever b'een my privilege to 1nstruct; and Jerry Willis, who for two years was my field assistant and sounding board . Tim Chowns, AI Staheli, Bill Rivers, and Ron Taylor accompanied me to the field on several occasions and made valuable observations and corrections. I wish to take this opportunity to thank those mentioned as well as everyone else who helped and listened, and listened, and listened.

REFERENCES CITED

Allen, J.R.L., 1963, The classification of cross-

stratified units, with notes on their origin:

Sedimentology , v. 2, p. 93-114.

Berner, R.A., 1971, Principles of chemical sedimen-

tology : New York, McGraw-Hill Book Co ., 240

p.

Berry, E.W., 1923, The age of the supposed Lower

Cretaceous of Alabama: Wash . Acad . Sci .

Jour., v. 13, p. 433-435.

Campbell, C.V ., 1971, Depositional model-Upper

Cretaceous Gallup beach shoreline, Ship Rock

area, northwestern New Mexico: Jour. Sedi-

mentary Petrology, v. 41, p. 395-409.

Carter, C .H ., 1978, A regressive barrier and barrier-

protected deposit: depositional environments

and geographic setting of the Late Tertiary

Cohansey Sand: Jour. Sedimentary Petrol-

ogy, v. 48, p. 933-950.

Clifton, H .E.. Hunter, R.E ., and Phillips, R.L., 1971,

Depositional structures and processes in the

non-barred, high-energy nearshore: Jour.

Sedimentary Petrology, v. 41, p. 651-670.

Cooke , C.W., 1943, <3eology of the Coastal Plain of

. Georgia : U.S. Geol. Survey Bull. 941, 121 p.

Dav1s , R.A. Jr., 1978, Beach and nearshore zone, in

D avis, R.A. Jr. , ed., Coastal sedimentary envi-

ronments : New York, Springer-Verlag, p. 237-

285 .

Drennen, C.W., 1959, Geology of the Piedmont-

Coastal Plain contact in eastern Alabama and

western Georgia: Univ. Alabama, Tuscaloosa,

M.S. thesis.

_ _ 1953, Reclassification of the outcropping Tus-

caloosa Group in Alabama: Am. Assoc . Petro-

leum Geol. Bull., v. 37, p . 522-538.

Eargle, D.H., 1955, Stratigraphy of outcropping Cre-

taceous rocks of Georgia: U .S. G eol. Survey

Bull. 1014, 101 p.

Friedman, G .M . and Sanders. J.E ., 1978, Principles

of sedimentology: New York , John Wiley and

Sons, 792 p.

Harms, J .C., 1975, Stratification and sequence in

prograding shoreline deposits, in Harms, J.C.,

Southard , J.B. , Spearing , D .R., and Walker,

R.G ., Depositional environments as inter-

preted from primary sedimentary structures

and stratification sequences: Soc. Econ .

Paleontologists and Mineralogists Short

Course No . 2 notes. p. 81-102.

Hilgard, E.W., 1860, Report on the geology and agri-

culture of the State of Mississippi: Miss. Geol .

Survey, 391 p.

Hobday. O.K . and Tankard, A.J ., 1978, Trans-

gressive barrier and shallow-shelf interpreta-

tion of the lower Paleozoic Peninsula Forma-

tion , South Africa : Geol. Soc. America Bull v

89, p. 1733-1744.

., .

51

Kumar, N. and Sanders, J .E., 1974, Inlet sequence: a vertical succession of sedimentary structures and textures created by the lateral migration of tidal inlets: Sedimentology, v. 21, p. 491-532.
Langdon, D.W., 1891, Variations in the Cretaceous and Tertiary strata of Alabama: Geol. Soc. America Bull., v. 2, p. 587-605.
McFarlane, M.J ., 1976, Laterite and landscape. London, Academic Press, 151 p.
McGowen, J.H. and Garner, L.E., 1970, Physiographic features and stratification types of coarse-grained point bars : modern and ancient examples : Sedimentology, v. 14, p. 77-111.
Marsalis, W.E. and Friddell, M.S., 1975, A guide to selected Upper Cretaceous and Lower Tertiary outcrops in the Lower Chattahoochee River valley of Georgia: Ga. Geol. Survey Guidebook 15, 87 p.
Selley, R.C ., 1968, A classification of paleocurrent models: Jour. Geology, v. 76, p. 99-110.
_ _1978, Ancient sedimentary environments (2nd ed.) : Ithaca, New York, Cornell University Press, 287 p.
Smith, E.A. and Johnson, L.C ., 1887, Tertiary and Cretaceous strata of the Tuscaloosa, Tombigbee, and Alabama Rivers : U.S. Geol. Survey Bull. 43, 189 p.
Spencer, J.W.W., 1890, "Southern drift" and its agricultural relations: Ga. Agr . Expt. Sta . Bull. 6, p. 90-94.
Stephenson, L.W., 1911, Cretaceous, in Veatch, J.O. and Stephenson , L.W., Preliminary report on the geology of the Coastal Plain of Georgia: Ga. Geol. Survey Bull. 26, p. 66-215 .
_ _1957, Fossils from the Eutaw Formation, Chattahoochee River region , Alabama-Georgia: U.S. Geol. Survey Prof . Paper 274-J, p. iii, 227-250.
Stephenson , L .W. and Monroe, W.H ., 1937, Prairie Bluff chalk and Owl Creek formation of eastern Gulf region : Am . Assoc . Petroleum Geol. Bull. , v. 21, p. 806-809.
Veatch, J.O ., 1909, Second report on the clay deposits of Georgia: Ga. Geol. Survey Bull., 18, 453 p.
Visher, G .S., 1972, Physical characteristics of fluvial deposits, in Rigby, J.K . and Hamblin, W.K., eds ., Recognition of ancient sedimentary environments : Tulsa, Okla., Soc. Econ. Paleontologists and Mineralogists Spec . Pub . No . 16, p. 84-97.
Weimer, R.J. and Hoyt, J.H., 1964, Burrows of Callianassa major Say, geologic indicators of littoral and shallow neritic environments: Jour. Paleontology , v. 38, p. 761-767 .
52

PALEOCENE TO MIDDLE EOCENE DEPOSITIONAL CYCLES IN EASTERN ALABAMA AND WESTERN GEORGIA
Thomas G. Gibson U.S. Geological Survey
Washington, D.C.

ABSTRACT
Six Paleocene to middle Eocene marine units are present in eastern Alabama and western Georgia. The composition of these units varies from predominantly carbonate sediment, deposited during times of low clastic influx, to predominantly carbonaceous clay, silt, and sand deposited during times of higher clastic supply . As much as 150 m of modern topographic relief in the Chattahoochee River drainage area provides an unusually long and nearly continuous north-south sequence of exposures in an area in which the strata generally dip 4 to 6 m per km southward. These north-south sequences commonly include the transition from nonmarine or marginal marine to marine strata. Where preserved, fluvial and marginal marine deposits that consist of kaolinitic clay, crossbedded fine- to medium-grained sand, and poorly sorted, coarse clastic material grade downdip into calcareous and glauconitic sand, silt, and silty clay containing abundant macro-invertebrate fossils. The lower, marginal marine to marine parts of the transgressive units consist of fine to coarse sand and generally are preserved; the upper regressive phases consist of silts and clays and are less well represented.
Biostratigraphic information from calcareous nannoplankton and foraminifers indicates that these transgressions are generally coeval with those of the Atlantic Coastal Plain and with global transgressive patterns, but that some regional differences exist.
The Clayton Formation of early Paleocene (Danian) age represents the most widespread Cenozoic transgressive unit in the Chattahoochee area. During the Clayton encroachment, Providence Sand (Upper Cretaceous) was reworked and forms the basal part of the formation; deposition of this sand was followed by deposition of shelly carbonate debris and calcareous sands, indicating low clastic influx into the basin.These limestones thicken rapidly downdip. Marginal marine deposits are limited to thin clays in the northernmost part of the outcrop belt.
The record of two transgressions is found in the upper Paleocene deposits. In the updip outcrop area, the Nanafalia Formation largely consists of kaolinitic clay, locally bauxitic, of fluvial to marginal marine origin, grading downdip into abundantly fossiliferous marine glauconitic sand and clay that overlie crossbedded medium to coarse clastic deposits containing abundant carbonaceous debris. The overlying Tuscahoma Sand thickens rapidly downdip. The basal transgressive glauconitic coarse sand of the Tuscahoma is overlain by a thick sequence of laminated silt and carbonaceous clay that represent restricted marinlj! to shallow marine environments.

The glauconitic sand and clay of the Bas hi Marl Member of the Hatchetigbee Formation represent an extensive transgression during the earliest Eocene. In contrast to the other units, the Bashi thins downdip, suggesting a restricted sediment supply. The upper part of the Hatchetigbee Formation is not present in this area.
The Tallahatta Formation of early middle Eocene age unconformably overlies the Bashi. Basal coarse sands and gravels are found in channels incised into the Bashi. Downdip, the lower part of the Tallahatta is composed largely of fossiliferous sand and limestone.
INTRODUCTION
The relatively high elevation of the Coastal Plain (commonly reaching 150-210 m) and the high relief resulting from dissection in the Chattahoochee River drainage area in westernmost Georgia and easternmost Alabama provide an outstanding series of exposures of Paleocene strata in the eastern Gulf Coastal Plain (Toulmin and LaMoreaux, 1963). This relief, together with the gentle southward dip of strata into the Southwest Georgia Embayment, has resulted in a long series of north-south exposures in which both the updip and downdip facies of individual units may be observed. The outcrop area is in the transition zone from marginal marine to marine environments, and the change from nonmarine or marginal marine sediments to open marine facies is usually present. Another aid in following units is that the larger outcrops may expose more than 30 m of section in an area where the formations are relatively thin, generally less than 30 m thick; thus, several formational contacts can be seen within a single outcrop. As an example, lower Paleocene strata are present at elevations of about 200 m in the northern end of the study area (fig. 1) and can be followed southward to elevations of less than 45 m. Because the strata have a generalized dip of 4 m per km, a 30- to 50-km long sequence of exposures exists in an area of transition from mixed marine and marginal marine environments in the north to completely marine environments in the south. Most stratigraphic sections are selected from the abundant outcrops in eastern Alabama, but coreholes have been drilled in critical locations for additional stratigraphic control.

53

./'

TENNESSEE

/''

-

_J_- __,_r-

----r '

NORTH
- CAROLINA
~ - -----.
'

' ~

'. \

\

SOUTH

\ CAROLINA

l

\

GEORGIA .... \

: ALABAMA

\

~,

I
~

__JI

r'

I !.---

~- ---- ----......'

\

[:~:J Residuum
D Tallahatta-Lisbon Formations
IHWHH:i Tuscahoma-Hatchetigbee Formations

-

Nanafalia Formation

H IClayton Formation

D Cretaceous units

Figure 1. Geologic map of Paleocene to middle Eocene strata in eastern Alabama and western
Georgia (modified from MacNeil, 1946, 1947). Note change from eastward strike in Alabama to northeastward in Georgia.

Six depositional cycles in Paleocene to middle Eocene rocks of this area were delineated by lithostratigraphic mapping. One of the breaks between cycles was 3-4 million years (m. y.) long; the other five breaks were shorter intervals (fig. 2). Age assignments for the units were obtained by using biostratigraphic data from calcareous nannofossils, foraminifers, and sporomorphs. Generally, few planktonic foraminifera are found in these strata because of deposition in shallow marine environ-

ments; however, sufficient calcareous nannofossils are found to permit correlation of many of the units with the worldwide microfossil zonations.
The environments of deposition for the strata are interpreted from the paleontologic data (foraminiferal species diversity, planktonic-benthonic foraminiferal ratios, diversity and relative abundance of dinoflagellates, and molluscan assemblage), sedimentary structures, and regional patterns of deposition.

54

MY
40

NP17
1 - ...

~ Transgression Regression

NP16

4&
UJ
z
UJ
u 0
UJ

1-

NP15

_______> I NP14

Tallahatta

50

NP13

>-a-:-'

1--NP12

~ I--

NP11

I--

NP10

Non Deposition
---~ Bashi ~ ------ ---- --

55
UJ
z
UJ
u

NP9

-------------- Tuscahoma

1---

w

NPB

~- -~ --- -- --

~ ~ ~ ~

____.

~ Nanafalia ____,;r

I NP5

~----------------

0

NP4

GO

UJ ....1

1--1-----

<(

a..
NPJ

-- ~
a:
<w( i::Bff:

_,_.......-----=- Porters Creek ~-- - - ---- --
- =:5 Clayton

NPl

65

Figure 2.

Time and extent of depositional cycles in Paleocene to middle Eocene strata in eastern Alabama and western Georgia. A major time break occurs between the Bashi and Tallahatta and a lesser one between the ClaytonPorters Creek and Nanafalia. The northward extent of the cycles is shown by the amount of deflection of the curves to the right.

Acknowledgments
Many stimulating discussions regarding environmental significance of sedimentary features were held with Juergen Reinhardt, U.S. Geological Survey. Laurel M. Bybell of the U.S. Geological Survey provided age analyses of the calcareous nannofossil assemblages, and Norman 0. Frederiksen of the U.S. Geological Survey provided palynomorph biostratigraphy and paleoenvironmental information.

most Georgia is shown in figure 1. This figure is modified from the mapping of Tertiary strata in these two states by MacNeil (1946, 1947).1n Georgia the Clayton and Nanafalia Formations and the Tuscahoma Sand and Hatchetigbee Formation were combined into paired units and mapped together by MacNeil (1947). The strike of the formations changes from predominantly east in eastern Alabama to northeast in western Georgia; the generally north-south sections studied here are largely in Alabama and thus are approximately at right angles to the strike.
The lithologic sections presented here extend from Clayton, Ala., on the northwest to Blakely, Ga., on the southeast. These sections are in the area of transition from nonmarine and marginal marine environments in the north to marine environments in the south. The Clayton Formation and Bas hi Marl Member of the Hatchetigbee Formation consist of marine facies over much of the area and contain marginal marine units only near their northern limit: the Nanafalia and Tallahatta Formations have extensive areas of both marine and marginal marine facies; and the Tuscahoma Sand is composed largely of marginal marine facies except for one extensive marine facies at the base.
The lithologies of the formations vary as a result not only of differences in the depositional environments in which they formed, but also as a result of differences in rate of supply of clastic sediments into the basin. Carbonate sediments are dominant in marine facies of the Clayton Formation of early Paleocene age, but then they are essentially absent in outcrop until the Tallahatta Formation in the middle Eocene. Glauconitic strata are common in the transgressive parts of the Tuscahoma and Bashi and are persistent throughout the marine parts of the Nanafalia. These lithofacies reflect the low amount of detrital material being brought into the basin. Clay is the dominant clastic sediment in the Nanafalia Formation; it was trapped in marginal marine environments that existed north of Ft. Gaines, Ga. Where quartzose sands dominate the clastic sediment fraction, suc.h as the fine sands of the Bashi, the unit rapidly thins downdip, indicating a low influx of sand. The major time of significant clastic input is represented by the Tuscahoma Sand, which thickens downdip to 45 or possibly 60 m of clay and silt (Toulmin and LaMoreaux, 1963).

REGIONAL DISTRIBUTION
The outcrop pattern of the Paleocene to middle Eocene formations in eastern Alabama and western-

The lithologic and paleoenvironmental patterns of each formation will be presented from oldest to youngest, and finally the regional implications of the transgressive cycles will be discussed.

55

Mo '!fs 10

CLAYTON

67

55

-P.-" '::i~/: . - p ........-
- ~- . r:?.':' - ._ ..
~;:
,:. ~

Clayton

20

~~ ac;:l Gravel

~-~Silt

o

sand

I~! clay

j !::_.__. Calcareous sand

N

r-----------------~~~--------------~ ..........._ (
A L A B A M A j' ''; ___,.,__ _

Calcareous clay

fa 67

)- I I G E 0 !R G I A

55 ...~--r;--.._.--,

~---~-J l ~

- -~I'

',)~!~~T'o~n'---~----

I 1

)
I"\._

--

-

--l1~

i

~ , ~----

1

:

-

-'If.- --- -

-- - - -1\ ,

30 Kilometers

bottom of hole
If! Sandy limestone

0Limestone
0 Carbonaceous

1""".,..::_1Shells

\

I\..'-.\']Crossbedding

\ \

River Section Nanafalia
'i
. .- ' '.: ~. : ~:; -.-.,.,.__ ..-.--'.-:.:....
: j . ::'~o , :. - :
",' :..", -.-:.:--'.-..:.r.....:...:. -- .. .. ';.: , _ ,,, , r ,
_', ,.',.
.. - .'____._,__.,.,, .. '
~ . o ~ . .r:J,'
Providence

Figure 3. Lithology ano thickness of the Clayton Formation in eastern Alabama. Representative stratigraphic sections are from outcrops and core holes as show on location insert. Note change from sand and clay facies in north to mostly carbonate facies to the south.

STRATIGRAPHIC SUMMARY
Clayton Formation
The type locality of the Clayton Formation is at Clayton, Ala. in the northwestern part of the study area (fig. 3, lac. 18). The few outcrops of the Clayton Formation in this area that have yielded datable marine microfossils give an early Paleocene

age, probably belonging to nannofossil zone NP3 (Laurel M. Bybell, U.S. Geological Survey, written commun., 1979). Only calcitic mollusks or molluscan molds and casts remain in many exposures because of leaching of the calcareous microfossils and aragonitic megafossils, and therefore, correlation of these localities with the international zonations is not possible.

56

The Clayton Formation in the study area was deposited mostly in shallow marine environments, with fewer strata formed in marginal marine environments. In.the more northerly outcrops, massive or crossbedded quartzose sands, sometimes containing Ophiomorpha and other burrows,dominate. These sands represent nearshore subtidal sand sheets and associated bars. They form the most northward exposure of the Paleogene units, being found 6 km northwest of Clayton at an elevation of 198 m. These nearshore sands commonly contain local shell lenses, 1.5 to 3 m in length and 0.5 to 1 m in thickness, predominantly composed of oysters and Turritella . These lenses generally are indurated because of local leaching of carbonate shell material and redeposition of calcite cement.
In the type area at Clayton (fig. 3, loc. 18), the sequence of buff to red sands and sandy limestones is divisible into an upper and lower sequence by gray to black clay beds that are approximately 9 m above the base of the formation. The clayey strata range in thickness from 0.9 min a railroad cut on the northeast side of Clayton to as much as 4.5 m 1-2 km farther south and southwest. The clayey strata 0.9 m thick are laminated with quartz and muscovite silt interbeds; abundant leaves belonging to only a few species are prese nt in th ese beds. T hese ch aracteristi cs plus the presenc e of large , heavy pollen and spores and a low rel ative abundance and diversity of dinoflagell ates suggest deposition in a marginal marin e lagoon. In th e thi cker cl ay inte rvals t o the south and southwest, the clays are more massive and weather with a blocky appearance because of subconchoidal-fracturing montmorillonite- cristobalite clay facies found here (Reynolds, 1966). An exposure of the clay unit, about 8 km east of Clayton, contains abundant glauconite and suggests a more open marine influence toward the southeast.
To the southeast of the type area, the Clayton Formation thickens rapidly and is represented by a predominantly carbonate section (fig. 3). A section of 55 m of mostly sandy limestone was reported by Toulmin and LaMoreaux (1963) to be at the Walter F. George Dam on the Chattahoochee River near Ft. Gaines. The limestone is highly fossiliferous; oysters and bryozoan fragments are the dominant constituents.
The Clayton Formation represents the most widespread transgression during Paleocene to middle Eocene time in this part of the Southwest Georgia Embayment as indicated by the geographic location of the facies (fig . 3). The sequence of lagoonal to marginal marine clay beds indicates at least one minor regression during Clayton time. The largely carbonate composition of the Clayton in most of the basin shows a paucity of clastic influx. Quartzose sands are prevalent only in the lower part of the Clayton and probably are largely derived from the thick underlying sands (as much as 50 m) of the

Providence Sand (Upper Cretaceous). Additional support for this provenance is from the large number of reworked sporomorphs of Late Cretaceous age found in the lowermost leaf-clay bed of the Clayton (Norman 0. Frederiksen, U.S. Geological Survey, written commun ., 1979).
Porters Creek Clay
An exposure of waxy-appea ring , dark-gray to black, silty clay of th e Po tte rs Cree k Cl ay is near the type area of the Clayton Fo rm at ion nort heast of the center of Clayton. T he beds c rop out on both sides of a road and expose about 1.6 m of section; the total thickness here of the Porters Creek is 7.3 m as determined from a corehole. The presence of small mollusks, foraminifers, and calcareous nannofossils indicates a shallow, open-shelf environment of deposition. The lowermost 0.6 m was dated by calcareous nannofossils as probably belonging to zone NP3 of early Paleocene age (fig. 3) ; the upper 6.7 m is assignable to zone NP4 of late Paleocene age (Laurel M. Bybell , U.S. Geological Survey, written commun., 1979).
The exposure of the Porters Creek at Clayton is the only one presently known in the entire study area. However, the presence of open-marine Porters Creek strata as far updip as Clayton indicates that this unit probably covered much of this area, but since has undergone extensive stripping. The large area that was stripped is indicated by the absence of Porters Creek strata even in the most downdip exposures in the study area along the Chattahoochee River where the Nanafalia Formation rests directly upon Clayton strata.
The composition of the Porters Creek at Clayton, plus the generally clastic nature of the Porters Creek throughout the eastern Gulf Coast indicates that clastic sedimentation was increasing as far east as the Chattahoochee River area at this time. The clastic nature of the Porters Creek is in contrast to the dominance of carbonate sediments in the underlying Clayton, although both formed in shallow marine environments.
Nanafalia Formation
The deposition of the Nanafalia Formation followed an interval of approximately 1 m.y. during which significant erosion took place (fig. 3) . The Porters Creek Clay was largely stripped from this area and the karst topography on top of the Clayton Formation probably formed during this time interval. The northward or updip extent of the Nanafalia transgression was less than that of the underlying Clayton and Porters Creek as the transition from nonmarine or marginal marine to marine beds of the Nanafalia is found 50 km south or downdip of marine beds in the underlying two units.

57

The lower part of the Nanafalia is composed of a sequence of nonmarine to marginal-marine carbonaceous, micaceous sands, commonly containing clay-clast conglomerates at or near its base. In updip areas, these deposits rest in broad channels formed in the top of the Clayton. Downdip, as seen near Ft. Gaines, they commonly are preserved in sinkholes in the top of the cavernous Clayton limestones. These lower beds probably are equivalents of the Gravel Creek Sand Member of the Nanafalia in western Alabama (Marsalis and Friddell, 1975). The remainder of the Nanafalia is sharply divided into a marginal marine or possibly in part nonmarine facies found to the north-northwest of Ft. Gaines and a marine facies found to the south. The marginal marine section consists of kaolinitic clays, commonly bauxitic, in which channelized units of medium to coarse micaceous crossbedded sands and carbonaceous to lignitic clays are found (fig. 4, loc. 55 and 65). Dinoflagellate assemblages of low diversity are found in these beds and indicate deposition in a marginal-marine, lagoonal-type environment rather than a nonmarine one for most localities.
Farther downdip, near Ft. Gaines, the facies change to shelly, glauconitic fine sand (fig. 4, Chattahoochee River section). These strata were deposited in inner-shelf environments in an area where most of the limited clastic influx was trapped in lagoons behind bar complexes. Changes in relative sea level are indicated by the presence of clay beds containing foraminiferal assemblages of low diversity within the middle part of the glauconitic sequence; these clay beds suggest marginal marine conditions within a generally marine succession.
Sporomorphs of late Paleocene age are found in the marginal marine beds. More detailed biostratigraphic zonation is possible in the marine beds of the Nanafalia Formation; here calcareous nannoplankton indicative of zones NP6 to NP8 are found, indicating that the Nanafalia occupies the middle part of the upper Paleocene (fig. 2).
Tuscahoma Sand
The basal unit of the Tuscahoma is a glauconitic medium to coarse sand, usually containing quartz and phosphate pebbles, clay clasts to 10 em, and abundant mollusks, particularly Chlamys greggi Harris. These strata represent a strong transgressive pulse that extended 30 km or more northward or updip from the contact between marine and marginal marine facies of the underlying Nanafalia Formation. The contact between these dark marine beds of the Tuscahoma and the light-colored kaolinitic and bauxitic clays of the underlying Nanafalia marks a conspicuous datum in many of the bauxite

mines in this area. Strata of the marine unit range in thickness from 1 min the updip areas to as much as 6 min the more downdip exposures (fig. 5). Overlying the glauconitic beds is a thick regressive sequence, ranging in thickness from 15m updip to 45 m downdip, of laminated silts and clays, commonly carbonaceous. Calcareous fossils have not been found in these beds. The fine-grained, laminated nature of the beds and the low diversity of dinoflagellate assemblages found in them indicate that these beds formed in a protected lagoon of lowered salinity. Laminated beds of the Tuscahoma extend across Alabama and into Mississippi (Toulmin, 1977);- therefore, a complex of protected lagoons or sounds probably extended across much of the eastern Gulf Coast area during this time.
Coreholes slightly south of the outcrop belt have not penetrated marine beds in the upper part of the Tuscahoma; thus the regression must have been considerable. The thickness of silt and clay indicates that significant amounts of clastic material were ponded in this protected area during the late Paleocene.
The basal marine strata of the Tuscahoma Sand contain calcareous nannoplankton indicative of zone NP9 (fig. 2). As the underlying upper beds of the Nanafalia are placed in zone NP8, a short time break may separate the two formational cycles. The upper, marginal marine part of the Tuscahoma does not contain calcareous microfossils, but it does contain sporomorphs of late Paleocene age, resulting in a late Paleocene age for the entire formation.
Bashl Marl Member of the Hatchetigbee Formation
This lower member of the Hatchetigbee Formation represents another transgression of the considerable extent throughout this area (fig. 2). As in the Tuscahoma, the beds at the base are highly glauconitic and contain abundant molluscan shells. In the downdip exposures, the entire Bashi is only 10.6 m thick and is composed of glauconitic and shelly clay, silt, and sand, entirely of shallow marine origin (fig. 6). Updip, the member changes to an upper and lower sand unit sequence separated by a clay unit that is commonly laminated. The lower sand unit is strongly crossbedded arid is gravelly at the base; the upper part of the lower unit is similar to the upper sand unit in being fine to very fine, wellsorted sand containing scattered shell molds. The sands appear to have been deposited in very shallow, nearshore environments; the laminated clay suggests a more restricted marine or marginal marine environment.

58

NANAFALIA
~~.;.") Gravel
D Sand
~~-==~Clay



Lignite

0 Glauconite

Q Carbonaceous

G

aauxite

I"::<? l Shells

55

.....,._,

A L A B A M A ;' '':--r-- -

/ G E 0 !R G I A

)

!

l r---~i__j'_./ ~ ~""-"-"--1

i
------4
1

65 \\Chatta?ho~ee-r---~River Section ~

1
IN I ! I I

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t I

'1 \_,

1

:

L________) 0'--~-.-'---JJO

- -'

Kilometers

65

River Section

Meters

Nanafalia

."1!' ' 'p
-~ g
.cr. ..
.~: - ~..

covered _--

--- --Clayton

/
15 0

Figure 4.

Lithology and thickness of the Nanafalia Formation in eastern Alabama. Representative stratigraphic sections are from outcrops and well holes as shown on location insert. Note change from bauxitic and carbonaceous clay in north to mostly shelly sand to the south .

The foraminiferal assemblages in some of the downdlp exposures along the Chattahooc hee River suggest greater depths of deposltloh than In most of the underlying units, sho win g the updip extent of the transgression . Depositional en vi ronments approaching 60 m of water depth are indicated by

samples having 30 species of benthonic foraminifera plus 20 to 30 percent planktonic specimens. As shown in figure 6, the updip sections approximate 21 min thickness but thin downdip to 10.6 m. This thinning suggests that clastic sediments were being concentrated in nearshore environments rather than passing further into the basin during this time.

59

TUSCAHOMA
~~~o!j Gravel
Q sand
=~Silt 1~1 Clay ~ Glauconite ~ Carbonaceous
I"'",,,pj Shells

......,,(

r/ A L A B A M A

'';--.r---

1 G E 0 !R G I A

)

!

55 ..../\-..._---r

~--~--J ~ ~

I
1 ------l


s5 ' \

I~~---r----

1
1
IN ! ! I

l_ JC' hattahoochee

t::-- River --{{'\

I

\. . __

,

~I -------- -1\ 0

__ ,

"

30 Kilometers

Tuscahoma

d(l

Figure 5.

Li tho logy and thickness of the Tuscahoma Formation in eastern Alabama. Representati ve s'trati graphic sections are from outcrops and well holes as shown on locat ion insert. Note marine facies of glauconitic, shelly sand at base, overlain by carbonaceous clay and silt section which rapidly thickens downdip.

Calcareous nannofossil assemblages are found throughout the downdip sections of the Bashi. All samples belong to zone NP1Q, indicating -a short time span for Bas hi deposition. As the lithology and age of the downdip sections is consistent with what is known of the Bashi Marl Member in western Alabama, it appears that the upper, unnamed member of the Hatchetigbee Formation is not present in this area.

Tallahatta Formation
The Tallahatta Formation reflects less transgressive conditions than the underlying Bashi. This is indicated by the occurrence of beds of marginal marine to nonmarine origin of the Tallahatta resting upon Bashi strata of marine origin both in eastern Alabama and western Georgia. The time break between these two units is one of the longest in the Paleogene (3-4 m.y.), consisting of much of early Eocene time (fig. 2) .

60

BASH I
IS] Sand
~Silt
IE-11 Clay
c:::!J Glauconite
l1.\\..\.j Crossbedding
97 Tallahatta

-~ (
A L A B A M A ,1' '"-J--r-- -

) I G E 0 !R G I A

.. /" \ - ' - ' - - 1

.-----~-J l ~

_______JI



\

101 \

?
'---r-----

1

I

l

N

i Bj

) "\_..- - _ }'\

I!

I

1

~99

~---------) 0

__ ,

~---
30 Kilometers

101
Tallahatta

99 Tallahatta

Meters
0

10 15

Tuscahoma

Figure 6.

Lithology and thickness of the Bas hi Marl Member of the Hatchetigbee Formation in eastern Alabama and western Georgia. Representative stratigraphic sections are from outcrops and core holes as shown on location insert. Note general thinning pattern to south and southwest.

In most outcrops, the basal part of the Tallahatta rests in channels on the upper surface of the Bashi. Updip, the lower part of the Tallahatta consists of medium to coarse sand that is commonly gravelly and crossbedded and contains a prominent bed of clay clasts at or near its base. The channels in which these deposits rest are of marginal marine to possibly fluvial origin in the northern updip areas. A

cristobalitic clay unit 1.0-1.5 m thick, plus several thinner beds, each less than 0.3 m thick, is present6 m or more above the base. Downdip sections contain sand that is finer grained and commonly fossiliferous,and sandy limestones.
The Tallahatta Formation was placed in the lower part of the middle Eocene by Toulmin (1977}. Calcareous nannoplankton and foraminiferal assemb-

61

Global Sea Level from Vail and others (1977)

Chattahoochee River area

Rising

Falling

MY

45-r~-L~~~~~~~~~--------------------------------------~

Present

Sea Level

55

~

Nanafalia
Porters Creek Clayton

Figure 7. ~omparison of sea levels in the Paleocene to middle Eocene strata of the Chattahoochee River area and the global sea-level curves proposed by Vail and others (1977).

lages in the study area are too poorly preserved for more precise dating, although sporomorphs in the clay indicate a middle Eocene age .
SUMMARY
Six transgressive cycles of varying geographic extent are preserved in the lower Paleocene through lower middle Eocene strata in this part of the Southwest Georgia Embayment (fig. 2). The extent of the transgressions is interpreted from the distribution of the marine facies and from the transition point of marine to marginal marine facies within a formation. The greatest marine incursions took place in the early Paleocene (Clayton Formation and Porters Creek Clay), in the later part of the late

Paleocene (basal part of the Tuscahoma Sand), and in the earliest Eocene (Bashi Marl Member). Lesser transgressions took place in the middle part of the late Paleocene (Nanafalia Formation) and the early part of the middle Eocene (Tallahatta Formation) .
All the transgressive cycles are separated by depositional breaks, the greatest being the break between the Bashi and Tallahatta which encompasses much of the early Eocene. Visually, the most striking erosional interval occurs between the Nanafalia and underlying Clayton Formation and Porters Creek Clay; during this interval, the Porters Creek was largely stripped from the area, and an extensive karst topography formed upon the Clayton. Although the total thickness of lower Paleogene strata

62

totals only about 150 m, much of Paleocene and earliest Eocene time is represented by these strata.
The supp ly of clastic material into the basin during the Paleocene to middle Eocene was limited. A significant amount of clastic detritus was brought in only during the deposition of the Tuscahoma in the late Paleocene, and lesser amounts were deposited in the Tallahatta and Porters Creek. Marine facies in other units consist largely of carbonate deposits (Clayton), glauconite (Nanafalia) , or fine clastic deposits that thin into the basin (Bash I) . Apparently, lagoonal environments behind bars trapped much of the clastic material as Indicated by the kaoliniti c clays in the Nanafalia Formation and extensive thinly bedded silt and clay in the Tuscahoma.
IMPLICATIONS

The patterns in the Chattahoochee River area are similar to those found in the remainder of the eastern Gulf Coastal Plain according to the compilation by Toulmin (1977) . Pitman {1978) suggested a series of factors. including the rate of sediment supply, that might influence sea- level changes. The thinness of most of the Paleogene formations in this area suggests that differences in rate of sediment supply were minimal; the main exception to this is found in the Tuscahoma Sand where a relatively thick clastic wedge coincides with a regression pattern . Therefore, pending further data, it appears that regional changes in rates of subsidence caused the eastern Gulf Coast to have patterns of sea-level changes in the Paleocene and Eocene that are somewhat different from the generalized global pattern of Vail and others (1977).

The times of transgression in the eastern Gulf Coastal Plain as interpreted in the Chattahoochee
River area agree m general with those times of high
sea level found on a global scale by Vail and others (1977); however, some differences in the patterns suggest the effect of a regional overprint in the eastern Gulf area (fig. 7). The similarities between the Chattahoochee area pattern and the global patterns of Vail and others (1977) are as follows.
1. A major transgression in the early Paleocene, of greater extent than any other in the lower Paleogene.
2. A major regression near the boundary between the early and late Paleocene followed by a transgression in the late Pal eocene of lesser extent than that of the early Paleocene..
3. A small regression near the Paleocene-Eocene boundary.
4. A significant regression at the end of the early Eocene followed by a transgression in the early part of the middle Eocene of a lesser extent than that of the early Eocene.
The differences between the pattern for the Chattahoochee River area and the global one are as follows.
1. The regression at the end of the early Paleocene is found in zone NP3 by Vail and others (1977); in the Chattahoochee River area, marine deposition continues across this boundary and into zone NP4, a time of significant regression in the Vail and others (1977) chart (fig . 7).
2. The global pattern of Vail and others includes zone NP9 as a time of significant transgression; in the Chattahoochee area, zone NP9 is a regressive sequence following a widespread transgression in the beginning of this zone.
3. The Chattahoochee area has a significant transgression in zone NP10, but the remainder of the early Eocene is represented by a widespread regression; this pattern is in contrast to the continued high stand of sea level throughout the early Eocene noted by Vail and others.

REFERENCES CITED
Hardenbol, J ., and Berggren, W.A., 1978, A new Paleogene numerical time scale, in Cohee, G.V., Glaessner, M.F., and Hedberg, H.D., eds., Am. Assoc. Petroleum Geol., Studies in Geology No.6, p. 213, 234.
MacNeil, F.S., 1946, Geologic map of the Tertiary formations of Alabama: U.S. Geol. Survey Oil and Gas lnv. Prelim . Map 45, scale 1:500,000.
MacNeil, F.S., 1947, Geologic map of the Tertiary and Quaternary formations of Georgia: U.S. Geol. Survey Oil and Gas lnv. Prelim . Map 72, scale 1:506,880.
Marsalis, W.E., and Friddell, M.S., 1975, A guide to selected Upper Cretaceous and lower Tertiary outcrops in the lower Chattahoochee River valley of Georgia: Georgia Geol. Soc., Guidebook 15, 70 p., 4 pis.
Pitman, W.C ., Ill, 1978, Relationship between eustacy and stratigraphic sequences of passive margins: Geol. Soc. Amer. Bull., v. 89, p. 1389-1403.
Reynolds, W.R., 1966, Stratigraphy and genesis of clay mineral and zeolite strata in the lowerTertiary of Alabama, in Copeland , C.W., ed ., Facies changes In the Alabama Tertiary: Fourth Ann. Field Trip Guidebook, Alabama Geol. Soc., p. 26-37.
Toulmin, L.D., 1977, Stratigraphic distribution of Paleocene and Eocene fossils in the eastern Gulf coast region: Geol. Survey of Alabama Monograph 13, 602 p.
Toulmln, L.D., and LaMoreaux, P.E., 1963, Stratigraphy along Chattahoochee River, co nnecting link between Atlantic and the Gulf Coastal Plains: Am. Assoc . Petroleum Geol. Bull., v. 47, p. 385-404.
Vail, P.R., Mitchum, R.M., Jr., and Thompson, S., Ill, 1977, Seismic stratigraph and global changes of sea level, Part 4: Global cycles of relative changes of sea level, in Payton, C.E., ed., Seismic stratigraphy - applications to hydrocarbon exploration: Am . Assoc. Petroleum Geol. Mem. 26, p. 83-97.

63

A STRATIGRAPHIC FRAMEWORK
FOR CRETACEOUS AND PALEOGENE MARGINS
ALONG THE SOUTH CAROLINA AND GEORGIA COASTAL SEDIMENTS
Gregory S. Gohn, Laurel M . Bybell, Raymond A. Christopher, and James P. Owens
U .S. Geological Survey Reston, Virginia and Charles C. Smith
U.S. Geological Survey National Museum Washington, D.C.

ABSTRACT
Unpublished lithostratigraphic and biostratigraphic data from a subsurface stratigraphi c reconnaissance of the coastal counties of Georgia and South Carolina, in conjunction with publish ed subsurface data, have provided a basis for describing the onshore Cretaceous and Paleogene stratigraphic framework of the Southeast Georgia Embayment. Onshore, in the broadest sense, the Southeast Georgia Embayment is a southeast-plunging sedimentary basin bound ed in southern North Carolina by the Cape Fear arch and in Georgia and north er11 Fl orida by the central Georgia uplift and the Fl orida pe ninsular arch . Above a "basement" that includes ro c ks possib ly as young as Early (?) Jurassic , Upper Cretaceou s sedi ments reach a maximum thickness of about 675 m at the basin axis and a minimum of about 375 m on th e Cape Fear arch (at the coast) and on the peninsular arch . Samples from the studied wells yi elded no fossil evid ence to support either a Jurassic or an Early Cretaceous age for any Coastal Plain sediments, whereas late Cenomanian pollen, foraminifers and calcareous nannofossils were foun d at or nea r base ment in many wel ls. Upper Cre taceous Cenomania n strata (1 25-1 80 m lll lck) are con fined to the su bsurface In th e cent ral pa rt of the embaym ent and are abse nt i n th e updi p outcrop areas of eastern Geo rgia, So ut h Ca roli na , and Lhe Cap e Fea r arch . ! hey also are absen t o r th in (0- 10om) In the subsu rfac e on the peninsu lar and Cape Fear arches . An un con l ormiiy of large bu t uncert ain magn itude, perhaps re pres.enting most of th e Tu ronian an d Co niac ian Stages, separa tes Ce nomania n beds rrom young er stra ta throug hout til e emb aym ent. Sedimen ts of San ton ian to possib ly ea rt les l Campania n Ag e are widespread ac ross the embayment (30- 125 m) and are the oldes t Cretaceous beds to co ver mos t parts o f the arches and t he upper Coas tal Plain. Cyclical marine strata of Campanian to middle Maestrichtian Age are widespread in th e subsurface (250-350 m) and crop out on the Cape Fear arch.
Pal eocene (D an ian and Th aneti an) terrige nous cl ast ic sediments bec ome i ncreas in.g ly ca lca reo us an d thi cke n fro m a wed ge- ou t co ntact in th eir outcrop belt on th e fl ank of the Cape Fea r arch to ab out 100 m near Char leston , S.C., and rea ch a max imum thi c kn ess of abo ut 200 to 230 m in easter n Ge orgi a, Nea r t he coast, carbo nat e sedi ments of Eocen e age (Ypre si an to Pri ab onia n) thi c ken

from a wedge-out contact in their outcrop belt in eastcentral South Carolina to about 130 m near Charleston an d exceed 400 mi n eastern Georgi a. Thin sequences of calcareous Oligocene se dim enl s (0- 60 m) are apparently presen t thro ughout much o f tl1e su bsurface study area, but are poo rly defined litholog ica lly and paleontologically outsid e the Char leston area.
INTRODUCTION
Prompted by the increasing interest in the oil and gas potential of offshore areas in the Southeast Georgia Embayment, this report represents a preliminary effort at establishing a moderately detailed litho- and biostratigraphic framework for the subsurface Cretaceous and Paleogene sediments of the onshore part of the embayment. For the purposes of this report, the Southeast Georgia Embayment is defined in its least restricted sense as that onshore area bounded on the northeast by the Cape Fear arch, on the northwest by the Fall Line, and on the southwest by the Florida peninsular arch and the central Georgia uplift (fig . 1). In attempting to erect a stratigraphic framework for such a large area, we decided that a single cross section would be drawn along the modern coast (fig. 1, section A-A ' ) using published data and data potentially available from an examination of samples from deep wells. In all, samples from 12 wells were examined , and geophysical logs and published data were considered from about twice that number (table 1) . Of the 12 wells, two are continuously cored test holes: Clubhouse Crossroads #1 , Dorchester County, South Carolina; and Davis-Hopkins #1, Wayne County, Georgia .
In the sampled wells, cuttings or cores were examined to construct a gross lithologic log which was compared with the existing geophysical logs to establish a lithostratigraphic framework. In those wells, samples were also examined for Tertiary calcareous nannofossils, Cretaceous calcareous nannofossils and planktic foraminifers, and Cretaceous pollen. The Tertiary nannofossil zonation used in

64


OEORGIA

SOUTH ~AOLINA

---100 KILOMETERS

Figure 1.

Map of the Southeast Georgia Embayment showing contoured depths (m) below mean sea level to the pre-Cretaceous surface. The studied deep wells (in part numbered along cross section A-A-') are shown along the coast in South Carolina and Georgia and in western Georgia. Major structural features are labeled. Structure contours modified in part from Popenoe and Zietz (1977) .

Table 1. Deep boreholes used in this report. [Detailed locations and related information may be found in Applin and Applin (1967) ,
Brown and others (1978), and Gohn and others (1978a , b; 1979)]

Borehole

County

New data 1

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12a. 12b.
13. 14. 15. 16. 17. 18. 19.

Calabash water well Myrtle Beach-10th Avenue water well Penny Royal water well Estherville Plantation water well Isle of Palms water well U.S.G.S. Clubhouse Crossroads #1 Kiawah Island water well Fripp Island water well Parris Island #2 water well Pooler #1 water well Larue-Jelks and Rogers #1 W.K. Davis-C.D. Hopkins #1 W. K. Davis-C. D. Hopkins #2 (data combined with 12a) Pan American-Union Camp #1 Humble-Union Bag Camp Paper#ST-1 California-J.A . Buie #1 Pan American-Union Camp #B-1 Hunt-H.L. Hunt #1 Stanolind-J.H. Pullen #1 Dunlap-Saunders Co #1

Brunswick, N.C. Horry, S.C. Georgetown, S.C. Georgetown, S.C. Charleston, S.C. Dorchester, S.C. Charleston, S.C. Beaufort, S.C. Beaufort, S.C. Chatham, Ga. Liberty, Ga. Wayne, Ga. Wayne, Ga.
Glynn, Ga. Glynn, Ga. Camden, Ga Camden, Ga. Baker, Fla . Mitchell, Ga. Seminole, Ga.

F. Cu F, Cu F, Cu
F. Co F, Cu
F, Co F, Cu F, Cu F, Cu F, Cu
Co F, Cu

Unpublished fossil identifications (F); lithologic data from cuttings (Cu) and cores (Co) .

Total Depth (m)
407 436 248 560 691 792 698 966 1053 1038 1300 968 1332
1353 1412 1515 1430 1021 2283 2163

65

this report follows that of Bukry (1973, 1975, 1978), Gartner (1971) , and Martini (1971) . The Cretaceous planktic foraminiferal zonation follows that proposed by Pessagno (1967) and Smith and Pessagno (1973) ; mod ifications are in progress . The Mesozoic calcareous nannofossil zonation follows a modified version of the zonation proposed by Thierstein (1976). The palynological zonation follows that proposed by Brenner (1963) , Doyle (1969), Sirkin (1974), and Wolfe (1976), which has been modified by Doyle and Robbins (1977) and Christopher (in press ; see Christopher, this volume, for an outline of this zonation) . Ostracodes, dinoflagellates, Cretaceous mollusks, and Tertiary pollen were also examined from various parts of the two cored wells (Hazel and others , 1977; F.E. May, unpublished data; N.O. Frederiksen, unpublished data) .
Acknowledgements
We gratefully acknowledge the considerable efforts of William Abbott of the South Carolina Geological Survey and Harold Gill, Allan Zack , Michael Hig gi ns, and James Rhett , all of the U.S. Geological Survey, wh o sup plied us with cuttings, geophysical logs and other data from deep wells in South Carolina and Georgia. We also thank Joseph Hazel, Norman Sohl, Norman Fredericksen, Lucy Edwards, Page Valentine , Wyl ie Poag, Charles Paull , and William Dillon, all of the U.S. Geological Survey , for their discussions and for their permission to use some of their unpublished data related to the onshore and offshore stratigraphy of the Southeast Georgia Embayment. Technical assistance was provided by Melodie Hess, Ray Schneider, Diane McNeave, and Kathy Kilduff, all of the U.S. Geological Survey.
PRE-CRETACEOUS SURFACE
Figure 1 shows the overall configuration of the Southeast Georgia Embayment and structure contours on the pre-Cretaceous surface. From the broad Cape Fear arch, the pre-Cretaceous surface dips to the south through South Carolina and steepens abruptly in southeastern Georgia. From that area, the surface rises again on the peninsular arch and central Georgia uplift. This deepest part of the embayment in Glynn and Camden Counties, Georgia, is referred to as the Southeast Georgia Embayment in the restricted sense of many authors . Thicknesses of the Coastal Plain section reflect the depths of the pre-Cretaceous surface, about 400 to 500 m of sediments being found along the coast on the Cape Fear arch, 900 to 1,000 m on the peninsular arch , and a maximum of about 1,500 min southeastern Georgia.

PREVIOUS INVESTIGATIONS
A detailed review of the many studies of Coastal Plain sediments in South Carolina , Georgia, and northern Florida is beyond the scope of this report; only the most important investigations of subsurface stratigraphy in that area are listed here. Historically, the much thicker stratigraphic section in Georgia and northern Florida has attracted more exploratory drilling than has the generally thinner section in South Carolina. By 1974, about 148 oil tests had been drilled in Georgia (Pickering, 1974), whereas only 11 have ever been drilled in South Carolina (Olson and Glowacz, 1977). Stratigraphic studies in South Carolina and adjacent areas in Georgia have therefore had to rely on data from deep water wells.
In South Carolina, early studies of subsurface stratjgraphy include those by Stephenson (1914), Cooke (1936), Mansfield (1937), Richards (1945), and Mclean (1960) . More recent ground-water studies that present stratigraphic data include those by Siple (1969, 1975) and Zack (1977) . Recent stratigraphic studies include those by Valentine and Poag (1976), Zupan and Abbott (1976), Hazel and others (1977), and Gohn and others (1977, 1978a, 1978b).
The section in Georgia has been more extensively studied; important among the reports on this area are th ose on Cretaceo us stratig rap hy by E.R. Ap plin and P.A. A pp lin (A pp lin , 1955 ; Ap p lin and A p plin , 1947, 1964 , 1965 1 1967) . Ot her pap ers providi ng stratigraphic data include tl1 ose by Hurst (1960) . Her ri c k (1 96 1), Herri c k and Vorhls (1963), Chen (1965), Marsalis (1970), Cramer (1974), Brown (1974), and Gohn and others (1979) .
New regional syntheses of subsurface stratigraphic data are also available and provide a broader perspective to the study of stratigraphy in the Southeast Georgia Embayment. Important among these recent summaries are papers by Maher and Applin (1971), Valentine (1979), and Cramer and Arden (this volume) for the Cretaceous and Tertiary sections , and by Brown and others (1978) for the Cretaceous. Stratigraphic studies of the COST GE-1 well (Amato and Bebout , 1978; Scholle , 1979) provided the first detailed account of the Mesozoic and Cenozoic sections in the offshore part of the embayment.
CRETACEOUS SYSTEM
Basal beds
The oldest sequence of Coastal Plain sediments on the cross section is a thin and discontinuous layer of unfossiliferous sand and clay informally

66

referred to here as the basal beds (grouped with Cenomanian beds on fig . 2). The basal beds typically consist of red, yell ow , or b rown sa n dy clay and feldspathic medium- t o ve ry coarse-grained sand . Along the lin e of the cross section, these beds are thickest, about 60 m, near tl1e So ut h Caro linaGeorgia borde r, and th ey are confined p rincipa ll y to the ce ntral par t of tl1e embayment. T l1ey do not cross th eh igher par ts of the Florida peninsul ar arch (Applin and Ap p lin , 1965, 1967 ), and they probably c ross the Cape Fear arc h only nea.r t he coast . Dependi n g upo n wh ich of th eir repo rts is co nsu lted (App li n and App lin, 1947, 1965, 1967; Appli n, 1955) , the Applins assigned tt1ese beds eit her to the un differe nt iated Lo wer Cretaceous Series or to t he lower member of their Atkinson Fo rmation (Cenomanian) . Cramer (1974) assign ed these beds in Georgia to the undifferentiated Lower Cretaceous Series . Brown and others (1978) typi cally include these beds in the Unit F (Albi an to lower Cenomanian) .

The traditional Early Cretaceous age for these basal beds is derived primarily from their apparent lithologic continuity with a much thicker section of similar sand and clay in southwestern Georgia (Applin and Applin , 1965; Cramer, 1974). However, to our knowledge , no fossils have ever been reported from this unit anywhere in Georgia or South Carolina, nor did we find any in our samples from eastern Georgia other than obvious cavings. However, during the present study, samples examined from the thick Lower(?) Cretaceous section in the Dunlap-Saunders #1 well (well 19, fig . 1) in extreme southwestern Georgia (Seminole County) were found to contain pollen indicative of zone IV of late Cenomanian Age (Christopher, this volume), as well as long-rangin g ca lcareous nan nofossi ls. An equal or greater nu mber of poll en and microf ossi l species indicative of post-Cenom ani an Cretaceous and Tertiary age are also prese nt in th e same samples. Splits of cores from the Lower(?) Cretaceous

A

FLOAIOAI GEORGIA

I GEORGiA SOUTH CAROLINA

I

17

16 15 14 13 12 11

I

10

9 8

7

6

5

MEAN SEA LEIJEL

43

SOUTH

I CAROLINA NORTH
CAROLINA
I

2

1

uPPER

20 L_
METERS ~0 KILOMETERS
Figure 2. Stratigraphy of the subsurface Coastal Plain sediments along the line of section A-A' in figure 1. Numbered wells are listed in table 1.
67

section in the Stanolind-Pullen #1 well in southwestern Georgia (we\118 , fig . 1) were also examined but were found to be barren of pollen and calcareous fossils. Because the Dunlap-Saunders samples are cuttings and contain some obvious evidence of downhole contamination, the late Cenomanian Age cannot be readily accepted at present for the traditional Lower Cretaceous sequence (basal beds) . Age determinations for vertically adjacent beds in eastern Georg ia and So uth Caro li na Ind ica te o nly that th e basa l be d s of thi s rep o rt are th e same ag e or olde r t h n o verly ing late Ce no manian fossils , and th e same age o r yo un ger tha n u nderl yi ng basa lt fl ow s and ass o ciate d co ntin ental red beds o f Late Triassic and (or) Early Jurassic age (Gohn and others, 1978c; Chowns, this volume).
Upper Cretaceous Series
Cenomanian Stage
Above the basal Cretaceous beds of uncertain ag e is a th icker late Ce no man ian-( mld dle Eagl eford lan) - Ag e sequence of calcareous, dark sa ndy o r s ilty cl ay .(clay lit11ofa c ies) an d a laterally eq uivalent se que nce of reddi sh , f eld spath ic , coa rseg rain ed sand and associated reddis h clay (sand !itl1ofaci es) in th e ce nt ral part of th e embaym ent (fig. 2) . T he c lay lith ofa cies con stitut es most o f t he southern part of this unit; a lower and possibly an upper clay tongue extend into South Carolina (Gohn and others, 1979). In South Carolina and northeastern Georgia, the same lithofacies dominates.
The upper Cenom ania n st rata are thickest, about 180m, near th e So uth Ca rol i na- Geo rgia border and thin toward both arch es . Pro bab ly only the sand lithofacies c rosses t he Cape Fea r arch and does so on ly near the coas t. Si mil arly , only a thi n se que nce of the cl ay lithofac ies in Georgia and nort hern Florida cr osses the pen insul ar arc h: this u nit is loca lly abs ent , as shown i n th e Hun t #1 Well (well 17, fig . 2), wh ere Santonian- Age sedim ents rest upon Paleozoic ro c ks (see also Appli n and App lin, 1967, p late 3).
Applin and Applin (for example, Applin and Applin, 1967) traditionally assigned all these beds to the lower and upper members of their Atkinson Formation . Til e A ppl ins assign ed a Woodblnian Age to t he lo wer meml)er of th e Atk inso n and an Ea gl efordian Age to the upper member. primarily on th e basi s of ben thic for am in i fera. Thi s age ass ig n ment is herein co nside red to represen t th e Euro pean middl e Cenom anian to Tu ro n ian Age. Haze l (1969) noted th e reported occu rrence e f tw o late Cenomanian guide fossils in the lower member of the Atkinson Formation; the ostracod Cythereis eaglefordensis Alexander was reported by Swain and Brown (1964), and the planktic foraminifer Rotalipora cushmani (Morrow) was reported by Applin

(1955) . Hazel suggested, therefore, that the lower member is of late Cenomanian (middle Eaglefordian) Age. Brown and others (1978) placed most of the sediments assigned herein to the Cenomanian Stage in their Units F (Fredericksburgian to Washitan), E (Woodbinian). and D (Eaglefordian) , thereby suggesting Albian through Turonian Age.
In the wells studied for this report, strata of Cenomanian Age are of nonmarine and shallow or marginal marine character. Although planktic foraminifers are rare and consist almost entirely of globigerine forms, species such as Guembelitria harrisi Tappan and Globigerinelloides caseyi (Bolli, Loeblich, and Tappan) , as well as Hedbergella brittonensis Loeblich and Tappan and H. delrioensis (Carsey), provide strong evidence for a late Cenomanian Age. Distinctive and diverse calcareous nannofossil floras, including Lithraphidites alatus Thierstein, Parhabdolithus asper (Stradner), and Podorhabdus albianus Black further confirm a Cenomanian Age for these strata.
Several pollen species considered guide fossils to the late Cenomanian pollen zone IV were also o bserved In the coas tal w ells. Amon g the more diag nostic forms are Al/an topo /l is verr ucosa (G root and Groot ) Gocza n, Groot. Krutzsc h, and Pac ltova. and nu merous spec ies o f Co mp lex iopollis . (Ch ri stoph er, th is volume, provid es a mo re com pl ete discuss ion of t he palynologi ca l c haracteris ti cs o f upper Cenomanian strata in the southeastern United States.)
Turonian Stage
Specific fossil evidence for the presence of sediments o t T uroni an (late Eagl efo rdi an) Age w as not f o un d in any o f tl1 e studi ed well s. T he p rese nce o f se di ments co nt aining late Ceno ma ni an poll en and calcareou s rnic ro- and na nnofo ssi ls im mediately below se dim en ts c on tain in g Santoni an poll en and ca lcareou s fo ssi ls in many well s su gg es ts t hat t l1e T uron ian Stage is un re pre sented o nsho re in t he Southeast Georgia Embayment. Hazel and others (1977) noted this stratigraphic pattern in the Clubhouse Crossroads #1 core and commented that the late Eaglefordian was a time of widespread regression in the eastern Gulf coastal and Atlantic coastal areas. Christopher (this volume) discusses the absence of sediments representing the Turonian and most of the Coniacian Stages in Cretaceous outcrop areas of Georgia.
In contrast, Valentine ( 1979, personal commun., 1979) interpreted Turonia n se dime nt s as being present at the bottom of th e Fri pp Isla nd w ell (well 8 of this report) in South Caro lin a on the bas is of the concurrence of the calcareous nannofossils Eiffe/lithus eximius (Stover) and Corrolithion achy/osum (Stover). Samples at the bottom of this well also

68

contain late Cenomanian pollen and are included herein with the Cenomanian Stage. In the offshore part of the em ba ym ent. in t he COST GE-1 well, Valentin e (1979) an d Po ag and Hall (1979) have recognized a moderately thick Turonian section and no Cenom anian sedi ments. Brown and others (1978) recognized the presence of their Unit D of middle and late Eaglefordian Age (Turonian of their report) in many of the wells described herein. These sediments contain late Cenomanian fossils in several wells and have been included in the Cenomanian Stage in our report.
Coniacian Stage
Sediments of Coniacian (early Austin ian) Age are questionably present onshore in the Southeast Georgia Embayment. The presence of Santonian sediments in some of the studied wells was determined in large part by the presence of pollen indicative of pollen zone V. At present, the boundaries of zone V can be defined only to the degree that the zone is known to represent the Santonian Stage, but it may also include the earliest Campanian and some unknown, perhaps small fraction of the Coniacian. Given these constraints, some Coniacian sediments may be present, but they cannot be temporally or lithologically distinguished from overlying Santonian beds. Therefore, a Con iacian unit is not shown separately in figure 1, although some of the basal Santonian sediments may actually be Coniacian. In the studied wells, sediments assigned by Brown and oth ers (1978} to th ei r Unit C (Au stini an) potentia lly i nclude any Co niac ian sed im ents th at may be p rese nt. Valenti ne (197 9) sho wed Coniac ian sedi ments g rou ped with Sa nton ia n se diment s in the Frip p Island w ell , and Valentin e (1979 ) and Poag and Hall (1979) rec og ni zed a C on iac ian un it In the COST GE-1 well.
Santonian Stage
A subsurface marine unit consisting of fossiliferou s silty c lay , ca rbo naceo us c lay , and coa rseg rained sand princ ipally o f Santonian Ag e is wid esp read ac ross the embaym ent. Sedim ents ot t h is ag e are th e o ld est Cretaceo us be.ds to c ov er the arc hes co mp lete ly and to reac h th e vi ci ni ty of th e Fa ll Li ne in th e embaym ent. Th is secti o n consists of terr ig eno us c las ti c sedime nts th roug ho ut South Carol in a and Georg ia but cha ng es to a dominan tl y carbonate facies in northern Florida . On the cross section (fig . 2), the Santonian sediments range in thickness from about 30m in parts of South Carolina to as much as 125 m in eastern Georgia .
An assignment of possibly late Coniacian, certainly Santonian, and possibly earliest Campanian Age (collectively a middle to late Austinian Age) is

derived from samples from many wells containing pollen, planktic foraminifers, and calcareous nannofossils. Within the onshore Southeast Georgia Embayment area, beds of Santonian Age stratigraphically represent the oldest sedimentsto contain a rich and diverse microfauna and nannoflora. Planktic foraminifers are represented by numerous keeled species assignable to the genus Marginotruncana , includng abundant M. concavata s.l. (Brotzen), one of the particularly distinctive species indicative of strata of Santonian Age. Calcareous nannofossil floras are especially diverse , most samples conta ining 50 or more speci es. Samples containing Ma rthasterites furca tus (Deflandre), Litha strinus gril /ii St rad ner, L. flora/is Stradner, and Tetralithus obscurus Defl and re are common throughout the embayment area and are diagnostic for strata of Santonian Age. Palynologic assemblages are also rich and diverse in this unit. Forms diagnostic of pollen zone V include Porocolpopollenites spp ., Ho/kopol/enites spp., Nyssapo/lenites spp. , and others (see Christopher, this volume).
Sediments assigned herein to the Santonian Stage have been interpreted in a similar manner by Brown and others (1978) and by Valentine (1979) . The outcropping Cape Fear, Middendorf, and basal part of the Black Creek Formations in the Cape Fear arch area, and much of the outcropping sediment traditionally assigned to the Middendorf and "Tuscaloosa" Formations in the upper Coastal Plain of South Carolina and eastern Georgia are also of Santonian Age (Christopher and others, 1979; Christopher, this volume) .
Campanian and Maestrichtian Stages
Above the Santonian section, cyclical marine beds of early Campanian to middle Maestrichtian (Tayloran-Navarroan) Age are widespread throughout the subsurface in the Southeast Georgia Embayment. Shelly clay and clayey sand are typically repeated in 40- to 80-m-thick, upwardcoarsening cycles that represent repeated transgressions and regressions in South Carolina and northeastern Georgia. South of the present-day Altamaha River, these terrigenous clastic sediments are replaced by laterally equivalent carbonate sediments of similar age. Both the terrigenous clastic and carbonate sections maintain a fairly constant thickness across the embayment ; thicknesses typically range from 250 to 350 m.
The lower Campanian section typically consists of one relatively thick cycle that is readily distinguished from younger Cretaceous cycles (Gohn and others, 1978a, 1979). Similarity of lithologies, downhole caving of fossils and cuttings and carbonate-sediment recrystallization make tem-

69

poral and lithologic division of the late Campanian and Maestrichtian cycles difficult in many of the studied wells .
The younger part of the carbonate section was included by Applin and Applin (1967) in the Lawson Limestone. The terrigenous clastic sediments crop out on the Cape Fear arch where they constitute the Peedee and upper part of the Black Creek Formations. The sediments assigned herein to the Campanian and Maestrichtian Stages have, in general, also been assigned to these stages by Brown and others (1978), Valentine (1979), Applin and Applin (1967), and Maher and Applin (1971) .
The sediments of Campanian and Maestrichtian Age contain a well-preserved and diverse calcareous nannofossil flora which has permitted a detailed biostratigraphic zonation and refined correlation ~f these sediments in wells where downhole contamination of cuttings and sediment recrystallization are not extensive. These sediments also contain abundant planktic foraminifers including numerous keeled forms assignable to the genera Globotruncana and G/obotruncane/la, as well as abundant nonkeeled Rugoglobigerina and Archaeoglobigerina. Species diagnostic of upper Maestrichtian strata including Abathomphalus mayaroens1s (Bolli), A. intermedia (Bolli), and Pseudotextularia intermedia de Klasz, have not been observed 1n any of our sampled material. The absence of these species, among others, indicates that strata of late Maestrichtian Age were erosionally removed during latest Maestrichtian and early Danian time or were never deposited , resulting in a widespread and persistent unconformity extending throughout the Gulf and At lantic Coastal Plain area. Among the Campan ian and Maestrichtian pollen species observed in thes e sed iments are Plicapollis usitatus Tschudy, OscJiapollis aequa/is Tschudy, Endoinfundibu/~ polis distinctus Tschudy, and several forms co~sl dered by Wolfe (1976) as indicative of Campan1an and (or) Maestrichtian Age (for example, his morphotypes MPH-1, MPH-2, N0-2, N0-3, and others).
TERTIARY SYSTEM
Paleocene Series
Paleocene sediments of both Danian and Thanetian (Midwayan to early Sabinian) Age thicken, as shown on figure 2, from their outcrop belt on the flank of the Cape Fear arch in South Carolma toward Georgia . The Paleocene section is thickest, about 200 to 230 m, in northeastern Georgia and southern South Carolina; a depositional hinge line in South Carolina (between wells 7 and 8) corresponds to the change from terrigenous clastic (northeast) to carbonate (southwest) se?iment d.epos.ition in the Thanetian. The Dan1an sect1on IS

composed essentially of marine terrigenous clastic sediments southward to the latitude of the presentday Altamaha River, where that section bec.om~s increasingly calcareous. The Paleocene sectiOn .In southeastern most Georgia is very sparingly fossilif-
teeromup~sraalndanbdecliathuossetroaftitghreadphififcicuunltiytsininrtehcio~ ghneiazvini!Yg
recrystallized carbonate section, the strat1graph1c interpretations of the Tertiary section have not been extended to the south any father than about well13.
Recognition of Paleocene sediments in the studied wells by means of calcareous nannofossils is relatively simple, although the use of cuttings in most wells makes determination of individual zones tenuous because of downhole contamination. Poor preservation in many of the samples is an additional complication. These problems are compensated for, in part, by the study of samples from the two coreholes (wells 6 and 12a). The oldest definitely recognizable Paleocene sediments are approximately equivalent to Martini 's (1971) zone NP3 (Danian, but not oldest Danian) on the basis of the lowest occurrence of Chiasmolithus consuetus (Bramlette and Sullivan). The first evolutionary occurrence of Toweius craticulus Hay and Mohler marks the base ot zone NP4. Zone NP5 may be missing in Georgia and so uthern South Carolina, whereas there is so me evidence for its presence farther north In South Carolina on the basis of the first evo lutionary occurrence of th e genus Fasciculithus . The lowest occurrence of He/iolithus kleinpelli Sullivan coincides with th e i)ase o f zone NP6. The base of zone NP7, which is usually determined by the evolutionary appearance of the genus Discoaster, is unidentifiable in the study area because of the paucity of these forms. The zone NP8 marker Heliolithus riede/i Bramlette and Sullivan is not common , and because of the poor preservation of the nannofossils in most wells examined, it is rarely observed. Oiscoaster multiradiatus Bramlette and Riedel, the marker for zone N P9, is consistently present in small numbers in samples from Georgia and most of South Carolina, but in northern South Carolina, this zone, and perhaps younger zones, apparently are absent.
Eocene Series
Ypresian Stage
Ypresian (upper Sabinian) se d iments make up a persistent stratigraphic unit that maintains a regu lar thickness, typically less than 20 m, from its outcrop belt in eastern South Carolina southwest w ard to at least the Altamaha River. The unit consists primarily of glauconitic impure limestone that marks the beginning of a period of widespread deposition of carbonate sediments across the embayment, deposition that persisted into the Oligocene.

70

Lower Eocene nannofossil zones NP10 and NP11 are missing in all the studied wells. Fairly abundant nannofossil assemblages indicative of zones NP12 through NP14 are present in Georgia, whereas probably only zone NP12 is represented in South Carolina. Typical early Eocene forms observed include Chiasmolithus grandis (Bramlette and Riedel), Cyclococcolithus formosus Kamptner, Discoaster barbadiensis Tan Sin Hok, D. /odoensis Bramlette and Riedel, Discoasteroides kuepperi (Stradner), Helicosphaera lophota (Bramlette and Sullivan) , H. seminulum Bramlette and Sullivan1 Rhabdosphaera inflata Bramlette and Sullivan, Sphenolithus radians Deflandre, and Transversopontis pulcher (Deflandre) .
Lutetian, Bartonian, and Priabonian Stages
Middle and upper Eocene (Lutetian to Priabonian; Claibornian and Jacksonian) carbonate sediments are widespread in the central and southern parts of the embayment and thicken dramatically from north to south. Near their wedgeout contact in the Eocene outcrop belt in South Carolina, these carbonate sediments are about 60 to 100m thick, whereas in eastern Georgia they are about 400 m thick . Although many formations have been recognized in this section, these sediments have not been subdivided on figure 2 because calcite recrystallization and dolomitization have obscured many of the primary lithologic characteristics and have obliterated most of the calcareous fossils in many wells.
Accordingly, it is difficult to zone the middle and upper Eocene sequence in the study area using the typically sparse and recrystallized calcareous nannofossils or any other fossil group. Calcareous nannofossils indicative of middle and (or) late Eocene age that are present in some wells include 8/ackites spinosus (Deflandre and Fert), Cyc/ococcolithus reticulatus Gartner and Smith, C. floridanus (Roth and Hay), Helicosphaera compacta Bramlette and Wilcoxon, Helicosphaera bramletti (Muller), Discoaster saipanensis Bramlette and Riedel, Jsthmolithus recurvus Deflandre, Pemma papillatum Martini, and Reticulofenestra bisecta (Hay, Mohler, Wade).
Oligocene Series
During the study, sediments containing Oligocene fossils were found only in wells near Charleston, S.C., although other authors have described thin Oligocene sections throughout southern South Carolina and Georgia (for example, Herrick, 1961; Siple, 1969) . Near Charleston, in the Clubhouse Crossroads #1 core (well 6) and nearby wells, an irregularly thick unit (0 to 60 m) of calcareous,

phosphatic clayey sand contains calcareous nannofossils, ostracodes, foraminifers, mollusks, dinoflagellates, and pollen of Chattian (late Vicksburgian to Chickasawayan) Age (Hazel and others , 1977) . No identifiable early Oligocene calcareous nannofossils or other fossils were found in the study area. On the basis of the nannofossils, the upper Oligocene sediments in the Charleston area may be assigned to zone NP24. Typical zone NP24 forms that are present include Cyc/ococcolithus neogammation Bramlette and Wilcoxon, Discoaster woodringi Bramlette and Riedel , Helicosphaera sp . ct. H. carteri (Wallich), H. recta (Haq), Pontosphaera clathrata (Roth and Hay), Sphenolithus ciperoensis Bramlette and Wilcoxon , S. distentus (Martini), and S. predistentus Bramlette and Wilcoxon.
STRATIGRAPHIC COLUMN AND SUMMARY
Figure 3 is a geologic column that summarizes the stratigraphic distribution of subsurface Cretaceous and Paleogene depositional sequences in the onshore part of the Southwest Georgia Embayment. The relationships shown between European and North American Provincial Stages are modified from Hazel and others (1977) and from Hardenbol and Berggren (1978).
Viewing the coastal Georgia-South Carolina cross section as a whole, virtually all the units are thicker in Georgia than in South Carolina and are thicker on the peninsular arch than on the Cape Fear arch , thereby giving a considerable asymmetry to the embayment. In the area of thickest sedi mentation in Glynn and Camden Counties, Georgia, the section consists of roughly 50 to 60 percent Tertiary sediments, well over half of which are Eocene carbonate rocks. The post-Eocene section consists primarily of upper Oligocene beds in the Charleston, S.C . area and primarily of Miocene sediments in southern South Carolina and Georgia. In considerable contrast to the stratigraphic sections in the Salisbury and Raritan Embayments of the northern Atlantic Coastal Plain (Minard and others , 1974), the onshore part of the Southeast Georgia Embayment contains little or no Lower Cretaceous sediment, relatively thin sections of basal Upper Cretaceous clastic sediment, and relatively thick and more calcareous lower Tertiary sediment.

71

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Geologic column showing the stratigraphic distribution of Cretaceous and Paleogene depo sitional sequences onshore in the Southeast Georgia Embayment. Thicknesses of strati graphic units and durations of ages are not im plied. North (right)to-south (left) distribution of terrigenous clastic facies (stippled pattern) and carbonate facies (limestone pattern) is shown. Moderate to long periods of nondepo sition and (or) erosion are shown by vertical lines.

REFERENCES CITED
Amato, R.V., and Bebout, J.W., eds ., 1978, Geological and operational summary, COST No. GE-1 well, Southeast Georgia Embayment area, South Atlantic OCS: U.S. Geol. Survey openfile rept. 78-668, 122 p.
Applin, E.R., 1955, A biofacies of Woodbine age in the southeastern Gulf Coast region: U.S. Geol. Survey Prof. Paper 264-1, p. 187-197.
Applin, E.R., and Applin, P.L., 1964, Logs of selected wells in the Coastal Plains of Georgia: Georgia Geol. Survey Bull. 74, 229 p.
Applin, P.L., and Applin, E.R., 1947, Regional subsurface stratigraphy, structure, and correlation of middle and early Upper Cretaceous rocks in Alabama , Georgia, and north Florida: U.S. Geol. Survey Oil and Gas lnv. Prelim. Chart 26, 3 sheets .
_ _,1965, The Comanche Series and associated rocks in the subsurface in central and south Florida: U.S . Geol. Survey Prof . Paper 447, 84
p. _ _,1967, The Gulf Series in the subsurface in
northern Florida and southern Georgia: U.S. Geol. Survey Prof. Paper 524-G , 34 p. Brenner, G.J., 1963, The spores and pollen of the Potomac Group of Maryland: Maryland Dept. Geology, Mines and Water Resources Bull. 27, 215 p.
Brown, P.M., 1974, Subsurface correlation of Mesozoic rocks in Georgia, in Stafford, L.P., camp., Symposium on the petroleum geology of the Georgia Coastal Plain: Georgia Geol. Survey Bull. 87, p. 45-59.
Brown, P.M., Brown, D.L., Reid, M.S., and Lloyd, O.B ., Jr., 1978, Evaluation of the geologic and hydrologic factors related to the waste-storage potential of Mesozoic aquifers in the southern part of the Atlantic Coastal Plain, South Carolina and Georgia : U.S. Geol. Survey open-file rept. 78-292, 86 p.
Bukry, David, 1973, Low-latitude coccolith biostratigraphic zonation Cretaceous-Recent, in Edgar, N.T., Saunders, J.B., and others, Initial reports of the Deep Sea Drilling Project, v. 15: Washington, U.S. Government Printing Office, p. 685-703.
_ _,1975, Coccolith and silicoflagellate stratigraphy, northwestern Pacific Ocean, Deep Drilling Project Leg 32, in Larson, R.L., Moberly, R. , and others , Initial reports of the Deep Sea Drilling Project, v. 32: Washington, U.S. Government Printing Office, p. 667-701 .
_ _,1978, Biostratigraphy of Cenozoic marine sediments by calcareous nannofossils: Micropaleontology, v. 24, p. 44-60.
Chen, C .S., 1965, The regional lithostratigraphic analysis of Paleocene and Eocene rocks of Florida: Florida Geol. Survey Bull. 45, 105 p.

72

Christopher , A. A., Normapolles and tri porat e po lle n asse mbl ages from t11e Raritan and Magothy Form ations (Upp er Cret aceou s) of
New J erse y : Palynology, v. 3.. in press ,
Chri stoph er, R.A. , Ow e ns, J .P., and Soh I, N.F. , 1979, Pa lyn o log ic al evidence for ass ig ni n g a Late C re taceo us age t o t he Cape Fear Form ation o f North Carolin a: Southeastern Geology , in press.
Cooke, C.W., 1936, Geology of the Coastal Plain of South Carolina: U.S. Geol. Survey Bull. 867, 196 p.
Cramer, H.R ., 1974, Isopach and lithofacies analyses of the Cretaceous and Cenozoic rocks of the Coastal Plain of Georgia, in Stafford, L.P., comp., Symposium on the petroleum geology of the Georgia Coastal Plain : Georgia Geol. Survey Bull . 87, p. 21-43.
Doyle, J .A. , 1969, Angiosperm pollen evolution and biostratigraphy of the basal Cretaceous formations of Maryland, Delaware, and New Jersey: Geol. Soc . America Abs . with Programs, (v. 1), pt. 7, p. 51.
Doyle, J .A ., and Robbins, E.l. , 1977, Angiosperm pollen zonation of the continental Cretaceous of the Atlantic Coastal Plain and its application to deep wells in the Salisbury embayment: Palynology, v. 1, p. 43-78.
Gartner, Stefan , 1971, Calcareous nannofossils from the JOIDES Blake Plateau cores and revision of Paleogene nannofossil zonation: Tulane Studies Geology and Paleontology, v. 8, p . 101-121 .
Gohn, G.S., Bybell, L.M., Smith, C .C., and Owens, J.P., 1978a, Preliminary stratigraphic cross sections of Atlantic Coastal Plain sediments of the Southeastern States: Cenozoic sediments along the South Carolina coastal margin: U.S. Geol. Survey Misc . Field Studies Map 1015-B, 2 pl.
Gohn, G.S. , Christopher, R.A ., Smith, C .C., and Owens, J.P., 1978b, Preliminary stratigraphic cross sections of Atlantic Coastal Plain sediments of the southeastern United States: Cretaceous sediments along the South Carolina coastal margin : U.S. Geol. Survey Misc. Field Studies Map 1015-A, 2 pl.
Gohn, G .S., Gottfried, David , Lanphere, M .A ., and Higgins, B .B., 1978c, Regional implications of Triassic or Jurassic age for basalt and sedimentary red beds in the South Carolina Coastal Plain : Science, v. 202, p. 887-890.
Gohn, G .S., Higgins , B.B., Smith, C .C ., and Owens, J .P., 1977, Lithostratigraphy of the deep corehole (Clubhouse Crossroads corehole 1) near Charleston, South Carolina: U.S. Geol. Survey Prof . Paper 1028-E, p. 59-70.
Gohn , G .S., Smith, C .C., Christopher, R.A., and Owens, J .P., 1979, Preliminary stratigraphic cross sections of Atlantic Coastal Plain sedi-

ments of the southeastern United States: Cretaceous sedime.nts along the Georgia coastal margin : U.S. Geol. Survey Misc. Field Studies Map 1015-C, in press. Hardenbol, J ., and Berggren , W.A., 1978, A new Pal eoge ne num eri ca l tim e scale, in C o hee, G .V., a nd o t hers. ed ., Con t ribut io ns to the geologic ti me scale: Am . Assoc . Petro leum Geologists Stu d ies Geology No . 6, p. 213-234. Hazel. J.E., 1969, Cytherefs eaglefordens is Al exan der, 1929- A gu id e fo ss il fo r d eposits of latest Cenomanian age in the Western Interior and Gulf Coast regions of the United States: U.S. Geol. Survey Prof. Paper 650-D, p. D155-D158. Hazel, J .E. , Bybell, L.M ., Christopher, R.A ., Frederiksen, N.O., May, F.E., Mclean, D.M ., Poore, R.Z ., Smith, C .C. , Sohl, N.F., Valentine, P.C., and Witmer, R.J., 1977, Biostratigraphy of the deep corehole (Clu b ho use C ross roads corehole 1) near Charl es ton, So u th Carolina : U.S . Geol. Survey Prof. Paper 1028- F, p. 7 1-89. Herrick, S.M ., 1961, Well logs of t he Coasta l Plain of Georgia : Georgia Geol. Survey Bull. 70, 461 p . Herrick, S.M., and Vorhis, Robert C., 1963, Subsurface geology of the Georgia Coastal Plain: Georgia Geol. Survey lnf. Circ. 25, 79 p. Hurst, V.J., 1960, Oil tests in Georgia: Georgia Geol. Survey Int. Circ. 19, 14 p. Maher, J .C., and Applin, E.R ., 1971, Stratigraphy, in Maher, J.C ., Geologic framework and petroleum potential of the Atlantic Coastal Plain and Continentia! Shelf: U.S. Geol. Survey Prof. Paper 659, 98 p. Mansfield, W.C., 1937, Some deep wells near the Atlantic Coast in Virginia and the Carolinas: U.S. Geologic Survey Prof. Paper 186-1, p. 159-161 . Marsalis , W.E., 1970, Petroleum exploration in Georgia : Georgia Geol. Survey Int. Circ . 38, 52 p. Martini, Erlend, 1971, Standard Tertiary and Quaternary calcareous nannoplankton zonation, in Farinaci, A., ed., Proceedings of the Second Planktonic Conference, Roma 1970: Edizioni Technoscienza, p. 739-785. Mclean, J .D., 1960, Stratigraphy of the Parris Island area, South Carolina: Mclean Paleont. Lab. Rept. 4, unpaged.
Minard, J P., Perry , W.J., Weed, E.G .A. , Rhodehamel , E.C ., Robbins, E.l., and Mixon, R.B., 1974, Preliminary report on geology along Atlantic continental margin of northeastern United States: Am. Assoc. Petroleum Geol. Bull., v. 58, p. 1169-1178.
Olson , N .K ., and Glowacz , M.E., 1977, Petroleum geology and oil and gas potential of South Carolina: Am. Assoc. Petroleum Geol. Bull ., v. 61 , p. 331-343.

73

Pessagno, E.A., Jr., 1967, Upper Cretaceous planktonic foraminifera from the western Gulf Coastal Plain : Palaeontographica Americana, v. 5, p. 245-445.
Pickering, S.M., Jr., 1974, Petroleum potential of Georgia, in Stafford , L.P., comp ., Symposium on the petroleum geology of the Georgia Coastal Plain : Georgia Geol. Survey Bull. 87, p. 11-14.
Poag, C .W., and Hall, R.E. , 1979, Foraminiferal biostratigraphy, paleoecology, and sediment accumulation rates, in Scholle, P.A ., ed ., Geological studies of the COST GE-1 well , United States South Atlantic Outer Continental Shelf area, U.S. Geol. Survey Circ. 800, p. 49-63.
Popenoe , Peter, and Zietz, Isidore, 1977. The nature of the geophysical basement beneath the Coastal Plain of South Carolina and northeastern Georgia: U.S. Geol. Survey Prof. Paper 1028-1 , p. 119-137.
Richards, H.G ., 1945, Subsurface stratigraphy of Atlantic Coastal Plain between New Jersey and Georgia : Am. Assoc . Petroleum Geol. Bull., v. 29, p. 885-995.
Scholle, P.A ., ed ., 1979, Geological studies of the COST GE-1 well, United States South Atlantic Outer Continentia! Shelf area : U.S. Geol. Survey Ci rc . 800, 114 p.
Siple , G .E., 1969, Salt-water encroachment of Tertiary limestones along coastal South Carolina: South Carolina Div. Geology Geol. Notes, v. 13, p. 51-65 .
_ _ ,1975, Ground-water resources of Orangeburg County, South Carolina : South Carolina Div. Geology Bull. 36, 59 p.
Sirkin, L.A., 1974, Palynology and stratigraphy of Cretaceous strata in Long Island, New York, and Block Island, Rhode Island : U.S. Geol. Survey Jour. Research, v. 2, p. 431-440.
Smith , C.C., and Pessagno, E.A. , Jr., 1973, Planktonic Foraminifera and stratigraphy of the Corsicana Formation (Maestrichtian), north-central Texas : Cusman Found. Foram. Research Spec. Pub . 12, 68 p.
Stephenson, L.W., 1914, A deep well at Charleston , South Carolina: U.S. Geol. Survey Prof. Paper 90-H, p. 69-94.
Swain, F.M., and Brown, P.M., 1964, Cretaceous Ostracoda from wells in the southeastern United States: North Carolina Div. Mineral
. Resources Bull. 78, 55 p. Thierstein, H.R., 1976, Mesozoic calcareous nanno-
plankton biostratigraphy of marine sediments: Marine Micropaleontology, v. 1, p. 325-362 .

Valentine, P.C., 1979, Regional stratigraphy and structure of the Southeast Georgia Embayment, in Scholle, P.A., ed., Geological studies of the COST GE-1 well, United States South Atlantic Outer Continental Shelf area: U.S. Geol. Survey Circ . 800, p. 7-17 .
Valentine, P.C ., and Poag , C. W., 1976, Cross sections, showing regional stratigraphi c relationships, in Hathaway, J.C ., and others, Preliminary summary of the 1976 Atlantic margin coring project of the U.S. Geological Survey: U.S. Geol. Survey open-file rept. 76-844, p. 198-205.
Wolfe, J.A., 1976, Stratigraphic distribution of some pollen types from the Campanian and lower Maestrichtian rocks (Upper Cretaceous) of the middle Atlantic states: U.S. Geol. Survey Prof . Paper 977, 18 p.
Zack, Allen, 1977, The occurrence, availability, and chemical quality of ground water, Grand Strand area and surrounding parts of Horry and Georgetown Counties, South Carolina: South Carolina Water Resources Comm . Rept. No.8, 100 p.
Zupan, A .J., and Abbott, W.H., 1976, Comparative geology of onshore and offshore South Carolina, in Hathaway, J.C., and others, Preliminary summary of the 1976 Atlantic margin coring project of the U.S. Geological Survey, U.S. Geol. Survey open-file rept. 76-844, p. 206-214.

74

UPPER EOCENE STRATIGRAPHY OF EASTERN GEORGIA
Paul F. Huddlestun and John H. Hetrick Georgia Geologic Survey Atlanta, Georgia

ABSTRACT

The upper Eocene Barnwell Formation is herein raised to group status. Three formations of t!le Barnwell Group are recognized: the Clinchfield Sand, the Dry Branch Formation (new name), and the Tobacco Road Sand. Four members of the Clinchfield Formation are recognized: the Riggins Mill and Treadwell Members of eastcentral Georgia, and the Albion and Utley Members of eastern Georgia. The Dry Branch Formation is divided into two members, a lower Twiggs Clay Member and an upper Irwin ton Sand M ember. An unn amed c alcareous sand / sandy limestone subdivis ion of ll1 e Dry Bran c h is recognized In th e shal low subsurface of Screven and no HI1 ern Eff i ng l1am Counties , Georg ia The Sandersville limes tone Is recog ni zed as a member or th e Tobacc o Road Sand.
The three upper Eocene rock groups in the southeastern United States may best be viewed as lithosomes: a sand lithesome (Barnwe ll Group of 111e south Atl antic Coastal Plain). a clay lithesome (Yazoo Group olthe Gulf Coastal Plain), and a carbonate lithesome (Ocala Group of the Florida banks) . These li l110somes tntertongue in

central and eastern Georgia. Two tongues of the Ocala Group are recognized: the lower tongue, the Tivola Limestone, is present only in the western part of eastern Georgia and is equivalent to the lower part of the Dry Branch Formation with which it intergrades both laterally and vertically. The upper tongue, the Ocmulgee Formation (new name. previously Cooper Marl) is equivalent to the Tobacco Road Sand. The Twiggs Clay, thick and predominating the Dry Branch Formation in the west, is very thin to absent in the east. The Twiggs Clay probably represents the easternmost tongue of the Yazoo Group of the Gulf Coastal Plain For practical usage in Georgia, the Twiggs Clay is considered a part of the Barnwell Group.
Three minor sedimentary cycles are represented in the Barnwell Group: the Clinchfield represents the first sedimentary cycle, the Dry Branch the second cycle, and the Tobacco Road the last cycle. Sedimentation in each of these cycles was terminated by a relative lowering of sea level or stillstand . The greater concentration of cut and fill channel sands in the middle of the Dry Branch may indicate a third very minor event.

75

UPPER JURASSIC SMACKOVER PETROLEUM GEOLOGY OF SOUTHWEST ALABAMA

Ernest A. Mancini
State Oil and Gas Board of Alabama and the University of Alabama, University, Alabama

The f o l low i n g is a vers i on o f a pa pe r to b e pu bli sh ed in J o urn al o f H y d ro logy, Sp ec ial Geoche mi cal V olume .

ABSTRACT
Upper Jurassic Smackover deposition in southwest Alabama was primarily controlled by the Mississippi Interior Salt, Manila, and Conecuh Basins and closely approximated carbonate sedimentation in the Persian Gulf. Each of these basins has distinctive lithofacies and faunal assemblages. Early salt movement resulted in local variations in carbonate sediment distribution, and pre-Jurassic paleo-highs, such as the Wiggins Uplift and Conecuh Arch , also modified carbonate sedimentation.
Throughout most of southwest Alabama, the Smackover Formation consists of a lower member which overlies the Norphlet Sandstone and an upper member which is overlain by the Buckner Anhydrite. Where present, the lower Smackover member includes stromatolitic laminated and bioturbated mudstone, fossiliferous wackestone and packstone, and/or dolomite.The upper member usually consists of oolitic, fossiliferous grainstone, bioturbated, pelletal, or fossiliferous mudstone to packstone, stromatolitic mudstone, and/ or dolomite.
Petroleum traps in southwest Alabama are principally combination traps involving favorable stratigraphy and salt anticlines, faulted salt anticlines, or extensional faults associated with salt movement. Reservoir rocks include oolitic grainstones, leached and dolomitized wackestones, packstones, and grainstones, dolomitized stromatolitic mudstones, and granular dolomite. Porosity is facies-selective and is preserved chiefly in lithofacies of the upper Smackover member. The algal stromatolites that characterize the lower Smackover member and are interbedded with upper Smackover lithologies throughout most of southwest Alabama make excellent petroleum source rocks.
The .flanks of the Wiggins-Conecuh trend and updip Smackover grainstones associated with salt structures are excellent areas for petroleum exploration in southwest Alabama . The key to successful prospecting is the delineation of traps associated with salt movement and identification of original high to moderate-energy lithofacies that have been leached and/ or dolomitized.
INTRODUCTION
Petrol eu m ex ploration has in creased rap id ly In south west Al ab ama since t he disco very of petroleu m in the G i lbert own Fi eld in C h octa w Coun ty in 1944. In 1967, only 10 pro d uc ing oil and gas f ie lds ex isted in Al aba rna , and by 1977, the number of

producing fields in southwest Alabama alone increased to 31 (Masingill and others, 1977) . The value of oil , condensate, and gas produced in the State during 1977 approximated 192 million dollars (Masingill and others, 1977). The primary exploration target in southwest Alabama has been the Upper Jurassic Smackover Formation (fig . 1).

PERIOD

GROUP OR FORMATION

COTTON VALLEY GROUP

HAYNESVILLE FORMATION
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Figure 1.

Jurassic and probably Triassic subsurface stratigraphy in southwest Alabama .

The geologic factors that make a successful Smackover petroleum prospect include the petroleum trapping mechanism, petroleum reservoir, petroleum source rock, and relationship between hydrocarbon migration and structural deformation. Regional geologic trends must be understood before a successful Smackover exploration strategy can be formulated . This research determines the regional stratigraphic and structural relationships associated with Smackover deposition and deformation in southwest Alabama (fig . 2) . Reg ional relationships are identified through subsurface geological study utilizing well logs and core materials . Establishment of the regional trends will help in delineating the geologic processes controlling Smackover petro-

76

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Figure 3. An idealized model for carbonate deposi-

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framework indicating environments of

a...

deposition and textures of carbonate rocks

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accumulating in the various environments.

(/)
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slope. Carbonate lithofacies are not protected by a

shelf-margin barrier and tend to be distributed in

bands which parallel the coastline and reflect the

Brewton

greater wave and current activity near the shore. Patch reefs may be developed on local topographic

FLORIDA

paleo-highs. Recent examples of the "ramp" frame-

0 Miles 20

N
1

work are the Campeche Bank (Yucatan Peninsula) and the Trucial Coast of the Persian Gulf. Ancient analogs are the Jurassic Cotton Valley Formation of the northwestern Gulf of Mexico and the Jurassic

Smackover Formation from south Texas to Florida

(Ahr, 1973).

Figure 2. Location map of study area.
leum accumulation . Emphasis has been placed on the Mobile County area because of the recent petroleum discoveries in that area (McCaslin, 1975; Oil and Gas Journal, 1975).
GEOLOGIC SETTING
Carbonate deposition commonly takes place on either a "shallow shelf" (fig. 3) or a "ramp" (fig. 4) depositional framework . The "shallow shelf" model involves a nearly flat platform and a clearly defined shelf-slope break. Lithofacies are governed by topography, with grainstones and boundstones occurring on shoal areas and mudstones and wackestones occurring in lagoons or behind barriers. Generally, a continuous reef occurs at the shelf edge. Modern examples of the "shallow shelf" framework include Florida and the Bahamas. Ancient analogs are the Cretaceous Edwards of Texas, Cretaceous El Abra of Northern Mexico, and the Permian Capitan of West Texas and New Mexico (Ahr, 1973).
The "ramp" model is an inclined platform that extends basinward without a pronounced break in

Offshore

Figure 4.

An idealized model for carbonate depostion in a "ramp" depositional framework indicating environments of deposition and textures of carbonate rocks accumulating in the various environments.

The lithofacies distribution associated with the "ramp" model is affected by topographic highs which develop on the platform. These topographic highs may be a result of paleo-highs or salt movement. In the Persian Gulf, Purser (1973) found that lithofacies patterns are controlled primarily by the distance between a salt structure and the shoreline. The highest wave and current activity occurs on the crest of the salt structures, with a progressive decrease of energy off the structure. Structures located basinward tend to have high-energy carbonate lithofacies concentrated at their crests and lower-energy lithofacies distributed in concentric

77

bands around the structure as a function of depth and decreasing energy. Topographic highs near the coast usually have high-energy lithofacies on the basinward side and low-energy lithofacies on the shoreward side.
Smackover accumulation in southwest Alabama closely approximated present-day carbonate sedimentation in the Persian Gulf. The Louann Salt was primarily responsible in forming the ramp surface. A regional structure map drawn on top of the Smack-

over illustrates a gentle south to southwest dip for the formation (fig . 5). This trend is locally interrupted by extensional faults, such as the PickensGilbertown , Foshee-Pollard, and Jackson-Mobile, and by salt anticlines, such as the Chatom and Klepac. Early salt movement resulted in local variation in carbonate sediment distribution. Pre-Jurassic paleo-highs, such as the Wiggins Uplift and Conecuh Arch, also modified carbonate sedimentation (fig. 6).

APPROXIMATE UPDIP LIMIT OF SMACKOVER FORMATION NP SMACKOVER NOT PRESENT
.._.__.__.__, FA U L T CONTOUR INTERVAL = 500 FT

10

20 Ml

Figure 5.

Regional structure map on top of the Smackover Formation for southwest Alabama. Faults have been defined by Gary V. Wilson , Alabama Geological Survey.

78

N
1

CONTOUR INTERVAL ~50FT

0

10

20 Ml

Figure 6.

Regional isopach map of Smackover Formation for southwest Alabama (modified from Wilson, fig. 6, 1975).

In the area of study, three probable basins, the Mississippi Interior Salt, the Manila, and the Conecuh Basins, are recognizable (fig. 7). These basins have been delineated on the basis of thickness of the Smackover Formation (fig. 6) and the depth to basement and basement configuration as indicated by geophysical gravity anomalies (Wilson, 1975, fig. 4) . The most westerly basin , which occurs primarily in Washington and southern Choctaw Counties, is an extension of the Mississippi Interior Salt Basin of eastern Mississippi. The Manila Basin of eastern Clarke, western and southern Monroe, and northern Mobile and Baldwin Counties, is named after the town of Manila, which is located near the apparent center of the basin in eastern Clarke County (figs. 2 and 7). The most easterly basin, the Conecuh Basin as defined by Sigsby (1976), occurs in Escambia and southwestern Baldwin Counties and extends into northern Florida.

The Wiggins-Conecuh trend separates the Conecuh and Manila Basins (fig. 7). Smackover carbonates thin to less than 100ft over this structural trend (fig. 6). Seismic refraction and gravity data suggest that the Wiggins-Conecuh trend acted as a stable basement high throughout Smackover deposition (Wilson, 1975) . The composition of this basement complex consists of granitic, basaltic, and volcanic rocks (Neathery and Thomas, 1975; Neathery, 1979, personal commun). The basement complex is believed to be a continuation of the Piedmont structural trend (Neathery and Thomas, 1975).
The Manila Basin appears to be separated from the Mississippi Interior Salt Basin by a basement paleo-high or salt ridge (fig. 7) . Smackover carbonates thin to less than 100ft over this trend located in northern Mobile, eastern Washington, and western Clarke Counties (figs. 6 and 7) . In the Manila

79

INTERIOR
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) SALT

(

BASIN

t
l
I
\ I

.--- ......
I
/
\
'\

BASIN

FLORIDA

+

APPARENT BASEMENT H16H

.......-,. APPROXIMATE BASIN OUTLINE

- - - AREA OF KNOWN THICKEST SMACKOVER

0

10

20 MI.

Figure 7. Paleogeographic map for southwest Alabama during Smackover deposition.

Basin and the eastern part of the Mississippi Interior Salt Basin the Smackover exceeds 400 and 550ft, respectively.
STRATIGRAPHY AND LITHOFACIES
The Jurassic section normally present in the subsurface of southwest Alabama is shown in figure 1. The contact between the Smackover and underlying Norphlet Formation in Mobile County is conformable, grading upward from dolomitic sandstone to a silty dolomite. The Smackover conformably underlies the Buckner Anhydrite Member of the Haynesville Formation. The contact is gradational and generally grades from dolomite through interbedded dolomite and anhydrite to anhydrite.
In the study area, the Smackover Formation can be divided into a lower and upper member, each of which contains distinctive carbonate lithologies. Where present the lower member includes stroma-

tolitic, laminated and bioturbated mudstone, fossiliferous wackestone and packstone and/or dolomite. The upper member usually consists of oolitic, fossilferous grainstone, bioturbated, pelletal, or fossiliferous mudstone to packstone, stromatolitic mudstone and/or dolomite. The contact between these stratigraphic units is gradational.

Smackover lithofacies are distinctive for three

basins, suggesting that depositional conditions var-

ied among them. The lower member represents

intertidal and subtidal lithofacies that were depos-

ited during a marine transgression which was prob-

ably initiated during late Norphlet time. The upper

Smackover member represents supratidal to subti-

dal deposition. Although numerous shoreline oscil-

lations are evident during deposition of this lithofa-

cies, the overall trend in most of the study area is

regressive. Deposition of the Buckner Anhydrite

completes the regressive carbonate phase.



80

The lithofacies observed in the Placid Oil Jackson No.1 (281ft of core), 4 mi north of Toxey, Choctaw County, Ala., are typical lithologies for the Mississippi Interior Salt Basin (fig. 8). In this core, the Buckner consists of anhydrite interbedded with dolomite which is characteri stic of supratidal deposition. The upper part of th e Smackover is a dolomitic, oncoloidal, fossiliferou s grainstone interbedded with dolomitic packstone with c alcite replacing anhydrite laths. Underlying these carbonates is a fossiliferous, bioturbated packstone which grades into an oo litic, fossiliferous, crossbedded grainstone containing terrigenous grains. These lithologies Indicate Intertid al and subtidal deposition. The next unit is a fossiliferous, pelletal , bioturbated, argi llaceous, lami nated wackeston e which probably accum ul ated in a subtidal en vironment. The lower part of the core consists of an oolitic, oncoloidal, fossiliferous grainstone interbedded with fossiliferous, bioturbated, stromatolitic mudstone and pelletal, oncoloidal wackestone. These lithologies primarily represent intertidal to subtidal deposition. The mudstone, however, was occasionally subaerially exposed, as evid ence d by mudcracks and collapse solution-brecciation features. The lower Smackover, as observed in well cuttings (~72ft) from this dry hole, is an argillaceous, laminated mudstone which probably accumulated in intertidal and subtidal environments.
The Smackover lithofacies present in Choctaw County are sim ilar to those described by Badon {1974) for Clarke County, Mississippi , and by Wake lyn (1977) for Perry and Stone Counties, Mississippi. In Clarke County, Mississippi, upper Smackover lithofacies consist of a peritidal dolomite, a nearshore high-energy oolitic grainstone, and a subtidal low-energy pelletal mudstone (Badon, 1974). In Perry and Stone Counties, the upper Smackover includes interbedded grainstones, packstones and wackestones, which were deposited in supratidal to subtidal environments (Wakelyn, 1977), whereas laminated mudstone of the lower Smackover represents subtidal deposition (Wakelyn, 1977). The Buckner in both of these areas consists of interbedded dolomite and anhydrite which accumulated in a supratidal environment (Badon, 1974; Wakelyn, 1977). The fauna found in the Jackson No. 1 core is also similar to that described by Badon (1974) and Wakelyn (1977) for eastern Mississippi. These lithol ogic and faunal similarities suggest that the carbonate rocks deposited in western Al abama and eastern Mississippi accumulated in the same depositional basin, the Mississippi Interior Salt Basin.
The Smackover in the Manila Basin is predominantly a dolomitized, laminated mudstone and wackestone, which probably accumulated in intertidal and subtidal environments. Fossils are rare to absent in cores from the Getty C.D. Broughton no. 3
(50ft of core), 7 .5 mi northwest of Uriah, Monroe County, and Getty Blacksher Estate No.1 (60ft of

core), 1 mi northwest of Uriah, Monroe County. The scarcity of taxa in this basin compared to the Mississippi Interior Salt Basin suggests environmental conditions were more hosti le. These faunal differences and distinctive lithofacies imply that the Manila Basin was isolated from the Mississippi Interior Salt Basin during Smackover deposition.
The lithofacies present from top to bottom in the Exxon L&N Railroad No . 1 core (287ft), 1.5 mi. west of Pollard, Escambia County, Ala., include an intertidal bioturbated, argillaceous, laminated, pelletal dolomitic mudstone, intertidal to subtidal fossiliferous, pelletal, dolomitic packstone and wackestone, and an intertidal laminated, argillaceous, pelletal mudstone interbedded with dolomite (fig. 9). These lithofacies are similar to those described by Ottmann and others (1973) and Sigsby (1976) for the Jay trend located within the Conecuh Basin. Sigsby (1976) reports that the upper Smackover member in this basin is represented by pelletal dolomite and mudstone, and the lower Smackover member includes a fossiliferous mudstone, pelletal mudstone, pelletal oncoloidal mudstone, and dolomite. Fossils were observed in the L&N Railroad No. 1 core and have been reported by Sigsby (1976) from other cores in the basin. Faunal diversity in the Conecuh Basin is higher than in the Manila Basin but lower than in the Mississippi Interior Salt Basin. The faunal differences and distinctive lithofacies suggest that the Conecuh Basin was separated from the Manila Basin during Smackover deposition.
In the Chunchula-Hatters Pond area, probably only the upper Smackover member is present. The laminated mudstone characteristic of the lower Smackover member was not observed in any of the 16 cores studied from this area. Lithofacies typical of these fields are found in the Getty Peter Klein No. 1 (104ft of core), 12 mi northeast of Mobile. These lithofacies include a granular dolomite interbedded with a massive dolomite, a bioturbated wackestone, and a massive, bioturbated dolomite (fig. 10). Fossils were very rare or absent in the cores studied from Mobile County.
Smackover deposition in Mobile County was dominated by the Wiggins Uplift. The Smackover is absent on the crest of this structure (fig. 5) and is much thinner (50-150 ft) along its northern flank compared to ty pical Smackover thickness in southwest Alabama (figs. 6 and 11) . The apparent absence of the lower member and the upper member not attaining normal thickness for this area suggests that the Wiggins was a positive feature during early Smackover time. Immediately west of Mobile County in Stone and Perry Counties, Mississippi, the Smackover is 800 to 900ft thick, and the laminated mudstone lithofacies of the lower Smackover member is well developed in these counties (Wakelyn , 1977). The reduced thickness of the Smackover section in the Chunchula-Hatters Pond area, therefore, is probably due to nondeposition of carbonate sediments.

81

~Limestone
oolomite
D Sandstone
[g} Anhydrite
"
~Granular Dolomite ~ Grainstone ~Packstone ~Wackestone ~Mudstone

~Anhydritic
I .Il l :Ir Dolomitic

~Calcitic

B

Argillaceous

liD Oil-Stained

[TI Fossiliferous

~Oolitic

~Pelletel

~ Oncoloidal

~ lntraclastlc

W Bioturbated

EJ Stromatolitic

G

Nodular Anhydrite

Feet

"I "I "

A

A

A

-t03 00 OiL JC

~

-!--' ~~l-

+- E
-1031~
f

(;) ",-'\
Iii
:J: :z:l
I 6

- t0330

A.

f)

Anhydrite, Interbedded w/ Dolom1te Grainstone, OolitiC, lnlerbedded w/ Packstone
Packstone, Fossiliferous

BUCKNER

-1o3e
.....

r-:

-1o3eo

.

-1037!5 -10390 -1040!5

.
A A
G
.


j I
_......
"
en

" :J:

- 10420

. ..... -

-1043~
- 10480 -1 04.05

<D
._i)
1.1
.....

. . \:>'_.&_
- 10-4180
..... .

Cil

-o~e -101!510

A.

t)

......

c.
....,

-10G2& --10&40

.....
""'
"""'

r>.

-10&&1>

_l ....._ I
c.

!)

l 0

- 105?0 _l


Ir " I
0

I"" II I

.....

v _j}
'V "'-/

Grainstone, Oolitic, X-Bedded

Wackestone, Argillaceous

Grainstone, Oolitic

Mudstone, Bioturbated

Grainstone, Oolitic

lfnufl an 61HIInlahl1 c.. C3ralnstone, Oolitic

M ild I OI't

aml o lltl

l'lr "'o "' Ot:~ 1 11e

Mudstone, Stromatolitic

W c. het l '9 " Fo$llfrou

Mudstone, Stromatolitic

Wackestone, Interbedded w/ Grainstone
Mudstone, Stromatolitic

Wackestone, Interbedded w/ Grainstone

SMACKOVER

Figure 8.

Carbonate lithologies identified in the Placid Oil Jackson No.1 core, 4 miles north of Toxey, Choctaw County, Ala.

82

~ Fa J

1\

~

ft.

A

\~

...

A

~
'
--

Anhydrite Mudstone, Anhydritic
Mudstone

I BUCKNER

- 1&.:!'2'0

Mudstone, Bioturbated

Feet

~ A-""""-"AA ,..,.. ,.....,...,...,... ,...,...~,...,.....,.../"

,_[ !i:::ll
_,...or
A A
l -~'o ~ I ~ I ~ I ~I

Mudstone
Mudstone, Argillaceous Mudstone
Mudstone, Argillaceous Mudstone

I

I

I

I

I

I

I I SMACKOVER

-18020 / 5/ 7--

/ _.._ / / )

7 _.._ j x :r. /"' " /

1 -18030

I JL I

1~ I I

I I I _,

-18040

T () I T
s

7 1 7

/ 1 1/ I

1/ -18050 / / 11

I

I I

-18060

0w 0

' '

I l'i':J,----,-----~

tJ ~~40~; 1j !

Mudstone, Laminated
Wackestone Packstone, Dolomitized

I

-18070

I

Waeke.stona
Packstone, Dolomitized

I

I

-m{! J( ~ i ;1

Mud1111ttn lii..I'I"'j naJ.d

I

I

Dolomite

_,_~H~~!wh~l

I I

Mudstone, Laminated Interbedded w/ Wackestone

if. !tD "'
-ISOJOft 1

Dolomite Mudstone, Laminated

I

I

I

I

~ ...I ..I ...'I

Mudstone, Arg1llaceous Sandstone

I NORPHLET

-18080
I ....._ I I
I / CP 7 / A" I I -18090 7 7 _.._ 7
j ep j I
/ / A"'- /
-18100 I "-"I I
I I/ / CD 7 7 ; -18110 . 1 1 1 7TTI 7 11 1 / "' " / 7
. . . . -18120 1 1 1 :0: E' ~~~

Anhydrite Dolomite, Bioturbated
Dolomite. Massive
Wackestone Dolom1te. Granular
No Recovery
Dolom1te. Mass1ve
Dolomite, Granular Sandstone, Dolomitic

BUCKNER SMACKOVER NORPHLET

Figure 9.

Carbonate lithologies identified in the Exxon L&N Railroad No. 1 core, 1.5 mi west of Pollard, Escambia County, Ala. See lithologic legend for figure 8.

Figure 10.

Carbonate lithologies identified in the Getty Peter Klein No. 1 core, 12 mi northeast of Mobile, Hatters Pond Field, Mobile County, Ala. See lithologic legend for figure 8.

HJW
N '

209 ..
0

206 2
0
2293
0

2322 0
1950 0

1886-B
0
2120 0

2350
0

Rw
:
N
2'!160
0
2 461
0
'207 1
0

I
~

N
1

0 Wf:LL LOCATION ANO Pf:,.MIT NUMIIE..

I I Plf...CI!MI!NT SALT

.

-

,.11!1-0 OUTl.INf.

s J

CONTOU.. INTI!..VAL z: 2D I"T

0

, "' '

L---....1

t A e..1. ,.., ft

Figure 11 .

Isopach map of Smackover Formation for Chunchula-Hatters Pond area, Mobile County, Alabama (modified from Mancini and Stow, fig . 8, 1977).

84

PETROLEUM EXPLORATION

moldic dolomite porosity is the leached product of dolomitized pelletal grainstone. lntercrystalline

Petroleum traps in southwest Alabama are principally combination traps involving favorable stratigraphy and salt anticlines, faulted salt anticlines, or extensional fault traps associated with salt movement or with the updip limit of Louann Salt deposition. In the Mississippi Interior Salt Basin, Washington and Choctaw Counties, traps are primarily salt anticlines or faulted salt anticlines. In the Conecuh Basin, Escambia County, petroleum is principally trapped by a combination of extensional faulting and salt movement. Such a trapping mechanism is common throughout the Jay trend area (Sigsby, 1976).1n the Manila Basin, southern Monroe County, domal paleo-highs possibly related to igneous intrusions form the petroleum trap. The petroleum traps in Mobile County involve a combination of trapping mechanisms. The Chunchula structure appears to be a moderate-relief salt anticline (fig . 12), and the Hatters Pond structure is a faulted salt anticline associated with salt movement along the west side of the Jackson-Mobile fault system (Mancini and Stow, 1977).

dolomite is the result of leaching and dolomitization of pelletal wackestone and packstone, and leached matrix porosity represents dolomitization of algal stromatolites. Sigsby (1976) estimates that 90 percent of the effective porosity in the Jay trend area is a result of leaching and dolomitization of pelletal lithofacies.
lntercrystalllne poros1ty IS dominant in the Peter Klein No. 1 core . It is difficult to discern the original composition and texture of the reservoir in the Chunchula-Hatters Pond area because of the severity of the dolomitization process. The Smackover (fig . 5) is absent near the crest of the Wiggins, but is productive on the northern flank of the uplift, suggesting the Wiggins was a positive feature during Smackover deposition. Employing Purser's (1973) model for the Persian Gulf, moderate energy lithofacies probably were deposited on the flanks of the Wiggins in concentric bands around this basinward structure. Therefore, the original lithology of the reservoir may have been a pelletal packstone or wackestone.

Stratigraphy plays an integral part in forming a Smackover petroleum trap. Smackover thickness does not appear critical , as indicated by the Smackover isopach map constructed for the ChunchulaHatters Pond area (fig. 11 ). In fact, 8 mi northeast of these fields, the Smackover increases in thickness and wildcats drilled on structural highs in this area have been noncommercial. The carbonate lithofacies in northwest Mobile County are mudstones

The algal stromatolites that characterize the lower Smackover member and are interbedded with upper Smackover lithologies throughout most of the study area make excellent petroleum source rocks. Although these rocks do not appear to be present in the Chunchula-Hatters Pond area, they were penetrated in wildcats drilled about 8 mi northeast of those fields in Mobile County.

with typical reservoir-forming packstones and grainstones being rare to absent.
Reservoir rocks in southwest Alabama include oolitic grainstones, leached and dolomitized wackestones, packstones, and grainstones, dolomitized stromatolitic mudstones, and granular dolomite. Porosity is facies selective and is preserved chiefly in lithofacies of the upper Smackover member. Preservation of original porosity and the formation of secondary porosity are controlled by diagenetic alteration . Dolomitization and leaching are the most critical processes in the formation of secondary porosity.
In the Jackson No. 1 core, porosity is both primary oolitic and oncoloidal interparticlate and secondary moldic, resulting from leaching and dolomitization of oolitic and oncoloidal grainstones. Badon (1974) reports that the principalS mackover reservoir rocks in Clarke County, Mississippi, are oolitic grainstones with primary depositional interparticle porosity.
Porosity in the Exxon L&N Railroad No.1 core is secondary, resulting from leaching and dolomitization of pelletal packstone and wackestone. Ottman and others (1973) state that the major porosity types in the Jay trend area are grain moldic dolomite, intercrystalline dolomite, and leached matrix. Grain

Integrating the regional structural, stratigraphic, and lithofacies relationships with the style of petroleum trapping mechanisms and reservoir and source rock distributions, a successful Smackover exploration strategy can be formulated for each of the basins in southwest Alabama. Exploration in the Mississippi Interior Salt Basin should involve prospecting for grainstones on the basinward side of salt structures and for updip oolitic grainstones associated with salt movement. In the Conecuh Basin petroleum stored in dolomitized and leached pelletal packstones and trapped by extensional faulting and salt movement should continue to be an excellent petroleum target. Prospecting in the southern part of the Manila Basin should be directed toward exploring for dolomitized reservoir rocks associated with paleo-highs. The flanks of the Wiggins-Conecuh trend through Mobile and Baldwin Counties are an excellent area to explore for petroleum as demonstrated by the recent discoveries in Mobile County. The key to successful prospecting along this trend is the delineation of traps associated with salt movement and identification of original high-to moderate-energy lithofacies that were deposited on the flanks of structures and that have been preserved or have undergone favorable diagenetic alteration. The process that is probably the most critical for porosity enhancement is dolomitization.

85

Ptw
r "'

N
1

1978 0 WfLL LOCATION AND Pt.RMIT NUMSlfof
I I ~lf.RCf.ME.NT SALT

-

lltLO OUTliNt

CONTOU~ INTtRVAL

:H) ' I

I Mt
~-"""
RIW

Figure 12 .

Structure map on top of the Smackover Formation for Chunchula-Hatters Pond area, Mobile County, Alabama (modified from Mancini and Stow, fig. 3, 1977) .

86

CONCLUSIONS
1. Smackover accumulation in southwest Alabama closely approximated present-day carbonate sedimentation in the Persian Gulf. The Louann Salt was primarily responsible in formin g th e ramp surface. Carbo nate depos it ion was affected by ea rly salt moveme nt and paleohighs, such as the Wigg ins- Conec uh tre nd .
2. T hree pro ba ble basins are present in so utl1west Al abama. T hese include t he Mi ss issippi Interior Salt, the Manila, and the Conecuh Basins. The Wiggins-Conecuh trend separated the Conecuh and Manila Basins during Smackover deposition. The Manila Basin appears to have been separated during Smackover times from the Mississippi Interior Salt Basin by an apparent basement paleo-high or salt ridge. Smackover lithofacies and faunal assemblages are distinctive for each of the three basins.
3. The Smackover Formation can be divided into lower and upper members. Where present, the lower member includes stromatolitic laminated and bioturbated mudstone, fossiliferous wackestone and packstone and/or dolomite.
4. Petroleum traps in southwest Alabama are principally combination traps Invo lvin g favorab le stratigraphy and salt inc lines, fa ulted salt anticlines, or extensional faults assoc iated wit h sa lt movement. Reservoir rocks inc lude oolitic gra instones, leached and dolomitized wackestones, packstones, and grainstones, dolomitized stromatolitic mudstones, and granular dolomite. Porosity is faci es- se lective and is preserved c hi efly In lit hofac ies of the upper Smackover member. T he algal stromatolites that characterize the lower Smackover member and are interbedded with upper Smackover lithologies make excellent petroleu m source rock s.
5. The flanks of the Wi gg ins- Conec uh t re nd and updip Smackover grainstones assoc iated with salt structures are exce ll ent areas tor petro leum ex plorati o n in sout hwest Al abama. Th e key to successful prospectin g is t he de lineati on of traps assoc iated with salt movement and ide nt ification of o ri gin al high to moderate energy lit hof ac ies that have been leac hed and/o r dolomitized.
ACKNOWLEDGMENTS
This research was done principally under Alabama State Oil and Gas Board Contract No. OGB 77-6011 . Research support was also supplied by the Geology and Geography Department and Mineral Resources Institute, The University of Alabama.
I acknowledge the State O il and Gas Board an d Geological Survey of Al abama for th e use of c ores and well logs. I t han k Kendall P. Hanby and John M. Masingill of th e A laba ma Stat e Oil and Gas Boa rd,

Charles W. Copeland and Gary V. Wilson of the Alabama Geological Survey, and D. Joe Benson, Geology and Geography Department, The U niversity of Alabama, for informative discussions dealing with the Upper Jurassic of south Alabama.
I express appreciation to D. Joe Benson and Gary V. Wilson for their constructive criticsm of the manuscript.
REFERENCES
Ahr, W.M ., 1973, The carbonate ramp: an alternative to the shelf model: Gulf Coast Assoc. Geol. Sacs. Trans., v. 23 ;. p. 221-225 .
Badon, C.W., 1974, Petrology and reservoir potential of the Smackover Formation, Clarke County, Mississippi: Gulf Coast Assoc. Geol. Sacs. Trans., v. 24 , p. 163-174.
Mancini, E.A., and S.H. Stow., 1977, Preliminary delineation of geologic trends and processes controlling petroleum accumulation in the Upper Jurassic of southwestern Alabama. Univ. Alabama Min . Res. Inst. Tech. Rept. No. 3, 12 p.
Masingill, J.H., Hall, P.F., and Tolson, J.S., 1977, The petroleum industry in Alabama, 1977: Alabama, 1977: Alabama State Oil and Gas Board Oil and Gas Rept. 3, 34 p.
McCaslin, J.C., 1975, Jurassic finds multiply in southwest Alabama: Oil and Gas Jour., v. 73 , no. 33, p. 157.
Neathery, T .L., and Thomas, W.A., 1975, PreMesozoic basement rocks of the Alabama Coastal Plain: Gulf Coast Assoc. Geol. Sacs. Trans, v.25, p.86-99 .
Oil and Gas Journal, 1975, Alabama's deep Jurassic play spreads: Oil and Gas Jour., v. 73 no. 33, p. 34-35.
Ottmann , A.D ., Keyes, P.L., and Ziegler, M.A., 1973, Jay Field- a Jurassic stratigraphic trap: Gulf Coast Assoc . Geol. Sacs. Trans. v. 23, p. 146-157 .
Purser, B.H., 1973, Sedimentation around bathymetric highs in the southern Persian Gulf, p. 157-178: In Purser, B. H., ed ., The Persian Gulf, New York,Springer-Verlag.
Sigsby, R.J., 1976, Paleoenvironmental analysis of the Big Escambia Creek-Jay-Blackjack Creek Field Area: Gulf Coast Assoc. Geol. Sacs. Trans., v. 26, p. 258-278.
Wakelyn, B.D., 1977, Petrology of the Smackover Formation (Jurassic): Perry and Stone Counties, Mississippi: Gulf Coast Assoc. Geol. Sacs. Trans., v. 27, p. 386-408.
Wilson, G.V., 1975, Early differential subsidence and configuration of the northern Gulf Coast basin in southwest Alabama and northwest Florida: Gulf Coast Assoc. Geol. Sacs. Trans., v.25, p.196-206.

87

STRUCTURAL CONTROL OF JURASSIC SEDIMENTATION IN ALABAMA AND FLORIDA
James A. Miller U .S. Geological Survey
Atlanta, Georgia

ABSTRACT

The extent and thickness of Jurassic strata in Alabama and Florida w ere m appe d as part o f a U .S. G eol og ica l Surve y regio na l geohyd ro lo gi c st udy. Roc ks eq uivalent to t he Wern er, Lo uan n, No rp h let , S mackover, Haynesville, and C otto n Va ll ey sequ ences of M i ss issip p i and Arkansas have bee n recog nized and , except fo r the Wern er equ ival e nt, are herei n exte nded into panh ahdle Florida. The predominantly fluvial Jurassic sequence in Alabama and Florida was interrupted at least twice by

barred-basin conditions which resulted in the deposition of extensive evaporite deposits, and at least once. during Smackover time, by a major marine transgression. The updip limits and isopach map trends of the Jurassic units mapped appear to have been controlled by a major northwest-trending, right-lateral wrench fault, the dominant master shear in a regional wrench-fault system active throughout Jurassic time.

FORAMINIFERAL BIOSTRATIGRAPHY AND PALEOECOLOGY OF THE MARLS ASSOCIATED WITH THE TUSCAHOMA SAND (PALEOCENE/EOCENE) OF SOUTHWEST ALABAMA
Gary E Oliver University of Alabama
University, Alabama

ABSTRACT

T o better del ineate t he Pa leocen e/Eoce ne boundary in the eastern Gulf Coast area, the foraminifers of the marls associated with the T uscahoma Sand were studied from seve n samp led loca lities in the type are a in southwes t Alabama. Planorotalites pseudomenardii ((3olli} occurs in the lower two unnamed marls. Th e occu-rrence of this plank tonic fo raminifer plac es thes e marls in the Planorota/ites pseudomenardii Range Zo ne as defined by Stainforth and others (1975). T he Bells Landing and Greggs Land in g Ma rl s, wh ich lie above th e unna med ma r ls, are characterized by Morozovella velascoensis (Cushman), Morozovella acuta (Toulmin), Morozovella aequa (Cushman & Renz) , P/anorotalites chapm ani (Pa rr ), Pse udohastigerina wilcoxensis (Cushman & Ponton) . and .'lcarinina

mckannai (White) . The presence of M. velascoensis and absence of P. pseudomenardii p laces these marls in the uppermost Pa leocene Morozovella velascoensis Interva l Zone as defined by Stainforth and others (1975) The Paleocene/ Eocene boundary, therefore, occurs within the Tuscahoma Sand between the Bells Landing Marl, w hi ch is th e upp ermost mar l of t he Tuscahoma Sand, and the Bashi Marl which forms the base of the overlying Hatchetigbee Formation.
Benthic foraminiferal popu lations indicate that the lower two marls accumu lated in a middle neritic environm e nt. Th e Bells Landing Marl and Greggs La nding M arl were deposited in middle to inner neritic conditions.

88

LITHOFACIES AND DEPOSITIONAL CYCLES IN UPPER CRETACEOUS ROCKS, CENTRAL GEORGIA TO EASTERN ALABAMA
Juergen Reinhardt U.S. Geological Survey
Reston, Virginia

ABSTRACT
The Upper Cretaceous rocks of the eastern Gulf Coastal Plain are composed largely of siliciclastic sediments , which were deposited in marginal-marine and shelf environments. At the eastern margin of the basin (central Georgia) and in updip areas farther west, the outcropping deposits consist dominantly of fluvial feldspathic sand and kaolinitic clay and grade to open-shelf glauconitic sand , marl, and chalk both downdip and westward into the basin (central and western Alabama). Changes in the distribution of lithofacies are most notable in marginalmarine environments along the basin margins; the sequences of lithofacies indicate four major marine transgressions during the Late Cretaceous.
Sedimentation apparently began during the Cenomanian along the Piedmont margin when the Tuscaloosa Formation was deposited. The overlying Eutaw Formation (Santonian) resulted from the first marine transgression and regression. This unit is composed dominantly of cross bedded quartz sand containing Ophiomorpha burrows, laminated carbonaceous silt to fine sand, and local accumulations ofOstreacretacea valves. The Eutaw sediments record the encroachment of a shallow sea onto an unconsolidated shoreline and the subsequent formation of a barrier-island complex.
The second trangression took place during the early Campanian and "drowned" the Eutaw barrier system. The resulting Blufftown Formation consists largely of innershelf glauconitic sand and shelly marl. Near the top of the Blufftown, the unit shoaled and was subsequently transgressed. A final "drowning" of the barrier-bar complex (Cusseta Sand) took place during the latest Campanian. After this fourth transgression, inner-shelf, massive glauconitic sand (Ripley Formation) was deposited.
The timing of marine transgressions was probably the major factor in determining the distribution of lithofacies during the Late Cretaceous in the eastern Gulf Coastal Plain. Local fluctuations in water depth, circulation, water chemistry, and sediment supply controlled the composition of lithofacies and the distribution of small-scale (less than 10m thick) cycles within the basin. Controls on the large-scale (tens to hundreds of meters thick) cyclicity of transgressive and regressive phases of these Upper Cretaceous deposits were global and resulted from major changes in the world's water budget.
INTRODUCTION
During the past three years, the U.S. Geological Survey, in a project entitled "West Georgia Coastal

Plain", has been attempting to identify and describe the stratigraphic and structural elements in the Upper Cretaceous and lower Tertiary rocks in the Chattahoochee Valley of Georgia and Alabama. A first statement of results from the Tertiary part of this project is presented by Gibson (this volume) and should be viewed as a companion to this paper. Beyond attempting to formulate a detailed history for the eastern margin of the Gulf Coastal Plain, the specific missions of the project have been: 1) to identify tectonic elements that might be reactor hazards within the area and, more recently, 2) to identify the nature and level of uranium and thorium concentrations within the sedimentary sequence.
In this paper, an attempt is made to integrate lithofacies analysis with a time stratigraphy developed by U.S. Geological Survey biostratigraphers from surface and shallow subsurface rocks in the eastern Gulf Coastal Plain. The paper will outline the major lithologies that compose the Upper Cretaceous section and suggest the range of continental, marginal-marine, and marine environments that the lithologies represent. Further, the vertical organization of the sediments into depositional cycles will be documented and, finally , the overall patterns of sedimentation will be related to sea-level changes during the Late Cretaceous. The problems being addressed in this region at the edge of the Gulf Coastal Plain are three-dimensional. The discussion of updip-downdip changes will, however, be somewhat limited; vertical sequence within the Chattahoochee Valley will be the focus of this paper.
Acknowledgements
Many thanks go to Raymond A. Christopher, Norman F. Soh I, and Charles C. Smith for the biostratigraphic support that has made this study possible. Special thanks go to James P. Owens for his encouragement and constructive criticism of my work in the Coastal Plain. G.S. Gohn, J.P. Owens, N.F. Sohl (all U.S.G .S.), and M.S. Friddell (Georgia Geological Survey) reviewed an earlier version of this manuscript; their comments have substantially improved this paper. James Estabrook, Dennis Duty, and Art Donovan have given excellent field support during the past three years.

89

GEOLOGIC FRAMEWORK
The map presented in figure 1 is a compilation modified from mapping by Eargle (1950, 1955) and Monroe (1941). This figure serves to present the gen eral distribution of Upper Cretaceous units in the study area as they have been mapped with relatively little modification since the early reports by Smith and Johnson (1897) in Alabama and Stephenson (1911) in Georgia. The units as presently defined from Tuscaloosa Formation to Providence Sand are thick packages of clastic sediment that show considerable variation in composition and te xture within the outcrop area and in the shallow subsurface. Our view of these rocks is necessarily biased by the present outcrop pattern , which is largely controlled by the drainage pattern of the Chattahoochee River (see fig . 1) and its dissection of the landscape. The sedimentary environments in which the Upper Cretaceous rocks were deposited range from continental for the Tuscaloosa to predominantly marginal marine and marine for the Eutaw, Blufftown, Cusseta, Ripley, and Providence.

Simply stated, Upper Cretaceous shorelines, or more specifically, barrier-island chains, trended generally east-west. The distribution of facies in the units younger than Tuscaloosa is largely controlled by this paleogeographic constraint. Given the outcrop patterns (fig . 1), it is apparent that more continental facies will be represented toward central Georgia, and more open-marine facies will be represented in the Chattahoochee Valley . From the Flint River west, the depositional basin also opens to the west and southwest (Herrick and Vorhis , 1963) .
LITHOFACIES
Continental facies
The Tuscaloosa Formation in the eastern Gulf Coastal Plain can be traced in outcrop from just west of Macon, Ga., to the type section in western Alabama (see Christopher, this volume). In the central part of the Gulf Coast (downdip) the section is thicker, and the stratigraphy and lithofacies are more complex (Monroe and others, 1946). In the

TERTIARY ROCKS

PROVIDENCE

RIPLEY
I ...
CUSSETA
l!H
BLUFFTOWN
[;:'::. .;-:.'!
EUTAW
TUSCALOOSA
I. .
CRYSTALLINE ROCKS

; -

, ..-,--L.,'-r--N C

!. \

s c.

ALA. r GA \

20 MILES

f -- - - . - -- - - '

0

20 KILOMETERS

Figure 1.

Generalized geologic map of Upper Cretaceous units (modified from Eagle, 1950, 1955; and Monroe, 1941 ). Note the NE-SW trend of the outcrop belt between the Flint and Chattahoochee Rivers. C = Columbus, GA; E = Eufaula, AL; B =Butler, GA; JC =Junction City, GA; AK =Alabama Kraft locality; CB = Chimney Bluff locality.

90

eastern Gulf Coast, the Tuscaloosa is characterized by kaolinitic, arkosic sand (probably equivalent to the Gordo Formation of western Alabama) and medium-scale, unidirectional, trough crossbeds. The sand beds commonly contain intraformational clay clasts, which are typically brick red and locally show conspicuous reduction rinds. The reduced state of the iron on the outer parts of the clasts indicates a change of oxidation state from the initial environment in which the clay was deposited (subaerial flood plain or flood basin) to its final depositional site in a fluvial channel. Thickly bedded red to mottled clays interfinger with the crossbedded sands and are lithologically similar to beds defined as the Vick Formation in Alabama (Conant, 1946) . In the Chattahoochee area, all the Tuscaloosa lithologies are clearly fluvial in character (except as defined by Ray , 1958) in outcrop and are marine only considerably downdip and to the west (Applin, 1964; Soh!, 1964) .
Similar (though less kaolinitic) high-energy unidirectional sands are present near the base of the Eutaw Formation in the northeastern part of the study area in the vicinity of Junction City and north at Butler, Ga. (see fig. 1). Interbedded thin to medium-thick clay beds provide abundant clay clasts to the channel fills that are generally less oxidized than clasts in the Tuscaloosa .
Marine facies
The basal part of th e Eutaw Fo m1a tio n some wh at downdip, near the Cl1att al1ooc hee River, is also composed of cross bedd ed q uart z sa nd and lo c all y abundant clay clasts. T he re are, 11owev er, key differences in the sedimentary structures : (1) strong bimodality in crossbed directions within single outcrops and, (2) extremely abundant Ophiomorpha nodosa burrows, indicating near-shore, openmarine sedimentation (Weimer and Hoyt, 1964; see also Frey and others, 1978). Well-defined, clay-lined channels occur within this part of the Eutaw, apparently preserving tidal channel fillings within a barrier-island complex.
The high-energy barrier-bar facies is commonly overlain by a poorly bedded micaceous, clayey sand interval containing extremely abundant wood fragments (large pieces are commonly bored) and a bivalve fauna, which suggest a slightly to moderately restricted back-barrier environment (N.F. Sohl, written commun., 1977). For such a vertical sequence to be deposited, the barrier system had to migrate seaward or prograde; this could reflect either a local or a regional marine regression.
This brief discussion of vertical sequences introduces the concept of lithologic transitions and repetitions or cycles. Sedimentary cycles were first des-

cribed for the Cretaceous rocks in this region by Eargle (1950). Cycles reflecting sea-level changes are best developed in the marginal marine sediments near the Chattahoochee drainage. Two types of cycles , regressive and transgressive, will be described from this general area.
Sediments deposited during regressive cycles (fig . 2) constitute the bulk of the Upper Cretaceous sedimentary pile in the Chattahoochee region . The entire Eutaw Formation, for example, following the initial transgression across the Coastal Plain composed of Tusca loosa san ds and clays, represents a s ingl e re gressi ve cy cle. T he great thickness of these regressi ve cyc les (co mmonly greater than 50 m) or even th e thi c kn ess o f a single lithofacies (as much as 30m) means that the record of an entire cycle cannot be seen in a single outcrop, but records of four such cycles are preserved within the total Upper Cretaceous section. The cycles may have resulted largely from progradation due to sedimentation rate exceeding basin subsidence or a general slow sea-level drop. This contrasts sharply with the view that sea level may have dropped rapidly several times during the Late Cretaceous (Vail and others, 1977).
The Regressive Cycle.
The major lithologies that constitute an ideal regressive cy c le rep rese nt p rogressively more co ntine nta l facies upw ard in the cy c le and are ge nera lized o n f ig ure 2. From base to to p, th e idea l cy c le is compose d o f lith ofacies f rom in ne.r-s hell, baaie rbar, open- bay, and rest ricted-l ag oo n en vironm ents.
The inner-shelf lithologies vary from clayey shell marl to very fine glauconitic sand. These lithologies grade to marls and chalks of the Selma Group in central and western Alabama (Monroe, 1941). Bedding is typically massive and commonly bioturbated rather than distinctly burrowed. Variable amounts of shell debris or whole shells are scattered through the shelf lithologies; locally, shell lags delineate bedding planes , storm layers, and omission surfaces . In outcrop, distinct concretion bands are seen within the thick sequences of shelf lithologies (lower part of the Blufftown and Ripley Formations) . Toward the top of this facies. bedding becomes thinner, and the amount of carbonaceous debris increases considerably . Faunal diversity and preservation of shell material decrease correspondingly.
The barrier-bar facies is characterized by trough crossbedded, Ophiomorpha-burrowed, quartz sand. Bedding features are smaller in scale and are progressively more modified by crustacean and polychete worm burrows from updip to downdip areas . Clay drapes and clay clasts are common lithologic components that delineate bedding tea-

91

tures. This lithofacies is best preserved within a regressive cycle at the base of the Eutaw in the Chattahoochee Valley, at the base of the Cusseta Sand, and in the "continental facies" of the Providence Sand.
The open-bay, or back-barrier facies, is characterized by lenses of well-sorted fine quartz sand containing planar-bedded shell lags in a highly bioturbated clayey sand . The faunas in this lithology can vary considerably and may be difficult to distinguish from a lower shore-face assemblage (N.F. Sohl, written commun., 1978). Locally high concentrations of wood and woody debris are another of the distinguishing characteristics of back-barrier environments. This lithofacies is especially welldisplayed in the Eutaw Formation west of the Chattahoochee River and in the Blufftown considerably east of the Chattahoochee.
Another well-represented back-barrier lithofacies is considered the result of sedimentation in a

restricted-lagoon environment . This lithofacies is dominated by thick clayey intervals, containing thin sand beds laminated by carbonaceous debris ("coffee grounds" ). The sand interbeds may contain a rather abundant infauna preserved only as burrows, which disrupt the carbonaceous laminae. Shell debris and molds are not typically preserved in this lithofacies. Locally, linguloid brachiopods and whole leaves are, however, well preserved. The Eutaw and the Cusseta, especially east of the Chattahoochee, contain rather thick intervals representative of this lithofacies.
In an idealized cycle, a fluvial component could also be added at the top, but vertical transitions from marginal-marine to fluvial lithologies are not well preserved in the Chattahoochee Valley sections. The lateral transitions from fluvial to marine lithofacies are much better preserved . The basin fill as a function of marine regression is only part of the cyclic record as seen in vertical sequences.

REGRESSIVE CYCLE

>50 M THICK

RESTRICTED lAGOON
CLAY AND THIN SAND

OPEN BAY
MOTTLED CLAYEY SILT TO SAND
BARRIER BAR OR INLET FilliNG
CROSS-BEDDED SAND
INNER SHELF
GLAUCONITIC SAND TO SHELL MARL
Figure 2. The generalized regressive cycle that includes the bulk of the Upper Cretaceous sedimentary units near the eastern margin of the Gulf Coastal Plain. Inferred depositional environments and predominant lithologies are shown; see text for discussion of lithofacies.
92

The Transgressive Cycle.
Numerous well-exposed sections document transgressive events. For example, at Chimney Bluff (see location, fig . 1) on the Chattahoochee River, the transition upward from a barrier-bar sand looks superficially like a transition to a back-barrier lithofacies. The channeled top of the sand is filled with abundant carbonaceous debris, coarse quartz grit and pebbles in a sandy clay matrix. This very poorly sorted unit (ravinement unit of fig. 3) is overlain by massive open-marine clays. Farther west and downdip, the documentation of barrier drowning is not possible, but a vertical transition from massive clean quartz sand to overlying glauconitic silt and micaceous marl records the effect of transgression on sediment size and composition within the innershelf environment.
TRANSGRESSIVE CYCLE
< 20 M THICK
INNER SHELF
MASSIVE CLAY AND SILT
RAVINEMENT UNIT
POORLY SORTED PEBBLY SAND TO CLAYEY SAND
BARRIER BAR
CROSS-BEDDED SAND
BACK BARRIER
CROSS-LAMINATED SAND TO LAMINATED CLAY AND SILT
Figure 3. The generalized transgressive cycle as preserved within barrier-island destructional events. Note that units are not to scale.
Cycles recording sedimentation during a transgressing sea are not well preserved in the geologic record (Fisher, 1961; Swift, 1968; Ryer, 1977). However, the record of a transgressing sea has been noted as thin sheet sands (Kraft, 1971) and as sedimentary packages up to 750 m thick (Hobday and Tankard, 1978). A somewhat idealized cycle based on field examples in the Chattahoochee Valley is presented in figure 3. The lithofacies are generally similar except for the ravinement unit and thicknesses of the individual units. Two obvious differences in the regressive and transgressive cycles can be noted: (1) the vertical arrangement of lithofacies and, (2) the scale of the cycles.

The scale of the transgressive cycles (less than 20 m thick) enables us to see the record of an entire cycle at a single locality. For example, along the Southern Railroad Spur into Alabama Kraft Paper (location figure, fig. 4), sediments from an entire transgressive cycle are preserved. Within this exposure, three sharp lithologic transitions may be seen. Ripple cross-laminated and channeled micaceous silt (fig . 4, unit A) at the base contains very abundant carbonaceous debris (back-barrier). This unit is overlain by a thin crossbedded sand unit (fig. 4, unit B) containing well preserved Ophiomorpha nodosa burrows (barrier). The sand unit is sharply overlain by a massive very poorly sorted pebbly sand to clay (fig . 4, unit C, ravinement unit). The top of the exposure is made up of a fissile, poorly bedded, clay to silty-clay unit containing a diverse bivalve and gastropod fauna (inner shelf) .
The study of transgressive cycles as an integral part of the sedimentation at the eastern margin of the Gulf Coastal Plain has relied on access to good exposures and the recognition that "upward deepening" as well as "upward shallowing" patterns are repeated in the Upper Cretaceous section near the Chattahoochee River. Further, the interpretation of the ravinement unit as the result of barrier-island destruction in these cycles is central to the risingsea model.
Although thin (less than 10m thick) alternations of the major lithofacies may have resulted from local bottom topography, circulation, and sediment supply, systematic vertical changes on larger scales (typically 15-50 m thick) resulted from what can be recognized as oceanic changes (see for comparison, Poag, this volume). This paper does not attempt to critically evaluate the control on these changes (see for example, Fisher and Arthur, 1977), but the Earth's albedo has been seen as central to similar cycles during the Cenozoic (Berger, 1979).
GEOLOGIC SUMMARY
Combining the various lithologic elements and the two types of depositional cycles described above, we can document a history of sea-level change as seen in the Upper Cretaceous stratigraphy near the margin of the eastern Gulf Coastal Plain. Figure 5 summarizes schematically the pattern of deposition . The record of deposition is tied biostratigraphically to European stages from samples in the project area. The absolute ages for the European stages are from Van Hinte (1976) and may be modified somewhat (J. Hazel, written commun., 1978).
The pattern of deposition shown for the Tuscaloosa is largely inferred (note the dashed line in fig. 5) from farther west (Monroe, and others, 1946).

93

Figure 4.

Railroad cut near Alabama Kraft Paper, Omaha Quadrangle, Ala. The sequence preserves an entire transgressive cycle as generalized in figure 3. A= back barrier deposits; 8 =poorly preserved barrier bar sands; C = ravinement unit; D = open marine clays. The lighter unit in the upper part of unit Dis largely a weathering profile plus a thin terrace gravel. Photo courtesy of N.F. Sohl.

Apparently only the end of Tuscaloosa deposition is recorded at the eastern margin of the Gulf Coastal Plain (see also C hristopher, this volume). After a substantia l mterval ol' nondepos itiOn (about 8 m.y .), the sea transgressed across a broad coastal plain margin leaving only a thin rework ed surface. Most of the Eutaw Formation is the record of a marine regression that continued with only minor fluctuations until the sea transgressed near the beginning of the Campanian. The basal sands of the Bl.ufftown Formation record the landward migration of barrier bars. In much of the area, these barriers were actually breached, and the ravinement has been preserved. The considerable thickness of marls and glauconitic sands in the lower part of the Blufftown is the record of a major marine transgression . A thin regressive phase separates the lower part from the upper part of the Blufftown. A second wellpreserved ravinement unit marks the later Campan-

ian transgressive event (Alabama Kraft section, fig. 4).
The transition upward from the Blufftown to the Cusseta represents a shoaling event; the regression is recorded by a flood of coarse clastic sediments caused either by sea-level retreat (changing stream gradients) or by progradation of a deltaic system. as favored by Hester (1968). The transition to the shelf sediments of the Ripley (another major marine transgression) is poorly seen in outcrop, but a transgression cycle is indicated through the Cusseta-Ripley contact. The Ripley-Providence transition is within a regressive cycle and looks much like the Blufftown-Cusseta contact in scale and composition. The Providence is unconformably overlain by the Clayton Limestone of Paleocene (Danian) age; the gap in sedimentation probably represents about 3 m.y.

94

w
0
<( I-
V)
w
70

SEA lEVEl

lOW

HIGH

NON-DEPOSITION

PROVIDENCE

RIPLEY

~USSETA

75 CA

BlUFFTOWN

80 EUTAW

85 NON-DEPOSITION

90

L ________ _

95 CE

TUSCALOOSA
-------~

100

-

TRANSGRESSION

-

REGRESSION

Figure 5. Schematic representation of sea-level fluctuations during the Late Cretaceous as inferred from the deposits in the eastern Gulf Coastal Plain .

CONCLUSIONS
The sedimentary column of Upper Cretaceous rocks near the margin of the eastern Gulf Coastal Plain has been discussed in terms of major lithofacies and their vertical organization. I have described, in a general manner. the main lithologic components within cycles that resulted from changes in sea level. These patterns have been applied to the stratigraphic column, and the dynam ics of this stratigraphy have been presented.
The cycles discussed in this paper are of two types : transgressive and regressive. The transgressive cycles are thin and record the effect of a rapid and, in some places, a destructive event. Regressive cycles represent the bulk of the Upper Cretaceous basin fill and result either from progradation or from an actual gradual lowering of sea level.
The complexity of what happened through Late Cretaceous time near the margin of the Gulf basin

presents us with an ideal opportunity to document the interplay of continental sedimentation, which results largely from onshore tectonics, and eustatic sea-level changes, which result from a variety of factors involving the world water budget. At least during the last 20 m.y. of the Late Cretaceous, the nature and distribution of sediments were largely controlled by eustatic sea level changes.
REFERENCES
Applin, E.R., 1964, A microfauna from the Coker Formation, Alabama: U.S. Geol. Survey Bull . 11600, p. 65-70.
Berger, W.H., 1979, Deep-sea drillings and major themes of ocean evolution; Am. Assoc. Petroleum Geol. Bull . v. 63, p. 419.
Conant, L.C., 1946, Vick formation of preTuscaloosa age of the Alabama Coastal Plain : Am . Assoc . Petroleum Geol. Bull ., v. 30, p. 711-715.
Eargle, D.H., 1950, Geologic map of the Selma group of central and eastern Alabama: U.S. Geol. Survey.Oil and Gas lnv. Prelim. Map 105.
_ _1955, Stratigraphy of the outcropping Cretaceous rocks of Georgia: U.S. Geol. Survey Bull. 1014, 101 p.
Fisher, A.G., 1961, Stratigraphic record of transgressing seas in light of sedimentation on the Atlantic Coast of New Jersey: Am . Assoc. Petroleum Geol. Bull ., v. 45, p. 1656-1666.
Fisher, A.G., and Arthur, M.A., 1977, Secular variations in the pelagic realm: in Cook, H .E., and Enos, Paul, eds., Deep-water carbonate environments, SEPM Special Pub. 25, p. 19-50.
Frazier, W.J., 1976, Origin of septarian concretions in the Cretaceous Blufftown Formation of Georgia's Coastal Plain: Geol. Soc. Am. Abs. w. Progr., v. 8, p. 177.
Frey, R.W., Howard, J.D ., and Pryor, W.A., 1978, Ophiomorpha : its morphologic, taxonomic and environmental significance: Paleogeography, Paleoclimatology, Palaeoecology, v. 23, p. 199-229.
Herrick, J.M., and Vorhis, R.C., 1963, Subsurface geology of the Georgia Coastal Plain: Georgia Geol. Survey lnf. Circ. 25, 78 p.
Hester, N.C., 1968, The origin of the Cusseta Sand (Cretaceous): Unpub. Ph.D dissertation, Univ. Cincinnati, 219 p.
Hobday, O.K ., and Tankard, A.J ., 1978, Transgressive-barrier and shallow-shelf interpretation of the lower Paleozic Peninsula Formation, South Africa: Geol. Soc. America Bull ., v. 89, p. 1733-1744.
Kraft, J.C., 1971 , Sedimentary facies patterns and geologic history of a Holocene marine transgression: Geol. Soc.America Bull., v. 82, p. 2131-2158.

95

Monroe, W.H., 1941, Notes on deposits of Selma and Ripley age in Alabama: Alabama Geol. Survey Bull. 48, 150 p.
Monroe, W.H., Conant, L.C., and Eargle, D.H., 1946, Pre-Selma Upper Cretaceous stratigraphy of western Alabama: Am. Assoc. Petroleum Geol. Bull., v. 30, p. 596-607.
Ray, L.L., 1958, Geology with engineering data, 1:25,000 in Engineer intelligence study E15211: Terrain study of Fort Benning and vicinity,, U.S. Army Corps Engineers, p. 47-62 .
Ryer, T.A., 1977, Patterns of Cretaceous shallow water sedimentation, Coalville and Rockport areas, Utah: Geol. Soc. America Bull., v. 88, p. 177-188.
Smith, E.A., and Johnson, L.C., 1897, Tertiary and Cretaceous strata of the Tuscaloosa, Tombigbee and Alabama Rivers: U.S. Geol. Survey Bull., no . 43, 189 p.
Sohl , N.F ., 1964, Pre-Selma larger invertebrate fossils from well core samples in western Alabama: U.S. Geol. Survey Bull. 1160C, p. 55-64.
Stephenson, L .W., 1911, Cretaceous (rocks of the Coastal Plain of Georgia), in Veatch , J .O., and Stephenson, L .W., Preliminary report on the geology of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 26, p. 66-215 .
Swift, D.J. P., 1968, Coastal erosion and transgressive stratigraphy: Jour. Geol., v. 76, p. 444456.
Vail, P.R., Mitchum, R.M. , Jr., and Thompson, S., Ill, 1977, Seismic stratigraphy and global changes of sea level, part 4: Global cycles of relative changes of sea level: in Payton, C.E., ed., Seismic stratigraphy-application to hydrocarbon exploration, AAPG Mem . 26, p. 83-97.
Van Hinte, J .E., 1976, A Cretaceous timescale: Am. Assoc. Petroleum Geol. Bull., v. 60, p . 498,516.
Weimer, R.J., and Hoyt, J.H., 1964, Burrows of Callianassa major Say, geologic and shallow neritic environments: Jour. Paleontology, v. 38, p. 761-767.
96

MICROPALEONTOLOGY OF THE TWIGGS CLAY,
GEORGIA COASTAL PLAIN
Walter Schmidt Florida Bureau of Geology
Tallahassee, Florida and
Sherwood W. Wise, Jr. Department of Geology Florida State University
Tallahassee, Florida

ABSTRACT
Fossil diatoms, foraminifera, ostracods and calcareous nannofossils of the Twiggs Clay Member of the Dry Branch Formation (Eocene: Barnwell Group) of eastern Georgia have been studied in surface samples and well cuttings. Paleoecologic data derived from these microfossils coupled with macrofossil data suggest that the Twiggs Clay was deposited in an inner con-tinental shelf province.
In the past, major portions of the Twiggs have been considered unfossiliferous due to the mode of preservation of the siliceous microfossils. Scanning electron microscopy of many samples shows that these often occur as molds and casts. This type of preservation would be lost in any standard microfossil washing procedure.
The Twiggs Clay can be assigned to the lsmolithus recurvus calcareous nannofossil zone of most authors. This, in conjunction with its stratigraphic position somewhat below the Eocene/Oligocene contact, suggests that Twiggs time spans the middle part of the late Eocene.
INTRODUCTION
The Twiggs Clay of Georgia (fig. 1) has long been of interest to Coastal Plain geologists because of its commercial deposits of opaline claystone ("fuller's earth") and the problematic environments of deposition they represent. By latest interpretation, the Twiggs Clay is considered a member of the Dry Branch Formation of the upper Eocene Barnwell Group (Huddlestun and Hetrick, this volume). In general, updip sections of the Twiggs tend to be sandy and opaline, whereas downdip sections are calcaerous and montmorillonitic (Carver, 1972b). Southward, the Twiggs becomes more calcareous and gradually merges into the Ocala limestone in the west and into marl and shell beds in the east.
Not surprisingly, a wide variety of environments of deposition has .been identified or postulated for the Twiggs. These range from estuarine conditions in the updip locality near Grovetown, Ga. (Berry, 1924) to those labeled "very near shore marine" (Darrell, 1974). "normal marine" (Shearer, 1917).

"quiet, low energy" (Pickering, 1970). "regressive" (Carver, 1966, 1972a). '.'transgressive" (Weaver and Wise, 1974), and "peculiar" (Cushman, 1945) for the rest of the outcrop belt, depending primarily on the type of evidence examined by each investigator and where the unit was examined.
Similarly, the question of origin of the opaline claystones has also elicited a wide range of opinions. Cooke (1943). LeGrand (1962), King (1962). and Noble (1962) considered the Twiggs Clay a bentonite or weathered volcanic ash, an opinion challenged by Pickering (1970) and Weaver and Wise (1974) on the basis of the abundance and mode of preservation of various microfossils found within the unit. Pickering (1970) speculated that the Twiggs Clay was precipitated as colloidal particles formed by the action of saltwater on normal terrestrial clay minerals. Weaver and Wise (1974, 1975; also Wise and Weaver, 1974) suggested that the silica of the opaline claystones (opai-CT of Jones and Segnit, 1971) was derived from the dissolution and reprecipitation of biogenous silica.
In light of the above, the present paper examines the microfauna and flora of the Twiggs Clay with special interest in paleoenvironmental aspects of the assemblages. Groups treated are diatoms, calcareous nannofossils, foraminifers;, and ostracods. Systematics for all illustrated specimens are given in Schmidt (1977) . Palynomorphs are not included but have recently been examined by Darrell (1974). In addition, a lithologic analysis of our samples has been completed (Schmidt, 1977). and will be presented in a subsequent publication.
In general, there has been little microfossil work done on the Twiggs Clay. Cushman (1945) recorded a foraminiferal fauna from a locality near Sandersville, Ga.; Herrick and Vorhis (1963) listed many additional species; and Pickering (1970) noted some foraminifers along with macrofossils near Clinchfield, Ga. Darrell (1974) reported in abstract on palynomorphs from Houston and Washington Counties, Georgia.

97

oo
N
l
u"oo'

n1 oo
EAST CENTRAL GEORGIA

25 '--S~CA~"---' MILES

EXPLANATION
/-COUNTY BOUNDARIES ~TWIGGS CLAY OUTCROP BELT
ADAPTEO f'AON lt,G. RIC ti AAO~C I U9) AND R.E,CARIJ ER (1 91Z)
e20 OUTCROP SAMPLES 0 7 SUBSURFACE SAMPLES

... .

Figure 1. Study area and sample location map.

Among some of the other known localities where the Twiggs Clay crops out are a number previously considered unfossiliferous. Apparently, the major reason for these localities being unworked and thought to be unfossiliferous was the mode of preservation of the siliceous microfossils, particularly the diatoms and sponge spicules. These occur primarily as molds and, therefore , cannot be extracted by standard washing and sieving techniques.
All of our sample localities are shown in figure 1 and listed in appendix I. Samples referred to in this paper are keyed to those localities by number. Where more than one sample was collected from a locality, the locality number is followed by a hyphenated sample number as indicated in appendix I. The distribution of fossils by type at each locality as determined by this study or as reported in the literature is indicated in table 1. No samples, however, from localities 9, 13, and 26 were examined for fossils. Instead, only published mineralogical data exist for these sites.
FOSSIL DIATOMS
Scanning electron microscopy of fracture surfaces of the opaline claystones revealed siliceous microfossils which occur as molds and casts in a number of samples. These fossils occur mostly in samples which contain the highest percent of Si02. The opaline material, after X-ray diffraction studies, proved to be opai-CT which, on free growth surfa-

ces, exhibited characteristic lepispheres (Wise and Kelts, 1972; see also Wise and Weaver, 1974; Weaver and Wise, 1974). Most of the microfossil molds are of marine diatoms including pen nates and large and small centrics. Sponge spicules and a number of unidentified organic molds (possible radiolarian remains) are also common. From the apparent abundance of microfossil remains it would appear the opaline claystones represent highly altered diatomite deposits rather than ash beds. Most microfossils in the clay of these locales have been completely destroyed by dissolution, and only the reprecipitated opai-CT remains, preserving in some cases the shape of fossil skeletons.
Early diagenesis of these siliceous clays probably followed a pattern recently postulated for deep-sea siliceous ooze diagenesis, that is, in situ dissolution of biogenous opal with silica reprecipitated inorganically as authigenic opai-CT (Wise and Weaver, 1974). In places where the opal content of a clay is extremely high , molds of microfossils may not be preserved. Significantly, once diagenesis begins, practically all available biogenous opal in the affected material may be converted to opai-CT with little trace remaining of the original substance. Thus, most of the microfossils originally deposited in the material probably were not preserved , not even as molds, but were destroyed by in situ dissolution following burial. The silica released by dissolution, however, was subsequently reprecipitated to form a significant proportion of the rock matrix and constitutes the principal lithifying agent in the material.

98

TABLE I
Distribution of Fossils by Sample Locality

Sample Locality

I 234

Diatoms

X

1 -1 -

Calcareous Nannofossils

XX X

1- -

Foraminifera Ostracods

-X

X X 1 -1 -

-

0

X XX

Other Fossils

X

0 X

5 6
-
0

7 8
.

9 10 II 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30-

X

X

:t

X -

r- X X

-
-

0

0

0

0
-0 - -
0

6. -
0
0 0

'--

0

X

0

Other Fossils = sponge spicules, molluscs, sharks teeth (all marine) X = fossil groups identified in this study
0 = fossils reported by Pickering (1970) at or near the sample lo c illitv 0 = fossils reported by Carv e r (1972) at or near the sample lo c al itv 6 =fossil s reported by Cushman {1945) at or near the sample 1ocal1tv
Blank .. no fossil remains found

Sample Preparation
To find arid identify diatom frustules in this opaline clay, two methods proved to be most useful over the other conventional methods generally in use today. The first was to make smear slides for the light microscope, and the second was fracture surface observation in the scanning electon microscope.
It was discovered that a number of diatom frustules did remain intact, undissolved, and needed only to be separated from the surrounding matrix. The procedure for diatom preparation generally follows well-known microfossil separation techniques; however, modification had to be made to best suit these particular samples. For a list of procedures used, see appendix II. Generally, species identification was best carried out on the scanning electron microscope.
Other methods of sample preparation proved to be of little value and were not pursued . Thin sections were prepared using epoxy immersion but yielded no significant results. A low-power binocular microscope was used for surface observation, but only a few diatoms are large enough to be see.n by this method.
Marine Ecology
Diatoms are found wherever there is moisture and sufficient light for photosynthesis; therefore, the widest range of variation and environmental factors is encountered.
Many species enjoy a wide distribution, and it is difficult to decide whether they are oceanic or neritic . It is also common to find truly oceanic forms associating with neritic planktonic forms. It seems these divisions, therefore, should be accepted for some species only in general terms.

Within the Twiggs Clay, the number of individuals (microfossils) present is not large enough to w.arrant a complete statistical study to determme detailed temperature and ecologic niche. However, there is among the fossil remains a fairly diverse number of species which, when only the most abundant forms are used, suggest a narrow range of environments which can be compared with other fossil groups to infer the paleoecology during Twiggs time.
A brief analysis of the environment represented by diatoms from the Twiggs Clay can be made after considering each species separately.
Coscinodiscus radiatus Ehrenberg (pl. 1, figs. 1, 2): this species is reported as marine neriticoceanic, warm water.
C. oculus iridis Ehrenberg (pl. 1, figs. 3,4): living representatives of this species are widely distributed throughout all oceans; considered an oceanic, pelagic species.
Actinoptychus senarius (Ehrenberg) Ehrenberg (pl. 2, figs. 1-3): A senarius is a cosmopolitan species found in neritic and oceanic plankton.
A. splendens (Shadbolt) Ralfs (pl. 2, fig. 4): species considered a common littoral form, often near coasts.
Trigonium barbadense Greville (pl. 2, fig. 8): the ecology ofT. barbadense is hard to define; however, a temperate to tropical climate is called for. This species also is one of a few that appears to have a short stratigraphic range (upper Eocene to lower Oligocene) which would suggest high stratigraphic value.
Para/ia su/cata (Ehrenberg) Cleve (pl. 2, fig. 7): this species lives attached to the substrate for reproduction although it may be found occa-

99

sionally in plankton. The species then is littoral and is said to frequent brackish waters.
Odontella aurita (Lyngbye) Agardh (pl. 2, fig. 9): 0. aurita also lives in chains attached to the substratum . A neritic or littoral coastal species, it is sometimes found floating free.
Eupodiscus radiatus Bailey (pl. 3, figs. 1, 2) : common in neritic seas .
From the species present, certain environments are apparent. With the exception of Coscinodiscus oculus iridis, they all have in common a neritic or littoral domain and most are planktonic from warm marine waters.
The fairly pure aspect of the clay or, more correctly, the lack of detritus and other continentalassociated material may point to a marine environment a fair distance offshore. This may be verified by the presence of Odontella aurita and Paralia sulcata, both bottom dwellers and probably not able to withstand a great deal of wave action. Their benthic life style, however, limits the water depth since they must receive enough light to photosynthesize. The presence of Coscinodiscus oculus iridis reinforces an offshore interpretation since it is an oceanic pelagic species. One species, Paralia sulcata, can be associated with fresh or brackish water. From this variety of environmental domains, it would appear we are dealing with an offshore coastal assemblage. An inner shelf province where many niches tend to overlap would fit the assortment of specific ecologies represented.
CALCAREOUS NANNOFOSSILS
As previously stated , a calcareous facies of the Twiggs exists as the member trends southwestward. This fact was originally apparent when fossil mollusks, foraminifera, and ostracods were noted within the clay, and again later when the clay was prepared for X-ray diffraction, and both wellordered and disordered calcite were found to be present.
It is now known from this study that in addition to these calcareous fossils, there exists a wellpreserved calcareous nannofossil assemblage. The coccoliths were obtained from exposures of Twiggs Clay in Houston County, Georgia. These localities (Nos. 2-4 in appendix 1) were visited_. during the Geological Society of America Southeastern Meeting and Field Trip, 1974 (Huddlestun and others, 1974). Locality 2 provides an essentially complete section of the Twiggs, whereas the others are partial sections . There was little variation in the distribution of coccoliths within these sections.

The coccoliths were observed first while scanning a fracture surface for diatom molds. A routine calcareous nannofossil preparation was then made with good results. The following coccolith species were identified by light microscopy (listed by species epithets; bibliographic references are provided by Loeblich and Tappan, 1966, 1968, 1969, 1970a, 1970b, 1972, 1973, and Wise 1973):
Discoaster barbadiensis Tan Sin Hok, 1927
Reticulofenestra bisecta (Hay, Mohler, and Wade) Roth, 1970 Coccolithus eopelagicus (Bramlette and Riedel) Bramlette and Sullivan, 1961
Coccolithus formosus (Kamptner) Wise, 1973
Helicopontosphaera lophota (Bramlette and Sullivan) Haq, 1971
Sphenolithus moriformis (Bronniman and Stradner) Bramlette and Wilcoxon, 1970
Pontosphaera multipara (Kamptner) Roth, 1970
Transversopontis obliquipons (Deflandre) Hay, Mohler, and Wade, 1966
Coccolithus pelagicus (Wallich) Schiller, 1930
lsthomolithus recurvus Deflandre, 1954
Reticulofenestra reticulata (Gartner and Smith) Roth, 1972
Discoaster saipanensis Bramlette and Riedel, 1954
Discoaster tani Bramlette and Riedel, 1954
Reticulofenestra umbilica (Levin) Martini and Ritzkowski, 1968
The above species are useful in helping to define the age of the Twiggs Clay as well as in providing limited ecological information. Using other fossil evidence, Cooke and Shearer (1918) long ago assigned a Jackson Age (late Eocene) to the Twiggs. Since then, a number of other studies also placed it within this interval. The major criterion used was Foraminifera along with the stratigraphic position of the unit within the coastal plain sediments.
The coccolith data are in agreement with this general assessment, and place the Twiggs within the lsthomolithus recurvus Zone of Hay and others (1966), defined as the interval from the first occur-

100

renee of/. recurvus to the last occurrence of Discoaster barbadiensis (fig . 2). In the Gulf Coast, the Cocoa Sand, the Pachuta Marl , and the Shubuta Marl of the Yazoo Group, studied by Levin (1965) and Levin and Joerger (1967), belong to this zone. Huddlestun and Hetrick (this volume) believe the Twiggs Clay probably represents the easternmost tongue of the Yazoo Group of the Gulf Coastal Plain, but for practical purposes, include it in the Barnwell Group.
Other authors have defined an lsthomolithus recurvus Zone or Subzone more narrowly, placing it between the first evolutionary occurrence/. recurvus and the first occurrence of Sphenolithus pseudoradians (Roth and others, 1971 ; Martini , 1971) . This corresponds to zone NP 19 of Martini (1971). The Twiggs Clay may well fall within this more narrowly defined interval which is middle late Eocene; however, evidence for this is somewhat incomplete. While it is true no Spheno/ithus pseudoradians were noted in our samples, neither was its evolutionary precursor, Sphenolithus radians, found . The absence of S.pseudoradians , therefore, is only considered suggestive of a middle late Eocene age.
The position of the Twiggs Clay within the sequence of coastal plain sediments can also be considered in this evaluation. The Twiggs is a lower facies of the Barnwell Group which is upper Eocene. Since we know the clay does not continue to the uppermost Eocene and from the nannofossil evi-

dence it is younger than early late Eocene, it can be reasonably inferred that Twiggs time occurred during the middle part of the late Eocene as indicated in figure 2.
Although ecologic information is limited for the calcareous nannofossils, Bukry (1973) has made a few generalizations. He states that during the late Eocene, there was little evolution in the warm-water genus Discoaster which developed the greatest number of species during intervals of warmest temperature in the early to middle Eocene and middle Miocene. The reduced Oiscoaster speciation and the generally long-ranging zones in the late Eocene and Oligocene indicate a cooltemperature interval. He further notes that Reticulofenestra reticulata is a nearshore species whereas /sthmolithus recurvus is a cool-water marker. This indicates a somewhat temperate or subtropical rather than a strictly tropical environment.
TRENDS OF FORAMINIFERAL DISTRIBUTION
Table II lists foraminiferal species identified here and by others (Cushman, 1945; Herrick and Vorhis, 1963; and Pickering , 1970). Combined with this are environmental interpretations based on generic data given by Murray (1973).
From the species present, the ancient environment can be recognized , after noting the individual

...
gw ...J
-:lEzw
u 0
... - a:<.!)
lt ...J oO
...J

TWIGGS DEPOSITION

...
...J Q
Q
::1

Figure 2.

Nannofossil range chart showing approximate time of Twiggs Clay deposition.

1. lsthmolithus recurvus

4. Reticu/ofenestra umbilica

2. Discoaster tani nodifer

5. Disc oaster barbadiensis

3. Coccolithus formosus

6. Discoaster saipanensis

101

TABLE ll

Foraminiferal fauna from the Twi~~s Clay with some genera li z ed ec oloqi ca l data from Mu rray (197 3 ) . The dat a are

8iH'1.G'J ir. Nlf:)~l~l'1 ~lts i { llc:J nsrlt 1cJQ 111 !O"{ 2i ti ~l~)n~'Jb

- 6 1<:J to 9~)f19 111J n o r2s 1 s ri J o t 2-U'rl l ,-,)~) 1 .\ to "J:J~FYI

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te -2f> 'J

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3 4

sr~lfu> M,,.llll' ~l lo
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t>":,Oitht'bcrll1i Pbloll!o~~mflrai11'm~1 t!fq.w!j'EtaIuJtr~~1r.f0l .

2.'1?.1\~\<1;~~~
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so :.Hh

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erl t 1ot bstimil ai noitFINHotni ~igolo::Je liguorltiA

::m-o-_:, :-oirit n-J p--rto'c' cPlAlrO rN ~tt ~ O'NJH9-!N)Tt9u,L bnfi r;ivs - 1 br1s o;il ~:>lfeiisd 'Jrnulcv ,, , , JIIJOH ons rwlcelbiJuH

f) l~ ~ Lu~ . ,- 1:. a b'a l lu Cu ~ rl~r~:u, ~

OfHII>il 21.1091G;JI

-, I'~ --rrr---J

... r.tc rJH . 2110il~:-:sils1ene(! W8l

1s-k ~o n 1 -~ ~-~P ' ).J. ~PisM.i%Hc~v~SHf\ I cf'i w f.:'19 r!I ,e n~l~;G::J

:J:..Jt_, u b,l>otll" li l ,i. u'S hlll'l n I 1, 11 , I "\':) 1'2-CO 'J(',\Q (;lJ(j ~j(}

f c ii)6Q,f;"a'\~; ~,~pf.l, ,{~ rls .,ndVt1~rl ili nt, ctlc J (\X,~'I'c ; J'O,PQ wT I F. !~e:-{1} nt ~ lfill_i)'l ;:lirllJndtQIP~~ ''"' tJ v~ l _<;sY sri! lo 9UQnOJ :-lril ni ti sbui::Jr1i 2cJ20q~uq lh:jiJ:JS1Cl 101 IIJcl nisici
qu01D ll9wmsE'J

r 1 ., , 1 , 1

r; c ' 1



~ R a.~ l!l u s,

a

]

;. ~l'

-

,l

nrl

~~

~ru ~,
J=-=-

1 (r.~rbe J )

(} IJ8q2 to 19d rn un ' t - , 8 1l n1 ::nu, fn ~-)q ;n g,

Zllr\i\\omo:\1 ?.\ flf; bGnitBb ':JVBri 8l(jrtJus writO

1 ~\l.l!.l,!.!,t!;DA I ,<1 1:, a. ~n.>fu. \C u_l l"n.\.rl!' 'c:riT .en G:)oiM ~:Ji b 9!fi:Jn'inn~ic6:a'}Q~'iislflfltQMhQ1lOI y !lmen9~? s ilt bni;

Ji gni:)slq .'{IW011f)rl .:nom (Jnosdu2lo nrw S: 21.J\I 'll 0 ~:rl
-ll .l ~j (1\ I s:ms11U:J:JO \''iBrro',ulov9 J21it 8riJ nSJewl~id

- l o'. t~ c/~ n ~n -..'l's. ICto'dh,.fil n ~ tJl ~&,r,JiiH) b rt B 9 n :3 ;) 0 3

- -~ ..1, , -:- , J fl 11 e H .IBvl s tni fnutmsqnJ e l

c ., ~ndo~ g(
v 'J- i I

ia
-

I ~L !! .lutt alot .H-::tt"'~

f.t unl ll e ' I

l

va.r~-~~rqligefi\i ll b l:-:1 .J ~ Hl- I ,-_!

s___ b\

1.u?,s..h9l]\tHa.jIt\

0

. \

2i I I . >111"1! t' ' '( 1t l G ;::i 6 \J '~'\ \J::t9\ 2.\.J (\\\\(!fCI,[\\ (, \

.r IB

~ l.a<loI n>~ qcI

11t I <'

lcos 11 t

r,, l.t>H 5< ,; '

9 1 lsrlW 9 fn02 f') c~rjf; ~)J_bfl l.

_1,__. h C')<.MJ ~?P. , fl\1 /1' I \''"F1) !1 :) i q01j ylbi'll2 fi n.F> rlt 'c!r1tE;1

-1.)()20, o?.\..11\!\\on~l(IC\G lo e::J;t911U:J~lo 121it sdi bnB ?..\1\1

(tH?.r initlr.M l\8t .e:nrilo bnr, rltof'-l) zm,\\)iJIOb
n ( t \8 ir11t1f;M io 8 r CJ~1 CHlOS ot 2bnOQ29llO:'l cirli

-:ls(-~;r1!.1i~lo'Sr)il;Cftilbaferf:1mlar;.>l:,irrle/'!st,lnemlirbulbdiutriYhWzse1ia\&rl:tmJ!iler9nttwW,

cV'rGiuCf1.btVBtri8op1Ge.lQir~liW
if>Vlstni t:>enileb

0T'-~rl"1:Swlro\T;

.e>tslqrno:mi J.BriVhlrnOe ei c=mU 10i oorr9biva .'t9V9Worl

1_. laevis ('lont a qru)

919W 2.1\B\\.)~;-IOGI.JGi:.(\ ?..11\\ l\lon ,3 r\Ci2. on 9LI'Il 2i ti 9 1i rlW

JAA3:'11Li!IMAAO=i =tO 20Li13RT
~bul ina gibb a DlfPOilf't.JS'tfl~ (Von 11u e n s te r )

yH>noitulove 2ti 2sw '1''H1.~iflll .r.:slqrni32. wo ni beion
8 f~~r7~~J~e)mr f''cffi~\'\'31;-, t~?lP,fffi\l')r\'9 {\f~e,i C~-1 Cc9.fEIQ.)81 q

-flO;) ylno zi ,s1ote1~)rlt ,zno\\w;1o'nuezq 2lo s;JnecdB

.sg.s ensoo3 etst eibbim s to svJt2;3QQU2. b919bic.

Hyposaline to normal marine sediment, cold to
snuronit\Jliwo-'(~~011. o~ei~NT ertl to noitic.oq erlT
9li oels ns::J 2tnsmibe2 nir,!q lstzoJ to eoneups2
1ewol B ai 2l_)QiwT oriT .noit:,;u\sVf:J Bir1! ni bs1sbieno ~l
.sn:'3;:J03 1sqqu zi rbirlw quo18l\swms8 eril to 2oiJst srq~eJ%Wl~{~t~(~i-J;''t1t(l ~~~~~siY"tfma INo111~tB'\IIti 't:fjn i2 -iva lieaolonnsn edt mmt bns ene:Jo3 teom1eqqu

Sed iment and veqetation, l-30"C, 0-50 m, tidal marshes and laqoons, nearshore

~~mal marine , muddy sediment, temperat J
l1elf

0-800 m,

Bolivina

ddy sediment, bathyal to marqinal mari e

Oiscorbis
D. assulata u'$ h". J"
~.'!.!.~ J .!!..lLVl ~"' '-
Eponides

~or~al marine, muddv sediment, cold, 100[ 4500 m,
~~ter shelf to bath~al
~~rmal marine, vegetation, >l2C, 0-50 m inner shelf
2JJIWT
q ~ o(l ime.\1 ~Jlli;Q '1~qera L , she 1f
"

I ll (l rt~ 'l marlr"' mu d dy s~ M i m~ot , ca lrl_ t o l~mperate,
~ - > JfJOO 111, 's he l l f o bti thva 'l Marine planktonic

Cibicides
. lobatulus

~ormal marine, clinginq to ve t1 etation, s ones, shells,
r 1!-tr.. ,arc.Ln: l i.L tr.o. p.:U:.al~ r)- >. lOQO.. t~. ~J1e 'l to bathyal

C. mississippiensis (Cu shma nJ

.notliaoqeb ye1:::.. aggi NT lo ~1mii 'J ismi x01q qs " iwon<: lH; ,i:-J e gnr;t ircP.olo:-trtsv~

C. planoconvexus Cushman and tT:3Mr_\[\'l\.l !-i\l?r.>t\e'lo\uo\',eR -~

01~1J\IJ0 \.n ?.IHI\\IOII\r'lc,l ~

Globi'!er i na sp .

Zlc-!lfJ\bnchsc\ l!llc.GO:lGIG .2
212.\191\bJ,\L?. \C\ZhO:w.\tJ (j

'\81\bO\ \r11:.1 \9\2.60::1::>.10 .S Mar\1.\Jc_l)'lMb\o~\\~111\Ct :<)O~) _[

species ecology and any trends which may exist. In

After looking at the entire spectrum of foraminif-

a general sense, porcelaneous species of foraminif-

era present, the depth ranges of the more abundant

era are characteristic of the inner part of the conti-

species yield a distinct depth correlation . There are

nental shelf of modern oceans (Bandy, 1956; Bandy

many more species present which represent an

and Arnal, 1957). Arenaceous foraminifera occur in

inner shelf biofacies than any other faunal zone. It is

shallow waters and on the continental shelf

in this zone, ranging in depth from a few feet to

(Zalesny, 1959). Hyaline species, also present in the Twiggs sa'mples in small numbers. seemto be less

nearly

200ft, ,:

that

the

Twiggs

Clay

w.as

deposited.

.

restricted, being found in abundance near shore ;:~_s

The presence of some bathyal and estuarine

well as in bathyal depths.



forms simply points out that this environment dur-

ing Twiggs time may not have been isolated from

The great marjority of forams present in the

adjacent facies, but accepted mixing of species and

Twiggs ~l.ay. a~e , porcela;neous, : with .auenaceous . , lithologies from neighboring provinces. This situa-

and hyaline forms being less common. This would immediately place th~' assemblage ecologic:ally iri

tion may have been introduced by relatively minor
''II ~Ctl.tatiohs of the slraridli ne position wftn concom-

the inner continental shelfran~e.

~ - , \, . ,, )!.,

i

,

: ..

.:

,,

itant migratipn of,facies belts.

,.:!:I i I , , , ...

I,

'

.

.

Another observation of a general nature was rC7P,~rtedpy . k~e~s p954} anp Bandy (r195,6), ~eali~~
w,i_~h1 ,the ,lnt'~ri~r' St~u~t ur,e, ~t ~hef?.st. T h ~y, repor~
1 a that those I pef'jera Wl1h slrn le lnterl rs e fre-
fn qt.iently v'Mi -ab un~~nt sHoal'' w1aterY,' w Mrea$
gknera wn;~ ' . c?mrlfe~ te'd i'n\erib:r ' s.t'r_ug~u~-~~ ' ~re
mdst chara1ctrr~~ti c ~~ bafh~~.' Cl~pths.N'9 i:J0';11' n~~l
style, however, 1s not1cei:lb le 1n hie Tw 19Q asse.molage. Thus, ana lysis of this parameter doe's lidt seem to be applicable ,in this case.

It Is not poss ible at th e present lil)le to generalize

oCnI ~S~ ~o~f'

Wb rl (Jt:
fol-'a'mi

~n_lltt,elte"ad, eopetd'hadui~~e!!tl hbe~rHeoh~assobfenle1nf' 1ln~slu~fPf-Jtl

cl~nt 'sn)dy df 'f'i{u_nas ',f dm tl11s partic't.l lar''pol t' 91

vi ~w.. 1hert:~ 1 has, ' hdw'ever, 'been' 'a1 cc5m ifa;tibn 6t

H3'rhP,eratufe a~~ JdeR H(ahge~ o~ afisi ~r.flca Jlt~l?.~~

cle's' f~om tNe areas 'Jvhf:rr,e pparen(fy rellat:) le'st u-

dl e~ ' hav~ :o\:!eH ade: -rh'i~- h gr ~~e~ ~Bt:?he:: ~x

Plll eg'e1r' ' (~96U).1 sahdy ' 0 '956), ~ d M'u'rray' (1973)..

li$'l'n'g' thei daia,'c hkra<ct.eri'stic wat'elr 'dtil~'ths'dt 'vat~

idus- s~ec'l:!s' ca n b'e dbt1ained. I I ., ' ~

1 1 '

J I) 'I .

1 I , I

,. ' : I 1 1 I ., II l

I

I -, ~Jc?r~fng 1fr~ni tl e $,h'O ~ OUt !3h:f, . th~ fir~~ fn'B!Qf
faunal' z'cMation Is th\~ esr an'es an.Cl bctys. ~He
Twfggs1GiaY 1has I so~e"'spelC'i1e~ 1 Wh_i ~ fafl 1int1b' fh'l~
cate.gbrt. Incl'ud'ed arfi'efptHCi/Jm fwitJ[jsanl./m ~ and BuJ/tnine/1 ''e'legarltrhY!-ha, aloHg' vJifti a nbtrt\b~r- b f
dstracb' s wihl ch 'also1are'tb hd 'cl'orh'ln'aht ly rn ay"M
and est uaries. The next biofacies~! th'ec i~ne1r she'lf

area which includes Nonionella hantkeni var.

spissa, and various.species of Textykarua, Cib-

icides, Bolivina, Nodosaria, Nonion, Siphonina and

Uvigerina. Tfie,middle andiOUter1shelf biofaci.es ate

represented tily speci'es of Robu1os.,. Uvigerina and

B o l i v i n a .. "

.l. ,., , . ''"'

-r;rr .~IP.

,~renmta),!y~rre1pit,Yrtsl{~f

nstp~ehpEi(f;l fl1~1~Pr.v_arelseb'i'~)NIee

t~e T~i~g_s
n t he.s hore-

llne and the o uter she lf; how ever. a few b.athya l
fprrrR ,~re a1 ~9 p r~.S~nt, ame lr V/:J t~Stlneria. i ackso_-

rer1SJs,1Bt;livi(l,a. iar;kso,ne,nsis,, an,d a feYy sea te(ea

G l o~i,ge r. ini.rae.

, ,

,I

Some species of foraminifera are diagnostic

guide fossils of the upper Eocene in Georgia. Those

from the Twiggs Clay Member include Textularia

h ?ckleyen~is Cush,man.. ano Ap~lin ,, ~?lvu lineria

facl<sodensis C~shman, N orione{laharlmenl (Cush-

m~n and ' Applln)' v~:k spissa cu~hd,an, 'and 1-f'lnr-

kenina alao'amensis CLlshm~n : ' hese a:lo ng w,i\h

th e

cqcc61ith

lnde'x

species,

ne l p

1
defi_nep\e

time

0~

deposit ion of the c lay.

' 1 tl 1 It

, lj

1
' I

- 11

,1

' '

.. .'osTRACOD' STUDIES :; ' ...

' ~ i I 1 , ./

' ~ ' . : i . i 1 ~ l !. i , ~ 1 ! ,

a,;?; ;:. oitnf c'od' speCI~s;; identified :in 'this#~t{y~

Cythereis montgomeryensis Howe and Chambers,

H(See,m~i~c~yth~~ar);:TerapctH;n}!~IftJa'bte~:ltsur.ci',_~(M!_-u'.t~iel~us~t~'~!!u:/r_1',, ~qfeyttw(rln~ics.

en'ti'rC,aiIeaa( leIa'UXe. avIngaetd.a r IQI

I-I owe
Pur'1. 'J

antJ l,

'CHambe II '

I

1

rs, a~d

.. I

1
.,

1

1

Cushm~-

I

' II

,

n

~

A lEHfriu1: bth!fl~hand~6~'i.tseoesn_w('11bb~9-~se'5;tc8rCa')a~ucGscp!M'dl:d'sr~~p~cl nraoetbl~q1We~henyrl.y .~'Tf19Wt11itpPtl'e,(lr~$''.tlt'Jtl/yr~d~l(rw:~s{~sY~r,.tariJ'~;Plic,.'h:(''ErpPr;i~,~cRio.rJ~~.,i;

(Hl!)4), 1 e'al with' reb'e t 'ostrac~o;B ecol_o_g_y in t~~ G,ult

o'f r\il~xit'o ' ar'ld ti y b~ usefl'l l 8 'cdrrela ing fo1 ssil

I Ql p?eI c ~ 11

i

J~~""IsLI

w
{'

irth

th-,e, i

e'" cole
fll

1c
'

nt ich~~e.

_ 1,

I

'

t

.
I

. It II '
tl I 1

-

1 adcrY,J?ni~,)hatr,PdfIy(Y.~uitmnr~l?ovsiHel~:Alr,,~s~it,irn.I.sf:n>hgn~l1t,i.(I:eg1t~'JJd'1o~~p~~lc'5o)byt~.(e,rqt),1aao'r'!tnfs-?i~tn,ss~o\s\~1atf1eh~1lats~ie:)n~e.lp,i1t~ct~YitMah.hs~~ude{rste,1'i~a_s(p'b'(,mu1e~,bppftt,ris1no~htd,rrne~a~~.n,tqtruf19!wrfn,1~ne.o)y~"h.s1,f'rt'1o1.i~~nnxa,~1'myyor,~t.ioE.rel,Qd~Vn1~(e,].~rt

lit. I,. I fl _ I'J, I
From the studies of Hulings an d Purl (1964). on y

tera'~oe.d:m~jaq.'~.

e~ytrpnf11~fl!~ l
w , s~line tap,rs



fyavc~ii,Ec1sh

C\fOoi';Jl~iq,q,o~es1i,dq.eelrierq

~'iHg~n~J a,rd~st~ ~~.ir~ .~~_n~
(less' than 35ft) nerrt1 c ssern

p tY.J?,ip~' ~~~~~pw
plaQe w1th h.lg h,er

vy,~.te,r
~'i\11 n-

itl~s. Of the' a'd tt1 ey lassifled as to bio~-'lcl~s, o qly

three genera are found as fossil s in the 'tiNig1gs

m~teria l . These are ,C~s l)manidea, 1-f~micythef,e and

C w

yth ate

e r

rneettrait1icaalls1soef'mwbhl

ich ~r~ age.

:fMS!dered

~

sn.allow

103

Figure 3. Cytheretta a/exanderi Howe and Chambers. Sample 30; x 45. Scanning electron micrograph . Figure 4. Cushmanidea laevigata Puri. Sample 2; x 70. Scanning electron micrograph. Figure 5. C. laevigata Puri. Sample 2; x 70. Hinge of right valve. Scanning electron micrograph.

SUMMARY
The diatoms present represent a cross section of living requirements including brackish water species, shallow water neritic species and oceanic pelagic species. At only a few locations were vertical sections of any substantial extent available. These locations, however, showed no significant faunal change in the intervals sampled. From such a variety of environmental domains it would appear we are dealing with an em bayed coast that may have fresh water input.
Other faunal evidence yields similar results. Foraminifera species are present, associated with estuaries, with inner continental shelf, and both outer shelf and bathyal depths. The majority of forams represent the inner shelf biofacies and it is in this zone, ranging in depth from a few feet to nearly 200 ft in depth, that the Twiggs Clay was deposited. However, we emphasize that no one environmental interpretation answers all questions dealing with the Twiggs Clay history. There are two species of foraminifera present from the shore (a brackish environment), three species from the middle and outer neritic zone, and three species from the bathyal zone. Clearly, the western end of the outcrop belt was deposited offshore in quieter water than in the Bibb County area, which is further updip and accepted considerable sediment influx (Schmidt, 1977). The eastern portion of the study area represents almost no clastic input but is certainly also inner shelf marine.
In addition to the fossils noted, a few echinoid and bryozoan remains have been found along with sponge spicules and a shark tooth. This wide array of marine organisms indicates a normal marine environment.
Another ramification of this study was the time zone set up from the coccolith zonation. It was pre-

viously known that the Twiggs Clay is late Eocene in age, and this was verified using published foraminifera ranges . However, by using a first occurrence and two extinction datum levels of three coccolith species, the time of Twiggs Clay deposition can be more accurately defined. It is now considered middle late Eocene.
ACKNOWLEDGEMENTS
This paper is based on a Master of Science thesis (Schmidt, 1977) submitted to the Department of Geology, Florida State University. We are grateful to Mr. Sam M. Pickering, Jr., who kindly made available the well-cutting and core collections of the Georgia Geological Survey. Dr. S. Duncan Heron also made available samples from his private collections. David M. McCollum, Dr. William I. Miller, Dr. Andrew M. Gombos, and Dr. Lyman D. Toulman assisted in the identification of various microfossils. Dr. Miller critically reviewed portions of the manuscript which was typed by LaVerne Lamb. Dr. Miller also took many of the scanning electron micrographs and Dr. Charlene R. Miller and Dennis S. Cassidy assisted with the photography. Support for the study was provided by the Donors of the Petroleum Research Fund administered by the American Chemical Society.
REFERENCES
Akers, W.H., 1954, Ecologic aspects and stratigraphic significance of the foraminifer Cyc/a. mir.'ina cancellata Brady : Jour. Paleo., v. 28, p. 132-152.
Bandy, O.L ., 1956, Ecology of foraminifera in northeastern Gulf of Mexico: U.S. Geol. Survey Prof. Paper 274-G, p. 179-204.
Bandy, O.L., and Arnal, R.E., 1957, Distribution of Recent Foraminifera off west coast of Central America: Am. Assoc. Petroleum Geol. Bull., v. 41' p. 2037-2053.

104

Berry, E.W., 1924, The middle and upper Eocene floras of southeastern North America: U.S. Geol. Survey Prof. Paper 91, 203 p.
Bukry, D., 1973, Low-latitude coccolith biostrati-
graphic zonation: in Deep sea drilling project
initial reports: U.S. Government Printing Office, Washington, D.C., v. 15, p. 685-703. Carver, R.E., 1966, Stratigraphy of the Jackson Group (Eocene) in central Georgia: Southeastern Geology, v. 7, p. 83-92 . _ _, 1972a, Absorption characteristics of opaline
clays from the Eocene of Georgia: in Geology
of phosphate, dolomite, limestone, and clay deposits, Florida Bur. Geology, Special Pub. No. 17, p. 91-102. _ _, 1972b, Stratigraphy of the Jackson Group in eastern Georgia: Southeastern Geology, v. 14, p. 153-181. Cooke, C .W., 1943, Geology of the Coastal Plain of Georgia: U.S. Geol. Survey Bull. 941, 121 p. Cooke , C .W., and Shearer, H.K., 1918, Deposits of Claiborne and Jackson Age in Georgia: U.S. Geol. Survey Prof. Paper 120, p. 41-81. Cushman, J.A., 1945, A foraminiferal fauna from the Twiggs of Georgia: Cont. Cushman Lab. 265, v. 21 ' 22 p. Darrell, J .H., 1974, A palynological investigation of the Twiggs Formation (upper Eocene) in central and east Georgia: Geol. Soc . America Abs., v. 6, p. 348. Hay, W.W., Mohler, H.P., and Wade, M.E., 1966, Calcareous nannofossils from Nal'chik (Northwest Caucasus) : Ecologae Geol. Helvet., v. 59, p. 379-400. Herrick, S.M., and Counts, H .B., 1968, Late Tertiary stratigraphy of Eastern Georgia: Georgia Geol. Soc. Guidebook, 3rd . Ann . Field Trip, 88 p. Herrick, S.M., and Vorhis , R.C., 1963, Subsurface geology of the Georgia Coastal Plain : Georgia Geol. Survey Info. Circ. 25, 79 p. Huddlestun, P.F., Marsalis, W.E., Pickering , S.M., Jr., 1974, Tertiary stratigraphy of the central Georgia Coastal Plain: Guidebook 12, Field Trip No. 2, Geol. Soc. America, Southeastern Mtg ., Atlanta, 35 p. Hulings, N .C., 1958, An ecological study of the Recent ostracods of theGulf Coast of Florida: Unpub. Ph.D. thesis, Dept. Geology, Florida State Univ., 214 p. Hulings, N.C. , and Puri, H.S., 1964, The ecology of shallow water ostracods of the west coast of Florida: Pubbl. Staz . Zool. Napoli 33 suppl., 308-344. Jones, J.B., and Segnit, E.R ., 1971, The nature of opal I. Nomenclature and constituent phase : Jour. Geol. Soc. Australia, v. 18, pt. 1, p. 57-68. Kong, E.A., Jr., 1962, Field investigation of Georgia tektites and description of new specimens : Georgia Min . Newsletter, v. 15, p. 84-89.

Le Grand, H.E., 1962, Geology and groundwater resources of the Macon area, Georgia: Georgia Geol. Survey Bull. 72, 68 p.
Levin, H.L. , 1965, Coccolithophoridae and related microfossils from the Yazoo Formation (Eocene) of Mississippi: Jour. Paleontology, v. 39, p. 265-272.
Levin , H.L. , and Joerger, A.P ., 1967, Calcareous nannoplankton from the Tertiary of Alabama: Micropaleontology, v. 13, p. 163-182.
Loeblich, A.R ., Jr. and Tappan , H., 1966, Annotated index and bibliography of the calcareous nannoplankton: Phycologia, v. 5, p. 81-216.
__, 1968, Annotated index and bibliography of the calcareous nannoplankton II: Jour. Paleontology, v. 42, p. 584-598.
_ _ , 1969, Annotated index and bibliography of the calcareous nannoplankton Ill: Jour. Paleontology, v. 43, p. 568-588.
_ _, 1970a, Annotated index and bibliography of the calcareous nannoplankton IV: Jour. Paleontology, v. 44, p. 558-574.
_ _ , 1970b, Annotated index and bibliography of the calcareous nannoplanktonV: Phycologia, v. 9, p. 157-174.
_ _ , 1972, Annotated index and bibliography of the calcareous nannoplankton VI: Phycologia, v. 10, p. 309-339.
_ _ , 1973, Annotated index and bibliography of the calcareous nannoplankton VII: Jour. Paleontology, v. 47, p. 715-759.
Martini , E., 1971 , Standard Tertiary and Quaternary
calcareous nannoplankton zonation : in Fari-
nacci, A. , ed., Proc. ll. Plank . Conf. Roma 1970, Rome, Tecnoscienza, v. 2, p. 739-785. Murray, J.W., 1973, Distribution and ecology of living benthic foraminiferids: New York, Crane, Russak and Co. Inc., 274 p. Noble, D.F., 1962, Origin of the expandable clay minerals in the Twiggs Clay of Eocene age: Unpub. M.S. Thesis, Dept. Geology, Florida State Univ., 85 p. Phleger, F.B., 1960, Ecology and distribution of Recent foraminifera:Baltimore, Johns Hopkins Press, 297 p. Pickering, S.M., 1970, Stratigraphy, paleontology, and economic geology of portions of Perry and Cochran Quadrangles, Georgia: Georgia Geol. Survey Bull. 81, 67 p. Roth, P.H., Bauman, P., and Bertolino, V., 1971, Late Eocene-Oligocene calcareous nannoplankton
from central and northern Italy: in Farinacci,
A., ed., Proc. II Plank. Cont., Roma 1970, Rome, Tecnoscienza, v. 2, p. 1069-1097. Shearer, H.K. , 1917, A report of the bauxite and fuller's earth of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 31, p. 158.. 163. Schmidt, Walter, A paleoenvironmental study of the Twiggs Clay (upper Eocene) of Georgia using fossil micro-organisms: Unpub. M.S. thesis, Dept. Geology, Florida State Univ., 1977. 140 p.

105

Weaver, F.M., and Wise, Jr., S.W, 1974, Opaline

sediments of the Southeas~ern Coastal Plain

and Horizon A: biogenic origin: Science, v.

184, p. 899-901. .

_ _, 1975, Origin of horizon .A: clarification of a

viewpoint: Sci,encE?.; V. 188, p. 1221-1222.

Wise, S.W ., 1973, Calcareous nannofossils from

cores recovered .during Leg 18, Deep Sea Dri 1-

ling Project : biostratigraphy and observations

of diag,ene.si,s: in Peep sea driJiing proj. initial

,, ,reports; U.S.. Gov,er,nment Pril)ting OHice,

, W;;~shingt9.n , . ,D.C. , v. 18, 569~E/15 , ,

.

wise, '$.W., and Kelts, I). R., ~ 972, lnfe,rr~d diage-

netic , history -of a weakly silicified deep sea

chal.k: Gulf Cqast Assoc .. ~eo I. Soc . Tra;ns., v.

22, 177-203.

.. . .

. ..

Wise, .S.W .. an.d We.aver, F.M .. 197,4, . C~h~rtific!=ltion of
' .oce~QiC sedi,r:n,er;~,ts> : ,fn Pelagic se.d.in;lents on

land and underthe .sea: Spec . .Pubs, Int. Asso.

. S,e.qiment, iv., 1. p. _301,-326 . . . .
Zales.ny, E.R., 1.959, ;F:orar;ninif,er.Q.I ~cq!ogy of;Santa

Monica Bay, Californ.ia: MicropaleoQtplogy, v.

,5, Pt)01-126, _ . '.

I:

' I

\.- J

'. 1

J I I I A'PPENDIX I

SAMPL.:E 'LOCA'IJTJES' '1

I ~

1 I '.1

t

arr '4' 1 R1 ich ' H~f 'Q
so utn..t. o( 'Coitu nt4y1

~ (~''_ dqhed) ,
,nll! ~' - ~aI!~J. 4?, .7

ac cess road

1-l j
111

~olu, ht}h

east

of Kn? villE:), Ga. Quarry ~bpu_t 0.~ rp1 'sout,h ~n

access road. E* po.sed" flere ar~ about sp tt of

secti6n vVfth the1 _~P.~er' 2'd'ft o'elrigfw'i'gg1s'Ciay.

1 u C:l~r'ne~HVire fab'o 12d(t1ofOca lalim'estone

I

t u

nvd

e(

r

w

hh
I

:htr

le
j:

ab6ut io

I

,I I

trpf:CIInc'hfie,la S'and .

I

I I

'I .,j

r r A 1 ~ '" t 1 ' f ll

r1 1 11

2. Stop . No . 4, G._$. f- ., F i~ l. . Gu.iqle BQQk JNp . 12

,' 1 (H~oJd ~ I Ej$ ti,J.fl aJld Qth ~rs,. 1974), ,frql]l1 1~ . $ . ~ . ,,r f$oytil~ast{~r1q, M e~tl ng_ Atla nta , 1974,, ,i.;i,me-

,s-~.one Q\J.~WY pn. ,t1h.e east sjde of the Rl3rr&~ - E i ko lioad about 2 mi sou t h o1f l?en:y. .oity ,Jirn its . i;:X.r19l?.~P. 1 t'le e , are ap,ovt 7g 1fct of the Tw. i gg~

CI;ry._. I I

!

'

anp: o.. ~-

9(.~1~9pdp_N,l,1~?s;t5u

,_G,
~

.S

,A .
o

,Fje ld
~r.eJ~

~,U(de !39dk
.-r9J 4) , f rom

1

~0-
s

,) 2
.A.

1 . '~TGalwofbi'.iugtoglg'n~she~u)Cs.a.sd1e~.ra~'ba0Moteeu'ett.e~r;-xl3Lnp.a94:.b1,.s,m.(Ae-Hcit'il'esr'iorn~ey?ta't.h~id11e/o97cf{14phH:.ppaae.lr6~:rt,tneec~v{el?tltPNlneSef,

we'M side St: th:e h\g'. l'lw'ay',' ~l

1 '

''

. I

I !I ' ' \

''

,.

'

I '

4~. StOpNo. 3'/ G.S.A.~,Field : Guid 'e:Book No. 12

(HliddlestUiti a'nd bth.ers , l97<4). from G:S.A.

Southeaster-n. Meeting, Atlanta, 191.4!. On U.S.

Route 341 o: o.3 mi -sbUth;'of' Clinchfield.Geo-

logic . sectio'ri e~posed in Medusa .Portland

Cement Go., west quarry. ,The Twiggs Clay

here measmes about 105 fL

r I

11

5. Road cuts along Georgia State Highway 247 between Big Indian Creek and the top of the first drainage divide to the south. Section of Twiggs about 90 ft thick; however, hard to measure due to covered intervals and dip approximati'ons.

6. Subsurface sample from Georgia Geologic

Survey~ Well No. 472. Location: 4 mi south of

Pulaski-Bieckley County line, east side of U.S. Highway 26. In this well the Twiggs is undiffe~-

. entiated and only the Barnwell Formation is

identified.

I!

l

7. Subsurface sample G.G.S : Wel'l No. 195.' Loca-

,tion: northeastern part of city; 0,5 mi east of
of Highway '129 in City Cochran . lri this well,

the Twiggs Clay is present and divlded into two

. I partsby a tongue of the Ocala Limestone (Tiv-

'ol a Tongue~ ; The total th ickriess is ~bout 85ft._

, I

:,

I

i'

)

8. ! Road cut about 7 mi north of Cochran in Sleck-

leyCounty , ori Houte 87. Here the'1wiqgs' Ciay.

is eroded and : indurated, a thickness

a n o-btai'ne'd .

' ''

1

9. ' Location from Carver (19T2a) southern Twiggs

County (m ineralogy ' data only).

1 ,

:. r

,,

10. Subsurface sample, G.G.S. Well No. 360. Loca-
. tion: about 3 ,5 mi east of Huber; 2.5 rni east of

-U:S. H'i.ghway 129, arid l.5 mi southof a cross-

roads .at machine stop; In this well theBarnwell

is identified ; however, the clay'Jn theupper 25

; .ft of the formation may be Ti.-viggs ..

'

. " .

,

I ,: 'I '

1

~ 1. -A road cut on the south tbank of -Ugly creek

about 2.2 mi south of Myricks Mill, on an

unnumbered dirt road. Here tl:le clay is fairly

pure !:>'Lif only partly exposed.

12. 'A road :cut along . a road from Fitzpatrick to Myric!ks Mill Pond . on th-e north side of the :roa'd abouH :5 mi friom' Route 80.

' I ;:

13. Locntion from Carve:r: ' (1 972a); northern Twiggs County (mineralogy data only) .

'I'' '

I

'

:' I '

14.' ' Pikes l?eak Station '(type locale) . About 2.6 mi

south of Dry Branch Station on U.S. Highway

1, .: 80, a raiJroad -cut which e.Xposes ab'out 100ft ..

Seven sam'ples were collected herte about

every 10 ft with No . l startin'g. at'the base (1 to

7) . Also near Pikes Peak an exposure'oh the

land of the Georgia Kaolin co ~ about 15-20 ft

exposed: On Route 80 coming s6uth f-rom Dry

Branch (about 1. 8 mi) at crest of -hill, a good cut

exists on the east side of ti;Je' road along the

railroad .

106

15: Stbp No.1 of.the G.-S:Ao. Field Guid~ I Book No ..

12 (Huddlestl!ln cihd 'others, 1974), from G.S.A.

Southeastern Meeting, Atlanta, 1974. Section

exposed on west side of Interstate Route 16 on

top and sides of .:~ il,l above ,Oc mulgee River

Valley, about 8.2 mi south from Ocmulgee

,1

1

fftiivthwick[3,rid,g~ 1

TheTvvigg,~ ,.. , .

CIR''-Y

~~ r 13.

is '

q.bo,w~ . .: .

?5


J ; r. ~ -. ! . I

:-.

\ ,. ! ! , i

16. Road cuts -at Mattie Wells School ; Ot:l' Georgia

State Highway 49, northeast of Macon, 2.2 mi

NE of the Bibb-Jones County line. Total thick-

ness here approximately 20 ft; however, the

base is not exposed . Six samples collected

starting at the base about every 3ft (1 to 6).

Also in south Jones County.~a location from

Carver (1972a) (mineralogy data only).

25: I At Wrensi Ga., mine of GeorgiaiTenhessee ' Minin~ 'and Chem'ical Co. " At it he mine, the :T..,.hggs thickness-is about40 ;fr :wit'h base not

''

exposed. Seven samples
ohe every 6' f.t stantihg at

were base.

collected (Ho i7).

'

ab~

out

.. I . I ( ) I i '

I p' I '

~ j '

:

I 1 I : -

26. Location from Carver (1972a) near Stellaville,

' Ga:."(rnineralo!jy data dnly). ,: r, i

Ca~v~r (f~7~afn8anHarlem, ' : f I I ; r :._1 1

i -) J

1;

'27. Lo'cation fr.om

, , , ~ :' ~
1

~ ! , . _.. r ,

Ga.

(mineralogy data).

!. , i ~,.;r. : ,;

28 . Subsurface sample G.G.S. Well No. 371. Location: Silver Crest and Fleming Heights, Gracewood. In this well about 30ft of clay occur in the Barnwell Formation.

17 .

Subsurface sample, G.G.S. Well No. 529. Loca-

29 .

tion : southwestern part of Wilkinson County,

near Danville. In this well the Barnwell Forma-

tion is identified and its clay member is proba-

bly Twiggs Clay, about 40ft thick.

~- ;i1 t ...

Stop No. 1 on Georgia Geological Society Third Annual Field Trip, Oct. 4-5, 1968 (Herrick and Counts , 1968). Southeast of Augusta, U.S. Highway 25 going south, turn right on Windsor Spring Road, go about 1.6 mi to road cut on both sides of road. Here Twiggs Clay is about

18. Subsurface sample G.G .S. Well No . 441. Location : within the City of lrvinton, which is in north-central Wilkinson County. In this well!

35 ft thick. Two samples were collected, August 1 and 2, with one being at base.. the second about 15ft higher.

only the Barnwell is identified ; however, about 4G' ft:.of ctay 'wilhin: the -formation is proba'tily'

': . ~p,,, "~t~th'~e~':~1~2s~rs~~~i~~!rfn~ng~~~~~:1'~JJ~:

Twiggs .

,1 I il I

' T l)r I' ,,,, 11G[iffin~ ~~oatt La ~llf D~1S~TJ1J;l(e.,p rpvid,e_q 1b1Y, !i)r.

19. ,South of Gordqn about 1.6 mi on Georgia

S. Duncan Heron (his samp le No. A- 148) .

a ' Highv\i~y 1' 8; ditch 1on th'e west sltl eb'fl hl{ tl~d ~ 1Y1111 )I 1') 1 11

I I\ .g ,

111 1

exposes a felfl.feet p,t}'{Vig:Q? C; I,~Y.:: , , '. ,:

.. . 1,

,

20. Road cut on Georgia Highwa.y .57, abou.t 1.~ . mi 1 ::~ 1 ,.: .,. j \, . ,::' ,) i ' 1; ~ : ~ I l i ,

' ;, . ' ::\ ', i I i ~ : \ , '...: , '

,,,_:1'

southeast of Toomsboro. Here about 10-12 ft

~~eM~;:a~sxe

d(194T6h,~. ~-

1~1c)~

1 e


IS

referenced

in

~;

, .

'SMEAR

SLIDE

APPENDIX II PREPARATION

FOR DIA-

' ( : ' ) : L ' i : ~

' :

! -' ' :.

I '' ' I

' '

I I ;.) ~ I

21 . Subsurface sample G.G.S. Wei I No. 438. Location : within tt'le ,city of . Duh>:lin ~ +rlere,comly the

.TOMS FBOM THE TWIGGS CLAY

' '~ ' . I 1 ', ( ,-~: ) ' / ,' I \h ., ,' ', ', \ 1 ,' ,I .' i' . ': \ i

i t l ! :!

, . p~~m: . 1, ,, .$.~~;~~ .9 ,3rl?f?,l,~, (qre.P,~)P..~Qrka .ble ,si.z,r),

Barnwell Formation is identified and appar-

thrs rncreases the surface area.

ently no TwFggs ' Ciay1 'is! present b'ec.M.Jse ': .. ,, i'''. .

. ', , . :~,: : :<:,. -.;. .";: ,., ~ ., , , ,..;

mostly limestone and marl compose the

Step 2. Dry sample completely.

I ;s'' e' c.' t'lo~ n., l \j l ': ~~: : ', ,~ u :i:;\ ,- ~ . :.(.: ~r' , t ~ l J :FI_, 1 ,! , !L .', .. il. \....., ' ... ..... '.' " ,. ._,.... : . ..:'/ .q \'> '\\ ~."'./\

:. :: i. 1: li'l

Step 3. Remove from heat.

22. In creek gully just east of Buft~!6' Creek . tPJ~kt it rr 1'1 l Olli'! .f <" ;- .,: . :;;. ,:: ' . , , , , , ,,\'' , ~ _, ::.; .:

;;r;.yrn . of Sandersvi lie on Route 24 ap.q,utrB ,m,i,.
south on a dirt road about 0.8 mi, g ully alo hg

Ste
111 ' f

~- - Whil e ~ample is still hot, add Stoddard (1' 1" sol l1'crn,''Vahs'al,:kerc's'ene: ar p'etrbleum

.road.

,, ' I

. . , :: , , ,, ,T rH 1 1

!J li,nu , ~~~ - i ~~t~, ,9f ,~em.~ swt. A,l,lo.vy~ to ~~}}~_,~o 4

23. Road cut on northeast ' side df'roa'd;.: ap pwxi~ < mately 4.3 mi southeast of Deepstep on the Sandersvilltfrda'd,' % mi 1sckrth 'cif Keg Cre:ek.
24. Subsurface sample, G.G.S. Well No. 554. Location : Within the City of Louisville . In this well the Barnwell is identified and is mostly marl and limestone, clay absent.

\,lrl~
Step 5.
1 r - rJ
Step 6.

; 1;: =,' J<'.l .' \ )f~,r ~, l ~ ;.~ \ \\.' \ . :. , ~

Decant Stoddard.



'1,': tr :!

: .,

V' :',} ~ , ; ; :, , ., # , , ~:, :.' :i

J\ : ;

Boil sample approximately one hour in

H20 + H202 + Calgon or sodium

pyrophosphate-about4: 1: 1/2 teaspoon.

Step 7. Sieve in 6311 sieve .

Step 8. If further cleaning is needed, a centrifuge
in distilled water at 3000 rpm for a few
minutes may help (repeat if needed) .

Step 9. Put sample back in beaker and add concentrated HC I (enough to get bubbles).

Step 10.

When bubbling has stopped, wash sample again in 63J.l sieve (at this point, if a great deal of clay remains, repeat steps 2 through 7) .

Step 11 . Mount sample using Hyrax or other suitable mounting medium.
POINTS TO PONDER
Always use distilled water in diatom preparation. In many areas, tap water contains diatom tests which may contaminate your sample.

PLATES
PLATE 1 Figure 1. Coscinodiscus radiatus Ehrenberg. Sample 25-7 at Wrens, Ga.; x 550. Transmitted light micrograph. Figure 2. C. radiatus Ehrenberg. Sample 25-2 at Wrens ; x 450. Transmitted light micrograph. Figure 3. Coscinodiscus oculus iridis Ehrenberg . Sample 29-1 near Augusta ; x 650. Transmitted light micrograph . Figure 4. C. oculus iridis Ehrenberg. Sample 25-2 at Wrens, x 450. Transmitted light micrograph. Figure 5. Coscinodiscus sp . Sample 16-2, x 350. Scanning electron micrograph .
PLATE 2 Figure 1. Actinoptychus senarius Ehrenberg. Sample 16-4; x 1100. Scanning electron micrograph. Figure 2. A. senarius (Ehrenberg) Ehrenberg. Sample 4; x 1025. Scanning electron micrograph. Figure 3. A. senarius (Ehrenberg) Ehrenberg . Sample 25-2 ; x 900. Transmitted light micrograph. Figure 4. Actinoptychus splendens (Shadbolt) Ralls in Pritchard. Sample 30; x 350. Scanning electron micrograph . Figure 5. Rhaphoneis sp . Sample 25-2, x 4,000. Transmitted light micrograph . Figure 6. Rhaphoneis sp. Sample 25-6; x 1,600. Transmitted light micrograph . Figure 7. Paralia sulcata (Ehrenberg) Cleve. Sample 25-7, x 1,400. Transmitted light micrograph. Figure 8. Trigonium barbadense Greville. Sample 25-5; x 1,500. Transmitted light micrograph . Figure 9. Odontella aurita (Lyngbye) Agardh . Sample 25-5; x 1,600. Transmitted light micrograph.
108

PLATE I
CD
109

PLATE II 110

PLATE 3

Figure 1. Figure 2. Figure 3. Figure 4., 5. Figure 6., 7. Figure 8., 9. Figures 10.-12. Figures 13.-15. Figures 16.-18. Figures 19.-21 . Figures 22.-24. Figures 25.-26.

Eupodiscus radiatus Bailey. Sample 4, x 215. Scanning electron micrograph.
Eupodiscus radiatus Bailey. Sample 14-2, x 310. Scanning electron micrograph. Note: two frustules, one case, one mold.
Stephanopixis sp.?
Discoaster barbadiensis Tan Sin Hok. Sample 3; x 2,000. 1) Transmitted light; 2) Phase contrast.
Discoaster saipanensis Bramlette and Riedel. Sample 3; x 1,800. 3) Transmitted light: 4) Phase contrast.
Discoaster tani Bramlette and Riedel. Sample 3; x 1,500. 5) Transmitted light: 6) Phase contrast.
Coccolithus formosus (Kamptner) Wise. Sample 3; x 2,100. 9) Transmitted light; 10) Phase contrast; 11) Crossed nicols.
Reticulofenestra reticulata (Gartner and Smith) Roth. Sample 3; x 2,200. 1) Transmitted light: 2) Phase contrast; 3) Crossed nicols.
Coccolithus pelagicus (Wallich) Schiller. Sample 2; x 2,200. 4) Transmitted light; 5) Phase contrast; 6) Crossed nicols.
Transversopontis obliquipons (Deflandre) Hay, Mohler, and Wade. Sample 3; x 2,000. 7) Transmitted light; 8) Phase contrast; 9) Crossed nicols.
Discolithia meltipora (Kamptner) Roth. Sample 4; x 1,500. 10) Transmitted light; 11) Phase contrast; 12) Crossed nicols.
lsthmolithus recurvus Deflandre. Sample 3; x 1,500. 7) Transmitted light; 8) Phase contrast.

PLATE 4 (All figures are scanning electron micrographs)

Figure 1. Textularia hockeyensis Cushman and Applin. Sample 3; x 35. Figure 2. Nodosaria ewaldi Reuss? Sample 1; x 110. Figure 3. Nonion sp. Sample 3; x 200. Figure 4. Lagena laevis (Montagu) Williamson. Sample 2; x 170. Figure 5. Nonion inexcavatum Cushman and Applin. Sample 3; x 60. Figure 6. Bolivina jacksonensis Cushman and Applin. Sample 3; x 65. Figure 7. Cibicides lobatulus (Walker and Jacob) Cushman. Sample 3; x 45. Figure 8. Cythereis montgomeryensis Howe and Chambers. Sample 3; x 40. Figure 9. C. montgomeryensis Howe and Chambers. Sample 4; x 90. Figure 10. C. montgomeryensis Howe and Chambers. Sample 3; x 90. Hinge of left valve. Figure 11. Hemicythere punctata Puri. Figure 12. H. punctata Puri. Sample 4; x 180, Hinge of left valve. Figure 13. H. punctata Puri. Sample 3; x 90. Figure 14. Trachyleberis citrusensis Puri. Sample 3; x 110. A complete specimen.

111

PLATE Ill
li' .... . f t ~ 112

PLATE IV 113

SEDIMENTOLOGICAL TOOLS FOR IDENTIFYING DEPOSITIONAL ENVIRONMENTS
William F. Tanner Regents Professor of Geology
Florida State University Tallahassee, Florida

ABSTRACT
Marine terraces of probable Pliocene age, at elevations of 80 m, 50 m, and 35 m, west of Tallahassee, Fla., have been identified on geomorphological grounds as barrierand-lagoon sets. The present paper uses sedimentological methodology to see if the same identification could be achieved were there no useful geomorphological evidence. Grain-size probability plot characteristics (surf break, tail of fines, dune hump) , a variability diagram (variability of sample means vs. variability of sample standard deviations), a plot of skewness vs . kurtosis, and the algebraic sign of the sample skewness, are all used to good effect. Bedding, crossbedding, ripple marks, fossils and facies change data were not available. Therefore, this study simulates a common coastal plain problem: to determine the site of deposition of more-or-less uniform sands where fossils are absent and exposures are poor. The sedimentological interpretation identifies the coastal setting correctly, indicates moderate rather than high or low breakerzone energy levels, suggests a barrier island location, and strongly supports the notion of local dunes, but does not identify the lagoons.
Three marine terraces west of Tallahassee, Fla., are located at altitudes of about 80, 50 and 35 m above MSL (fig. 1). They are tentatively considered to be between 2 and 10 m.y. old. Gremillion, Huddlestun and Tanner (1964), on the basis of geomorphology, identified them as barrier-and-lagoon sets, but inadvertently assigned a Pleistocene age (an older age was intended at that time).
It is the purpose of the present paper to show how sedimentological techniques can be used to help in the identification of such deposits. No crossbedding, ripple marks, or other such features were found to aid in the identification; there are no known fossil localities or visible facies changes, and exposures are generally poor.
The mean grain size (115 samples; Goetschius, 1971) for the entire suite of three terraces and two lagoons is 1. 770 phi units, (0.29 mm), and the mean standard deviation for the suite is 0.87 phi units, with the sensitivity associated with quarter-phi sieving for 30 min. (Mizutani, 1963). The settling tube was not used (Coleman and Entsminger, 1977). These data do not suffice to identify the depositional site, being common values for coastal, alluvial and eolian deposits.

FLORIDA GADSDEN COUNTY

10 I
KM

Figure 1.

Map of sample area, showing three high terraces, probably all pre-Pleistocene in age, representing former sea-level positions at (approximately) 35 m, 50 m, and 80 m. Map modified from Gremillion and othe rs, 1964 (in which the word " Pleistocene" was inadvertently used).

Thirty-three of the probability plots (fig. 2) show reasonably clear examples of the surf break (Tanner, 1966), and the tail-of-fines is present in many of these. This combination indicates low-tomoderate wave energy in the breaker zone . Fourteen of the sample size distributions are essentially Gaussian, and in the light of the preceding sentence, they probably indicate high-energy beach and nearshore conditions. Twenty-one of the probability plots show the dune hump (Stapor and Tanner, 1975). A few of the plots show evidence of both surf and eolian activity. Positive skewness values (closely related to the dune hump) were found in 79 samples, and negative skewness (commonly associated with the surf break) was found in 36 samples. This method of study does not identify or eliminate the possibility of river deposition.

114

0.1

1 2 15 10 20 30 50 70 eo 90

98

42

49

0 ~

SB

2

Figure 2.

Representative grain size plots, showing two examples of the "surf break" (SB), one example of the "dune hump" (DH) and two examples of the "tai I of fines" (TF) . If the eye is held close to paper level, and to one side of the lower right-hand corner of the figure, DH will become obvious . Sample 49 is perfectly Gaussian. This combination of four samples indicates coastal dunes and moderately high surf conditions . More than 125 other samples, from the same study area, showed only variations of what has been presented here.

A plot of the standard deviation (i.e., variability) of the sample means, against the standard deviation of the sample standard deviations, may be instructive. On such a plot, high-energy agencies tend to impart great variability to both parameters, whereas lowenergy agencies produce only small variability. More specifically, mountain and hill-country streams give maximum values for variability of both means and standard deviations, whereas eolian transport provides the smallest values for both. The sequence of agencies, from maximum to minimum, and with considerable overlap, is: river, offshore wave, swash, wind (fig. 3). Sediments in lower reaches of alluvial rivers overlap markedly the offshore and high-energy beach environments, whereas dune and low-energy beach sands overlap somewhat.
Variabilities have been computed for both means and standard deviations for five sets of samples (the three terraces, and the two lagoons) . All five sets fall in the "high energy beach, offshore wave, and coastal plain alluvial river" category (fig. 3). All five sets are closely bunched together on the variability diagram. An independent study of additional samples, collected at new locations and analyzed without knowledge of the previous work, verified the variability chart position of the 50-m terrace (within 20 percent for variability of means; within 40 percent for standard deviations; on the variability diagram, which extends across three orders of magnitude, this is close agreement). The lack of a dune position on the chart does not deny wind work, but puts it no higher than second rank.

0.1

.......... ~(v

........ <:;).:::)
O.OIL-~~~-~ LL----~--L-l-~~UU~--~W~F~T

Figure 3.

The variability diagram: the variability (standard deviation) of sample means has been marked along the horizontal ordinate, and the variability (std. dev.) of sample standard deviations has been shown along the vertical ordinate. The upper right hand corner is an area of relatively great variability, and the lower left hand corner an area of relatively little variability. This particular version has been prepared for medium sand, and sizes not too far removed from it, and is not applicable for coarse silt or for gravel of any size. The number fields for marine agencies are indicated on one side of the diagonal strip, and for nonmarine agencies, on the other side. In addition, dots outline the swash-and-dune, as well as pure dune, areas occupied by beach ridges. This chart does not permit the unequivocal identification of single agencies and sites; on the other hand, it does permit reasonably close assessment of the general setting. Sample suites are indicated for the 80-m, 50-m, and 35-m terraces, and for the 50-m and 35-m lagoons. Any one of these suites (or all five of them) is (are) shown, on this chart, to belong in the dune-beachestuary-lower-alluvial setting. They cannot represent hill country or mountain streams, nor can they represent inland dunes. Although glacial features are not shown here, it is clear that glacial deposits, if present, cannot be significant.

115

Once the beach-and-dune interpretation had been made, a plot of skewness and kurtosis values for 40 samples from the 50-m terrace showed that seven occupy positions generally assigned to beaches, five more fall in a "beach ridge or coastal dune" category, and the rest indicate wind work (fig. 4) . The mix of positive and negative skewness values, given in a previous paragraph, provides the same interpretation, but with slightly less effort.

SK -o.s

0

0 .6

i',
I '-
'-'

2

K*

B E

1.0

0.8

0.6

0

0

0

0

0

0

Oooo
0

N E

WPT

Figure 4.

A plot of skewness (Sk) versus kurtosis (K*) for modern sediments in the Florida Panhandle coastal zone, used as a base for examining moment measures (third and fourth) from the study area. K* is kurtosis-minus-two (if computations are so designed that K=3 for the Gaussian distribution) or kurtosis-plus-one (if Gaussian K is calculated as zero). Modern coastal dune and beach samples studied are covered without exception by the indicated number fields (shown by outlines only); all modern beach ridge samples fall in the area outlined by dashed lines, consistent with the observation that beach ridges are ordinarily constructed by some combination of wind and swash. Many workers have constructed plots of two or more moment measures, with only modest success, the exceptions for individual samples having been fairly numerous; therefore this plot must be used with caution . However, the interpretation of "beach, dune and beach ridge" origin seems to be moderately well supported, and can be accepted with confidence provided other indicators show the same thing . In the present case, a river origin cannot be ruled out by the Sk-vs-K diagram, but is largely eliminated by the probability plots.

Using only the sedimentological information, one should conclude:
Primary agency: offshore waves, surf-andswash, and/or coastal rivers in the lower reaches. Secondary agency: wind. First restriction : not a delta of the Mississippi or
Alabama River type. Second restriction : wave energy was low-to-
moderate much or most of the time, and probably had an average value in that range , but was high energy part of the time. Third restriction : the over-all mean and standard deviation do not permit much relief.
This collection of sedimentological statements can be streamlined by saying : coastal and nearshore sands, deposited on a gently sloping bottom, in the vicinity of a river mouth but not in a humid-climate delta (much clay and fine silt) . The "gently sloping bottom" suggests a further simplification: probably barrier-and-lagoon sands.
The chronology here is terrace type (highest is oldest), rather than standard stratigraphic (highest is youngest). If the geomorphological expression were not known, this might be a source of confusion as to the details of the historical sequence, but should not modify the conclusions given above, which are based on the entire sample suite, regardless of location. Looking at relative locations, which can be considered in terms of the direction toward the sea (a standard piece of information in the coastal plain), one can note the following changes: finer mean grain size seaward, more variability of the mean seaward, best sorting (numerically smallest standard deviation) in the middle of the land-to-sea line rather than at either end, and best evidences of eolian effects toward the land. Less clear, but suggestive, is the fact that grain size decreases toward the east, except for a small reversal near the eastern edge of the area. One might wish to deduce, from the information in the previous sentence, littoral transport from west to east. If crossbedding or ripple mark data were available (Tanner, 1962, 1965) , it might be possible to confirm or refute this interpretation without recourse to the geomorphological information, which suggests west-to-east littoral drift.
Without the geomorphological expression, one probably could not identify the lagoons, which were merely topographically low strips in the sand sheet, having no distinctive sedimentological characteristics at any of the sample sites.
The ages of the three terraces cannot be known with precision . Traditionally, marine terraces have been considered to be Pleistocene. The ironstonedating method of Maxwell (1971a), done by Maxwell

116

on the 9-m and 6-m terraces farther south, yielded an age of about 400,000 yrs.lf a published alluvial terrace curve from western Alabama (Maxwell,
1971 p) can be extrapolated in the project area, the
35 to 80 m terraces are roughly 1 to 4 m.y. old. A study of Huddlestun (personal commun.) indicated that these three terraces may be between 2 and 8 m.y. old. Published marine terrace curves, pertinent to the study area (Tanner, 1968),suggest ages perhaps as great as Miocene. All of these different approaches are thought to give rough agreement: probably Pliocene, but clearly pre-Pleistocene.
At many coastal plain localities, geomorphological evidence is not available and exposures may be so poor that crossbedding, ripple mark and other stratigraphic information cannot be obtained. Under this circumstance, sedimentological procedures, such as those outlined here, may be useful in determining the environment of deposition, or at least in narrowing the number of choices to an acceptable minimum.

Tanner, W. F., 1962, Upper Cretaceous coast of Georgia and Alabama: Georgia Min. Newsletter, v. 15, nos. 3, 4; p. 89-92 .
_ _, 1965, Cretaceous shoreline across the South : The shale shaker, v. 15, p. 118-125.
_ _, 1966, The surf "break": key to paleoge-
ography? Sedimentology, v. 7, p. 203-21 o:
_ _, 1968, Tertiary sea level symposium: Introduction, in Tanner, W.F. ed., Tertiary sealevel fluctuations: Paleogeography, Paleoclimatology, Paleoecology, v. 5, no. 1, p. 7-14.

REFERENCES
Coleman, Craig, and Entsminger, Lee, 1977, Sieving vs. settling tube: a comparison of hydrodynamic and granulometric characteristics of beach and beach ridge sands: in Tanner, W.F. ed. , Coastal sedimentology, Geology Dept., Florida State Univ. , Tallahassee, p. 229-312.
Goetschius, D.W., 1971,Preliminarysedimentological and geomorphological study of certain high terrace sands between the Ochlockonee and Apalachicola rivers, Liberty and Gadsden Counties, Florida: Unpub. M.S. thesis, Florida State Univ., Tallahassee, 98 p.
Gremillion, L.R., Tanner, W.F., and Huddlestun, P.F., 1964, Barrier-and-lagoon sets on high terraces in the Florida Panhar:~dle : Southeastern Geology, v. 6, p. 31-36.
Maxwell, R.W. ,1971a, Preliminary ionium date from marine terrace, Florida: Coastal Research, v. 3, no. 5, p. 9-10.
_ _,1971b,Origin and chronology of Alabama river terraces: Trans., Gulf Coast Assoc. Geol. Sacs., v. 21. p. 83-95.
Mitzutani, S., 1963, A theoretical and experimental consideration on the accuracy of sieving analysis: Jour. Earth Sciences, Nagoya Univ., v. 11 , no. 1, p. 1-27.
Stapor, F.W., and Tanner, W.F. , 1975, Hydrodynamic implications of beach, beach ridge and dune grain size studies: Jour. Sed. Petrology, v. 45, p. 926-931.
117

ENVIRONMENTAL IMPLICATIONS OF PALYGORSKITE (ATTAPULGITE)
IN MIOCENE OF THE SOUTHEASTERN UNITED STATES
Charles E. Weaver and K.C. Beck Georgia Institute of Technology School of Geophysical Sciences
Atlanta, Georgia

ABSTRACT
During early Mioce~ time palygorskite formed in the southeastern United States in shallow, brackish-water coastal lagoons. It altered from montmorillonite by the addition of Si and Mg. It formed in a humid, subtropical to tropical climate that was modified by ocean currents controlled by the movement of continental plates. It is unlikely that the palygorskite formed in a normal marine environment.
The Miocene sediments of the southeastern United States contain commercial deposits of palygorskitesepiolite and phosphate. These minerals formed in shallow-water coastal environments. Other minerals that formed in these environments include dolomite, calcite, opalcristobalite, and zeolite. The purpose of

the study was to determine the environmental conditions under which these minerals formed, particularly palygorskite (Weaver and Beck, 1977).
Sediments were deposited in shallow water in a mildly tectonically active hinge area separating the Atlantic Ocean and the Gulf of Mexico. Montmorillonite is the dominant clay mineral in the Tertiary of the Atlantic and Gulf Coastal Plains. However in the upper Oligocene and lower Miocene sediments of northern Florida, southeastern Georgia, southern South Carolina, the Georgia Shelf, and the Blake Plateau, palygorskite and sepiolite are commonly the dominant clay mineral. An isopach map of the Miocene and upper Oligocene Tampa Formation (fig. 1) shows the major structural features in the area: OcalaSuwannee Uplift, Atlantic and Apalachicola Em-

ALABAMA

z
<(
I.J.J
u 0

u

i-
z

<(

Figure 1.

_.J
i-

Generalized Miocene paleogeographic map

1-----i 20 KM

<(

showing two positive areas separated by two

depocenters. The Suwannee Uplift is an older

feature than the Ocala Uplift. Narrow sill separated Apalachicola Embayment from

CONTOUR INTERVAL

trough area of Atlantic Embayment.

!00'=30. 5 M

118

bayments, Gulf Trough. During at least part of Miocene time the Gulf Trough was separated from the Gulf of Mexico by a shelf or ridge and was open to the Atlantic Ocean.
Trangression over a karst topography started in the late Oligocene when the Tampa limestone an d dolomite were deposited. Palygorskite formed in the shallow-water feather edge of transgression. Montmoril lonite was deposited in the open marine environment. A regressive phase occurred towards the en d of early Miocene. A seco nd palygorskite horizon was deposited in the coastal environments of the retreating sea (fig. 2).

>-

(.!)

0 ...J

0 I I-

<>t-
...J

u

0

Fullers Earth (Pre Chi po la)

Figure 3 is a cross section in the northern part of the area along the Savannah River. Palygorskite and sepiolite are restricted to lower Miocene beds and stop abruptly at t he lower- midd le Miocene boundary . Numerous other cross sections show that the bedded palygorskite is restricted to the upper Oligocene and lower Miocene formations . The middle Miocene sediments are characterized by the presence of marine diatoms and opalcristobalite (fig. 4). Phosphate pebbles are concentrated at the lower-middle Miocene boundary and mark the beginni ng of the middle Miocene transgression. This boundary, characterized by phosphate and clay pebbles, can be traced overmuch of the area. This is th e period of time when much of the phosphate was concentrated in the coastal area.
Figure 5 is a north-south cross section down the center of the Trough. Palygorskite (stippled) is present in the upper Oligocene and lower Miocene beds. The commercial palygorskite clay beds occur in both the lower Miocene and middle Miocene sediments (southern part of section). The latter deposits are detrital and were derived from the authigenic lower Miocene deposits.

12
(/) 24 a:: w 1w--
2!
z
:r
1--
Q.
w
0
36

Figure 6 shows the general lithologic units of the lower Miocene. Coarse, high energy, gravelly deposits occur in the center of the Atlantic Embayment. These were deposited in an estuarine environment at the mouth of the ancestral Altamaha and Suwannee Rivers. The deposits are flanked by shallow-water brackish dolomite (limpid variety) and dolomitic palygorskite beds. Relatively pure clay beds occur to the northwest of the Ocala High and extend southeast into the embayment. The environment was shallowwater marine to brackish.
The distribution of palygorskite and sepiolite in the lower Miocene is quite extensive (fig. 7). Sepiolite is concentrated shoreward of the palygorskite and was apparently formed under less saline conditions. The Atlantic Embayment and Trough contain detrital palygorskite.

Much of the lower Miocene palygorskite was depos-

ited as 0.3 to 3 m discontinuous beds in brackish-

water or schizohaline environments. Montmorillonite

To rreya

occurs in the continental and marine sediments, and was also deposited in shallow brackish-water

lagoons. There, Si and Mg were supplied by sea water,

48

and under relatively high temperature and subtropi-

Mi ocene

cal conditions, the montmorillonite was converted to

Ti dal Lagoona l

Upper Oligocene Tampa

palygorskite. Most of the montmorillonite did not go into solution.

57
Oysters abundant
LAKE TALQUIN CORE
w- 6890
Figure 2. Transgressive-regressive sequence in core from northeast edge of Apalachicola Embayment. Florida.

Figure 8 is a sketch of a typical core from the mining area. Deposition started with the deposition of a marine barrier sand. Behind this was a shallow lagoon in which palygorskite formed . As regression continued, a classical soil zone was formed on montmorillonitic river flood plain deposits. This was followed by

119

EFFIO

EOCENE

Z Zeolite B Biotite

5 KM

MIDDLE MIOCENE LOWER MIOCENE OLIGOCENE

Figure 3. Northwest-southeast cross section along the Savannah River extends from northern Effingham County to near the coast. The Miocene shows an off-lap sequence. The uppermost sand unit is post-Miocene. The top of the Oligocene in the easternmost well may be at the top of the coquina or the top of the underlying massive limestone. Light stipple zone contains sepiolite; dark stipple, palygorskite. Eastern two wells are not plotted to scale. GGS-394 is 26 km east of EFF-3 and GGS-717 is 19 km east of GGS-394.
120

CLAY MINERALOGY
0

BPL

12

24

Figure 4.

Core hole Effingham no. 3 showing lithology, mineralogy and phosphate content.

en
0:: UJ 1UJ :!:
~ 36
:J:
1a.~

B =biotite;

I= illite;

48

K = kaolinite;

M = montmorillonite;

P = palygorskite;

and

S = sepiolite.

61

..",_,.'.. ""

.~

.",' "' 0

a;

0

E

!!!<r u0

zm<t
,.<t
U(f)

""I"' II I III ~~

0 ...J

.2<>
(D(!)

"0 ' e"n ' ""'

.., ... .m.. ~-
cn>
(00
"I'"I"

"'!:::: """''

"N ' "~'
(!)
"""' "'(!)

I<)
"""'''(!)
(!)

...
~
"g '
I

FLA : GA .

--1 l-t AnQie to Line l)f SecfioJn

I<)
!!!
"'(!)
(!)

.,_,. """"'''

~
I' t
I

Suwannee
0"' Diatoms- Sponge Spicules
Figure 5. Southwest- northeast cross section extending from St. George Island through Embayment and Trough t o Savann ah River. Section shows distri bution of clay minerals. White areas in lower part of section Indicate no data; In the upper part of section, wh ite indicates where kaol inite is the predom inant clay. Authigenic lower Miocene commercial clay beds occur between sections W6890 and GGS494; d etrital mi ddle Mi ocene commercial clay beds GG5205 and GGS175. Stipple= palygorskite, horizontal = montmorillonite.
121

N N
Bose I Limestone

MIOCENE
-20KM

LOWER MIOCENE CLAYS

Figure 6. Distribution of major lithologic units in the lower Miocene. Mixed area to the southwest contains beds of palygorskite,but overall lithology is complex. Palygorskite is major clay in the dolomitic sediments.

Figure 7.

Map showing distribution of palygorskite and sepiolite in the lower Miocene. Montmorillonite is the dominant clay in unlabeled areas. Dotted line indicates location of concentration of detrital palygorskite in middle Miocene sediments.

TRANSGRESSION

Meters 0
1 I
,.1..1..
~~
.....,..
2

Manne Clay Burrowed
Lagoonal
Ti da l

Figure 8. Lithology of MC-1 core from La Camelia Mine, Florida. Blank intervals contain relatively pure homogeneous palygorskite clay beds. General environments and direction of shore-line movement is indicated.
rapid transgression and a second period of regression. A second clay bed was deposited in a lagoonal environment. Palygorskite formation stopped as the sea again transgressed the area.
The presence of abundant mud cracks, limpid dolomite, and limited faunal data indicate that the palygorskite formed in a restricted brackish environment. Most of the palygorskite consists of short (1Mm) fibers and was formed directly from the montmorillonite. A minor amount grew from solution and developed 10 to 20:Mm fibers.
Figure 9 is a cross section of a middle Miocene detrital clay deposit. The deposits are generally lens shaped and contain abundant clay clasts and pebbles. The clay was deposited in a marine environment (diatoms) between submerged lower Miocene beaches. A soil zone is present at the base of the deposit and is presumed to mark the lower-middle Miocene boundary. Many of the clay pebbles in the deposit are rich

in apatite. Many of the phosphate pebbles in the Miocene were formed by apatite replacing palygorskite clay pebbles.
Palygorskite formed in the transitional area between the marine and continental environments. There are many references to a marine origin for palygorskite, but no direct or positive evidence. Adjacent beds may be marine, but there is no reported fossil evidence that the palygorskite beds themselves are marine. Palygorskite is abundant in many deep-sea cores; however, the marine palygorskite is nearly always offshore from continental palygorskite deposits and has textural features that indicate it is detrital.
Why does palygorskite not form in all brackish lagoons? What were the conditions in the southeastern United States that caused it to develop in the late Oligocene and what change in conditions caused it to stop being deposited at the end of early Miocene?
Thermodynamic calculations confirm that palygorskite formation is favored by a high concentration of Si and to a lesser extent, Mg. High Mg favors the formation of corrensite, mixed-layer chloritemontmorillonite. One concern is why there was no Mg-rich corrensite associated with the Mg-rich palygorskite and sepiolite. The high Mg concentrations needed for the formation of corrensite can best be obtained in an evaporitic environment.
Figure 10 shows the general distribution of some authigenic minerals through time. Corrensite and dolomite are abundant in the Paleozoic and early Mesozoic. As Mg-rich corrensite decreases in abundance, Mg-rich palygorskite increases in abundance, as does kaolinite. Various studies indicate that in North America, Europe, and presumably North Africa, the Paleozoic and Early Mesozoic climate was warmer and much drier than today. This would favor the development of evaporitic conditions and the formation of corrensite. Beginning in the late Mesozoic, rainfall increased. This increased rainfall caused more intense weathering and the formation of kaolinite. It apparently also created more brackish water conditions in the fringing marine environments. This favored the formation of palygorskite in areas where corrensite formed in drier periods.
Coastal marine palygorskite deposits range from Triassic to Miocene. Most deposits fringe the Tethys and South Atlantic Oceans. Phosphate deposits show a similar distribution and commonly are associated with palygorskite deposits. Upwelling cold ocean waters are 13ssumed to be the source of the P; they would also be a source of Si for the formation of palygors.kite.
The temporal data suggest that climate, that is, temperature and possibly more important, humidity, determine whether or not palygorskite will form. The

123

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global distribution of the major palygorskite deposits indicates they are restricted to the belt of tropicalsubtropical temperatures (fig. 11) . To a large extent the distribution was controlled by the pattern of the warm Tethys curtents.
During the Mesozoic, coastal palygorskite was formed along the warm margins of the Tethys and South Atlantic. During the early Cenozoic, the westward-flowing Tethys currents supplied warm waters to the Caribbean region. The African and Eurasian plates converged in the late Oligocene and early Miocene and allowed these currents to swing to the north and increase temperatures in the coastal waters of the southeastern United States, presumably creating the subtropical humid conditions that allowed palygorskite to form . The collision of Europe and North Africa at Gibraltar at the beginning of the middle
Miocene modified the Atlantic circulation pattern, allowing cold arctic waters to enter the western North Atlantic. This caused a decrease in temperature and humidity, and the growth of palygorskite ceased. The increased coolness is confirmed by a change in the faunal suite. Low rainfall is indicated by the presence and abundance of opal phytoliths characteristic of prairie grasses.

In conclusion, we contend that coastal palygorskite deposits form largely from montmorillonite in protected quiet-water environments and under climatic conditions that produce high rainfall, brackish waters, and subtropical temperatures.
REFERENCE
Weaver, C.E., and Beck, K.C., 1977, Miocene of the S.E. United States: A model for chemical sedimentation in a peri-marine environment: Sedimentary Geol., v. 17, p. 1-234.

125

DEPOSITIONAL ENVIRONMENTS IN THE JURASSIC NORPHLET FORMATION IN SOUTH ALABAMA
Richard P. Wilkerson Department of Geology and Geography
University of Alabama University, Alabama

ABSTRACT
In the western Gulf of Mexico area the Norphlet Formation (Jurassic) is typically characterized by nonmarine and red bed facies. In the eastern Gulf of Mexico area this formation is represented by a lower black shale, red beds, and an upper quartz sandstone member. .In south Alabama the Norphlet section, penetrated by deep-test wells, is predominantly the upper sandstone or Denkman Member. Overlying the Norphlet Formation are transgressive marine Smackover carbonates . The Norphlet Formation overlies either red beds, salt, anhydrite, or Paleozoic rocks.
Norphlet deposition in south Alabama took place in an arid climate near its source area, which included southern extensions of the Appalachian Piedmont. The thickest cored interval in Escambia County consists of red siltstone at the base, coarse- grained, gray feldspathie sublitharenite, and an upper fine-grained gray subarkose, overlain by carbonate mudstone. The siltstone and feldspathic sublitharenite were deposited in alluvial and braided-stream environments. The upper subarkose was deposited in a lower shoreface environment.
The thickest cored interval in Mobile County is rather uniform lithologically, and consists of a submature to mature arkose. Most of the core consists of high-angle, planar-crossbedded sandstone, inferred to be eolian, interbedded with massive sandstone, inferred to be intertidal. The massive intertidal subarkose at the top of the Norphlet section in both Mobile and Escambia Counties is the result of reworking during a marine transgression which continued into Smackover time. The upper massive sandstone is probably partially laterally equivalent to subtidal Smackover carbonates.
INTRODUCTION
The Upper Jurassic Norphlet Formation is an important petroleum reservoir in the eastern Gulf Coast area. Previous studies of the Norphlet Formation have indicated that it was deposited in fluvialdeltaic, braided stream, eolian or intertidal environments in parts of Florida, Alabama, and Mississippi (Sigsby, 1976; Badon, 1975; Tyrrell, 1973). The recent increase in exploration in the Mobile County area has resulted in new Jurassic deep-test corehole data. The objective of this study is to integrate this new data with information published in the past.

STRATIGRAPHY
In the western Gulf Coast area the Norphlet Formation is represented mainly by nonmarine red beds and is defined as the red clastic section between the Louann Salt and the Smackover Formation (Imlay, 1940) (fig . 1). In the eastern Gulf Coast area the Norphlet Formation consists, in ascending order, of black shale, red beds, an upper quartzose sandstone, and in updip areas, conglomerate. The upper quartzose sandstone is the thickest unit in the study area and has been designated the Denkman Member of the Norphlet Formation by Murray (1961) and Tyrrell (1973). This study is concerned mainly with the Denkman Member; which may overlie either one or both of the lower members, or it may overlie the Eagle Mills Formation, Werner Anhydrite, Louann Salt, or Paleozoic rocks in the study area.
GEOLOGIC SETTING AND STRUCTURE
The area of study is restricted to south Alabama (fig. 2). This area lies on the east flank of the Mississippi Interior Salt Basin and contains southward extensions

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of the Appalachian structural front which were positive features at the time of Norphlet deposition. These include the Wiggins Uplift, the Conecuh Ridge, and the Pensacola Ridge (Wilson, 1975). Sedimentary basins in the study area are the Mississippi Interior Salt Basin, the Conecuh Embayment, and possibly a third basin to the north of the Conecuh Ridge (Wilson, 1975).
The structure map on the top of the Norphlet Formation gives its overall orientation in south Alabama (fig. 3). It is present at its shallowest depths as far north as Wilcox County at a depth of 5,000 ft. It trends in a general northwest-southeast direction, dipping generally to the south, with its deepest penetration in Mobile and Baldwin Counties , at depths over 19,000 ft.
The Norphlet Formation is not present in Conecuh and western Escambia Counties over the Conecuh Ridge. This feature is composed of igneous and metamorphic rocks of the Appalachian Piedmont (Neathery and Thomas, 1975), and was probably a "high" during Norphlet times . The Conecuh and Pensacola Ridges were probably major sediment contributors to the Norphlet Formation .

The formation is also thin or not present over the Wiggins Uplift in Mobile and Baldwin Counties. The Wiggins Uplift was probably not an important sediment contributor. It was, however, important as a positive structural element and may have partially separated the sedimentary basin which extended from Mobile through Escambia Counties.
Faulting of the Norphlet Formation has occurred in several areas. Several fault systems trend in a general northwest-southeast orientation, and one (Mobile Graben) trends north-south. These faults are extensional in nature and related to movements in the underlying Louann Salt (Sigsby, 1976) . The faults shown in figure 3 were identified by Wilson and Kidd (1977, Alabama Geological Survey Smackover Structure Map) .
ENVIRONMENTS OF DEPOSITION
Since most of the data obtained for this study are from Escambia and Mobile Counties, a representative section from each area will be described and discussed . The lower black shale member of the Norphlet Formation is present in some areas of Escambia County. It was analyzed tor pollen and spore and kerogen content, and found to be practically barren of both (Schwab, 1979, personal commun .). This is probably an indication of the harsh environmental conditions which existed at least in lower Norphlet times.
The Exxon L&N Railroad core from central Escambia County provides the thickest cored interval in the eastern part of the study area, but does not contain the lower black shale (fig . 4) . The base of the core consists of about 32ft of red sandy siltstone in horizontal, discontinuous laminae and containing occasional laminae of medium sand. An 18-ft interval of interbedded red silt and medium- to coarse-grained sand overl ies the lower siltstone. Above this lithofacies are 34ft of feldspathic sublitharenite which is gray, fine- to coarse-grained, and contains slightly inclined planar laminae. The feldspathic sublitharenite grades vertically into a 7-ft interval of gray, fine-grained, well sorted, massive subarkose. Directly overlying the subarkose are finely laminated carbonate mudstones of the Smackover Formation. The sequence appears to be continuous from the red beds at the base into the carbonates at the top, with no evidence of erosion or n o n d e p o s i t i o n .
The presence of updip conglomerates in a core from Wilcox County indicates that alluvial deposition was taking place in the area. The lower red sandy siltstone in the L&N Railroad core represents the initial clastic influx into the area , and was probably deposited in the distal part of an alluvial fan . Migrating channels or braided streams prograded

127

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into the area, leaving an alternating sequence of fine silt and coarse sand. Petrographic analysis shows that the feldspathic sublitharenite consists of 72% quartz, 10% feldspar, and 18% rock fragments, most of which are igneous and metamorphic. Texturally, it is submature and is silt to coarse sand size, moderately well sorted, and subangular. The coarse nature of its laminae and the high percentage of feldspar and rock fragments suggest that deposition took place near the source area. Sigsby (1976) found Norphlet Formation isopachs thicken and thin in a northeast-southwest orientation, indicating the influence of Appalachian structure. The Conecuh and Pensacola Ridges, therefore, were probably the important sediment co:-~tributors in this area.

The feldspathic sublitharenite grades vertically into a massive, clean .subarkose, which was probably deposited in a lower-shoreface marine environment. This subarkose consists of 62% quartz, 7% feldspar, 21% calcite cement, and 7% rock fragments, which are igneous, metamorphic, and sedimentary. It is fine grained, well sorted, subrounded, and texturally mature. Directly overlying the subarkose are finely laminated carbonate mudstones that were deposited in subtidal to intertidal environments. The upper subarkose indicates the beginning of a transgressive phase which resulted in the reworking of earlier deposited sandstones. This transgression continued into early Smackover time. The subarkose is probably the shoreward equivalent of subtidal Smackover Formation carbonates.

128

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The texture and sedimentary structures indicate that this lower interval was deposited in an eolian environment. Above the eolian lithofacies is a 23-ft section of massive sandstone with some horizontal laminae, ripple marks, and bioturbation. This sandstone is very fine grained, moderately well sorted, and subangularto subrounded. It is inferred to have been deposited in an intertidal environment.
The rest of the core consists of an alternating sequence of mostly eolian sandstone with occasional intervals of intertidal deposits. This vertical sequence is similar to the lithologies described by Badon (1975) for Clarke County, Mississippi, and by Tyrrell (1973) for Rankin County, Mississippi. The composite section in Mobile County contains another 10 to 20ft of massive sandstone at the top of the Norphlet Formation, as observed in other cores from the Hatters Pond area. This subarkose is inferred to be intertidal, and is probably the result of reworking by the transgressing Smackover sea. Like the upper lithofacies in Escambia County, it probably represents the shoreward equivalent of subtidal Smackover carbonates.

Figure 4. L&N Railroad core, Escambia County, Alabama.

Peter Klein #1

Well control in the Hatters Pond-Chunchula Field area of northern Mobile County is excellent and provides deep downd lp data. Th e Norphlet Formation is very thick in this area, and its total thickness has not yet been penetrated . The greatest cored interval is obtained in Getty Peter Klein -# 1 well in the Hatters Pond Field (fig . 5).
The Norphlet Formation in Mobile County is significantly different from that in Escambia County. The 300ft of sandstone in the Peter Klein #1 core is fairly uniform lithologically, and consists mostly of a submature to mature subarkose.
The lower 55ft contains high-angle (up to 25) planar crossbeds with occasional slump structures. These sedimentary structures are characteristic of modern eolian environments. The slip faces of present-day transverse dunes have a maximum slope of 34, while dune bedding in the Permian Rotliegendes only reaches 25-2JD. Glennie (1972) attributed this difference to compaction. Preservation of slump features indicates that the surface of a dune had been dampened, possibly by rain , became heavy and unstable, and slid down over the underlying sand (Glennie, 1970) . The lower lithofacies consists of fine- to very fine-grained, subrounded to rounded, well-sorted, and fine-skewed sandstone.

Vertical Scale: 1 in.=57ft.
Figure 5. Peter Klein, #1 core, Mobile County, Alabama.

129

In summary, the Norphlet Formation in Mobile County consists of mainly eolian sandstone interbedded with some intertidal sandstone. An eolian topography generally develops where a sufficient sand supply is available and where winds are strong enough to shift the sands (Bigarella, 1972). In south Alabama during Norphlet times, eolian deposits are associated with alluvial and fluvial deposits. Fluvial erosion in Escambia County probably provided the sand supply which formed the dune topography in Mobile County. Deposition in Mobile County took place along an arid desert coastline. Usually these types of coastlines have no fluvial deltas (Glennie, 1972), and there is little evidence for one in south Alabama. Because areas of major accumulati.on of desert sediment are those of subsiding basins, the coastlines of these basins also are likely to be low and subject to marine transgression (Glennie, 1972). Minor sea-level fluctuations during Norphlet time produced alternating eolian and intertidal sandstones in Mobile County. Since no fossils have been found in this study, it is difficult to date or correlate these fluctuations. Sea-level fluctuations had no effect on Norphlet deposition in Escambia County, which was alluvial-fluvial and probably topographically higher than Mobile County.
CONCLUSIONS
Norphlet Formation deposition in south Alabama took place in an arid region, probably not far from the source area, which included southern extensions of the Appalachian Piedmont located to the east and north . Evidence for an arid climate is :
a) the association with underlying evaporites; b) the high percentage and fresh nature of the
feldspars; c) the overlying dolomites and limestones ; d) the scarcity of pollen and spores and kerogen ; e) the absence of invertebrate fossils.
Areas near the Conecuh and Pensacola Ridges were covered with alluvial and braided stream deposits. There was little vegetation to stabilize these sediments, and they were then reworked into eolian dune fields farther to the west in Baldwin and Mobile Counties. The upper Norphlet was reworked by a transgressing sea, and is at least partially laterally equivalent to subtidal Smackover carbonates.
ACKNOWLEDGEMENTS
The author would like to express his appreciation to the State Oil and Gas Board and Geological Survey of Alabama for the use of core materials in south Alabama. The supervision and advice of E.A. Mancini is gratefully acknowledged. I would also like to thank Gary V. Wilson and D. Joe Benson for infor-

mative discussions on the subject. Research support was supplied by Getty Oil Company, Houston Oil and Minerals Corporation , and the Department of Geology and Geography, University of Alabama.
REFERENCES
Badon, C.L., 1975, Stratigraphy and petrology of Jurassic Norphlet Formation, Clarke County, Mississippi. Am . Assoc. Petroleum Geol. Bull., v. 59, p. 377-392.
Bigarella, J.J., 1972, Eolian environments-Their characteristics, recognition and importance in recognition of ancient sedimentary environments: Rigby, J .K., and Hamblin, W.K., eds., Soc. Econ. Paleont, Mineralog. Spec. Pub. No. 16, p. 12-62.
Glennie, K.W., 1970, Desert sedimentary environments . Amsterdam , Elsevier, 222 p.
_ _, 1972, Permian Rotliegendes of northwest Europe interpreted in light of modern desert sedimentation studies: Am . Assoc. Petroleum Geol. Bull., v. 56, p. 1048-1071.
Imlay, R.W., 1940, Lower Cretaceous and Jurassic formations of southern Arkansas and their oil and gas possibilities: Arkansas Geol. Survey Int. Cir. 12, 64 p.
Murray, G.E., 1961 , Geology of the Atlantic and Gulf Coastal Province of North America: New York, Harper and Bros. , 692 p.
Neathery, T.L . and Thomas, W.A., 1975, PreMesozoic basement rocks of the Alabama Coastal Plain: Gulf Coast Assoc. Geol. Socs. Trans ., v. 25, p. 86-99.
Sigsby , R.J., 1976, Paleoenvironmental analysis of the Big Escambia Creek - Jay - Blackjack Creek Field area: Gulf Coast Assoc. Geol. Socs. Trans.,v. 26, p. 258-278.
Tyrrell , W.W., 1973, Denkman Sandstone Member (Norphlet Formation) , a Jurassic reservoir in Mississippi, Alabama, and Florida: Unpub. manuscript presented at 1972 Gulf Coast Assoc. Geol. Socs. Mtg., Corpus Christi, Tex.
Wilson, G.V., 1975, Early differential subsidence and configuration of the northern Gulf Coast Basin in southwest Alabama and northwest Florida: Gulf Coast Assoc. Geol. Socs. Trans., v. 25, p. 196-206.

130

II. HYDROLOGY AND ENVIRONMENTAL GEOLOGY
131

J5eynote Paper
GROUND WATER FROM THE COASTAL PLAIN FOR THE FUTURE
Philip E. LaMoreau P.E. LaMoreau and Associates
Tuscaloosa, Alabama

INTRODUCTION
It is predicted that by the year 2000 A.D. we will have a population of some six billion persons on earth. It will be necessary that we avail ourselves of every gallon of water and the proper and conservative use of all other energy and mineral resources. Every acre of usable land must be developed properly and we will see concentrations of people around our rivers, lakes, and coastal waters.
As these people congregate in areas, we will encounter polluted waters and polluted lands: we will be forced as a society to place available resources and potential pollution problems in their proper perspective and to thoroughly understand and develop our resources of minerals, energy, and water. Although there are many types of development, such as industrial, agricultural, and municipal, in this perspective we will discuss available ground-water resources in the Gulf Coastal Plain as related to the nation's future needs and demands for water.
By 1980 our national daily water requirements will be some 600 billion gallons, a great share of these needs coming from the water-rich areas of our nation of which the Gulf Coastal Plain is the richest. The Atlantic and Gulf Coastal Plains are underlain by tremendous volumes of relatively unconsolidated sediments capable of producing many billions of gallons of water per day. It is this sleeping giant among our nation's water sources that will be discussed in some detail.
AN IMPORTANT SOURCE OF WATER FOR THE NATION
Precipitation throughout most of the South exceeds 40 in./yr , as com pared with the national average of 30 in., and in much of the Southeast it exceeds 50 in. It is evident that the South is one of the areas of the United States most blessed by rainfall, the ultimate source of ground water. Accompanying this large potential source of usable water are favorable geologic conditions for replenishment and storage of water underground. In fact, no other large area of the United States and few other places in the world meet so favorably the requisite conditions for optimum supplies of ground water as do the southern Atlantic and Gulf Coastal Plain and the Mississippi Embayment.

The Atlantic and Gulf Coastal Plains are underlain by tremendous volumes of relatively unconsolidated sediments capable of producing billions of gallons of water per day, providing this resource is properly developed and managed.
GENERAL VOLUME OF SEDIMENTS INVOLVED
A few years ago the Geological Society of America authorized a Symposium on Sedimentary Volumes (Murray and others, 1952). The Gulf Cuastal Plain was chosen as the logical area for study because of the wealth of information from thousands of oil test holes and from surface geologic mapping. The results of this work were extremely valuable to geologists in the petroleum industry and educational field; however, its full implication has not been and still is not generally appreciated in the field of water resources.
Geologically,the Coastal Plain can be divided into a complex system of strata having definite physical character and traceable boundaries. Instead of a complex set of stratigraphic names, let it suffice to convey an idea of the volume and areal extent of this mass of material, most of which has a high porosity20 to 30 percent or more - and much of which is relatively permeable and capable of transmitting tremendous quantities of water.
The greatest bulk of the beds in the Coastal Plain consists of sand, clay, and gravel or a mixture of these materials; however, some notable exceptions are the chalk beds of Texas, Mississippi and Alabama and the shell limestone beds of southern Georgia, Alabama, Florida, and Texas. Outcrops of these formations are represented by bands of color on the geologic map that simulate a huge lazy W extending from Texas up the Mississippi Embayment, down across the eastern Gulf Coastal Plain, and northward along the Atlantic coast. In general, each formation dips gently coastward and thickens into a great tabular wedge of sediments. As we travel toward the coast, succeeding outcrop patterns, or bands of color on the geologic map, represent the outcrops of successively younger formations, each resting on older beds like the pages of a book. If cut open like a pie, the wedge of Coastal Plain sediments would appear as a featheredgein its northern extremity, thickening seaward to a total of something less than half a mile in the Atlantic Coastal

132

Plain north of South Carolina, to about 2 mi in southern Florida, and to an estimated thickness of more than 50,000 ft in southern Louisiana. This estimate is based on seismic studies and thousands of water, oil and gas well projections of geologic information.
When totalled up, these formations in the Gulf and Atlantic Coastal Plain underlie an area between the Mexican border and the Georgia-South Carolina lineofabout333,000sq mi (nearlyone-tenthofthe area of the United States), and the v,olume of these sediments is some 875,000 cu mi (Murray and others, 1952). The alternation of permeable sands and limestones with relatively impermeable marls and clay creates an immense artesian system in the Coastal Plain, simple in general design but complex in many details. The alternate layers of permeable and relatively impermeable beds and their gentle dips coastward are ideally suited to the occurrence of artesian water. The most important aquifers are commonly the coarser-grained sands or the limestones. The aquifers are separated by beds that are more clayey or limey, many of which are also very porous but less permeable. These less permeable beds are significant not only as confining beds for artesian conditions but also as sources of water, for it has been discovered that, as artesian pressures are reduced in the aquifers, water is squeezed out of the highly porous clays and marls. and is added to the water available to wells.
STORAGE OF GROUND WATER INVOLVED
Let us have a more specific look at the "payload"-the part in which we, as fresh-water explorers, producers, or managers, are interested. Beneath the Coastal Plain the ground water occurs in three zones in downward succession: (1) a shallow zone, approximately the upper 100ft of unconfined water in the outcrop areas of the waterbearing beds; (2) a zone of fresh artesian water below the point at which water becomes confined and commonly extending down to depths of as much as 2,000 ft; and (3) a zone of salty artesian water in the lower aquifers, or in the downdip extremities of the same aquifers that yield fresh water inland.
The shallow zone represents a volume of material nearly filled with water under water-table conditions. It extends throughout the Coastal Plain and contains fresh water everywhere except in a few places where the plain is narrow and is cut by channels connected with the sea. The relationship of rainwater to geology is very intimate in this nearsurface zone. A study of streamflow records in the Coastal Plain, when plotted on a base map, can be used to delineate many of the major geologic boundaries. This concept of the close relationship between precipitation, surface runoff, and recharge

into the ground is important in evaluating the ground-water resources of the South. It should be noted that practically all of the Coastal Plain area east of Texas lies within the area of highest average runoff. Highly permeable beds crop out across this area, and their water appetite must be satisfied before streams will flow across them. This is substantial evidence that these tremendous groundwater reservoirs are not only full but are rejecting recharge. In addition, the water table in much of this area is near the ground surface and substantial amounts of water are being lost by evapotranspiration.
The fresh-artesian-water zone-that part of the aquifer between the uppermost confining beds and the salt-water zone below-also is present throughout the Coastal Plain except beneath a thin strip along the northern margin of each aquifer and locally along the outer margin of the Coastal Plain. This zone may consist of many different waterbearing beds aggregating many hundreds of feet of sediments. The deepest known fresh water in the Coastal Plain is obtained from a well5,900 ft deep in Karnes County, Texas. Interpretation of electric logs from oil tests indicates that fresh water extends to depths of 5,000 ft in McMullen County, Texas, and to 3,500 ft just north of New Orleans, La. (Sundstrom, R.W., and Turcan, A.N., U.S .. Geological Survey, written commun., 1960). Pressure release resulting from withdrawal of water from wells in these systems is quite rapid and has been recorded over large distances-for example, as much as 60 mi in the Houston area of Texas. The actual movement of water at depths of several hundred feet and more in these aquifers may be quite slow; however, measured in feet per year or even in feet per century, in spite of the rapid transmission of pressure changes, this factor is of great practical importance. On the one hand, it affords protection from immediate encroachment of saltwater when artesian pressure is 1owered, but on the other hand, it retards the flushing out of saltwater in the downdip extensions of the aquifers by fresh water moving from outcrop areas.
The third, or saltwater, zone includes the deeper beds in the outer margin of the region,. and this saltwater zone occupies more than nine-tenths of the aggregate volume of sediments in the Coastal Plain. Even so, if 1,000 ft is a fair average for the thickness of sediments in the freshwater zone, there would be about 60,000 cu mi of sediments containing fresh water in the Coastal Plain area of Texas, Louisiana, Mississippi, Arkansas, Missouri, Illinois, Kentucky, Tennessee, Alabama, and Georgia, and more than 800,000 cu mi containing salt water. By further conversion, we can estimate that there is 20,000 cu mi of fresh water in storage in this same area, or enough fresh water to cover the 48 States to a depth of 35 ft.

133

GROUND-WATER QUALITY IS GENERALLY VERY GOOD
Even though a large source of water supply is known to exist, it would not be of value to us unless its quality allowed its extensive use. From a quick review of many hundred analyses of water from wells spaced geographically over the Coastal Plain and tapping more than 100 different water-bearing beds, it can be seen that, though the water varies greatly in quality, in general it may be classed as some of the best natural water in the 'nation. In most places the water in the shallow water-table aquifers is slow in dissolved mineral matter; however, in general it is slightly acid . Where fresh artesian water occurs in limestone, it is largely of the calcium bicarbonate type, the hardness ranging between 100 and 300 ppm. Where the fresh artesian water occurs in sand , there is generally a gradual increase in mineral content with depth in each aquifer, the character of the water changing from chiefly calcium bicarbonate to chiefly sodium bicarbonate.
The temperature of water in the water-table aquifers is usually about 2 to 3 F above the average annual air temperature. The temperature of the water increases with depth, in most places, at the rate of 1oF for each 60 to 90ft of increase in depth .
SYMPTOMS OF THE FUTURE
There are symptoms that our sleeping giant may have ills which, if not properly treated, may develop into major problems. The principal water problems for the South relate to surface water and specifically to floods and pollution . There also are problems related to the quality of water in coastal areas.
Not long ago, a list was prepared of ground-water problems, describing their magnitude and extent; these were then projected over the next 20 and 40 years. The list developed was rather long and seemingly somewhat formless, but when plotted on a map, certain patterns related to water use and geologic controls began to take shape. The problem areas were those caused by expansion of existing areas of overdraft, contamination by wastes, and saltwater intrusion in coastal areas, as related to existing or expected agricultural, industrial , and urban growth.
It should be noted, however, that the map prepared for the Senate Select Committee Report showing the problems and the projection of the ground-water problems, points out the favorable position of the South . Granted, problems are impending, but many of them can be minimized by good engineering and geologic practices, based on sound hydrogeologic facts which will allow much fuller and more economical development of water.

BIBLIOGRAPHY
Alabama Crop and Livestock Reporting Service, 1977, Alabama Agricultural Statistics: Montgomery, Ala., Alabama Dept. Agriculture and Statistics, 95 p.
Alabama Power Company, (undated), The Joseph M. Farley nuclear plant environmental report; Construction permit state: Open-file rept., 231 p.
Alabama Department of Public Health, 1969, Public water supplies on record : Montgomery, Ala., Alabama Dept. Public Health, 24 p.
Alabama Water Improvement Commission, 1969, Water pollution progress report for the years 1967-1968: Montgomery, Ala., Alabama Water Improvement Comm ., 92 p.
_ _, 1976, Water quality management plan, Upper Tombigbee River Basin: Montgomery, Ala., Alabama Water Improvement Comm ., 187 p.
Bidgood, Lee, 1962, Transition in Alabama: University of Alabama Press, Alabama Bus. Research Council, 106 p.
Butler, E.A., 1960, Paleontology of the L.L. and E. et al.well: Louisiana Geol. Survey Folio Ser., No.1
Considine, D.M., ed. , 1976, Van Nostrand's scientific encyclopedia, (fifth ed.) : New York , Van Nostrand Reinhold Co., 2370 p.
Counts, H .B., and Donsky, Ellis, 1963, Salt-water encroachment, geology and ground-water resources of Savannah area, Georgia and South Carolina: U.S. Geol. Survey Water-Supply Paper1611 , 100p.
Curtis, L.M., Rochester, E.W. , and Warman, J.C., eds., 1978, Proceedings of Auburn University Irrigation Workshop: Auburn, Ala ., Auburn Univ., 28 p.
Dufour, C.N., and Becker, Edith, 1964, Public water supplies of the 100 largest cities in the United States, 1962: U.S. Geol. Survey Water-Supply Paper 1812, 364 p.
Evans, Robert, and Mullis, C.H., Jr., 1968, Pollution control and water supply, in Report for development of water resources in non-Appalachia Alabama: Alabama Geol. Survey, app. D, 27 p.
Geological Survey of Alabama, 1978, Use of water in Alabama, with projections to 2020: Information series 48, University, Ala., 45 p.
Greg , D.O ., and Zimmerman, E.A., 1974, Geologic and hydrologic control of chloride contamination in aquifers in Brunswick, Glynn County, Georgia: U.S. Geol. Survey Water-Supply Paper 2029-D, 44 p.
Jordan, H.E., 1955, The problems that face our cities in Water, the yearbook of agriculture for 1955: U.S. Dept. Agriculture, p. 649-653.
Krause, R.E., 1972, Effects of ground-water pumping in parts of Liberty and Mcintosh Counties, Georgia, 1966-70: Georgia Dept. Nat. Resources Int. Circ . 45, 15 p.

134

_ _1976, Occurrence and distribution of color and hydrogen sulfide in water from the principal artesian aquifer in the Valdosta area, Georgia: U.S. Geol. Survey Open-file rept. 76-378, 11 p.
_ _1978, Geohydrology of Brooks, Lowndes, and western Echols Counties, Georgia: U.S. Geol. Survey, Water-Resources lnv. 78-117, 82 p., in
press. Linaweaver, F.P., Jr., Geyer, J.C., and Wolff, J.B.,
1967, A study of residential use: Baltimore, Md., Johns Hopkins Univ. Dept. Housing and Urban Devel. Tech . Studies, 12, 79 p. McKichan, K.A., 1951, Estimated use of water in the United States, 1950: U.S . Geol. Survey Cir. 115, 13 p. _ _1957, Estimated use of water in the United States, 1955: U.S. Geol. Survey Circ. 398, 18 p. McKichan, K.A., and Kammerer, J.C., 1961, Estimated use of water in the United States, 1960: U.S. Geol. Survey Circ. 456, 26 p. Mullis, C.H., Jr., 1968, Power supply and requirements, in Report for development of water resources in non-Appalachia, Alabama: Alabama Geol. Survey, app. B, 28 p. Murray, C.R., 1968, Estimated use of water in the United States, 1965: U.S . Geol. Survey Circ. 556, 53 p. _ _1977, Estimated water use in the United States in 1975: U.S. Geol. Survey Circ. 765, 39 p. Murray, G.E., Applin, P.L. Toulmin, L.D., Colle, Jack, Guzman, E.J ., and Nettleton, L.L., 1952, Sedimentary volumes in Gulf Coastal Plain of United States and Mexico: Geol. Soc. America Bull., v. 63, p. 1157-1228. Nace, R.L., 1967, Are we running out of water? U.S. Geol. Survey Circ. 536, 7 p. Newton, J.G., 1976, Early detection and correction of sinkhole problems in Alabama, with a preliminary evaluation of remote sensing applications: Alabama Highway Dept. HPR Rept. 76, Research Project 930-070, 83 p. Oak Ridge National Laboratory, 1978, Annual Progress Report, Excerpt from ORNL-5364 (April 1978), Regional and Urban Studies Section (R.M. Davis) per. ending Sept. 30, 1977. 129 p. Pierce, L.B., 1972, Use of water in Alabama, 1970, with projections to 2020: Alabama Geol. Survey Int. Ser. 42, 78 p. _ _, 1967, 7-day low flows and flow duration of Alabama streams: Alabama Geol. Survey Bull. 87, Part A, 114 p. Piper, A.M., 1965, Has the United States enough water?: U.S. Geol. Survey Water-Supply Paper 1797, 27 p. Southeast Basins Inter-Agency Committee, 1977, 1975 national assessment of water and related land resources: South Atlantic-Gulf Water Resources Region, v. 1, 94 p., app.; v. 2, 332 p.; v.
3, 529 p. Street, D.R., Criss, R.R., Burks, R.L., and Baker, J.H.,
1970, Industrial use and community supplies

of water in Alabama: Auburn Univ. Sch . Business, Research Ser. 1, 111 p.
Tompkins, F.V., 1966, Water use in the mineral industry of Alabama in 1962: U.S. Bur. Mines, Mineral Ind. Surveys Int. Circ. 11-43, 7 p.
University of Alabama, 1960, Water and economic growth: Univ. Alabama Sch. Commerce and Business Adm ., 45 p.
U.S. Army Corps of Engineers, 1969, Development of water resources in Appalachia: Dept. Army, Office Appalachian Studies, Summary Rept., 256 p.
U.S. Bureau of the Census, 1966, Water use in manufacturing, in Census of manufacturers, 1963: U.S. Bur. Census MC63(1)-10, 174 p.
_ _1967, U.S. census of agriculture, 1964: U.S. Bur. Census, v. 1, pts. 1-50.
_ _1976, Projections of population in Alabama counties: U.S . Dept. Commerce, Bur. Econ . Analysis, Ser. E, November 1976.
_ _1977, Federal-state cooperative program for population estimate U.S. Dept. Commerce, Ser. P-26, no. 76-1, September 1977, 10 p.
U.S. Federal Power Commission , 1964, Hydroelectric power resources of the United States, developed and undeveloped, January 1, 1964: U.S. Federal Power Comm., P-34, 159 p.
U.S. Geological Survey, 1974, State of Alabama, U.S. Geol. Survey Hydrologic Unit Map, 1974.
U.S. Geological Survey, 1978, State of Georgia: Ground-water levels and quality data for Georgia, 1977, Open-file rept. 79-213,88 p.
U.S . Public Health Service, 1964a, Municipal waterfacilties inventory as of January 1, 1963 (revised ed.): U.S. Public Health Service Pub. 775 , v. 1-9.
__1964b, Municipal water-facilties, communities of 25,000 population and over, United States and its possessions, as of January 1, 1964: U.S. Public Health Service Pub. 661, 186 p.
U.S. Senate Select Committee on National Water Resources, 1960, National water resources and problems: Comm. Print No.3, 42 p.
U.S. Water Resources Council, 1975, National assessment of water and related land resources:Southeast Basin Interagency Comm ., 1975 Water Assessment, v. 11, app. C, 332 p.
U.S. Weather Bureau, 1959, Evaporation maps for the United States: U.S. Weather Bur. Tech. Paper37, 13 p.
Wahl, K.D., 1966, Geology and ground-water resources of Greene County, Alabama: Alabama Geol. Survey Bull. 86, 93 p.
Wilson, Alfonso , 1967, River discharge to the sea from the shores of the conterminous United States: U.S. Geol. Survey Hydrologic lnv. Atlas HA-282.

135

HYDROCHEMICAL PROCESSES IN COASTAL PLAIN AQUIFERS
William Back, Mary Jo Baedecker, and Warren Wood U.S. Geological Survey Reston, Virginia

ABSTRACT

Tl1 e development and managemen t of aqu if ers ot th Southeastern Coas tal PI<~ in requires an understanding of the chemica l reactions and hydrog eoiog JC pro cesses c ontro lling the c hem ica l character or ground water. This u nd ers tandi ng is ac hieved p rima rily by com binln.g mineral equ lllblrl a studies. principles of o rgan1c geocllemistry. na tura l isotope investigations ftr1d mass tra.nster calculations .
Chemistry of water in the thin sediments, near the Piedmont. is controlled largely by the chemical constituents in atmospheric precipitation, hydrolysis of silicate minerals (primarily feldspars), leaching of soluble carbonates. alteration of clay minerals. and both mobilization and attenuation of metals. Downgradient,the water can continue dissolving magnesian calcite, gypsum. and dolomite with the resulting precipitation of stochiometric calcite. In those formations where ion-exchange material is present. solution of calcite c<~n continue in response to removal of calcium by exchange with sodium.
Organic compounds, either from landfills or deep well injection, can generate reactions that form acids and gases. reduce sulfate. influence redox conditions. mobil-

ize trace metals, and redistribute isotopes The effect of these biogenic processes directly on the chemistry of ground water and their influence on inorganic reactions is currently a significant topic of investigation.
Isotopic ratios of deuterium and oxygen in water and carbon-13 of inorganic carbon in both water and minerals are used to indicate sources of water and occurrence of mixing zones Carbon-13 also helps identify processes of bicarbonate generation. alteration of calcareous minerals and decomposition of organic materials in aquifers. Carbon-14 measurements can give velocity of groundwater flow. residence time within the aquifers and rates of chemical reactions.
Farther downgradient in the zone of dispersion, which results from salt water encroachment, the large change in ionic strength can cause significant modification in both the mineralogy and water chemistry. Mixing of fresh water and salt water can develop undersaturation with respect to carbonate minerals to permit additional solution; sea water can provide a continuing supply of magnesium to form mixing zone dolomite; and sodium ions can reoccupy exchange sites on clay minerals.

136

ENVIRONMENTAL GEOLOGIC MAPPING IN FLORIDA
Ernest W. Bishop and Walter Schmidt Florida Bureau of Geology Tallahassee, Florida

ABSTRACT
The State of Florida's Bureau of Geology has recently completed a state-wide surface lithologic mapping program. The physical characteristics of the rock units within 100-200 ft of the land surface were mapped. This method of plotting geologic data represents a new approach to understanding Florida's geology. Excluded from consideration were formations (including groups, members. etc.), biozones and time lines.
This type of map will provide an excellent data base for numerous future applications. Potential users of this type of data would be environmental planners, soil scientists, building engineers, and hydrologists. It will help to delineate potential mining areas, as well as to aid in !he production of karst density maps and landfill development maps.
INTRODUCTION
The Florida Bureau of Geology has recently completed a surface geologic (lithologic) mapping program. This was undertaken in response to numerous requests received by the Bureau from many governmental agencies, industry, and private landowners for information on subsoils. Requests for this type of information have become more common in recent years, possibly due to the rapid growth of Florida's population. Major requests appeared to stem from users involved with such growth-oriented projects as Environmental Impact Statements, county land planning, landfill planning, foundation support, and potential mining areas.
The lithologic data is presented on the 1:250,000 base maps published by the U.S. Geological Survey. There are fourteen of these maps, which cover the entire State of Florida. These maps are titled the Environmental Geology Series.
This program mapped lithologic units at or near the ground surface, but below the soil horizon . In most cases these materials represent the parent material that produced the soil sequence.
This type of map is different from a conventional geologic map, which uses geological formations as a basis for mapping. It is also different from hydrologic maps, which generally plot permeable vs. impermeable units.
PROCEDURES
To cover the more than 54,000 sq mi of Florida's land area in two to three years, a rapid data collection system had to be devised. The Florida Bureau of Geology has a well cutting and core library of nearly

15,000 wells. These samples were obtamed over the years from water-well contractors, oil wells, shallow auger holes, and the Bureau's own coring rig . After plotting this information on l V2-minute topographic quadrangles, and adding any information available from the literature, field work could begin . As many surface data points as possible were obtained from exposures such as quarries, borrow pits, canals, road and railroad cuts, streams and river bluffs, and construction excavations. In addition to such surface observations, valuable information was obtained from local residents, waterwell drillers, quarry operators, and consultants.
The development of what type and how many lithologic units to use involved lengthy discussion among the geologic staff. Nine categories were decided upon to represent main lithologic types. The main lithologic types are gravel and coarse sand, medium to fine sand and silts, clayey sands, sandy clay and clay, shell beds, limestone, dolomite, limestone and dolomite, and peat. These units represented, as best we could determine, the "C" soil horizon, or the parent material from which the soil sequence developed. The depth to the parent material varied from 0 ft (at surface) to 10ft or more, depending on the soil development.
USE
This type of presentation of geologic data is advantageous because of the relative speed at which an area can be mapped. In a few short weeks, hundreds of surface data points can be observed, and well samples examined to produce a lithologic interpretation of an entire county . In addition to its immediate value, the Environmental Geology Series of maps will provide the basic data needed for numerous future applications. A few examples of potential users would be well drillers, environmental planners (city, county, state and federal), soil scientists and conservationists, landfill developers, building engineers, mining companies, and hydrologists.
PUBLICATIONS
A text accompanies each map to explain the major geologic and physiographic features of the area covered. An introduction covers such topics as economic growth, the population trends, local climate, transportation available, and industrial development. Other sections discuss the economic geology, ground water, local outcrops of interest, and a reference list to other related geological publications.

137

DEVELOPMENT AND IMPLEMENTATION OF WATER RESOURCE INVESTIGATIONS UTILIZING SURFACE RESISTIVITY TECHNIQUES IN THE SUWANNEE RIVER WATER MANAGEMENT DISTRICT, FLORIDA
David W. Fisk Suwannee River Water Management District
White Springs, Florida

ABSTRACT

In mid-1977, the Suwannee River Water Management District purchased and implemented surface resistivity equipment to augment ongoing ground-water resource s.tudies . Due to the nature of the equipment purchased, the District has been able to conduct deep electrical

soundings using symmetric Schlumberger arrays with electrode spacings (AB/2) of greater than 10,000 feet. Field procedures, data tabulation, data interpretation,and an estimation of surface resistivity application to groundwater investigations are presented .

138

HAZARDOUS WASTE DISPOSAL IN THE SOUTHEASTERN UNITED STATES: AN IMMINENT PROBLEM
Richard C. Fountain, CPGS, PG and Arthur W. Hayes, Ph.D., PG; Richard C. Fountain and Associates
Winter Haven, Florida, and Atlanta, Georgia

ABSTRACT

The needs, services and applications of geological science have come around full .::ircle during the development of mankind. Its history has involved seeking out and exploiting raw materials from the Earth since the dawn of civilization. Now geological science is being charged with disposing of the waste products of those raw materials after they have served the demands of society. The same exploration tools, techniques and thought processes used for mineral exploration and development today are applicable to addressing the recently imposed disposal problems. This may be indicative of the maturity of geological science: that it has "come of age." Geologists must undertake this new challenge because of their particular understanding of the Earth developed through many years of study.
The growth of population and industry, and with it the production of an array of wastes, require that suitable methods for isolating hazardous waste materials from the biosphere be developed Included in this category of wastes are the radiogenics, biocides, carcinogens and other highly toxic wastes , which possess great longevity and which cannot be rendered safe by conventional waste disposal methods.
The southeastern United States is a case in point because of its tremendous growth in industry resulting from favorable climate, land availability, transportation systems, tax rates, labor pool, energy supply, and sympathetic political environment.
In other regions of the nation recent news releases have indicated the type of problem that can arise from the improper disposal of hazardous waste materials. The concerns presented by adverse publicity are bringing pol-

itical pressures to bear, which may later dictate that hazardous wastes not be transported across state lines.
The choice of the word, imminent, in the title is quite deliberate. It implies that the problem is capable of being resolved or at least ameliorated. In the southeastern states of Alabama, Florida, Georgia and South Carolina, the geology is such that it permits alternative solutions to the problem of hazardous waste disposal, but only by thorough, careful investigation and analysis. This knowledge generally becomes available through exploration conducted by industry, which is very often accused of being the villian in the environmental drama.
In the subject southeastern states, earth materials exist which are capable of containing, isolating and confining hazardous wastes both near the surface and in the subsurface. Various formations exhibit suitable chemical and physical properties relating to permeability, plasticity, ion exchange capacity, and other parameters which favor their suitability for hazardous waste disposal. In addition, formation thickness, depth below ground surface, structural configuration , seismicity and site surface and ground-water hydrology must be considered.
On a regional scale, f,avorable geologic units are identified and discussed which are accessible by present technology and methods, and which provide an alternative tor rational disposal of hazardous wastes. The real problem rests not so much with finding suitable disposal conditions, but in securing competent scientific investigation and data interpretation, resulting in approval from legislative and governmental authorities and the general public, and ultimately in the safe long-term operation of the chosen site. "There are no simple solutions, only intelligent choices."

139

THE GEOHYDROLOGY OF THE GULF TROUGH
Carol Gelbaum1 and Jul1.an Howe112 Georgia Geologic Survey Atlanta, Georgia

ABSTRACT
The Gulf Trough is a subsurface geologic feature that affected the deposition of sediments from probably as early as upper Eocene, Jackson time through Miocene time. The trough can be found parallel to a hydrologic anomaly trending N 53 E from northern Thomas, Colquitt and southern Tift Counties. It is hypothesized to extend into northern Effingham County. Ground-water availability is adversely affected by the Gulf Trough. A study of water-well yield shows that in the trough, wells yielding 50-100 gpm are typical, whereas in areas outside the trough's influence, 500-1500 gpm are common. The low yields have discouraged the growth and development of communities, industries and agriculture along the geographic extent of the trough.
Lithologic properties of the aquifer affect the porosity and it is postulated that they are primarily responsible for the reduced yields. Upper Eocene samples taken from wells drilled near the axis of the trough show a finer microcrystalline texture with fewer bioclasts than samples from the aquifer outside the trough. A change in texture from coarse grained to fine grained can inhibit ground-water flow. Other possibilities such as reduced aquifer thickness and multiaquifer wells may be considered partly responsible for the reduced yields. Faulting has been considered by other investigators as the cause for the reduced yields.

Herrick and Vorhis (1963) used the expression "Gulf Trough of Georgia" for a zone of thick sediments of Miocene to Recent age in Grady, northwestern Thomas and Colquitt Counties. They suggest that the trough extended into Tift, Irwin and northern Coffee Counties based on the thick deposits of sediment. Herrick (1973) alluded to the trough's existence in counties northeast of this area based upon an anomaly found on potentiometric maps of the principal artesian aquifer. Contours on the potentiometric surface are very closely spaced in the central portion of the Coastal Plain (fig . 2) , showing that the gradient of the surface is especially steep (roughly 10 ft/mi) . This steep gradient coincides with the axis of the Gulf Trough, and may represent a zone of reduced transmissivity.
This report describes the geometry and the areal distribution of the Gulf Trough. The structural development of the trough through time is shown by a series of structural contour and isopach maps. The ground-water availability of the study area is also shown and the causes of the potentiometric anomaly referred to above are discussed.

METHOD OF STUDY

INTRODUCTION
The Gulf Trough is a major subsurface geologic feature that extends northeastward across the Georgia Coastal Plain from Decatur County in the southwest to Bulloch County in the northeast (fig . 1). The Gulf Trough is about 235 mi long and its axis trends approximately N 53 E.
The Gulf Trough was at one time considered to be the same as the Suwannee Strait, a feature first described by Dall and Harris in 1892. Misinterpretation of the earlier literature, starting about 1956, led to the discrepancy. Based on information gathered for this study, it is concluded that the Suwannee Strait is not the same feature as the Gulf Trough . The two are separated geographically by 40 mi; they affect rocks of different ages; they are dissimilar in structural configuration; and the Suwannee Strait does not affect ground-water availability as does the Gulf Trough.

The data used to prepare this paper were obtained from well records compiled by the U.S. Geological Survey, the Georgia Geological Survey, the Ground-Water Prog-ram of the- Georgia Environmental Protection Division, and the records of individual water-well drillers. Lithologic logs prepared from over 330 sets of cuttings and core, 200 of which were examined by the authors, were used to construct the isopach and strucure maps. Data from approximately 100 wells were used to prepare the water availability distribution or specific-capacity index map.
The designation "GGS" preceding a well number in this report indicates that the cuttings or core from this well are stored in the sample library of the Georgia Geologic Survey. The lithologic logs prepared from these wells are on file at the Georgia Geologic Survey. Figure 1 shows the locations of GGS wells used in this report, the location of the axis of the trough, and the locations of three representative cross sections.

1Present affiliation : 2Present affiliation :

Department of Geology, Georgia State University , Atlanta, Ga.

Striser Petroleum Co., Columbus, Ga.

140

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GEOLOGY
Scattered oil test wells show that a wedge of Coastal Plain sediments ranging in thickness from 3500 to 6000 ft underlies the area where the Gulf Trough is found (Herrick and Vorhis, 1963) . However, most wells in the study area do not penetrate rocks older than the Ocala limestone of late Eocene age. Accordingly , the configuration of the Gulf Trough and its effect on sedimentation are best known in Ocala and younger rocks The stratigraphic units discussed in this paper are, from oldest to youngest, the Ocala Limestone, the Suwannee Limestone of Oligocene age, and Miocene to Holocene sediments.

Eocene Series
Ocala Limestone
Lithology and Porosity
The Ocala Limestone is generally a bioclastic, skeletal limestone consisting of the remains of bryozoa. coralline algae, and larger foraminifera bound by a minimal amount of micritic to fine crystalline calcite cement. Certain diagnostic foraminifera are frequently found at or near the top of the Ocala Limestone. These include Lepidocyclina ocalana Cushman. Operculinoides oc a/ana Cushman ,1\stero cyc/ina sp., and Heterostegina oc a/ana Cushman . The bioclastic Ocal a appears to be an exceptionally porous unit with visible porosity estimated to be on the order of 30 percent .

141

_,...2oo......_ POTENTIOMETRIC CONTOUR- Shows

altitude at which water level would

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Figure 2. Potentiometric surface of principal artesian-Florida aquifer in southeastern Georgia and northeastern Florida, January-May 1976 . After Hester and others, 1977.

So uth of the G u l f T rough , in southern Co lq ui tt, Broo ks an d Thomas Co unties. the Oca la can be di vided into uppe r and lower parts based on grada-
tio nal lith ol ogic changes. The lo wer porti o n Is biom-
icrite or fi nely g ranula r li mesto ne . w hi c h c ontai ns sparse faun a representing few species , grading upward into the bioclastic porous limestone desc ribed above . Lipidocyc/ina ocalana Cushman is common in the lower port ion , but is much sm aller than normal. . The lower unit is very dense, lacks appreciable visible porosity, and is not found northwest of the Gulf Trough .
Samples from wells within the trou gh, su c h as GGS 3186 in northwestern Thomas County show that th e Ocal a Limestone has a micriti c to microg ranular texture and somet imes conta ins Int ra clasts. Wells loc ated w ith in t he tro ugh in Too mbs County (fo r ex ample G GS 146) show that the Ocala contains minor clay an d spa rse mica in add itio n to

the more usua l constitue nts. Faun a are not always p rese nt (fo r examp le GGS 3186) eith er because the deposi ti ona l e n vi r onme nt w as unsui t ab l e o r because alterat ion du r ing diage nesi s has destroyed them .
The Ocala Limestone is dolomitized to varying degrees at many localities. North of the trough, dolomitization is minimal with the dolomite occurring as scattered euhedral crystals at random horizons . On the south si de of th e trou gh, in southwestern Georgia, the dolomite occurs in almost a cyclical fashion altern at ing with beds of limestone . Most dolomite beds range in th ickness from 5 to 50ft and the degree of dolomitization varies from complete replacement with no textural and faunal preservation to partially dolomitized beds containing chalky fossils . Laterally these horizons are not continuous except for a dense dolomite near the top of the Ocala, which produces a distinctive signature on the neutron log.

142

On the south side of the trough, in southwestern Georgia, the lower part of the Ocala contains scattered gypsum nodules and some thin beds of nodules of chert. The upper part contains intergranular gypsum near the gradational boundary with the lower unit. No chert or gypsum has been found north of the trough.
Thickness Trends
The Ocala Limestone is completely penetrated by only a few wells in the study area, especially within th~ trough, and therefore, a detailed isopach map of th1s un1t cannot be prepared. Certain thickness trends, however, can be observed.
The Ocala Limestone appears to be thickest in southern Colquitt, Thomas and Brooks Counties. For example, in Thomas County (GGS 132, fig. 3, cross section C-C') and in GGS 3188, the Ocala is more than 700ft thick. The exact thickness in many wells is uncertain because the basal Ocala is in gradational contact with the middle Eocene and is difficult to distinguish from that unit. The Ocala in southwest Georgia tends to become a dense, nonfossiliferous micrite, losing its typical bioclastic character altogether.
In Bulloch County, in the northeastern portion of the study area, the Ocala ranges in thickness from 80 to 200ft and thickens gradually to more than 240 ft toward the coast near Savannah (see fig. 3, cross section A-A')
In the central portion, in Ben Hill and Irwin Counties, the thickness of the Ocala ranges from 250 to 375 ft. Southeast of the trough in Coffee County (GGS 51 0), the Ocala is 440ft thick.
Structural Surface
The configuration of the structural surface of the Ocala Limestone, shown on figure 4, closely resembles that of the Suwannee Limestone (fig. 6). Several elongate basins trending northeastward are evident and become more pronounced on the maps of the younger (Suwannee) formation.
. The Ocala surface, northwest of the trough, is dissected by two broad drainage basins, one in Worth County and the other on the border of Tift and Irwin Counties. Each basin terminates at its widest point, where it intersects, at right angles, an elongate basin within the trough. South of the trough in Thomas, southern Colquitt and western Brooks Counties, the Ocala surface has more than 100ft of topographic relief relative to the surface eastward toward Brooks and Lowndes Counties and is at least 300ft higher than the Ocala surface in the trough. From this high the Ocala slopes gently eastward into Brooks and Lowndes Counties. Sever (1966) noted a high on the Ocala surface in approx-

imately the same area and attributed the elevated surface to arching. The data obtained during this study do not support the theory of arching. Howev.er, the Oc~la is relatively thick (600 to 700ft) in th1s area, wh1ch may suggest a depositional basin. In the eastern half of the study area, the Ocala dips southeastward toward the Southeast Georgia Embayment.
Oligocene Series
Suwannee Limestone
The most widespread Oligocene formation found in the study area is the Suwannee Limestone of late Oligocene age. Rocks of Vicksburg age have been found in isolated wells, but are of little regional significance in the context of this report. Therefore, only the Suwannee Limestone will be discussed here.
Lithology and Porosity
The Suwannee Limestone is white, granular to nodular in texture, and usually contains abundant foraminifera. The limestone is always recrystallized and is partially replaced by dolomite to varying stages at random localities. The Suwannee Limestone is usually very porous. Diagnostic foraminifera are commonly found at or near the first appearance of white limestone in cuttings and core. Included among these are Pararotalia mexicana Nutall, Lepidocyclina sp., Numulites sp., and Oictyoconus sp. Abundant molluscan and echinoid fragments are found at many localities.
In the Gulf Trough the fauna and texture of the Suwannee are not well preserved. Samples studied from the southwest segment of the trough show the Suwannee there to have the poorest preservation. The limestones in this area have been micritized and they have very little visible porosity. To the northeast alteration is not so severe; the limestone texture is not completely changed to micrite and fauna are less sparse. The result is a limestone with more apparent porosity.
Isopach Map
Outside the Gulf Trough the Suwannee Limestone is generally 100 to 200 ft thick, as shown in figure 5. In areas of local relief, thicknesses fall outside this range. For example, south of the trough the Suwannee thins to less than 100 ft in Thomas County, then thickens eastward to 220ft in Brooks County. The thin veneer of Suwannee overlies the thick basin sequence of Ocala Limestone that is shown as a topographic high in figure 4. The Suwannee thickens eastward into Brooks and Lowndes Counties where the underlying Ocala is topographically low. The Suwannee is more uniformly thick northeast of Brooks County, and gradually thins to less than 20ft in Effingham County.

143

400'

A

EXPLANATION
RECENT TO MIOCENE OLIGOCENE { SUWANNEE LIMESTONE)

30d
zoo'
tod SEA LEVEL
-1001
-zoo'
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D UPPER EOCENE (OCALA LIMESTONE)
D MIDDLE EOCENE {CLAIBORNE GROUP)

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6 11

GGS WELL IDENTIFICATION NUMBER

400' 3 00'

0~--~--Z--~3 MILES

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VERTICAL SCALE GREATLY EXAGGERATED

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Figure 3. Three representative geologic sections across the axis of the Gulf Trough .

144

EXPLANATION

STRUCTURE CONTOUR-- Showo

__ tOO-- attitude of top of the Ocala Limestone.

-

Dashed where approximately located.

Contour interval 100 feet. Datum is lftlan sea level

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EX PLANATION

\/~ A/ UGUSTP~ ,r~

LINE OF EQUAL THICKNESS

--QF SUWANNEE LIMESTONE--

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The Suwannee Limestone is thickest in the Gulf Trough , particularly in four large elongate basins. The basin in Coffee County is a downfaulted block, where the Suwannee attains a thickness of 500 to 600ft (for example GGS 1825). In a narrow band adjacent to the southside of this basin, the Suwannee is absent, and the Ocala Limestone is unconformably overlain by Miocene sediments (for example GGS 51 0). The shaded area on figure 6 shows the band where the Suwannee is absent.
Structural Surface
A map of the structural surface of the Suwannee Limestone (fig. 6) clearly shows the configuration of the Gulf Trough. A chain of deep elongate basins extends northeastward from Decatur and Grady Counties in southwest Georgia to Toombs and Tattnall Counties in the eastern Coastal Plain. The northernmost basin becomes shallow and less depressed in a northeastern direction and finally disappears in Candler and Bulloch Counties. The deep, elongate basins are separated by shallower interbasin areas. A good example of such an interbasin area is in central Colquitt County.
In Mitchell, Worth and Tift Counties the Suwannee Limestone surface is dissected by postOligocene erosion. The contour pattern on figure 5 indicates a southward-flowing drainage system. Less well-developed drainage can be seen on the northwest side of the trough in Toombs and Montgomery Counties. These drainage features, like those on the Ocala surface, terminate at the trough, where they intersect elongate basins. On the south side of the trough, drainage patterns indicating a northward flow are not found.
Certain trends on the south side of the trough are also of interest. The surface of the Suwannee slopes gently to the northeast at the rate of about 3.3 ft/mi from Thomas through western Atkinson County. In central Atkinson County, the slope changes direction to the southeast. Topographic relief on the surface of the Suwannee throughout the study area generally corresponds to relief on the Ocala Limestone surface.
During the late Oligocene, faulting occurred in several places. Faulting shaped the Toombs County basin, resulting in an abnormal thickness of Suwannee on the downthrown side of the faults that transect the basin. These fault traces are most apparent on the map showing the configuration of the top of the Ocala Limestone, since they offset the Ocala sediments. However, the fault traces are nearly healed by sediments accumulated during Suwannee time and faulting is not obvious on the map of the Suwannee structural surface.

Block faulting is thought to be the explanation for the thick section of Suwannee Limestone previously noted in the basin in Coffee County. The fault traces bounding this basin are shown on the maps of the Ocala surface and Suwannee thickness (figs. 4 and 5), and may be implied on the structure contour map of the Suwannee where the surface of the unit is depressed.
Miocene to Holocene Series
Lithology and Porosity
Miocene to Holocene sediments,as grouped collectively in this report, include the Tampa Limestone, the Hawthorn Formation, and post-Hawthorn sediments. The Tampa is the earliest Miocene unit recognized in well cuttings in this study. The Tampa overlies the Suwannee Limestone in much of the southwest portion of the report area. The earliest Miocene unit in the northeastern section of the study area is lithologically similar to the Tampa, but whether it is correlative in age is yet to be determined . The Hawthorn Formation is believed to overlie the Tampa throughout the study area. It is in the Hawthorn that certain thick sediment sequences occur that appear to be unique to the trough. No units younger than the Hawthorn Formation are distinguished in this report.
In most of the southwest portion of the report area, the basal Miocene is predominantly a white arenaceous limestone, sometimes dolomitized and phosphatic and containing sparse macro-shells. However, a significantly different basal Miocene lithology occurs in the deep elongate basins in this area. In these basins, the basal sediment~ (GGS 3179, for example) are poorly sorted sands with varying amounts of silt and minor phosphate. Overlying these sands are black waxy clays occurring as beds several feet thick that are bedded with silt and fine-to medium-grained sand.To the northeast in the Toombs County basin, the basal Miocene along the trough's flanks and in the immediate surrounding area is a gray arenaceous limestone which is occasionally dolomitic and locally very phosphatic with abundant bivalves, barnacles and gastropods. The black waxy clays characteristic of the southwestern basins are not found in the basal Miocene of the Toombs County basin.
One of the constituents of the basal Miocene unit within the trough is a breccia composed of fragments of the Suwannee Limestone. These angular clasts of Suwannee Limestone occur in an arenaceous limestone matrix. In many of the samples examined, reworked Oligocene fauna are found in basal Miocene sediments.

147

EXPLA~ATION

-200---

STRUCTURE CONTOUR-- Shoon attitude of top of Suwannn Limeatone DoMed when~ appr01.imately loeat1d. Contour interval 100 feet. Datum is m-.on Mt:J lev.a.

~ SUWANNEE LIMESTONE ABSENT

- - u -
0

- FAULT-- Dashed where approamot~ly
located , U1 upthrown side; D1 downthr0wn side.

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20

30

40 MILES

82"

Figure 6. Configuration of the top of the Suwannee Limestone surface in the Gulf Trough area.

Within the Gulf Trough, Miocene to Holocene sediments are abnormally thick as depicted in figure 7, in a zone approximately 10 mi wide which extends the entire 235 mi length of the trough. The series of narrow elongate basins contain the thickest accu mulation of sediment. The Miocene to Holocene units thin in all directions from the elongate basins.
The deep, elongate basins are very steep sided. In all probability they are fault bounded. For example, on cross section B-B' (fig. 3) the suggestion of faulting is very strong. On this cross section, GGS well 3179 in Colquitt County has a very thick Miocene to Holocene section, while the wells on each side of it show that the top of the Suwannee is hundreds of feet higher.
Faulting during the early Miocene was not restricted to shaping the Gulf Trough. The southeastern Coastal Plain appears to be significantlyaffected by an extensive offset which trends southeastward through Jeff Davis, Bacon and Pierce Counties. This offset is herein named the Big Sat ilia fault for the nearby Big Satilla Creek which it parallels. The Gulf Trough forms the northwest boundary of the fault, which may extend farther eastward toward the coast of Georgia. The Ocala Limestone and Suwannee Limestone are offset vertically 150 to 200ft by the fault (see figs. 4 and 6). The type of faulting is thought to be high-angle gravity or block faulting which may have a lateral component. Repetition of beds has not been found. The surface of the Suwannee Limestone in the Toombs County basin is 200 ft lower than the Suwannee surface in the Coffee County basin on the southwest side of this major fault. This discrepancy may be related to fault movement. As well as can be determined from existing well data, the placement of the Big Satilla fault is within a 1 mi range of the dashed line shown on figure 6. Miocene strata dip east and southeast across the fault, forming a monocline.
Structural Hypotheses
Structural development of the Gulf Trough began prior to the Oligocene Epoch. However, due to sparse well data, direct evidence of exactly when the trough began to develop is lacking. Indirect evidence from well data outside the trough suggests that the trough may have been a viable feature during late Eocene time. Lithologic trends of the Ocala . Limestone suggest that the trough may have been an area of separation between depositional environments or may have become an obstacle to the late Eocene transgressive sea. South of the trough, in the soutwest portion of the study area, the Ocala can be divided into a bioclastic, porous upper unit and a micritic, non-porous lower unit, with a significant amount of gypsum occurring at the boundary of these units and below. On the north side of the trough, only the upper porous unit is found.

Subsidence occurring during Oligocene time allowed a thick sequence of Suwannee Limestone to be deposited in the trough. Downwarping was steady and moderate over a long period of time, as shown by the fact that the Suwannee within the trough is free of clastic components and the strata are not disrupted. However, the Suwannee in the trough is generally fine grained, and contains fewer biota than normal.
High-angle gravity or block faulting occurred after Suwannee deposition and downwarping, and prior to post-Suwannee erosion. Examples are the Coffee County basin and the southwestern part of the Toombs County basin, where anomalously thick sequences of Suwannee Limestone are found. After faulting, erosion removed all the Suwannee on a portion of the southeastern, upthrown block bordering the Coffee County basin and on the northwestern upthrown block of the Toombs County basin.
Downwarping and gravity faulting continued with greater intensity into the early Miocene. Erosion of the Suwannee Limestone was one result of this intensified tectonic activity. Almost concurrently, the subsiding basins were infilled with sediment.
At first, the sediment supply came primarily from older rocks northwest of the Gulf Trough via rivers that incised larger valleys on the north side of the trough. The Suwannee Limestone contributed sediment both as fragments and as dissolved carbonate. The Suwannee south of the trough may not have been actively eroded away as that to the north, although locally the Suwannee was completely eroded away. The thick accumulation of Suwannee in the Coffee County basin may indicate that the unit was originally thicker over its entire depositional extent than the Suwannee isopach map shows. However, there is not enough evidence from other localities to support the idea that the Suwannee was originally 600 to 700ft thick. After a period of erosion, most of the Suwannee was submerged by shallow water and covered with a thin veneer of white arenaceous limestone.
Rapid subsidence accompanying erosion resulted in the Gulf Trough being filled in Miocene time with thick accumulations of poorly sorted sands, silt and beds of black waxy clays in the southeast basins and thick accumulations of white arenaceous macrofossiliferous limestone in the northeast basin. The deep basins contain over 700ft of Miocene to Holocene sediment, while in the less downwarped interbasin areas, only 400 to 500ft of sediment of this age are present. The elongate trough basins are probably bounded by disconnected faults rather than a single long fault extending the entire length of the GulfTrough. Eventually, the trough was completely filled with sediment as tectonic activity declined. This infilling healed or disguised many fault traces.

149

EXPLANATION
LINE OF EQUAL THICKNESS OF RECENT -2.00--- THROUGH MIOCENE SEDIMENTS---
Dashed where approaimotely located. lrdwwal 100 feet

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Figure 7. Thickness of Miocene through recent sediments, Gulf Trough area.

The Big Satilla fault occurred during the period of intensive tectonic activity that took place during the early Miocene. The time of movement of this fault is placed after the erosion of the Suwannee and during the deposition of early Miocene sediments.
HYDROLOGY
The area of study, like much of the Georgia Coastal Plain, is underlain by a thick sequence of late Eocene to early Miocene limestone strata that is hydraulically interconnected and is referred to as the principal artesian aquifer. Clastic rocks and carbonate rocks which belong to the Lisbon Formation (middle Eocene) form the lower confining bed of the principal artesian aquifer in the study area. The upper confining bed consists of clastic rocks and carbonate rocks of low permeability, all of which are part of the Miocene to Holocene Series. Within the Miocene to Holocene Series, the Hawthorn Formation comprises a confining or semi-confining unit for the principal artesian aquifer, although the Hawthorn is known to locally produce adequate supplies of water for domestic purposes. The Tampa Limestone and its equivalents which underlie the Hawthorn are locally considered hydraulically connected to the aquifer.
Water Availability Distribution
Water-well drillers have reported consistent problems associated with obtaining water from wells in the GulfTrough. A major problem is the great depth to which holes must be drilled (over a thousand feet in some cases) before an adequate source of water is encountered. Even wells that reach the principal artesian aquifer at great depths often yield little water, sometimes 50 gpm or less. Outside of the trough, in the southwestern portion of the study area, conditions are more "normal"; wells drilled to an average depth of 400ft in the principal artesian aquifer yield as much as 3200 gpm. In the southeastern part of the study area wells yield up to 1250 gpm, and in the northeastern portion 1000 gpm can be obtained.
The distribution of ground-water availability in the study area is shown on figure 8. This map illustrates the distribution of the specific capacity indices of municipal, industrial and domestic wells. Maximum indices are used in areas with a high concentration of wells. The shaded zone on figure 8 represents the narrow, steep gradient anomaly shown on the potentiometric map (fig . 2).
The water-availability map was constructed by plotting the specific capacity index (Davis and DeWiest, 1966) for each well selected. Specific capacity of a well is defined as the yield per unit drawdown measured in gallons per minute per foot, (gpm/ft)

Since each of the wells used for the map does not penetrate the aquifer to an equal depth, the specific capacity for each well was divided by the depth of hole open to the aquifer in the well to obtain a unit value-the specific capacity index, expressed in units of gpm/ft2. This value provides a useful method of comparing water availability in large areas where many wells penetrate the aquifer to different depths. A later publication will present the tabular data for the wells used to construct figure 8.
The symbols on the map represent ranges of the specific capacity. For example, a well in northwest Thomas County (located within the Gulf Trough) yielded 175 gpm with 94ft of drawdown. The well penetrates 548 ft of the principal artesian aquifer. Its specific capacity index is:
175 gpm
94 ft = .003 g pm/ft 2
548ft
a This figure signifies a very low production well. On
the other hand , well in central Thomas County (located outside the trough) yielded 3200 gpm with 9ft of drawdown and an aquifer penetration of 242 tt, with a specific capacity index of 1.47. This is considered an excellent well.
Wells can be divided into two categories based on specific capacity: those outside the Gulf Trough and those within its boundaries. For wells located outside the Gulf Trough , the specific capacity indices increase from the northeast to the southwest. To the northeast in the Toombs-Tattnaii-Bulloch County area, the specific capacity index ranges from 0.01 to 0.9. In the central part of the study area values ranging from 0.1 to 0.9 are common. Farther southwest in the Tift-Thomas-Grady County area, specific capacity indices as high as 10.0 are often found. For wells located within the Gulf Trough , specific capacity indices are everywhere lower than those outside. Wells within the trough show a marked decrease in specific capacity index from northeast to southwest, a trend opposite that shown by wells outside the trough. The lowest yielding wells in the entire study area are located in the southwestern segment of the Gulf Trough.
The specific capacity index increases southward, away from the trough . On the south side of the trough in northern Colquitt County, the index ranges from 0.01-0 .09; southward toward central Colquitt County, the values increase from 0 .1 to 9.0. This trend indicates a change in aquifer permeability with the higher permeability occurring away from the trough. Such a permeability change would occur if less permeable material were downfaulted forming a subsurface barrier which would impede the southeastward flow of ground water.

151

EXPLANATION

SYMBOL

RANGE OF SPECIAC CAPACITY INDEX (GPII/112)

0

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ZONE OF POTENTIOMETRIC ANOMALY

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In effect, the Gulf Trough behaves as just such a barrier to ground-water flow. In Colquitt and southern Tift Counties and southwest to Decatur County, thick Miocene clastics help form this barrier. Water movement across the deeper basins in the trough is probably minimal; most water probably flows across the trough interbasin areas, where Miocene sediments are thinner. In addition, many wells drilled in the deep basins are completed in the Miocene; very few wells penetrate the upper surface of the Suwannee Limestone, which comprises the upper part of the aquifer. The barrier effect of the trough is shown on the potentiometric map (fig. 2). North of the trough, water moves laterally eastward and westward toward major rivers rather than to the southeast across the trough.
Within the trough itself more water is able to flow across the deep basin in the northeastern area because, unlike the other deep basins, this one is filled with a thick sequence of early Miocene arenaceous limestone that contains abundant macrofossils, has moderately developed secondary porosity and is hydraulically connected to the principal artesian aquifer. In addition, the Suwannee Limestone is more porous in this area of the trough than in the southwest. Therefore, ground-water availability from the northeastern area is reflected by more moderate specific capacity indices.
SUMMARY
The Gulf Trough is a long, narrow geologic feature that was produced by a combination of depositional and structural conditions. The trough is approximately 235 mi long, about 10 mi wide, and trends N53 E from Decatur through Bulloch Counties. A chain of elongate, narrrow, deep basins exists with the Gulf Trough. These basins are separated by interbasin areas which are topographically higher than the basins but are considerably lower in elevation than the area outside the trough.
Development of the GulfTrough began, at least as early as Oligocene time, with subsidence of several elongate basins and infilling of these basins with a thick sequence of Suwannee Limestone. Faulting occurred in limited areas, forming parts of two basins.
During the early Miocene, development of the trough accelerated as downwarping and faulting deepened the basins that formed during the Oligocene. Erosion of the Suwannee Limestone surface resulted in the development of surface drainage and contributed to the sediment supply for the trough. Erosion left the Ocala Limestone exposed along the south rim of the Coffee County basin and left thin veneers of Suwannee Limestone rimming the other basins.

Movement along the Big Satilla fault occurred during the early Miocene, after the Suwannee was eroded. The result is that the eastern third of the study area is downthrown 150 to 200ft with respect to the southwest portion of the study area.
During the middle Miocene, as the tectonic activity declined, , the basins were completely filled and fault scarps were healed over by sediments.
The GulfTrough is coincident with a steep potentiometric gradient anomaly on the potentiometric map of the principal artesian aquifer. Both the trough and the anomaly extend from Decatur County in southwest Georgia northeastward to Bulloch and Effingham Counties,wherethey disappear. The Gulf Trough creates the potentiometric anomaly and, by acting essentially as a vertical boundary to ground-water flow, is responsible for reduced ground-water availability.
Several problems remain to be solved, including: 1. The determination of the mechanisms that
created the Gulf Trough. 2. The quantification of the effects of the Gulf
Trough on the aquifer such as permeability, transmissivity, recharge and water quality. 3. The redefinition of the geologic and hydrologic data by drilling test wells and conducting aquifer tests.
REFERENCES CITED
Dall, W.H., and Harris, D., 1892, Correlation Papers: Neoc~ne: U.S. Geol. Survey Bull. 84,349 p.
Davis, S.N., and DeWiest,R., 1966, Hydrogeology: New York, John Wiley and Sons, Inc., 463 p.
Herrick, S.M., 1973, Subsurface geology of the Ocala Limestone, Cooper Marl, and Suwannee Limestone in Georgia: Unpub. rept., on file at Georgia Geol. Survey, Atlanta, Ga.
Herrick, S.M ., and Vorhis, R.C., 1963, Subsurface geology of the Georgia Coastal Plain: Georgia Geol. Survey Info. Circ. 25, 80 p.
Hester, W.G., and others, 1977, Potentiometric surface of principal artesian-Fioridan aquifer in Southeastern Georgia and northeastern Florida, January-May 1976: U.S. Geol. Survey, openfile map.
Sever, C.W., 1966, Reconnaissance of the ground water and geology of Thomas County, Georgia: Georgia Geol. Survey Info. Circ. 34, 14 p.

153

GEOLOGICAL EVALUATION OF POTENTIAL PIPELINE CORRIDOR SITES ALONG THE GEORGIA COAST
Vernon J. Henry and Robert T. Giles University of Georgia
Department of Geology and Marine Institute, and Skidaway Institute of Oceanography Savannah, Georgia
and
James L. Harding University of Georgia Marine Extension Center
Savannah, Georgia

ABSTRACT
In anticipation of the onshore impacts that will result from offshore oil and gas production, the Georgia State Office of Planning and Budget, in 1977, instigated a highresolution seismic and sidescan sonar survey of the Georgia coast as a first step in evaluating optimal locations for pipeline corridors. The principal objective of the survey was to determine the presence and nature of physical and geological hazards and constraints to pipeline emplacement and stability in the upper 15m of the estuarine/nearshore zone to a distance offshore of 5 km.
Areas containing a high degree of risk, or hazard, to pipeline stability were eliminated as potential pipeline corridors, while areas containing moderate to low risks, or constraints, must be given due consideration in developing engineering design criteria or in planning alternative routes.
Except for possible shallow faults or karst features 3 km seaward of the south end of Jekyll Island and in the Brunswick River, approximately 1 km southeast of the Sidney Lanier Bridge (U.S. Highway 17), conditions considered hazardous to pipeline stability are limited to (1) major sounds and rivers where severe bottom scour and/or bottom instability occurs in ebb deltas and inlet throats, and (2) shoreline segments with a history of significant erosion.
INTRODUCTION
Contracted by the Georgia Office of Planning and Budget in 1977, this study centered on a highresolution seismic and sidescan sonar survey of the coast from approximately 5 mi offshore into inlets and estuaries for the purpose of obtaining information on the physical and geological characteristics of the surface and shallow subsurface deposits. Such data are directly applicable to pipeline route siting decisions which would be required of the S!ate of Georgia as a result of outer continental shelf petroleum activity. Objectives were to identify

or infer geologic constraints and potential hazards, such as soil instability, active bottom scour, faults, cut and fill structures, buried river channels, shallow rock outcrops, shoreline erosion, and mobile bottom features, such as sand waves.
Specific geological characteristics identified in the present study that are considered to be potential hazards and constraints to pipeline route siting are discussed. The surveys were designed to narrow the scope of later phases of evaluation so that any area identified by the initial seismic/sonar surveys as being hazardous could be eliminated from further study and consideration as a pipeline corridor.
ACKNOWLEDGEMENTS
Gregory J. Nash ably assisted in all facets of the field operations and with preparation of maps and figures. The facilities and services provided to the University of Georgia Marine Geology Program by the Skidaway Institute of Oceanography are gratefully acknowledged.
METHODS AND PROCEDURE
Geological field data were acquired during the period April- December, 1977. Seismic/sonar instrumentation consisted of a high-resolution seismic profiling system (EG&G Model 255 UNIBOOM), a sidescan sonar system (EG&G Mark IB), and a 3 cu in. air gun system (Bolt, Associates).
The UNIBOOM and sidescan sonar were operated along track lines approximately 1.5 and 3 mi offshore of the barrier islands and parallel to the regional strike of the coastal deposits. Selected lines were run perpendicular to the shoreline along regional dip. Track lines in the sounds and tidal channels behind the islands were chosen on the basis of prior coverage and accessibility. The air

154

gun survey was carried out along the Atlantic Intracoastal Waterway as well as along a track approximately 5 mi offshore from St. Marys Entrance Channel to Wassau Sea Buoy .
Research vessels used in the survey were the 22m KIT JONES and the 14m SPARTINA, operated by the University of Georgia Marine Institute on Sapelo Island, and the 24 m BLUE FIN operated by the Skidaway Institute of Oceanography, Savannah, Ga. Inshore navigation was by sight fixes on topo map-identified land/ cultural features and channel markers, and by radar ranging and Loran A off the island fronts.
The identification of geological constraints and hazards resulting from the sidescan sonar and UN IBOOM surveys is presented in maps 1-4. Unless deeper structural hazards were present, only the top 15m of the UN IBOOM data were utilized in preparing maps 3 and 4, as depth of pipeline burial would be well within this interval. A summary of hazards and constraints is given in map 5.
EXPLANATION OF TERMS USED IN EVALUATION OF DATA
General Discussion
The terms" constraint" and" hazard" relate to geological conditions as well as long- and short-term energy levels affecting the physical environment. A constraint is considered to be a geological or physical condition for which engineering criteria can be established and incorporated into the pipeline design so as to safely and economically mitigate detrimental effects. Examples of such constraints are active bottom features, such as sand waves, and the variation in geotechnical properties in sediments associated with buried river channels and cut and fill structures that result from channel migration. Hazards, on the other hand, are geological or physical conditions that impose a relatively high degree of risk to pipeline stability and integrity. Hazardous conditions would involve faulting, slumping or slope failure, and s~vere scour. The length of time over which an .event occurs and the rapidity at which it is initiated are important factors in determining constraints or hazards to pipeline stability. Short-term events such as faulting, storm scour, and shoreline erosion present severe hazards compared with longer-term events associated with the movement of large sand waves, the development of mid-island shoals, and geotechnical conditions, such as differential compaction .
Hazards
Scour
Scour refers to the removal of bottom sediment by wave and/or current action. Storms can cause

immediate and marked increases in horizontal and vertical stresses superimposed on the normal or steady-state conditions. Even under relatively low energy conditions, the cumulative effects of waves and currents may eventually expose a buried pipeline. Scour potential increases where the bottom is composed of easily erodible materials and/or is topographically irregular. Scour can undermine a pipeline causing it to rupture-a condition described as " spanning" (Kreig, 1965).
Faults
A fault is a hazard because, even if inactive, it represents a plane or zone of weakness along which movement of unpredictable occurrence and extent could be initiated by even minor seismic activity or subsidence associated with ground-water removal. Although consolidated sediments typically present in the shallower portions of coastal plain formations can undergo considerable movement without fracturing, such displacement could cause pipeline rupture.
Constraints
Mobile Bottom Features-Sand Waves and Giant Sand Waves
Small sand waves (wave length< 1Om, amplitude< 30 em) indicate the presence of lower velocity currents associated with wave action and/or normal tidal currents, both of sufficient velocity to place unconsolidated material in motion resulting in minor bottom scour. Large sand waves (wave length> 10 m, amplitude >30 em) indicate significant scour by higher velocity currents associated with storms and possibly spring tide conditions.
Large sand waves and giant sand waves (wave lengths> 100 m) represent ongoing and/or periodic processes associated with strong tidal and/or storm currents. Because their presence infers mobility as well as an adjacent area of significant scour, the larger sand waves are considered to be a constraint with regard to route selection. Neither the frequency nor the rate of movement of these features is known for the Georgia Bight.
Shallow Rock or Other Resistant Material
Depending on the intensity of lithification, the occurrence of shallow rock along a potential pipeline route could be merely a constraint to burial of the pipeline, or could actually prevent burial because of the costs involved. In any case, the most serious condition would exist at the boundary between the rock or other resistant material, such as dense clay layers, and adjacent unlithified or unconsolidated sediment where abrupt changes in grain size and composition could cause differential compaction and consequent bending or rupturing of the pipeline.

155

Subsurface Sedimentary Structures
Several types of large sedimentary features common to coastal deposits exhibit wide variability in grain size, mineralogy, water content, chemical composition, and compactibility. Such geotechnical conditions can result in significant changes in bearing capacity along a pipeline route leading to differential compaction and consequent spanning of the pipeline.
High-Angle Bedding-Areas of high-angle beds are considered to be potential constraints because this type of bedding indicates rapid deposition with little or no reworking after deposition. Large contrasts in bearing capacity almost certainly exist between the relatively poorly ~orted stream deposits and the containing strata. Also, the bearing capacity of the gravels, sands, and clays that commonly comprise alluvial deposits in this region can vary markedly over short horizontal or vertical intervals.
Buried River Channels-Buried stream channels are considered to be potential constraints due to large contrasts in bearing capacity between the rei-

atively coarse, probably high water content, deposits and adjacent, often finer-textured, sediment. Also, as with the high-angle beds, the texture of the channel deposits can vary significantly over short horizontal or vertical intervals, causing differences in bearing capacity that could result in fatigue failure or flotation of the pipeline.
Cut and Fill Structures-Cut and fill structures are formed by lateral migration of stream channels. Interlayering of sand and clays and other textural contrasts can result in differential compaction along the pipelong route.
OCCURRENCE AND DISTRIBUTION OF HAZARDS AND CONSTRAINTS
Bottom Survey Using Sidescan Sonar
Sidescan sonar records (sonograms) augmented by UN IBOOM and fathometer profiles were used to map areas of scour, sand waves, and outcrops of resistant material (see maps 1 and 2).

GOPB Project-UUAJanuary 1978

Norlh

S ope.Jo Sa\lnd
156

MAPl
BOTTOM SURVEY I SIDE SCAN SONAR POTENTIAL HAZARDS AND CONSTRAINTS

............._. SAND WAVES llen'illh ovr 100m I

W $

SAND WAVES llenQih 10- 100m I

.~ ....S .....C ....O . UR

~ OUTCROPS OF RESISTANT MATERIAL
~

~

FIGURE LOCATION

SCALE

10

1$

GOPil Project-UGAJanuary 1978

Bollvillo River

Doboy Sound Allomoha Sound

--'t
St Andrew Sound
MAP 2
BOTTOM SURVEY I SIDE SCAN SONAR POTENTIAL HAZARDS AND CONSTRAINTS

Sl. Meryl River
FLA.
Scour
Severe scour is present in ebb tidal deltas, at bends and intersections of tidal rivers and streams, and within the sounds and entrance channels to depths of over 25m . Severe scour is present also in each of the major sounds. An example of scour in Sapelo Sound is shown in figure 1. The shifting or

G) FIGURE LOCATION
SCALE
-=-=~====~5----1~0==~5
kilometer
Entrance
migration of major ebb and flood tidal channels associated with the tidal deltas also produces scour of the channel walls. This is a normal condition which may be significantly intensified during severe storms . This type of scour is inferred by bathymetry, the presence of large bedforms, and by channel migration. Documentation of the latter process is based on the comparison of historical and contemporary hydrographic charts by Nash (1977) .

157

Mobile Bottom Features-Sand Waves and Giant Sand Waves

Small sand waves (megaripples) with wave lengths

less than 10 m were the most common bedform

encountered. In offshore areas they were usually

associated with and often irregular sand sheets (figs.

on 2,

3t,haensdu4rf)a. cTeheoflalottwe~

features are less than 0.5 m relief. Small patches of

megaripples not associated with sand sheets occur-

red randomly and relatively rarely. Fields of meg-

aripples were commonly present in tidal rivers.

Neither megaripples nor the sand sheets are consi-

dered to constrain pipeline emplacement or stabil-

ity.

Large bedforms were found associated only with tidal rivers, sounds, and ebb tidal deltas. Giant sand waves were found in St. Marys Entrance, St. Andrew Sound (fig. 5), Doboy Sound, Sapelo Sound (fig. 6), and the Brunswick River. Large sand waves were found in all sounds, entrance channels, and larger rivers. They are particularly well developed in Sapelo Sound, Altamaha Sound (fig. 7), and in St. Catherines Sound (fig. 8). The larger bedforms associated with sounds and entrance channels displayed a variety of geometric shapes and orientations. Smaller sand waves were commonly superimposed on larger sand waves with the two size

groups in differing orientation. Sand transport in these areas is obviously controlled by complex current systems.
Outcrops of Resistant Material
Areas of outcrop were commonly observed where scour or dredging operations have exposed rock or other resistant strata, such as dense clay or marl. Outcrops of resistant material were primarily identified in the southern half of the Georgia coast including dredged portions of the Turtle and Brunswick Rivers (fig. 9), the Intracoastal Waterway south of St. Simons Sound and the Kings Bay entrance channel, portions of the Satilla and St. Marys Rivers, Cumberland Sound and the St. Marys Entrance Channel. Most of the outcrops in the region from Brunswick to St. Marys are thought to be limestones and marls of the Pliocene Charlton Formation (Woolsey, 1977).
Subbottom Survey Using High-Resolution Seismic Technique
High-resolution subbottom profiling (UNIBOOM and air gun) was used to identify subsurface structures and sedimentary features defined as hazardous or posing constraints to pipeline emplacement or stability (see maps 3 and 4).

GOPB Projcci-UGAJanuary 1978

- 10 meter dapl.fto

Norlh
Bellville River - ...: .q-

S t. Cclherines Sound
Sapelo Sound
158

MAP 3

SUB BOTTOM SURVEY I UNIBOOM AND AIR GUN
POTENTIAL HAZARDS AND
CONSTRAINTS

~ ~
W.Y.%'-1
tWB! ~

HIGH ANGLE FORESETS DUfiii: C Ct'I~ NN f"-5 CUT &. Fill POSSIBLE FAULT
FIGURE LOCATION

S c; ALE
~~~0==~----'0==~' kilometer

GOPO Pruj~c!-UGA January 1978

Doboy AUomoho Sound

SI Andrew Sound
MAP4
SUBBOTTOM SURVEY I UN I BOOM AND AIR GUN
P 0 T E N.T I A L H A Z A R D S AND
CONSTRAINTS
HIGH ANGLE FORESETS BURIED CHANNELS CUT !I FILL POSSIBLE FAULT
FIGURE LOCATION
SCALE

Sl Mory1 River
FLA.

High-Angle Beds
High-angle beds with ~ips up to60 m/km underlie the Georgia coastline within 15 m of the bottom between the Vernon and Satilla Rivers. These features probably represent foreset beds of extensive coastal deltas that were active during the Pliocene (Woolsey, 1977). The zone of foreset beds ranges in thickness from 26 m in St. Catherines Sound and Doboy Sound to a maximum of 30 m and 34 m in

Sapelo Sound (fig . 10) and Altamaha Sound , respectively.
South of Village Creek, the foreset trend is located predominately offshore and appears to extend southward along the Florida coast as reported by Meisburger and Field (1975). In the Altamaha Sound and off Cumberland Island the top of the foresets is deeper than 15 m below the bottom.

159

A shallower, somewhat thinner zone of highangle beds that cut into the underlying foreset beds also is present beneath the Georgia coast. These beds appear to be Quaternary deltaic deposits, occur infrequently, and are best developed near the mouth of the Hampton River beneath Village Creek (fig. 11) and behind Sapelo Island where the zones are 30 m and 20 m thick, respectively.
Buried Stream Channels
Buried stream channels are present both offshore and beneath the salt marshes and estuaries behind the barrier islands along the entire Georgia coastal zone (see maps 3 and 4 and fig. 12).
Offshore, buried stream channels of Pleistocene (?)age occur extensively between Tybee Roads and WassawSound (fig.13). Channels from0.5 km to 1.5 km wide and cut to 10 to 25 m below the bottom underlie3 to20 m of horizontally bedded sediments interspersed with cut and fill structures. Buried channels are found from near Wassaw Sound entrance (just south of House Creek on Little Tybee Island) to more than 6 km from shore. A large channel incised to 25 m below the bottom of Wassaw Sound is located just north of Wassaw Island (fig. 14) and several buried channels, generally 2 km or less from shore, are present between St. Catherines and Altamaha Sounds. Numerous channels are present about 1 km north and south of McQueens Inlet near the center of St. Catherines Island. Depths range from 2 m to 23 m below the bottom, the deepest being about 2 km from shore.
Between St. Andrew Sound and St. Marys Entrance, several buried channels are present within 2 km of shore and extend to less than 20 m below the bottom. Numerous buried channels occur in the vicinity of Stafford Shoals near the center of Cumberland Island. On either side of the shoals, the channels are overlain by 2m to 20m of horizontally bedded sediment.
Few buried channels are present between St. Simons Sound and Cumberland Sound, although several less than 30m deep occur behind Cumberland Island.
Cut and Fill Structures
Although most cut and fill structures occur in deposits beneath the streams and estuaries behind the island, they are common in Doboy Sound, Altamaha Sound, St. Marys Entrance, St. Catharines Sound, and the area offshore of Little Tybee and Tybee Islands where they extend to less than 15 m below the present bottom and in zones generally less than 1 km in lateral extent.

The Duplin River behind Sapelo Island is underlain by cut and fill structures that occur throughout a zone more than 2 km wide and extend to 12 m below the present bottom (fig. 15). Cut and fill structures beheath Village Creek generally extend 8 m to 20m below the bottom and are superimposed on the deeper buried channels and high-angle foreset beds (fig. 16). Structures extending 10 m to 12 m below the bottom occur behind St. Simons Island in both McKay and Frederica Rivers. South of St. Simons Sound, cut and fill structures are rare except along the St. Marys and Satilla Rivers.
Possible Faults
Two possible faults were found in the survey area, one on the Brunswick River just southeast of Sidney Lanier Bridge at Brunswick (fig. 17), and the other 2.5 km offshore from the south end of Jekyll Island (fig. 18). In the Brunswick River locality, acoustic penetration was poor, only about 20m, and multiple reflections resulting from rock cropping out in the channel bottom obscured acoustic returns below this depth. In the Jekyll Island locality, a zone of broken and reverse-dip reflectors more than 1.2 km wide and extending to at least 45 m below bottom was present. However, there was no indication of an extension of this feature in any direction. Both features may be solution collapse structures associated with underlying calcareous rocks.
SUMMARY OF DISCUSSION OF PIPELINE CORRIDOR EVALUATION
Areas considered to contain sufficiently hazardous geological and physical conditions to warrant elimination as potential pipeline corridors are shown on map 5. Except for the two sites indicated as possible faults, hazardous areas are limited to the outer portion of sounds, the inlet throats between the islands, the entrance channels and the ebb tidal deltas seaward to the 6m contour. The severe scour associated with migrating channels and the large sand waves present were the principal criteria used in evaluating these areas. The probable effects of storms and hurricanes on these areas were also considered.
Severe scour also is present in the more restricted localities of bends and intersections of tidal streams, and significant scour occurs within a 5 km inshore zone in association with sand waves and other large mobile bedforms. However, these conditions are not only localized, they are scattered throughout the coastal zone and must be dealt with on a site-specific basis. Furthermore, areas of scour in tidal rivers, streams, and creeks are predictable and can be taken into account in route planning.

160

MAP 5

SUMMARY OF HAZARDS AND CONSTRAINTS

Hazards

e Po..lble Flult

= =

Areas of Severa Scour - Sounda, Inlets, and Ebb Tldll Deltas

Constraints
Areas with or Underlain by High Angle Foreaet Bedding, Burled River Channels, and Cut and Fill Structures
Areas Underlain by Rock< 15 m Below Surface

Areas Free from Slgnlflcant Constraints Marsh Areas Urban Areas

161

Geological and physical constraints do not singularly prohibit pipeline emplacement or stability. They should, however, be given due consideration in pipeline design and in considering alternative routing of pipelines. Also, such constraints could reinforce ecological or other considerations to the extent that a coastal segment is declared unsuitable as a pipeline corridor.
Based on historical trends of shoreline erosion, pipeline landfall should not be made on the northern one-third of the Georgia barrier island or at any points where a breakthrough has occurred or is likely to occur, such as on the southern portion of the Cumberland Island.
Relative to pipeline corridors across salt marsh areas, it is recommended that any such routes be sited adjacent to the existing causeways connecting Jekyll-St. Simons Islands and Tybee Island to the mainland in the Brunswick and Savannah areas, respectively.

REFERENCES CITED
Kreig, J.C., 1965, Criteria for planning an offshore pipeline: Jour. Am. Soc. Civil Eng., Pipeline Div., v.91, p.15-37.
Meisburger, E.P. and Field, M.E., 1975, Geomorphology and sediments of the Florida Atlantic inner continental shelf, Georgia to Cape Canaveral: U.S. Army Corps of Eng., CERC Tech. Memo 54, 119 p.
Nash, G.J., 1977, Historical changes in the mean high water shoreline and nearshore bathymetry of South Georgia and North Florida: Unpub. thesis, Univ. Georgia, Dept. Geology, Athens.
Woolsey, J.R., 1977, Neogene stratigraphy of the Georgia coast and inner continental shelf. Unpub. dissertation. Univ. Georgia, Dept. Geology, Athens.

Figure 1.

Severely scoured area in Sapelo Sound. Note the presence of sand waves in the deeper portion of the scour trough. Ebb flow is toward right of figure. Distance between scale lines is approximately 25m. Location of figure is shown on Map 2.

162

Figures 2. & 3.

Central portion of Cumberland Island on Stafford Shoal. Irregular migratory sand sheets have developed down current from scoured areas (B). Megaripples (A) with wave lengths generally less than 1 m are superposed on the sand sheets. Scour troughs have depths of less than 1 m. Distance between scale lines is approximately 25 m. Location of figures is shown on Map 2.

163

Figure 4.

North end of Wassaw Island showing irregular, sinuous sand sheets. Darkened areas are caused by the presence of megaripples (A) on the surfaces of the sand sheets resulting in strong acoustic signature. Scoured areas (B) are present. Distance between scale lines is approximately 25 m. Location of figure is shown on Map 1.

Figure 5.

Giant sand waves (wave lengths up to 107 m and heights up to 2.5 m) 3 km off the north end of Cumberland Island within St. Andrew Sound ebb tidal delta. Note the strong ebb tide-oriented asymmetry with subparallel megaripples (wave lengths up to 4 m) superimposed on the flanks . Ebb flow is toward right of figure. Distance between scale Iines is approximately 25 m. Location of figure is shown on Map 2. UN IBOOM interference pattern is shown at A.
164

Figure 6.

Giant sand waves in Sapelo Sound with distinct ebb tide asymmetry. Large megaripples are superimposed on the sand waves . Ebb flow is toward right of figure. Distance between scale lines is approximately 25 m. Location of figure is shown on Map 1.

Figure 7.

Sand wave field with strong ebb tide asymmetry in Altamaha Sound . Megaripples occur in a subparallel alignment on the flanks of the larger waves . Ebb tidal flow is toward right of figure . Distance between scale lines is approximately 25 m. Location of figure is shown on Map 2.
165

Figure 8.

Entrance channel of St. Catherines Sound. Sand waves (wave lengths up to 17 m and heights up to 2 m) and megaripples (wave lengths 4-8 m) with different orientations are shown indicating a complex tidal current pattern. This section of record was taken crossing the scoured entrance of channel. The depth at the center of the channel is approximately 18m. Ebb flow is into the figure. Distance between scale lines is approximately 25 m. Location of figure is shown on Map 1.

Figure 9. Outcrops of resistant material (A) , probably Pliocene limestone, exposed by scour and/or dredging in the Brunswick River near the Sidney Lanier Bridge. A small field of sand waves occurs in the upper righthand corner of the record. Distance between scale lines is approximately 25 m. Location of figure is shown on Map 2.
166

Figure 10. Sap_elo Sound entrance channel abeam buoy N"8". West to east transect-left to right on profile. Highangle beds extend to within 10 m of the bottom. Distance between scale lines is approximately 8 m. Location of figure is shown on Map 4.

Figure 11 .

Figure 12.

Figure 11 . Village Creek, St. Simons Island, about2.5 kmfrom entrance into Hampton River. Transecteasttowestleft to right on profile. Pliocene foreset beds overlain by Pleistocene(?) cut and fill deposits. Foreset beds extend to within 10 m or less of the present bottom . Distance between scale lines is approximately 8 m. Location of figure is shown on Map 4.
Figure 12. Hudson Creek at Meridian dock, Sapelo Island. Transect northwest to southeast- right to left on profile. Buried stream channel approximately 50 m wide, cut to a depth of nearly 20m below the present bottom and overlain by up to 7.5 m of modern sediment. Scour to the left of buried channels is 7 m deep. Distance between scale lines is approximately 8 m. Location of figure is shown on Map 4.

167

Figure 13 . Wassaw Sound just north of northeast corner of Wassaw Island . Transect west to east- left to right on profile. Buried channel cut into Pliocene strata to a depth of over 35m below present bottom and overlain by up to 20m of sediment containing Pleistocene(?) cut and fill structures. Distance between scale lines is approximately 8 m. Location of figure is shown on Map 3.
Figure 14.. Offshore of Tybee Island 16 km east of the north end of Wassaw Island. Transect approximately northeast to southwest- right to left. Buried channels cut to 30m below the present bottom and overlain by up to 10 m of nearly horizontal younger Pleistocene/Holocene sediment. Distance between scale lines is approximately 8 m. Location of figure is shown on Map 3.
Figure 15. Duplin River near intersection with Barn Creek, Sapelo Island. Transect north to south- right to left on profile. Quaternary cut and fill structures to depths near 10 m below the present bottom. Distance between scale lines is about 8 m. Location of figure is on Map 4 .
168

Figure 16. Village Creek near Musgrove Plantation, St. Simons Island . Transect nearly north to south -left to right on profile. Pliocene foreset beds overlain by Pleistocene(?) foreset beds. Incised channels and cut and fill structures overlie the younger foresets. Distance between scale lines is approximately 8 m. Location of figure is on Map 4.

Figure 1i . t:lrunswick River 1.3 km southeast of Sidney Lanier Bridge (Hwy. 17). Transect northwest to southeastleft to right on profile. Possible fault or filled sink hole affecting a zone about 100 m wide . Distance between scale lines is approximately 8 m. Location of figure is shown on Map 4.

-- ~
~

--

--

-

--

---

.
---

-

-

:
--"' -

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..:;~---

-

--

---

---

-

-

- - ---- - - ;- - - -

. .: - - - -: - :. - - :.,. - - -~- - ~ - - - - ~ ~ :~,-~ ;-r- - - - - - - - - - - - - :-- ..: - - - - - - - - - -
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Figure 18. St. Andrew Sound , south end of Jekyll Island, about3 km offshore. Transect north to south- right to left on profile. Possible fault extends from 7 m to at least 40 m below the bottom . Distance between scale lines is approximately 8 m. Location of figure is shown on Map 4.
169

RELICT FRESH GROUND WATER OF THE U.S. ATLANTIC CONTINENTAL SHELF: AN UNEVALUATED BUFFER IN PRESENT-DAY SALTWATER ENCROACHMENT
F.A. Kohout U.S. Geological Survey Woods Hole, Massachusetts

ABSTRACT
Although extensive water-resources investigations have been made on the mainland of the Atlantic seaboard, observations made during the U.S. Geological Survey AMCOR (Atlantic Continental Margin Coring) Project of 1976 indicate that our knowledge of the offshore extent of freshwater aquifers is primitive . A line of 5 test holes off the New Jersey coast showed that relatively fresh ground water (less than 5 g/kg chloride) forms a lens about 200m thick extending about 100 km offshore. Similar conditions appear to exist in some aquifers off Massachusetts , Long Island (New York), Delaware, Maryl and, the Caro linas, Georgia, and Florida. Apparently, aquifers underlying the continental shelf were extensively flushed of salt water during low stands of Pleistocene sea level. As sea level rose and rapidly flooded the shelf' about 8000 years ago, the fresh water was trapped beneath clay-confining beds. An implication of present findings is that this relict fresh ground water presently serves as a temporary buffer to present-day saltwater intrusion in coastal well fields wherein heavy pumpage has caused water levels to decline to as much as 35m below sea level. There exists a great need for identifying the offshore location and nature of the fresh saltwater transition zone, the thickness and offshore ex ten t ott he aqu lfers, and the properties of their overlying confining beds to defi ne better the Initial and boundary conditions needed for predictive mathematical modeling of sa ltwater encroachment adjacent to coastal well fields.
INTRODUCTION
Possibly the most spectacular exhibit of the occurrence of fresh ground water beneath the Atlantic continental shelf was obtained during the JOIDES (Joint Oceanographic Deep Earth Sampling) drilling project of 1965. Figure 1 shows flow from test hole J-1 8, 40 km east of Jacksonville, Fla., taken from the deck of the Caldrill drilling vessel (Kohout, 1966 , fig. 6). The well flowed vigorously from the drill pi!:Je at 5 m above sea level after penetrating Eocene limestone about250 m below sea level. The chloride content of the water was about 0.7 g/kg. The pressure head was measured by closing in the well and carrying an attached garden hose up the derrick until the flow stopped at about 10 m above sea level (Kohout, 1966; G.W. Leve and R.L . Wait, oral commun. 1965). This is the only known groundwater pressure-head measurement that has ever been made for a test hole drilled on the continental margin of the United States.

In 1976, the drilling of 22 test holes during the U.S. Geological Survey AMCOR (Atlantic Continental Margin Coring) Project, for the first time, provided some indication of the offshore extent of relatively fresh ground water in subsea-floor aqui fers. The test holes were drilled to a rnaximum depth of 305m below the sea floor. Salinity of interstitial water was determined from 175 samples of pore water squeezed from sediment cores with a hydraulic press. The technique is described by Manheim {1966) . The refractive index of the water varies with sa linity and quick eva luation was accomp lished on shipboard shortly after core recovery with an EN DECO refractometer1. The original salinity values were reported in Hathaway and others (1976);the remaining water was heat sealed in a polyethylene pipe for later chemical analysis.
In 1976 and 1977, test holes were drilled through freshwater aquifers to basement rocks on Nantucket Island and Martha's Vineyard Island (respectively, 64 and 32 km off the New England mainland). This paper utilizes the offshore salinity information, augmented by data from onshore wells, to provide a preliminary view of the probable extent of relatively fresh ground water under the continental Shelf.
Geologic Framework
In general, sediments of the Atlantic continental margin thicken seaward and the aquifers do not crop out on the shelf. The sediments are mainly clastic at the north and grade increasingly to carbonates south of Cape Hatteras, N.C. Geologic formations of Jurassic, Cretaceous, and Tertiary age, generally cal led coastal plain sediments, typically dip seaward to form a thickening wedge of sediments overlying crystalline basement rocks. Pleistocene sediments that mantle the shelf tend to be fine grained in the south with increasing amounts of sand and gravel off the New England coast where g~acial outwash influenced deposition.
General Considerations and Definitions
1. The continental shelf is defined as extending from the shore seaward to the 200-m isobath.

Any use of trade names and trademarks is ror descriptive purposes only and does not constitute endorsement by the US Geological Survey
170

Figure 1.

The natural freshwaterflow from JOIDES test hole J-1 B, 40 km offshore from Jacksonville, Fla ., being sampled by G .W. Leve, U.~ . Geological Survey. The top of the pipe protrudes through the drilling hole in the center of the Caldrill drilling vessel to about 5 m above sea level. The bottom of the drill pipe was set opposite Eocene limestone about 250 m below sea level at the time of the photograph . Photo by R.L. Wait, U.S. Geological Survey.

2. A gradational zone of diffusion usually exists between fresh water and seawater in a coastal aquifer. Salinity in the zone of diffusion ranges from low values in fresh ground water (defined as containing less than 1 g/ kg of dissolved solids) to seawater of about 35 g/ kg (35,000 ppm) .
3. The Environmental Protection Agency (EPA) has designated total dissolved solids of 10,000 ppm (1 0 g/kg) as the boundary for protection of freshwater aquifers (U .S. House of Representatives, 1974). Zones of higher dissolved solids can be used for injection of industrial wastes, whereas aquifers conta ining less than 10,000 ppm are to be protected as potential water sources or feed stock for desalting plants . The 10 g/ kg salinity boundary occurs fairly close to the middle of the zone of diffusion where maximum salinity gradient takes place-the concentration depth curves usually becoming asymptotic toward freshwater and also asymptotic toward

seawater. The 10 g/ kg boundary is hydrologically significant, has quasi-legal status as used by EPA, and, therefo re, is considered useful as a mapping criterion for indicating areas of major water-resources interest in this documentation .
4. Water-table aquifers are eliminated from consideration because of their local nature and because discharge is generally complete at distances less than 1 km from shore. On the other hand, artesian aquifers protected by relatively low permeability confining beds can exend long distances offshore beneath the continental shelf. Low stand of sea level during the Pleistocene glacial maximum uncovered large areas of the shelf and infiltration of rainfall took place over extended periods of time. Rise of sea level rapidly flooded the shelf about 8,000 years ago (Emery and Garrison, 1967; Emery and others, 1967; Milliman and Emery, 1968; Dillon and Oldale, 1978).

171

REGIONAL DISTRIBUTION OF
GROUND WATER SALINITY UNDER THE CONTINENTAL MARGIN
A map showing minimum salinity observed in test holes drilled through sediments underlying the conti.nental' shelf is shown in figure 2. In general, very low salinity (less than 1 g/kg) occurs at distances less than about 16 km off the DelawareMaryland-New Jersey coast, but as far as 120 km off the Florida coast (Manheim and Horn, 1968). In the AMCOR test holes, the presence of fresh water in aquifers underlying the Continental Shelf was observed as a sharp decrease of salinity through the clay-confining bed before the drill penetrated more permeable sand and gravel of an underlying aquifer. The salinity profile for hole 6008 (inset, fig. 2) is typical of sites where an aquifer containing relatively fresh water underlies and is protected from rapid vertical intrusion of seawater by a low permeability confining bed. Based on the minimum salinity in the observed profile, the value above the line adjacent to the hole location is salinity in g/kg; the value below the line is the depth below sea level at which the minimum salinity was observed. To augment the offshore core-hole data, water-quality data from selected onshore observation wells are plotted adjacent to closed circles in figure 2. The depth of the well screen is below the line and the salinity of water obtained from that depth is above the line.
Data for inshore wells are plotted generally inside the coastline, and for offshore test holes, outside the coastline.
Aquifers Off the New England Shore
The general pattern of decreasing salinity below the floor of the continental shelf was observed on the landward side of Georges Bank about 250 km off the Massachusetts coast (inset graphs, fig. 2) . Caving, or sloughing, of Pleistocene glacial-outwash sand and gravel into the hole stopped the drill at relatively shallow depth. However, minimum salinity of about 22 g/kg in hole 6017 and 27 g/kg at the bottom of hole 6019 (general salinity of seawater in this area is about 33 g/kg; Bigelow and Sears, 1935; Bumpus, 1965) suggests that low salinity water also might be present under Georges Bank in this far offshore area (inset graphs, fig. 2). It should be noted that glacial ice with attendant ice-marginal lakes and streams occupied this part of the continental shelf in Pleistocene time.
In 1976, a test hole drilled at Nantucket Island, 64 km off the New England coast, found fresh ground water in coastal plain sediments to a depth of about

Figur~ 2.

Map showing estimated position of the 10 g/kg isohaline line in ground water underlying the U .S. Atlantic continental shelf. Based on minimum salinity in the observed profile, the value above the line adjacent to the hole location is salinity in g/kg; the value below the line is the depth below mean sea level (msl) at which the minimum salinity was observed. For onshore observation wells, the salinity (above the line) is related to the depth of the well screen (below the line).

172

500 m below msl (mean sea level) (Kohout, and others. 1977a). The coastal plain sediments thin and pinch ou t toward shore an d the crystalline rocks of the New Eng land mai nl and lack the recharge potential and hydrau lic conti nuity needed to account for the deep fresh water at Nantucket. Also, the shallow water-table aquifer underlying Nantucket lacks the head to provide recharge to the deep artesian system. A deep test hole subsequently drilled at Martha 's Vineyard Island , 32 km offshore, had a head of +5 .3 m compared to a head of +7 .3 m msl at Nantucket Island (Kohout and Delaney, 1979). The landward hydraulic gradient suggests that a freshwater artesian system, charged up during low stand of sea level in Pleistocene time, is now decaying as fresh groundwater is squeezed out by the advancing seawater(Collins, 1978 ; Kohout and Delaney, 1979).
Aquifers Off Long Island, New York
The circumstances are somewhat different at Long Island, N.Y . Although the island has no connection with mainland recharge areas, local precipitation infiltrates through Pleistocene deposits underlying the middle and northern parts of Long Island and moves vertically downward into the underlying Magothy and Lloyd Sand Member of the Raritan Formation, thence horizontally toward both north and south coasts. The Magothy has been heavily exploited in the New York City area and is affected by saltwater encroachment in coastal areas. The Lloyd Sand is fresh at a depth of 365 to 460 m below sea level at the south shore. The extent of fresh water in the offshore reaches of the aquifer is unknown, but the south shore beach communities depend on ground-water supplies obtained from the Lloyd Sand.
Aquifers Off the New Jersey-Maryland Coast
A line of five AMCOR test holes on a transect across the continental shelf east of the New Jersey coast permitted construction of a cross section through the lens of relatively fresh ground water and the transition zone to seawater. The cross section showed that low chlorinity water (less than 1 g/kg) extended about 10 km offshore and that relatively fresh ground water (less than 5 g/kg) formed a flatlying lens extending more than 100 km offshore (Hathaway and others, fig. 5, 1979).
Overlying the lens of relatively fresh water is an extremely sharp chlorinity gradient increasing upward to the chlorinity of seawater at the sea floor. The high gradient occurs in low permeability clay in the upper part of the Miocene deposits and in Pleistocene deposits. The clay serves as a conf ini ng bed

for the underlying permeable beds of the Kirkwood Formation. Water in the Kirkwood Formation was under artesian pressure on the mainland prior to intensive ground-water development in the early 1900's. Water levels in the offshore part of the aquifer underlying the barrier beach (particularly the "800-foot sand" at Atlantic City) are now (1978) drawn down to as much as 30 m below sea level by heavy pumping (Richard L. Walker, USGS, Trenton, N.J., oral commun., 1979). Clearly, the integrity of the confining bed is very important as an impediment to rapid vertical infiltration of seawater into barrier beach and mainland well fields.
An implication of the present work is that saltwater intrusion would have occurred long before now if it had not been for the existence of the offshore freshwater lens-the extent of which was not even guessed in early studies that expressed concern about saline encroachment (Barksdale and others, 1936).
The circumstances off the New Jersey coast also prevail off Ocean City, Md. AMCOR hole 6008 (inset, fig . 2) had freshened very sharply during penetration of the offshore extension of the Ocean City-Manokin aquifer (equivalent to the Miocene Kirkwood Formation of NewJersey) when the drill pipe became stuck and the hole lost in sandy aquifer material.
Aquifers of Miocene and Cretaceous age tend to contain inr,reasingly salty water southward toward Cape Hatteras (Brown and others, 1972) . However, Tangier Island, just below the Maryland-Virginia border in the middle of Chesapeake Bay (fig . 2), obtains artesian fresh water (0.7 g/ kg salinity at 314 m depth) from the Upper Cretaceous Mattaponi Formation . At Ocracoke on the Outer Banks of Cape Hatteras, an artesian aquifer yields water of about 3 g/kg salinity from a depth of 182m. Therefore, the 10 g/ kg boundary .is placed seaward of Cape Hatteras.
Aquifers Off South Carolina and Georgia
Geologic formations thin and their outcrops (or subcrops) are displaced seaward around the nose of the Cape Fear Arch, whose axis runs northwestsoutheast approximately coincident with the North Carolina-South Carolina border near its intersection with the shoreline. Sediments which are predominantly clastic to the north change increasingly to carbonates southward from the Cape Fear Arch . Predominantly carbonate Oligocene and Eocene rocks form a regional aquifer extending southward from South Carolina and Georgia, where it is called the principal artesian aquifer, into Florida, where it is called the Floridan aquifer.

173

An underlying aquifer in Cretaceous rocks contains fresh water at increasingly greater depth southwestward along the South Carolina shorefrom 244m a.t Myrtle Beach , 890 mat Parris Island , to 944 m at Savannah, Ga. These data suggest that fresh water should extend far offshore. Howev.er, AMCOR test holes 6004 and 6002 showed an increase of salinity with depth from that of normal sea water (35 g/kg to about 41 g/kg (inset graphs, fig. 2). This increase above the normal salinity of sea water has been associated with the presence of evaporite deposits in deeper strata in other areas (Manheim and Hall, 1976). The 10 g/kg line is deflected landward around these possible areas of evaporite deposition and then seaward east of the GeorgiaFlorida State line.
The Floridan Aquifer
The Floridan aquifer is a very thick section of carbonate rocks, capped by clay confining beds of variable thickness, that underlies all of Florida and parts of Alabama, Georgia, and South Carolina. The relationships of fresh water and saltwater are complex and are different at different points around the long coastline of Florida.
As noted previously, JOIDES J-1 B encountered a freshwater flow at about 300 m below sea level at a distance of 40 km offshore from Jacksonville, Fla. Water flowed from a zone that is equivalent to the Eocene Ocala, Avon Park, and Lake City Limestones ott he Floridan aquifer on the mainland. Based on the original piezometric surface near Jacksonville, Stringfield (1965, p. 161) calculated that there should be enough head remaining 100 km from the shore to cause fresh water to discharge at a depth of 500 m below sea level. This prediction was supported by data from JOIDES hole J-2. Pore water squeezed from middle Eocene cores decreased in salinity to 1.8 g/kg at 220m below sea level (Manheim, 1967, fig. 5). The correlation of low salinity with sediments equivalent to the top of the Floridan aquifer on the mainland provides good evidence that relatively fresh ground water is present and that discharge may be occurring at the edge of the continental shelf 120 mi east of Jacksonville, Fla.
Southward from this location, confining beds of the Miocene Hawthorn Formation become thinner and are breached by sinkholes. Saltwater encroachment occurs in the Floridan aquifer in the St. Augustine to Daytona Beach area (Leve, 1968). A sinkho le 465 ft. (142 m) deep ca lled Red Snapper Sink is locat ed about 40 m offshore southeast of St. Augustine, Fla. (Wilcove, 1975). The high oxygen content of seawater deep in the sinkhole, and the results of a dye-dispersion test performed by a SCUBA diver, suggest that there was a slight downward velocity of seawater and that Red Snapper Sink, Fla. may be a point of seawater intrusion into the Floridan aquifer (Kohout, and others, 1977b).

Southward from Daytona Beach, confining beds thicken and the Floridan aquifer deepens to 30004000 ft (914-1220 m) and possibly deeper at Key Largo in the Florida Keys. The upper part of the aquifer is the main source for thousands of municipal and irrigation water wells throughout the central and coastal parts of Florida.The deeper parts of this aquifer are occupied by seawater, particularly along the lower east coast where wells greater than about 900 m are used for injection of secondary treated sewage into cavernous Eocene limestone and dolomite. The 10 g/kg boundary has been placed outside of the 200m isobath from West Palm Beach to Miami because of the probability that discharge is occurring from the shallow parts of the aquifer below about 300 m along the continental slope of the Straits of Florida .
It has been hypothesized that cold seawater may be migrating inland in the deep part of the aquifer on the inland-flow part of a convective flow cell motivated by geothermal heat (Kohout and others, 1977c, and other papers In this special report on the geothermal nature of the Floridan Plateau) . It is probable that the deep parts of the aquifer in the Florida Keys may extend to depths greater than 5000 ft (1525 m) below sea level. During the drilling of an oil-exp loratory well at Marquesas Key near Key West . " 300% returns' of water were reported in th e drillers log . The quality of the water is unknown because samples were not collected during the drilling operations. The excess return of fluid suggests that an artesian flow may have been encountered far offshore, west of Key West.
Submarine springs occur off the west coast of Florida from Naples to St. Petersburg. About 12 mi offshore from Naples, Fla., the outflow from a warm submarine spring (97 F) has salinity similar to seawater. concentration (Kohout, and others, 1979). Geothermally heated saline water upwells through a sinklike depression at a depth of about 65ft (19m) below sea level. Water-quality data is not available from oil-exploratory drilling in this offshore area. The aquifers are extremely poorly understood except that they likely consist of highly permeable cavernous limestones overlain by confining beds. The western shelf of Florida was exposed land during low stand of sea level and was subject to freshwater recharge and probable development of caverns and sinkholes. The circu mstances are so obscure as to prevent proper hydrologic or ge.ologlc eval uation . The 10 g/kg boun dary has been placed at a distance of about 40 km from shore.entirely on speculation . Data are sorely needed in the entire western part of the Floridan Plateau , which extends several hundred ~ilometers off the west coast of Florida to the position of the 200 m isobath.

174

SUMMARY
At Nantucket Island, about 40 mi (64 km) off the New England coast, fresh ground water was found. in coastal plain sediments to a depth of about 1500 ft (500 m) below sea level. The coastal plain sediments thin and pinch out before reaching shore and the crystalline rocks of the New England mainland lack the recharge potential and hydraulic continuity needed to account for the deep fresh water at Nantucket.
These observations led to recognition that aquifers underlying the continental shelf were extensively flushed of salt water during low stands of Pleistocene sea level, and that fresh water was trapped beneath clay confining beds when sea level rose and flooded the Shelf about 8000 years ago.
The USGS AMCOR Project of 1976 confirmed that the observations at Nantucket were not unique. A line of 5 test holes off the New Jersey coast showed that relatively fresh ground water (less than 10 g/kg salinity) was present in a lens about 200 m thick extending about 100 km offshore. Similar conditions appear to exist in some aquifers off Long Island (New York), Delaware, Maryland, the Carolinas, Georgia, and Florida. Salinities lower than seawater also occur under Georges Bank off New England.
In this paper, salinity data from the offshore core holes have been augmented by data from selected onshore observation wells to formulate a map showing distribution of ground-water salinity under the U.S. Atlantic continental shelf. The EPA criterion of 10 g/kg salinity for protection of freshwater aquifers has been adopted to indicate areas of major waterresources interest.
Mathematical models or saltwater intrusion usually assume that dynamic equilibrium has already been established between fresh water and saltwater prior to development of wells for extraction. However, little is known of the whereabouts of the freshsalt transition zone or how fast the salt front might be moving towards centers of withdrawal. Further, the clay confining beds that overlie these aquifers in some offshore areas of the shelf are of singular importance in preventing rapid vertical influx of saltwater into heavily pumped well fields, some of which have drawdowns of more than 30m below sea level.
Mathematical models of saltwater encroachment require definition of the initial and boundary conditions of aquifers in order to produce reliable predic-

tions of the intrusion progress. Our present knowl-

edge of the offshore location and nature of the

fresh-salt transition zone, the thickness and off-

shore extent of aquifers, and the properties of their

overlying confining beds can be appropriately de-

scribed as primitive. The primary purpose of the

AM COR drilling program was calibration of seismic

profiles related to offshore oil and gas production.

The data obtained on water-resources aspects were,

for the most part, obtained as a result of serendipity.

Considering that some coastal well fields have

drawdowns well below sea level, the potential for

saltwater encroachment is great and is not being

confronted realistically. Obtaining the necessary

information for calibrating predictive mathematical

models is feasible if offshore drilling programs-are

formulated specifically for water-resources

objectives.



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175

Gill, H.E., Seaber, P.R., Vecchioli, John, and Anderson, H.R., 1963, Evaluation of geologic and hydrologic data from the test-drilling program at Island Beach State Park, New Jersey: New Jersey Dept. Conserv. and Econ. Devel., Div. Water Policy and Supply, Water Resources Circ. 12,25 p.
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Manheim, F.T., and Horn, M.K., 1968, Composition of deeper subsurface waters along the Atlantic continental margin: Southeastern Geology, v. 9, no. 4, p. 215-236.
Milliman, J.D., and Emery, K.O., 1968, Sea levels during the past 35,000 years: Science, v. 162, no.3858, p. 1121-1123.
Perlmutter, N.M., Geraghty, J.J., and Upson, J.E., 1959, The relation between fresh and salty ground water in southern Nassau and southeastern Queens Counties, Long Island, New York: Econ. Geol. v. 54, p. 416-435.
Soren, Julian, 1971, Ground-water and geohydrologic conditions in Queens County, Long Island, New York: U.S. Geol. Survey WaterSupply Paper 2001-A.
Stringfield, V.T., 1965, Artesian water in Tertiary limestone in the southeastern states: U.S. Geol. Survey Prof. Paper 517.
United States House of Representatives, 1974, Endangerment of drinkin water sources: House Report 93-1185, p. 32.
Wilcove, Raymond, 1975, The great Red Snapper Sink: NOAA Magazine, v. 5, no. 2, p. 46-47.

176

ALTITUDE OF THE FLORIDAN AQUIFER OF NORTHWEST FLORIDA
Tom Kwader Northwest Florida Water Management District
Havana, Florida

0

10

20

30

40

MILES

All contours in feet below sea level.

ABSTRACT

A detai led c o nto u r map dep ic ti ng th e top oi th e Fl o ri dan aqu ifer of nort11wes t Flori da has recentl y bee n comp le ted. In th is area the Floridan aq uifer consists of an oHiapping seque nce of Terti ary limes tones ~ a n glng i n age fro m Plioce ne to u pper Eocen e. Th e surfa ce of the aqui fer is app rox imately first order, but ranges g reatl y in altit ude. In th e recharg e area or no rth ern Jac kson and Ho lmes Cou nti es , th e aqui fe r Is approxi mat ely 150 It above mea n sea level. bu t dips sl1n.rp ly to thesou ti1West and lies more than 1400 ft below mea n sea level in t he Pensaco la area .

Most of the data used were obtained from well cuttings and co res described and flied at the Florida Bureau of Geology. Li tho lo g ic descri pti ons also w ere corre ll'! led with num erous geop hysica l lo gs on fi le at l he No rthwest Flo ri da Water Managem ent District and the U.S. Geo log ical Su rvey. Ove r 600 data poin ts were co nt ou red i n th e final map wit h the ai d o f the U.S. Geologi cal Survey CalCamp 2-D contouring programs.

LONG-TERM HYDROLOGIC STABILITY OF GULF COAST SALT DOMES AND MINES
Joseph D. Martinez and Madhurendu B. Kumar Louisiana State University Baton Rouge, Louisiana
ABSTRACT

Th e long-term hydrol.og ic stability O'f Gul f Coast sa lt dom es and mined open in gs Is a pa rameter that must be co nside red i n an assess ment of th e poten ti al utili ty o't these fea tures for the sto rage and/or dispo sa l of 11 ighlevel radi oactive was tes. One of th e to xic com po nents, Plut o nium . has a lo ng half- life whic h req ui res iso latio n o f thi s mater ial for periods poss ibly as lo ng as 25 0,000 yea rs.
An assessment of hydrologic stability requires a determination of the presence or absence of dissolution now and in the future. If dissolution is an active process , rates
177

and patter ns mu st be Iden ti fi ed. Evidence of dissol ution. w hic h involves th e exterior or t11e do me. is provi ded by th e prese nce o f sal ine plu mes in adjacent aq ui fers. Suc h plum es may be located by subsurface stl ldles o r new exp lo rato ry w ells. An equa lly imp ortant obj ec tive is th e d eve lo pme nt o f an und erstanding of wat er leaks In some existi ng min es . Th is Wi ll p rovid e a bas is fo r predi ctin g the hydrolog ic integrit y of mined openi ngs developed for the iso lation of radi oac tiv e w ast es.Data and tentative conc lusions are presented in this progress report.

THE STRATIGRAPHY OF THE FLORIDA-HATTERAS SHELF AND SLOPE AND ITS RELATIONSHIP TO THE OFFSHORE EXTENSION OF THE PRINCIPAL ARTESIAN AQUIFER
Charles K. Pauli and William P. Dillon U.S. Geological Survey
Woods Hole, Massachusetts

ABSTRACT
The stratigraphic units that contain the principal artesian aquifer onshore in northern Florida, Georgia, and South Carolina were traced by means of seismic reflection profiles to the area under the Florida-Hatteras shelf and slope, and contour and isopach maps were made. The existing hydrologic data suggest that the offshore extension of the aquifer contains fresh water as tar eastward as the she lf break off northern Florida, but that the fresh water does not extend very far under the shelf off central Georgia. A seaward extension in the salinity bouhdary within the aquifer off southern Georgia corresponds to a depocenter delineated by isopachs of Eocene and Oligocene units. The axis of this depocenter correlates with a Tertiary facies boundary onshore.
SEISMIC STRATIGRAPHY
In 1976 the U.S. Geological Survey collected more than 5,000 km of single channel seismic reflection profi les covering the Florida-Hatteras shelf, slope, and inner Blake Plateau (fig. 1) (Pauli and Dillon, 1979) . An analysis of these data indicated that three regionally traceable unconformities are in the Tertiary section. Seismic stratigraphic units, bounded by unconformities, were correlated with stratigraphic data from offshore boreholes: The JOIDES well J-1, J-2, J-5, and J-6 (JOIDES, 1965) ; the U.S. Geological Survey AMCOR wells 6002, 6004, and 6005 (Hathaway and others, 1976) : COST GE-1 (Scholle, 1979); the Coast Guard Tower Well (McCollum and Herrick , 1964); and wells along the coast. The major unconformities appear to separate Cretaceous units from Paleocene, Paleocene from Eocene, and Oligocene and older strata from Miocene and younger strata. We made structure contour and isopach maps of units (figs. 2 A-F) by using interval velocities obtained from multichannel seismic profiles in the area (Dillon and others, 1979). The Paleocene rocks were deposited in a fairly uniform blanket of sediments 100m thick or less (fig. 2 C). Eocene and Oligocene sediments are more than 700 m thick in a triangular basin off southern Georgia (fig. 2 E) . Miocene and youhger sediments are about 50 m thick on the shelf and thicken to more than 200m at the shelf break (fig . 2 F).

340
.,.

N

I

33

s.c

31

29 620

-+-Location of offshore wells

.& Location of dredge hauls

of Cretaceous ooe

, ' .,:

76

Figure 1. Location of seismic reflection profiles and dril hole data used in the analyses.

OFFSHORE EXTENT OF THE AQUIFER
Onshore In northern Florida, Georgia, and South Carolina, the principal artesian aquifer is generally contained within Eocene and, to a lesser extent, Oligocene rocks, and sealed above and below with the Miocene and Paleocene units, respectively (Counts and Dansky, 1963). The offshore extensions of these same Eocene and Oligocene units are traced in figure 2 E.
Only six boreholes are on the continental shelf off the southeastern United States from which hydrologic data were collected and which penetrate the unit corresponding to the principal artesian aquifer onshore (J- 1, J-2, J-5. COST GE-1, 6002, and 6004, fig. 1). Within the aquifer unit of J-1 and J- 2, water containing less than 1 ppt (parts per thousand) salinity was found (Manheim, 1965; Kohout, 1978). Data on the salinity of water within the aquifer unit at COST GE-1 and J-5 well are ambiguous. The available data suggest that water containing less than 20 ppt salinity is present; this

178

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Figure 2.

Structure contour and isopach maps of surfaces and units inferred to be Cenozoic age. Map A is an isopach map of Cenozoic sediments. Maps B and D are structure contour maps of reflectors which correlate with unconformities separating Paleocene and older strata from Eocene and younger strata, and an unconformity which separates Oligocene and older strata from Miocene and younger strata. Maps C, E, and Fare maps showing thicknesses of units bounded by the Cenozoic unconformities, and correlate with sediments of Paleocene, Eocene, and Oligocene age and Neogene to Recent age, respectively . Map E is an isopach map of the unit which corresponds with the principal artesian aquifer onshore.

179

amount indicates a freshwater influence at these locations (Manheim, this volume). In water from the AM COR wells 6002 and 6004, salinities were greater than 40 ppt (Hathaway and others, 1976); ()uch values are greater than those of seawater,l and probably indi1cate the diffusion of salts from brines at greater depths (Manheim and Paull, this volume).
The boundary between Tertiary units to the west that contain water of less than 10 ppt salinity and those to the east that contain water of higher salinity is shown in figure 3. Water of less than 10 ppt salinity is considered potentially usable and is to be protected as a resource, by definition of the Environmental Protection Agency (U.S. House of Representatives, 1974). An estimated boundary between Tertiary units that contain water of less than 1 ppt salinity, the limit of potable water, and those that have water of higher salinity is also shown in figure 3. This boundary has a seaward extension off the southern Georgia shelf.
The position of the seaward extension of lowsalinity values in interstitial water corresponds to the axis of a Tertiary depocenter offshore (fig. 3). The axis of the depocenter beneath the shelf appears to be coli near with the deepest part of the Southeast

Georgia Embayment onshore (Applin and Applin, 1967), which is shown by a thickening in the Tertiary units. This boundary forms a facies boundary between a predominantly carbonate province to the south and a mixed carbonate-clastic province to the north (Chen, 1965). The wells on the shelf suggest that this facies boundary may continue offshore. The seaward curve in salinity contours, indicating low-salinity waters beneath the outer shelf, suggests that increased flushing by artesian flow has taken place south of the depocenter; this flushing is perhaps related to more permeable rocks in the southern complex.
CONCLUSION
The unit that corresponds to the principal artesian aquifer onshore was traced seaward beneath the continental shelf . Within this unit, the boundary between the Tertiary rocks that contain relatively fresh water and those that contain salty interstitial water (Kohout, 1979, and Kohout, this volume) protrudes seaward between 30 and 31 o N. Thus, most of the area of the continental shelf south of southern Georgia appears to be underlain by a resource of fresh water. This boundary between fresh and salty interstitial waters corresponds to a facies

+ N
I

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32

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31

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Figure 3. The isopach map of Eocene and Oligocene sediments indicates a basin under the shelf that has an axis extending onshore toward southern Georgia. The seaward extension of strata containing low-salinity water appears to be bounded by the axis of the Tertiary depocenter.

180

change across the axis of a Tertiary depocenter from a predominantly carbonate province to the south to a mixed carbonate-clastic province to the north. We speculate that this change in rock type may be accompanied by a change in permeability that has allowed more extensive flushing of the principal aquifer. This unit should be protected during offshore petroleum developrpent until we have adequate hydrogeologic information to trace the aquifer precisely.
REFERENCES CITED
Applin, P.L., Applin, E.R ., 1967, The Gulf Series in the subsurface in northern Florida and southern 'Georgia: U.S. Geol. Survey Prof. Paper524 G, 35 p.
Chen, C.S., 1965, The regional lithostratigraphic analysis of Paleocene and Eocene rocks of Florida: Florida Geol. Survey Bull . 45, 105 p.
Counts, H.B., and Dansky, E., 1963, Salt-water encroachment, geology and ground-water resources of Savannah area, Georgia and South Carolina: U.S. Geol. Survey, WaterSupply PGper 1611, 100 p.
Dillon, W.P., Paul!, C.K., Buttler, R.T., and Fail, J.P., 1979, Structure and development of the Southeast Georgia Embayment and northern Blake Plateau: Preliminary an1alysis: Am. Assoc. Petroleum Geol. Mem. 29, p. 27-41.
Hathaway, J.C., Schlee, J.S., Poag, W.C ., Valentine, P.C., Weed, E.G.A., Bothner, M.H, Kohout, F.A., Manheim, F.T., Schoen, R., Miller, E., and Schutz, D.M., 1976, Preliminary summary of the 1976 Atlantic Margin Coring Project of the U.S. Geol. Survey: Open-file Rept. 76-884, 217
p.
JOIDES (Joint Oceanographic Institutions Deep Earth Sampling Program). 1965, Ocean drilling on the continental margin: Science, v. 150, p. 705-716.
Kohout, F.A., 1978, Map depicting probable extent of low salinity ground water in aquifers b~neath the Continental Margin of the United States: Unpub. rept., 28 p., 2 figs.
_ _, 1979, Relict fresh ground waters of the Continental Shelf: An unevaluated butter in present-day saltwater encroachment, this volume.
Manheim, F.T., 1965, Composition of deeper subsurface waters along the Atlantic Continental MarQin: Southeastern Geology, 4, no.4, p, 215-236.
Manheim~ F.T., and Paul!, C.K., 1979, Hydrochemistry of formation fluids in onshore and offshore strata in the Southeast Georgia Embayment, this volume.

McCollum, M .J., and Herrick, S.M., 1965, Offshore extension of the upper Eocene to stratigraphic sequence in southeastern Georgia: U.S. Geol. Survey Prof. Paper 501-C, p. C-61 - C-63.
Paul!, C.K., and Dillon, W.P., 1979, The subsurface geology of the Florida-Hatteras Shelf, Slope and inner Blake Plateau: U.S. Geol. Survey Open-file Rept. 79-448, 94 p.
Scholle, P.A., 1979, Geological Studies of the COST GE-1 Well, United States South Atlantic Outer Continental Shelf Area: U.S. Geol. Survey Circ. 800, 114 p.
U.S. House of Representatives, 1974, Endangerment of drinking water sources: House Report 93-1185,32 p.

181

GEOLOGIC HAZARDS AND CONSTRAINTS TO PETROLEUM EXPLORATION AND DEVELOPMENT ON THE SOUTHEASTERN U.S. CONTINENTAL SHELF, SLOPE, AND BLAKE PLATEAU

Peter Popenoe U.S. Geological Survey
Reston, Virginia
ABSTRACT

The U.S. Geological Survey and the Bureau of Land Management have been conducting environmentalhazards studies on the southeastern continental shelf, slope, and Blake Plateau since mid-1976. These studies include high-resolution seismic profiling of the shelf, slope, and northern Blake Plateau; depl6yment of bottom-instrument packages on the shelf to study sediment movement and its causes; coring and sampling programs to define sediment size, composition, and lithofacies; clay mineralogy; trace-metal analyses of sediments; composition and concentration of seston; side-scan sonar, and underwater television studies of reefs and hardgrounds; and submersible observations of marine habitats and uni:que bottom features . Several studies, such as the trace metal analyses of sediments, are intended to establish baseline levels. These studies 1ndi-

cate a relatively pollution-free environment. Regional reflection studies indicate that very little faulting is associated with shelf or Blake Plateau sediments although several large faults are present on the continent al slope, One slump was defined on the Florida-Hatteras slope near 32 N, 79 W, and an attempt to core this slump showed it to be covered by Jag phosphorite nodules.
Many geologic features on th e shelf, slope, and Plateau are constraints to commercial petroleum development, but planning and engineering can mitigate environmental damage to or from these features. These features include areas of scour or mass movement, channeling or steep topography, cut and fill structures, and reeflike features and hardgrounds which serve as marine habitats.

GEOLOGIC INVESTIGATIONS FOR DREDGING OPERATIONS, FBM SUBMARINE SUPPORT BASE, KINGS BAY, GEORGIA

Earl F. Titcomb, Jr. U.S. Army Corps of Engineers
Savannah, Georgia

ABSTRACT

The establishment of the Navy's Fleet Ballistic Missile Support Base at Kings Bay, Ga., has required extensive dredging to provide access and anchorage facilities for the Navy's nuclear submarines. The existing channel from the Fernandina Harbor entrance at Cumberland Sound through the sound and up the Intercoastal Waterway to Kings Bay required both widening and deepening. Within Kings Bay, extensive dredging was required to provide adequate space for support facilities such as dry dock and tender boat anchorage. The Georgia portion of the work was handled by the Savannah District of the Corps of Engineers, while the Florida portion was done under the Jacksonville District. The dredging presented numerous challenges. The quantities of material to be excavated in the Savannah District's four mile portion alone exceeded eight million yards. In addition to the very large quantities, hard "limestone" and dolomite were found in several areas. This presented special problems si nee the cost of excavation of the rock is much greater than for unconsolidated materials. Use of suitable sands from the required excavation for renourishment of Fernandina Beach beaches is being planned. The materials unsuitable for nourishment use are being spoiled in dike areas near Kings Bay or disposed of offshore. Disposal of unsuitable material, both on and offshore, required extensive special

treatment to minimize environmental impacts. In order to properly evaIuate the subsurface materials, 100 borings were made by Savannah District and an equal number by Jacksonville District. In addition, side scan sonar, proton magnetometer and seismic reflection profiling studies were conducted to assist in interpolation of data between borings and to locate any artifacts which might have been located within the expanded area. The borings were made from either conventional barges or Jacksonville District's jack-up drill barge. Where consolidated materials were encountered, the materials were drive sampled, using either split tube or solid tube barrels. The drilling was particularly difficult in the more exposed areas of the Intercoastal Waterway and Fernandina Harbor. No historic artifacts were found in the proposed expansion area during the magnetometer survey. Hard limestone was found to be concentrated in the northern portion of Kings Bay. In the southern portion of the Bay and in the Intercoastal Waterway, the depths to limestone were deeper or the limestone was not found. This made siting of the initial facilities in the southern portion of Kings Bay desirable. Future plans for expansion of the facilities are being considered by the Navy. These will involve additional dredging and construction of more permanent onshore facilities.

182

AQUIFER POTENTIAL OF THE SHALLOW SEDIMENTS OF THE COASTAL AREA OF GEORGIA
Thomas Watson Georgia Department of Natural Resources
Georgia Geologic Survey Atlanta, Georgia

ABSTRACT
In the coastal area of Georgia, there are three distinct aquifer systems. For many years, the principal artesian aquifer (a deep sequence of limestones) has been the primary source of all ground-water withdrawals in southeastern Georgia. The principal artesian aquifer of coastal Georgia is overlain by sediments ranging in thickness from less than 200 to more than 600ft. These sediments can be subdivided into two shallow aquifer systems. The surface aquifer system is a series of laminated sands and clays, attaining a maximum thickness of 70ft near the coast. These sediments are predominantly fine grained and have a low hydraulic conductivity.
The surficial aquifer is underlain by the secon.d groundwater system, a 400-500 ft thick series of Miocene clays and sandy clays with lens-shaped bodies of sand, gravel, and thin carbonate layers. Although the Miocene series varies widely in hydraulic conductivity, and the lower strata act a3 a confining bed overlying the principal artesian aquifer, it is commonly used as an aquifer. Wells with yields of over 200 gallons per minute (gpm) are being used by several industries in the coastal area.
Shallow aquifers have less aquifer capacity than the principal artesian aquifer. As alternative sources of good quality ground water, they have a potential of from 50,000 to over 300,000 gal/day, depending on location and well construction.
Induced recharge to the principal artesian aquifer through the use of connnector wells may be a feasible method to take advantage of water in the surface aquifer.
Water quality of the shallow aquifers varies with depth and lithology. In the surface aquifer, water quality varies from very low total dissolved solids to slightly alkaline, moderately hard water with total dissolved solids averaging less than 200 milligrams per liter (mg/1). Water from the Miocene sediments is somewhat more uniform in quality, with total dissolved solids averaging about 250 mg/1.
The surface aquifer is extremely vulnerable to contamination. Although some contamination is inevitable as population increases, careful planning of potential sources of pollution would minimize the spread of contaminated ground water.
The high clay content of theM iocene series reduces the vulnerability of these sediments to surface contamination. Here, as in the surface aquifer, care in planning would minimize the effects of pollution.

INTRODUCTION
The principal artesian aquifer of Georgia is a series of carbonate strata long recognized as one of the most productive aquifers in the world. For many years, the principal artesian aquifer has been the primary source of all large ground-water withdrawals in the coastal area. Heavy ground-water withdrawal and subsequent lowering of water levels have allowed saline water intrusion into the fresh water zone of the principal artesian aquifer in Brunswick (Wait and Gregg, 1973, p. 1). Current levels of withdrawal in the Savannah area may be approaching the limits of safe levels of water withdrawal (Counts and Krause, 1976, p. 3).
As competition for available fresh water becomes more intense, ground water from sediment overlying the principal artesian aquifer will almost surely play an important role in the future development of coastal Georgia. This report is intended to provide a basis for further research and to guide general water-management decisions.
PURPOSE
Future management of the ground-water resources of coastal Georgia may include redistribution of water withdrawals to minimize cones of depression in the principal artesian aquifer. Another resource management technique that is being considered is increasing recharge to the freshwater zones of the principal artesian aquifer. Both practices can include the use of secondary aquifers such as the Miocene and surface aquifers, collectively referred to as the shallow aquifer system.
The purpose of this study was to evaluate aquifer potential of the shallower sediments overlying 'the principal artesian aquifer. This information is necessary in determining to what extent the shallow aquifer may be used to augment the principal artesian aquifer. Augmentation through the use of secondary aquifers would help solve the problem of potential or existing salt water intrusion in specific areas of the coast by changing the hydrostatic pressure differential between fresh water and salt water bodies in the principal artesian aquifer. Using these shallower sediments as aquifers is not a new idea. Interviews conducted in the study area indic.ate that

183

as many as 80% of al l suburban and rural homes have at least one well drawing waterfrom a shallow aqui fer . Herrick ( 1971), Counts and Dansky (1963), Callahan (1964), and others , al l acknow ledged the ground-water pote ntial of the Neoge ne sediments. However, extremely high well yields and high artesian water levels of the deeper principal artesian aqu ifer have obscured the signif ica nce of shallow aq uifers.
Specific objectives ot shallow aquifer evaluation were: a physical description of the water-bearing strata Including grain size and sorting; mapping the thickness and distribution of potent ial aqui f ers; and, determination of general c11emical characteristics of the shallow ground water.

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I

.,

GEOGRAPHY
The 21 counties included in this report tie entirely within the Coastal Plain Province of Georgia (see fig. 1). Topography ranges from well-drained. gently rolling hills to relatively flat, featureless plains and swampland. Major population centers are Savannah in Chatham County and Brunswick in Glynn County.
The economy of this part of the State depends largely upon forestry and the pulp and paper manufacturing Industry. Approximately 77% of the report area is forested with commercial stands of loblolly and slash pine. Several large wood pulp and paper mills are Included In the study area. Additional regional income Is derived from manufacturing, shipping, commercial fishing, and agriculture.
Climate of the coastal region is mild with an average annual temperature of nearly 70 degrees F. Rainfall averages from 45 to 50 in . annually. Of the total rainfall, approximately 71% is returned to the atmosphere by plant transpiration and evaporation from surface water, 27% is returned to the ocean by rivers and streams, and 2% of the rainfall percolates downward to recharge the deep aqu ifers such as the principal artesian (Callahan, 1964, p. 50). 1t is significantto note that near ly one third of the annual rainfall of the coastal area, that portion which is returned to the ocean by rivers and streams, percolates through the sands of the surficial aquifer before being intercepted by stream systems. Although annual rainfall Is abundant, localized agricultural droughts can have serious results . Much of the annual rainfall is the result of scattered thundershower activity. Although a wea1her station may receive an averag e amount of precipitation over an entire year, several weeks of drought resulting in severe crop damage may occur during the hot growing season. For example, in Wayne County in the central portion of the study area, total rainfall for 1977 was only 2% below normal. However, the months from April through August averaged 42% below normal (U.S. Department of Commerce, 1977).

Figure 1. Location of study area.
ANALYTICAL METHODS
Much of the subsurface data for this report came from the exam ination of rotary drill cuttings from varIous sources. Lithologic togs of 84 wells were prepared from cuttings on file with the Georgia Geologic Survey. In addition, cuttings and geophysical logs from 500 exploratory wel ls drilled by the Exxon Corporation were used by the study team during the course of this investigation.
Geophysical logs of boreholes indicate the various lithologic units, their degree of saturation, and to some extent, the chemical nature of water contained by the sediments. Geophysical logs and descriptions of well cuttings provided a general framework for identifying areas of particular interest. Specifically, the initial phases of the Investigation sought to identify saturated sand layers, their depth below land surface, thickness, and lateral extent.
Hydraulic conductivity, the degree of ease with which water can move through a sediment, can be estimated from a description of the grain size, shape, and sorting. For this purpose, a hollow-stemmed auger and split-spoon sampling device were used to obtain an undisturbed sample for analysis. Core samples from 137 test holes were used, of which 76 were drilled specifically for this study. The remainder were donated by mineral-exploration companies. Hydraulic conductivity estimates obtained from grain size and sorting data. multiplied by aquifer thickness, provided estimates of aquifer potential (Lohman, 1972, p. 52).

184

When completing a water well, the contractor often measures the specific capacity of the well, the response of the water level in the well to pumping. Specific capacity figures can be used to estimate aquifer potential, especially when the geology of the aquifer is known (Brown, R.H., 1963, p. 336). Both grain-size analysis and specific capacity tests were used to determine potential water-yielding characteristics of the shallow aquifers. The results of both methods were in close agreement.
Ground-water chemistry samples for this study were collected according to methods described by Brown and others (1974, p. 6-12) to insure uniformly accurate results. Thirty ground-water samples were collected for this report, and chemical analyses were performed by the Georgia Geologic Survey or the U.S. Geological-Survey.
GEOHYDROLOGY
The sediments overlying the principal artesian aquifer can be divided into two distinct aquifer systems. These systems have dissimilar aquifer characteristics, and will be discussed individually. Figure 2 shows two generalized cross sections which illustrate the general relationship of the aquifers found near the coast.
Miocene Aquifers
The older of the two series lies directly above the principal artesian aquifer. This group of sediments was deposited in shallow seas which covered much of South Georgia during the Miocene epoch. Miocene sediments are thickest in Wayne County where they attain a thickness of over 500 ft as shown in figure 3. The Miocene section can be divided into lower, middle, and upper units, the lower being mostly carbonate rock which is hydraulically connected to the principal artesian aquifer.
Middle and upper Miocene units are hydraulically separated from the principal artesian aquifer by thick sequences of dense, greenish-gray, sandy clay. 1nterlayered with the clay are lens-shaped bodies of sand, which are of interest because of their aquifer potential. Although individual sand lenses are not continuous throughout the study area, data indicate that they are most common in the thicker portions of the Miocene units and generally occur at depths greater than 200ft below land surface. Below this depth, sand lenses often reach a thickness of 50 to 80 ft, and extend laterally for over a mile.
Texture of the Miocene sands varies somewhat. The coefficient of sorting is generally high, indicating poor sorting, with sands and gravels mixed. Median grain size is approximately one millimeter in diameter. No

apparent trends linking grain size with depth or.location were evident from the data examined during this study.
Surface Aquifer
Overlying the Miocene series are sediments of the surface aquifer system, the youngest shallow aquifer. These sediments form a relatively thin layer of sands gravels, and clays, extending from the surface to a depth of approximately 80ft. Figure 4 shows the distribution and thickness of this aquifer.
Data indicate that the surface aquifer system consists primarily of sand and thin layers of white to reddish-brown clay. Layers of pure sand or clay are generally no more than a few inches thick. Layers of sand-clay mixtures are usually less than 5 ft thick. Sand in the surface aquifer is fine grained and well sorted in most instances.
Two notable exceptions to this general description were observed. First, flood plain deposits of major rivers in the study area commonly exhibit a wide range of grain sizes from sand to fine gravel. The Altamaha River in Wayne County, for example, has an extensive system of medium-to coarse-grained alluvial deposits. These deposits are more than 120ft thick in some places.
Second, in the central portion of the study area at depths of from 30to 50ft below land surface, there is an extensive layer of coarse and fine gravel (see fig. 4). The thickness of this sand layer varies from 5 to 15 ft, and it is laterally persistent, occurring at the base of the surf,ace se-diments- In Wayne, Glynn, Long, and Mcintosh Counties.
GROUND-WATER USE AND AVAILABILITY
The surface aquifer receives recharge directly from rainfall which percolates through the sediments. In most areas of coastal Georgia the surface water table is quite shallow. During dry months the base flow of streams and rivers of the coastal area is maintained by ground water discharging from the surficial aquifer. The coastal area has very sandy soils which are actually part of the surface aquifer in many cases. The result is a very high rate of rainfall infiltration.
Recharge to the Miocene aquifers is the result of percolation from the surface aquifer, and in some areas, discharge from the principal artesian aquifer. Although clay layers conduct ground water very slowly, thickness and density of the clays are variable throughout the study area causing recharge rates to be variable as well.

185

A'

ECHOLS COUNTY
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SEA LEVEL

. .
- =P-_

A

EFFINGHAM

,.(/)
:I:

COUNTYj

r

r

0
:IE

,.

D
c

"TI 1'1
"'

PRir-JCIPAL ARTESIAN AQUIFER

8'
HORIZONTAL SCALE Ok:=:::a:=::=:::::2j;OS:=:==::=::=:::::4t;0=:==:=3:::=::::::::;j60 MILES
EXPLANATION
~LIMESTONE
[]sAND
1--J CLAY

8

SAVANNAH RIVER-.,

,.rn
:I:

SURFACE AQUIFER

r r
0

,.:E
MIOCENE

D
SERIES c

"TI
1'1
"'

PRINCIPAL AR TESI AN AQUIFER

Figure 2. Generalized cross sections showing stratigraphic relationship of shallow aquifers and the principal artesian aquifer.
186

EXPLANATION ar'

-400- LINE OF EQUAL THICKNESS OF SEDIMENT-Interval 50 feet



DATA POINT

83

__'

l . \,

I

82

Figure 3. Thickness of unconsolidated Miocene sediments.

At present, the shallow aquifer system is almost exclusively used as a source of water for domestic wells. In the central portion of the study area where the shallow sediments are thickest as shown in figure 5, it is estim'ated that more than 80% of all domestic wells tap the shallow aquifer system. The great depth of the principal artesian aquifer in this area makes the shallow aquifer system economically more attractive for most people.
In the counties along the coast, many dwellings also have a well tapping only the surface aquifer. These shallow wells are most commonly used as a secondary water supply for yard irrigation rather

than for drinking water. However, many rural homes use water from the surface aquifer for all water needs . Surface aquifer wells range from 10 to 80ft.
Figure 6 shows the variations in estimated waterwell potential of the Miocene and surface aquifers combined . Water-well potential is expressed as the estimated yield in gallons per day of a properly constructed well penetrating the full thickness of the saturated sand or gravel aquifers. Proper well spacing to prevent interference between two or more wells is assumed . A well. designed to make the best use of shallow aquifer potential would be receiving water from several zones.

187

EXPLANATION
AREA WHERE COARSE SAND AND FINE GRAVEL ARE PREDOMINATE , LINE OF EQUAL THICKNESS - J O - OF SEDIMENT- Interval 10 feet
DATA POINT

0

20

60 MILES

\, _.\
82 "

Figure 4. Distribution and thickness of sediments comprising the surface aquifer. Modified from Herrick, 1965.

GROUND-WATER DEVELOPMENT TECHNIQUES
There are several reasons why the shallow sand and gravel aquifers are not used more exte nsively for co mm ercial and agricultural wells. Developing a large capacity well in a san d and gravel aqu ifer req uires that t he well con tractor have specific equipment and experience Man y water well contractors in coastal Georgia have never constructed a well in a sand and gravel aquifer, largely because there was no need to do so. In addition, well construction and maintenance in a sand

and gravel aquifer can be more expensive than simply drilling an open hole in a limestone aquifer. Care must
be used to avoid well collapse and sand in the water. Finally, low hydraulic conductivity of the shallow aqu ifers In some areas of coastal Georg ia li mits ground- water flow and availability. Essenti ally , constructing a large capacity well in the sands and gravels of coastal Georgia has offered no apparent disadvantage over the use of the principal artesian aquifer, which produced water in seemingly unlimited quantity.

188

EXPLANATION
8 1"
-400- LINE OF EQUAL THICKNESS OF SEDIMENT -Interval 50 feet DATA POINT

'

\

83"

) '

' '
82.

Figure 5. Total th ickness of unconsolidated shallow sed iment.

Well construction techniques are available that can elim.inate well collapse and make good use of "tight" aqurfers of apparent low productivity. These special techniques have been used successfully in other ~reas of the country where water is much less abund-
ant.than in coastal Georgia. By taking advantage of optrmum well construction technology, more ground water could b~ obtained from the shallow aquifer system, thus helprng to reduce drawdown in the principal artesian aquifer.

Current Well Construction Methods
One type of shallow well commonly used in the study area is called a "rock" well. In constructing a "rock" well, a hole is drilled until a resistant layer is encountered. Resistant layers, usually thin limestones or dolomitic limestones, are common at the top of the Miocene Series. Drilling continues through the rock layer, and compressed air is used to create a hollow or reservoir immediately beneath. Casing is then set from the surface to the "rock".

189

EXPLANATION
Estimated wa'ter yield, in gallons per day, available to properly constructed wells topping shallow aquifer systems . Projected yields ore based on hydraulic conductivity and thickness of the aquifer material. Adequate spacing of wells is assumed .

~ ~.
; - - " '" . > : / "-"\. . H { \.EF~FoIN,oGoHoAJ~
J

r --~.

I

\

1
CLiNCH
50,000
\

CHARLT

f

.---\_
,

-....

~

.,

83"

0

20

40

60 MILES

82"

Figure 6. Estimated minimum well yield of shallow aquifers.

"Rock" wells are a popular variety of domestic well because they are economical to construct and yield from 2 to 10 gpm . However, the reservoir, which is not screened , can and often does collapse, greatly reducing pumping capacity. "Rock" wells are usually no more than 80-ft deep; however, a 200-ft deep "rock" well used by a seafood processing plant in Brunswick has been in use since 1969, delivering slightly over 100 gpm.
The best method for preventing the collapse of wells in unconsolidated aquifers is the use of well screens . Well screens are preferable to simply perfo-

rating the casing, because the size of openings in a screen can be selected to complement the sand size of a specific aquifer. This allows maximum surface area of the aquifer to be exposed to screen, while minimizing the quantity of sand which enters the well. The screen is welded or threaded onto the string of well casing at intervals to correspond with the sand aquifers.
If the sand aquifer is very fine grained, or if the grain-size sorting is poor, a technique known as filter packing can be used to enhance well yield . When a driller constructs a filter pack, the hole is purposely

190

I

EXPLANATION

I

I

TOOMBs(

AREA WHERE HEAD DIFFERENTIAL

/

t BETWEEN SHALLOW AQUIFER AND
PRINCIPAL ARTESIAN AQUIFER WOULD

I TAT T

1

+---'--=~'r----"--lr- ~-

ALLOW RECHARGE THROUGH

CONNECTOR WELLS

-,c c I N
.,.I

I
~ '

E C H

83

0

20

40

GO MILES

Figure 7. Well construction techniques.

drilled quite large, the casing and screen are installed as needed, and the annular space between the formation and the screen is filled with sand or gravel caretully graded tor size. The grain size and sorting of the ti Iter pack are chosen to keep sand in the aq uiter from being pumped into the well.
Perhaps the most common type of shallow domestic well in the study area is known as a driven or jetted well. Driven wells are usually installed by homeowners to serve as a secondary water supply. A drive point, or slotted galvanized pipe with a pointed tip, is driven into the surface sands, often with the help of water

pressure from a garden or portable pump. Driven wells are nearly always less than 40 tt-deep and no more than 2 in. in diameter. They generally provide from 1 to 5 gpm of water. Driven wells are common even where municipal water is available, and are used chiefly tor yard irrigation . The main drawback to driven wells is that they are vulnerable to surface contamination.
Figure 7 shows examples of various well construction methods. Exampl es B through E are in use in coastal Georgia, with D and E being the most common construction techniques.

191

Potential Ground-Water Development Techniques

Well capacity can be increased by enlarging the well diameter. Water in large diameter wells can be pumped from storage in the well bore, and pumpage can exceed the volume of water flowing into the well bore for short periods. A large diameter well also exposes a large surface area of the aquifer facilitating the flow of water into the well. A pond can be thought of as a shallow, large diameter, uncased well.

T.he pond-well technique is successfully used for agncultural irrigation in the Waycross area under
geohydrologic conditions similar to those found over a ~id e port ion of t his report area. T he pond Is ~es1g ne d t o ho ld enough water to operate an irrigation sy stem for a predetermined lengthor time. Water
In the p ond is dep leted during the irrigat ion and allowed to recover be fore the next ir rigat ion.

Calculations (Beck, 1978, p. 19) have shown that

ponds with a radius of 50ft and a depth of 15ft below

the water table are capable of yielding 100,000 gal-

/day . Initial construction costs are reasonable

depending upon location.

'

A

In addition to conventional withdrawal of ground water from wells, induced recharge by means of connector wells could be an alternative use for the surface aquifer.
Rainfall in the coastal area is rapidly absorbed by the surface aquifer. However, dense clay layers in the Miocene series prevent much of the water stored in the surface sands from percolating down to recharge the principal artesian aquifer. The main recharge areas for the principal artesian aquifer are to the west of the study area, where the confining layer is thin .
Connector wells within the study area would link the surface aquifer with the principal artesian aquifer, bypassing the Miocene clays. Water from the surface aquifer would then flow downward by gravity into the principal artesian aquifer. In effect, a connector well hastens the natural recharge process. In order for induced recharge to take place, the water table of the surface aquifer must be at a higher elevation than the artesian pressure level in the principal artesian aquifer. This situation exists throughout much of the coastal area. Figure 8 shows the portion of the study area where the hydraulic head differential is suitable for induced recharae.
c
E

(Limestone)
EXPLANATION
A. CONNECTOR WELL CONDUCTING ~ATER FROM S.URFACE AQUIFER TO PRINCIPAL ARTESIAN AQUIFER. DIRECTION OF WATER FLOW IS SHOWN BY ARROWS.
B. MULTIPLE AQUIFER WELL WITH THREE SCREENED INTERVALS AND ONE FILTER- PACKED INTERVAL .
C. PONDWELL UTILIZING SURFACE AQUIFER .
D. "ROCK" WELL DRAWING WATER FROM RESERVOIR EXCAVATED IN SURFACE AQUIFER .
E. DRIVEN OR JETTED WELL .
Figure 8. Map showing the area where connector wells may be feasible.
192

Calculations based on hydraulic conductivitY, of the Miocene clay layers (Callahan, 1964, p. 24; Counts and Donsky, 1964, p. 77) and measured hydraulic head potential indicate that approximately 48,000 gal/day/sq mi reach the principal artesian aquifer by natural percolation in the coastal area . This is equivalent to only 1 in . of rainfall per square mile per year. Using a method described by Lohman (1972, p. 23), estimates of recharge via gravity-flow connector wells show that approximately 19,000 gal/day could be injected into the principal artesian aquifer through one connector well. This is a 40% increase in the calculated natural recharge per square mile. A series of 3 or 4 connectcJr wells in a square mile could more than double the natural recharge in a specific area.
Connector wells are a potential management option. Their use in the Brunswick area, for instance, could help decrease head differential in the principal artesian aquifer, which would in turn slow the intrusion of brackish water. However, in any situation where human activity interferes with a natural process, results can be detrimental and difficult to anticipate. For instance, the greatest danger with artificial recharge is the introduction of interior quality water into an aquifer. At this time, additional research into the economic and technical feasibility of connector wells in Georgia seems justified.
GROUND-WATER QUALITY
The chemical quality of ground water is the result of chemical interactions between the aquifer materials and the water they contain. Rainwater is usually quite low in dissolved solids and neutral to slightly acidic. That portion of rainfall which percolates downward changes its chemical composition even as it moves through the soil zone. Si l)~e ground-water movement is quite slow, commonly-measured in teet per year, the ground water has time to adjust to the chemical properties of the aquifer material.
Thirty water samples were collected for this study to determine the range in chemical quality. Laboratory analyses were performed either by the Georgia Geologic Survey or the U.S. Geological Survey. Table 1 shows selected summary results for the samples evaluated.
Quality of water from Neogene sediment is good through most of the study area, based on Department of Natural Resources, Environmental Protection Division , 1977, Sate Drinking Water Standards. This applies only to the major inorganic dissolved solids included in the analyses. 'Bacterial and organic chemical determinations were not performed at this time.

In general, the quality of water is a relative indication of its source; that is, the level of dissolved solids increases with depth. Water from the surface aquifer is usually lower in dissolved solids than is water from the Miocene aquifers. Total dissolved solids average less than 100 parts per million (ppm) from swrface sediments, while water from Miocene sediments averages slightly over 300 ppm .

Table 1. Summary of ground-water quality analyses.

Constituent or Physical Property
TEMPERATURE
oc
SILICA Si02 IRON
Fe CALCIUM Ca MAGNESIUM Mg
SODIUM Na
POTASSIUM K
BICARBONATE HC03 SULFATE
so4
CHLORIDE Cl
FLORI DE F
NITRATE N03 DISSOLVED SOLIDS
CARBONATE HARDNESS
CONDUCTIVITY MICROMHOS
FIELD pH

ANALYTICAL RESULTS(!)
~~.,_,l'li\)"' "''(,<:;)\~~ "''~'1'/i\)~
23.8 21.9 20.5

42.0 20.7 4.0

2.6 0.6 0.0

65.0 29.5 1.6

38.0 10.3 0.0

146 20.5 2.5

22 .0 4 .0 0.1

348 133 0 .0

164 25

0

175 25.2 I

1.2 0.3 0.0 35d2) 312(2) 0 .0 s4s21 204 30

319 121

4

720 401 51

7.65 6.80 4.63

(I) Valu411 in milliQrams per liter, except Temperature (Degrees Celsius); Conductivity (Micromhos@ 25 Cl; and pH.
f2lvalues Qreater than recommended lim its.

193

Water from the shallow aquifers is of three chemical types: (1) Water from the Miocene aquifer is generally a moderately hard calcium-bicarbonate water; (2) Samples from the surface aquifer were a sodium bicarbonate type; and (3) Some wells in the surface aquifer yielded sodium chloride water, although the concentration was usually not in excess of safe drinking water standards.
Maintaining the chemical quality of water in the shallow aquifers will be a ser ious challenge. Although the surface and Miocene aquifers are not extensively used at present, they contain a substantial reserve of water available for future use.
The surface aquifer is especially vulnerable to contamination because permeable sands which form the aquifer are found at, or close to, land surface. With increased development of the coastal area, a certain amou nt of contami natio n to the surface aqu ifer is proba bly unavoidable, especially from non.-point pollution resu lting from su rface runoff. However, damage to su rface aquifers from identifiabl e point sou rces of poll ution is need less, and can be prevented. Locati on of potential points of contamination should be based on complete geologic and hydrologic data, including the thickness and extent of local clay layers and a water-table contour map.
The geology of the Miocene aquifer makes it less susceptible to contamination. Substantial thicknesses of clay surrounding the lenticular sand aquifers will slow the recharge of surface water and allow natural filtration and absorption to take place.
Care should be taken to prevent needless pollution of the Neogene aqu1fers. Complex relationships between surface water and ground water can lead to pollution in unexpected places, and a polluted shallow aquifer is useless, as well as dangerous to the health of those dependent upon shallow ground water.

Brown R.H.. 1963, Estimating the transmissibility of ~n artesian aquifer from the specific capacity of a
well: in Berital, Ray, comp., Methods of determining permeability, transmissibility, and drawdown: U.S. Geol. Survey Water-Supply Paper
1536-1' p. 336-338. Callahan, J.T., 1964, The yield of sedimentary aquifers
of the coastal plain southeast river basins: U.S. Geol. Survey Water-Supply Paper 1669-W, 56 p. Counts, H.B., and Donsky, Ellis, 1963, Salt water encroachment, geology and ground water resources of Savannah area, Georgia and South Carolina: U.S. Geol. Survey Water-Supply Paper 1611, 100 p. Counts, H.B. and Krause, R.E., 1976, Digital model analysis of the principal artesian aquifer, Savannah, Georgia area: Water Resources Investigations 76-133, U.S. Geol. Survey Open-file rept., 4 p. Folk, R.L., 1965, Petrology of sedimentary rocks: Univ. Texas, 159 p. Georgia Department of Natural Resources, 1977, Rules for safe drinking water: Chap. 391-3-5, Environ. Protection Div., Atlanta. Herrick, S.M., 1965, A subsurface study of pleistocene deposits in coastal Georgia: Georgia Dept. Mines, Mining and Geology , Int. Clrc. 31 , 8 p. _____, 1971 , Well logs of th e coastal pl ai n of Geor g ia:
Georgia Geol. Su rvey Bull . 70, 460 p. Lohm an, S.W.. 1972, Ground water hydraulics: U.S.
Geol. Survey Prof. Paper 708, 67 p. Masch, F.D., and Denny, K.J ., 1966, Grain size distri-
bution and its effect on the permeability of unconsolidated sands: Water Resources Research, v. 2, no. 4, p. 665-667. Wait, R.L., and Gregg, D.O., 1973,. Hydrology and chloride contamination of the principal artesian aquifer of Glynn County, Georgia: Georgia Dept. Nat. Resources, Georgia Geol. Survey, Hydrologic Rept. 1, 93 p. U.S Department of Commerce, 1977, Climatological data, Georgia, Annual Summary: Nat'l Oceanic and Atmospheric Admin ., Environ. Data Service, Asheville, N.C.

SELECTED REFERENCES
Beck, B.F., 1978, The feasibility of using ponds as shallow wells in the coastal area of Georgia: unpub. report prepared for Environ. Resources Center, Georgia lnst. Technology and Georgia Dept. Nat. Resources, 22 p.
Brown, Eugene, Skougstand, M.W., and Fishman , M.J., 1974, Methods for collection and analysis of water samples for dissolved minerals and gases: Techniques of water resources investigations, Book 5, Chap. A 1, 160 p.
194

Ill. STRUCTURE, TECTONICS AND GEOPHYSICS
' 195

PRE-CRETACEOUS GEOLOGY BENEATH THE COASTAL PLAIN OF THE SOUTHEASTERN STATES, U.S.A.

T .M. Chowns Department of Geology West Georgia College
Carrollton, Georgia

ABSTRACT

The most prominent feature of a paleogeologic map of the Fall Line unconformity beneath the southeastern coastal plain is a complex Triassic graben extending southwestwards from the vicinity of Charleston, South Carolina to Apalachicola, Florida. The graben occupies an area of approximately 50,000 square miles and contains at least 6000 feet of continental red beds with substantial volumes of basaltic lava and minor intrusives. Radiometric ages for the latter cluster around 180 m.y. and indicate rifting associated with the initiation of the Gulf of Mexico and Atlantic Ocean. The northern flank of the graben consists of medium-to high-grade metamorphic rocks, which represent the subsurface continuation of the Pied-

mont province. The southern flank comprises a sequence of unmetamorphosed to slightly metamorphosed felsic pyroclastic deposits and Lower Ordovician-Middle Devonian clastic sediments which extend southwards into peninsular Florida and appear to be underlain by a Precambrian granitic basement. At least part of the felsic volcanic terrane is Cambrian or Late Precambrian in age, but radiometric dates show a wide range of ages and it is possible that more than one volcanic association is present. Stratigraphic and paleontologic affinities suggest that this sequence was originally associated with the African craton and therefore lies on the eastern margin of the Appalachian orogen.

DRAINAGE PATTERNS, BURIED VOLCANIC NECKS, AND PLATE TECTONICS IN THE SOUTH GEORGIA COASTAL PLAIN
James E. Clark, Jr. Law Engineering Testing Company
Atlanta, Georgia

ABSTRACT

The flow patterns of the major streams and rivers in the Coastal Plain of South Georgia were studied by (1) Landsat-1 Imagery, (2) gravity surveys conducted on one km . spacing, (3) deep well borings, and (4) PotassiumArgon age date determinations on basalt and rhyolite cuttings from those borings. It was concluded that the underlying volcanic rock is a volcanic neck at a depth of approximately 4000 feet. This volcanic neck controls the radial drainage patterns in the Seventeen Mile River drainage basin near Douglas, Ga. (Coffee County, Latitude 31 o 45' N, Longitude 82 48' W). The gravity survey

across the Ocmulgee River near Lumber City, Ga. (Jeff Davis C.ounty), suggests a series of normal faults. Additional gravity surveys across the Ocmulgee River near Jacksonville, Ga. (Telfair County), and the Altamaha River near Baxley, Ga. (Appling County), can be modeled as near basement faults and/or basic igneous intrusions. The Potassium-Argon dates of the volcanic rocks indicate Triassic and Jurassic emplacement. The age and lithology of the volcanic neck, the inferred normal faults and the intrusions can be related to continental rifting during the initial breakup of Laurasia and the formation of the Atlantic Ocean .

HEAT FLOW AND THE GEOTHERMAL RESOURCE POTENTIAL IN THE EASTERN UNITED STATES
John K. Costain Virginia Polytechnic Institute
and State University Blacksburg, Virginia

Abstract not available.
196

SUMMARY OF DEVELOPMENT OF THE CONTINENTAL MARGIN OFF GEORGIA BASED ON MULTICHANNEL AND SINGLE-CHANNEL SEISMIC-
REFLECTION PROFILING AND STRATIGRAPHIC WELL DATA
William P. Dillon and Charles K. Pauli U.S. Geological Survey
Woods Hole, Massachusetts

INTRODUCTION

81

eo

79

78

The basement of the continental margin off the southeastern United States was formed by the pro- 35 cesses of rifting, which modified pre-existent basement, and continental drifting, which created new

0

100 200KM

--Seismic Profile TD5

basement. The present continental margin framework resulted from subsidence of this basement accompanied by reef growth and clastic-sediment accumulation, controlled in part by ocean-current patterns, sea-level fluctuations, rates of input of ter-

I

rigenous and biogenous sediments, etc. The U.S.

Geological Survey has collected a grid of 9000 km of

deep penetration, common-depth-point, seismic

reflection profiles on the U.S. southeastern contin-

ental margin for purposes of studying the structure,

development, and petroleum potential of this

region. Profile TD-5 (fig. 1) best exemplifies the

structure of the continental margin off Georgia, and

will be used with knowledge gained from the rest of

the grid to characterize the development of that

area. This profile passes across three drillsites;

therefore, the stratigraphy along this line is better

known than that along any other profile across the

eastern U.S. continental margin.

Profile TD-5 is discussed in Dillon and others (1979a) and Dillon and others (1979c) . Stratigraphic data for the COST GE-1 drillsite are presented in Poag (this volume) and in a series of papers in 29 Scholle (1979); for the DSDP390drillsite in Benson, Sheridan, and others (1978); and for the ASPC well in Poag (1978). Other deep structural studies of the region have been reported by Buttler and others 27 (1978), Dillon and Paull (1978), Shipley and others (1978), Buttler and others (1979), Dillon and others (1979b), and Klitgord and Behrendt (1979) . Struc- 2s ture of Upper Cretaceous and Cenozoic strata has been analyzed by Paull and Dillon (1979).

REGIONAL STRUCTURE AND NATURE OF BASEMENT
The continental margin area oft the southeastern United States is associated with three zones of basement subsidence, shown by stippled patterns in figure 1. These are the Blake Plateau basin, Carolina trough, and the Southeast Georgia Embayment (Kiitgord and Behrendt, 1979). The Blake Plateau

Figure 1.

Location of seismic profile discussed and physiography of the U.S. southeastern continental margin, contour interval 200 m. Major structural features are labeled in bold italics, with zones of subsidence shown in stippled pattern.

197

basin, in the southern part of the area, displays basement depths of 8 to 14 km in an irregular pattern. North of the Blake Plateau basin and paralleling the edge of the continent from about 31 .5 N to Cape Hatteras (35 N), the elongate Carolina trough contains depths of 10-11 km to basement . The Southeast Georgia Embayment is a gently subsided, eastward-plunging depression recessed into the continent between two platform areas-the Carolina platform on the north and the Florida platform on the south. Profile TD-5 extends from the outer part of th e Southeast Georgia Embayment, across the deepest part of the Blake Plateau basin at its northern end, and eastward to the deep sea (fig. 1). The profile typifies the structure of the continental margin at the Blake Plateau basin, where a deep broad basin underwent maximum subsidence near its landward side. The seaward side of this continental margin depositional basin was closed off by reefs that acted as sediment dams. Erosion of these reefs by deep-sea processes has left an escarpment more than 3 km high at the seaward side of the Blake Plateau (Blake Escarpment, fig . 1).
Basement beneath the Blake Plateau basin is probably formed by large amounts of continental basement fragments, mantle-derived intrusive and extrusive mafic rocks, and considerable quantities of included sediments; this is referred to as transi tional basement. Such basement is characterized by broad, low-amplitude magnetic anomalies and a crustal thickness of generally 15-20 km , intermediate between continental and oceanic thicknesses.
DEVELOPMENT OF THE CONTINENTAL MARGIN
Rifting between North America and Africa began in Triassic time. During the rift stage, continental basement was fractured and extended, and intrusion and extrusion of mafic, mantle-derived material took place. Eventually , as the continents moved apart, the rift stage was followed by the drift stage, in which new oceanic crust was formed from such mafic material. However, off the southeastern United States, these two stages were separated by an intermediate stage in which the transitional basement was formed. The zones of deepest subsidence of continental margin basins seem to be underlain by this transitional basement. The spreading center that was active during earliest opening of the ocean, when the Blake Plateau basin transitional crust was forming, ceased its activity at about 170 or 175 million years (m .y.) ago when a new spreading center developed to the east. This new spreading center has been active to the present time.
Figure 2 is a diagrammati c presentation of the inferred stages of development of the continental margin off Georgia at the location of line TD-5. The

NORTH AMERICA

AFRICA

140M.Y.

END OF

== ~RIDGIAN

140

..

170

116M.Y

END OF

NEOCOMIAN

100 M.Y.
END OF EARLY CRETACEOUS

~ENT

Fig u re 2.

Pro posed stages in t he develo pment of t he con t ine nt al margin o ff Georgia as inte r pre t ed from profile T D-5. In each idealized section, the de posits form ed bet wee n t he ti m e indicated and the previous stage are stippled. Crosses repre sent con t i n en t al base me nt. "vees" represen t oceanic baseme n t, and a mixture of the two symbols represents tra n sit io nal ba seme nt . T he ho ri zons w hi c h represent the sea floor at a stage are labeled wi th the ir age in la ter st ages as t hey a re progress ive ly more deep ly bur ied.

first diagrammatic section (170 m.y.) shows the continental margin at the time of the spreading-center jump. In figure 2, the two centers of spreading are shown by the symbol of diverging arrows, the right hand set representing the newly developing spreading center. By this time (170 m .y .), a well-defined post-rift erosional surface had formed and probably was being covered by sediments deposited in the newly formed Blake Plateau basin. Off South Carolina, northern Georgia, and southern North Carolina, a layer giving very strong reflections and high refraction velocities, probably of volcanic rock, covers the post-rift erosional surface. The renewed volcanic activity may have occurred because of stresses associated with the spreading-center jump.

198

After the spreading-center jump, truly oceanic crust began to accrete, and the eastern U.S. continental margin became progressively farther west of the spreading center as the zone of new oceanic crust became wider. At 140 m .y . (fig . 2), the ocean was broader and reefs began to function as sediment dams. These reefs, now beneath the outer Blake Plateau, were initiated on the African side before the spreading-center jump. The largest part of continental margin basin subsidence occurred before 140 m .y. (approximately the end of the Jurassic) . The pattern of this early subsidence was irregular; present basins and troughs subsided more than adjacent areas. Conversely, later subsidence was much more uniform across the entire continental margin region .
By 116 m.y. one of the developing reefs became dominant, and its growth and, eventually, erosion of its front formed the present Blake Escarpment. The Early Cretaceous (about 140 to 100 m.y. ago) was a period of extensive formation of back-reef and carbonate bank deposits on the outer Blake Plateau . Meanwhile, the shoreline oscillated across the inner Blake Plateau , as shown by the marine-continental facies boundary estimated from reflection characteristics of the strata. At about the end of Neocomian time, the main escarpment reef died and a new reef formed, growing during Aptian and Albian before it, too, died. This step-back of the reef occurred along much of the outer Blake Plateau . The reef, as a continuous feature, does not extend north of the Blake Spur (fig . 1), although the seaward part of the Lower Cretaceous shelf is marked by probable patch reefs and carbonate banks.
In th e Late Cretaceous and Paleocene (approximately 100-55 m.y. ago , fig . 2), rising ocean level and continued regional subsidence left the former shelf as a broad submerged plateau that extended

across the present Blake Plateau and outer continental shelf. Fine sediments, characteristic of outer shelf or slope depths, accumulated. The Cenozoic history of the continental shelf south of Cape Hatteras is summarized in figure 3. Near the end of the Paleocene, a major erosional event took place that left an irregular unconform'ty in a linear belt 100-km wide beneath the present outer continental shelf and inner Blake Plateau, and that is believed to have been caused by the initiation of the ancestral Gulf Stream. The erosional surface was buried in the Eocene by a seaward progradation of the shelf. This first Tertiary she!f progradation ended in the Oligocene with another regional erosive event, but one that did not produce as great erosional relief as the earlier Paleocene episode. The Oligocene erosion may have been related to a worldwide lowering of sea level. At about this time there also occurred an extensive episode of erosion in the deep sea that strongly affected the continental s.lope off the southeastern United States . That erosion probably removed considerable amounts of material from the Blake Escarpment south of the Blake Spur.
The Oligocene unconformity beneath the present continental Shelf is covered by a second Tertiary shelf progradation (fig . 3, Present). This progradational wedge is smaller than the Eocene wedge and apparently was delimited to seaward by the flank of the Gulf Stream. The Gulf Stream flow has been instrumental in forming the Tertiary depositional pattern; it has prevented deposition on the inner Blake Plateau by preventing progradation of the shelf toward the east. A very thin layer of Tertiary deposits has accumulated on the outer Blake Plateau seaward of the main flow of the stream (fig. 2, Present); these are chiefly pelagic oozes and not continentally derived sediments (Charm and others, 1969).

Fi9u re 3. Proposed stages in the deve lopment of the Florida-Hatteras she lf off Georgia during Cenozoic time. Symbols are used on ly to indicate deposits of specific ages and do not represent litho logy.
199

SUMMARY
The continental margin off Georgia probably began to form with rifting , mafic intrusive and extrusive activity, and rapid sediment deposition which led to development of a transitional basement. Early subsidence was rapid for the basement beneath the present Blake Plateau basin, and the Uppe r Jurassic deposits form the thickest unit. Reefs acted as sediment dams at the seaward side of the basin. Near the end of the Neocomian, the reefs died, but a new reef formed slightly to landward and continued to form a sediment dam until the end of the Early Cretaceous . Subsequently , the Blake Plateau has been a moderately deep water environment (several hundred meters) until present. The Gulf Stream became significant on the Blake Plateau near the Paleocene-Eocene boundary, and since then has prevented the shelf sediments from prograding across the plateau .
BIBLIOGRAPHY
Benson, W.E., Sheridan, R.E., and others, 1978, Initial reports of the Deep Sea Drilling Project, v. 44: Washington, U.S. Government Printing Office, 1005 p.
Buttler, R.T., Shipley, T.H ., and Watkins, J.S. ," 1978, Blake continental margin seismic section: Am. Assoc. Petroleum Geol. Seismic Sec. No.2
Buttler, R.T., Watkins, J .S., and Dillon, W.P., 1979, Geology of the offshore Southeast Georgia Embayment, U.S. Atlantic Continental Margin, based on multichannel seismic reflection profiles: in Watkins, J .S., Montadert, L., and Dickerson, P.W., eds., Geological and geophysical investigations of continental margins: Am . Assoc. Petroleum Geol. Mem. 29, p . 11-25.
Charm, W.B., Nesteroff, W.D., and Valdes, Sylvia, 1969, Detailed stratigraphic description of the JOIDES cores on the continental margin off Florida: U.S. Geol. Survey Prof. Paper 581-D, 13 p.
Dillon, W.P. and Pauli, C.K., 1978,Seismic-reflection profiles off coasts of South Carolina and Georgia: U.S. Geol. Survey Misc. Field Studies Map MF-936.
Dillon , W.P., Pauli, C.K ., Buttler, R.T. and Fail , J.P., 1979b, Structure and development of the Southeast Georgia Embayment and northern Blake Plateau: Preliminary analysis: in Watkins J.S ., Montadert, L., and Dickerson, P.W ., eds. , Geological and geophysical investigations of continental margins: Am. Assoc. Petroleum Geol. Mem . 29, p. 27-41.

Dillon, W.P., Pauli, C.K., Dahl, A.G. and Patterson, W.C., 1979a, Structure of the continental margin near the COST GE-1 well site from a common depth point seismic reflection profile:

in P.A. Scholle, ed., Geological studies of the COST GE-1 well, United States South Atlantic Outer Continental Shelf area, U.S. Geol. Survey Circ. 800, p. 97-107. Dillon, W.P., Poag, C.W., Valentine, P.C., and Pauli, C.K., 1979c, Structure, biostratigraphy, and seismic stratigraphy along a CDP seismic profile through three drillsites on the Continental margin off Jacksonville, Florida: U.S. Geol. Survey, Misc. Field lnv : . Map, MF1090.

Klitgord, K.D., and Behrendt, J.C., 1979, Basin structure of the U.S. Atlantic Continental Margin : in Watkins, J.S., Montadert, L., and Dickerson, P.W., eds ., Geological and geophysical investigations of continental margins : Am . Assoc. Petroleum Geol. Mem. 29, p. 85-112.
Pauli, C.K. Dillon, W.P., 1979, The subsurface geology of the Florida-Hatteras Shelf, Slope, and Inner Blake Plateau : U.S. Geol. Survey

Open-file Rept. 79-448, 94 p.

.

Poag , C.W., 1978, Stratigraphy of the Atlantic

Continental Shelf and Slope of the United

States: Ann . Rev . Earth Planet Sciences, v. 6,

p. 251-280. Poag, C.W., Biostratigraphy, sea level fluctua~ions,
subsidence rates and petroleum potential of the Southeast Georgia Embayment: this volume. Scholle, P.A. , ed., 1979, Geological studies of the COST GE-1 well , United States South Atlantic Outer Continental Shelf area: U.S. Geol. Survey, Circ. 800, 114 p. Shipley, T.H. , Buttler, R.T., and Watkins, J.S., 1978, Seismic stratigraphy and geologic history of Blake Plateau and adjacent western Atlantic continental margin: Am . Assoc. Petroleum Geol. Bull. , v. 62, no. 5, p. 792-812.

200

GEOCHEMISTRY OF PRE-CRETACEOUS ROCKS BENEATH THE COASTAL PLAIN OF GEORGIA AND SOUTH CAROLINA
David Gottfried and Michael W. Higgins U.S. Geological Survey Reston, Virginia
Abstract not available.
JOINTS AND MINOR FAULTS IN THE GEORGIA COASTAL PLAIN
Michael W. Higgins U.S. Geological Survey
Reston, Virginia and
Sam M. Pickering, Jr. Yara Engineering Company
Sandersville, Georgia
Abstract not available.
201

SEISMICITY OF GEORGIA
Leland Timothy Long Georgia Institute of Technology
Atlanta, Georgia

ABSTRACT
Earthquakes in Georgia occur in the Coastal Plain, Central Piedmont and folded Appalachian provinces. Six earthquakes are known to have occurred in the Georgia Coastal Plain. The most recent event occurred on December 27, 1976, near Reidsville, Ga., where it was felt with intensity V. On August 31, 1886, the Coastal Plain of South Carolina, near Charleston, was the location of the earthquake which caused the highest intensity of shaking in Georgia. Intensities of VIII were experienced near the South Carolina-Georgia border and the level of shaking decreased toward the northwest in Georgia to intensity V. The seismic activity in the Central Piedmont occurs in a zone which extends northeast from Central Georgia into South Carolina. Eight events have been felt in central Georgia and two near the South Carolina border in the Central Piedmont. The largest three of these events were felt with intensity VI. The folded Appalachians of northwest Georgia have experienced three events from within Georgia and others from adjacent areas of Alabama and Tennessee. The observed activity of that portion of the Southern Appalachian Seismic Zone implies that one event of intensity V should be expected approximately each ten years.
No geologic fault in Georgia has been found to be associated with seismic activity. Large geologic faults can be found throughout Georgia, but they are considered inactive.
INTRODUCTION
Earthquakes can be one of the most terrifying of the natural phenomena. Catastrophic loss of life and mass destruction of property are typical of major earthquakes that occasionally strike in populated regions of the world . However, the chance of experiencing an earthquake varies significantly from region to region. The historical record of earthquakes and their locations shows that most earthquakes occur in well-defined belts or zones that mark the boundaries of the earth's rigid crustal plates. Away from the plate boundaries and in the interior of the plates, the seismic activity is significantly lower. Georgia and the southeastern United States lie within the interior of the North American Plate.
Earthquakes at plate boundaries are adequately explained by the relative movement of the plates in accordance with the theories of plate tectonics (Wilson, 1971; Isacks and others, 1968). Earthquakes occurring in the interior of plates are not as easily

explained. Where mountainous continental crust occurs in the interior of a plate, a minor level of seismic activity is often observed, but the relation of this activity to plate tectonics is not always clear. Some zones of seismic activity may be related to landward extensions of major transform faults or to zones of weakness in continental crust (Sykes, 1978). Perhaps, also, local stresses related to vertical motion within plates contribute to earthquake activity.
The seismic activity levels in the southeastern United States vary with location (Bollinger, 1973a) . For example, the Southern Appalachians are notably more active than the surrounding areas. The activity level for some of these surrounding areas is so low that the 100 to 200 years of historical data do not allow satisfactory evaluation. In the Coastal Plain, the seismicity data may even appear to be contradictory in that the Charleston area has experienced many more earthquakes than any other Coastal Plain site. Ultimately, the relative seismic activity rates will be explained by physically measurable entities such as crustal thickness, crustal rigidity, vertical crustal movement or horizontal stresses. At this time we can define only some of the differences in seismic activity rates and some of the characteristics of earthquakes in more active areas.
DATA BASE
0 nly since the installation of the WWSSN stations ATL, OXF, BLA and SHA in the early 1960's has it been possible to adequately document the occurrence of earthquakes in the southeastern United States. Instrumental recordings of earthquakes allow measurement of earthquake magnitude. Magnitude is a single number which quantifies the excitation by an earthquake of certain seismic waves or ground vibrations. Magnitude can be determined to within the error of measurement from seismograms recorded at any distance. The magnitude scale is logarithmic and hence each increase of one unit corresponds to a tenfold increase in the amplitude of the ground vibrations. Richter (1935) developed the definition of magnitude and a function to correct for the normal attenuation of seismic energy with distance from the epicenter, (the point on the earth's surface above the zone of faulting that caused the earthquake vibrations). Hence, magnitude is often called "Richter Magnitude". At a magnitude of approximately 4.5, slight damage may

202

occur near the epicenter. At approximately 5.5 moderate damage may occur. and above 6.5 the damage can be considerable . The August 31, 1886, earthquake near Charleston, S.C. is the only event in the southeastern United States to possibly exceed a magnitude of 6.5.
Accounts of earthquakes occurring before the 1960's relied heavily on reports by people experiencing the earthquakes or on documentation of damage perpetrated by the earthquake. Such reports are evaluated according to the empirical Modified Mercalli scale for earthquake intensity (see Appendix I). Intensity measurements are intended to specify the severity of the earthquake motion at a given point by its effect on people, structures and landscapes. Intensity data provide essential information in studies of earthquakes because they provide data on earthquake shaking and damage potential not currently available from the very limited distribution of earthquake recording instrumentation. A standardized questionnaire is given in Appendix II. Instructions in the evaluation of intensity data can be found in Richter (1958). Care must be exercised in interpretation of some felt reports. If not obtained immediately, intensity surveys can be influenced by

news reports or hearsay. Also, reports of very local earthquakelike vibrations are occasionally reported along the Georgia Coast, but these are generally attributed to supersonic: aircraft or military tests offshore.
A location plot of southeastern United States earthquakes (fig . 1) does not directly reveal distinct trends within Georgia. The larger Georgia earthquakes are listed in Appendix Ill (from Stover and others, 1978). Only the central Georgia area near Milledgeville indicates an apparent concentration of activity. In fact, the two major previously identified seismic trends in the southeastern United States only border on Georgia. If one follows the usual definitions or seismic zones in the southeastern United States (Bollinger, 1973b), the South CarolinaGeorgia Seismic Zone, which has an axis that trends northwest, covers the northeastern third of Georgia and extends in width to the northeast across South Carolina. The Southern Appalachian Seismic Zone, (from Bollinger, 1973b) which has an axis that trends northeast, crosses only the northwest corner of Georgia. These seismic zones were drawn entirely on the basis of historical concentrations of earthquake epicenters, as there exists no clear relation

so Figure 1. Location plot of recent and historic seismic activity in the Southeastern United States, adapted and
updated from Bollinger (1975).
203

between faults or other near-surface geologic structures and earthquakes in the southeastern United States. In fact, no fault in Georgia has yet been found to be associated with seismic activity. Prominent geologic faults and zones in which multiple faults exist can be found throughout North Georgia. They have also been interpreted from geophysical data in the Coastal Plain of South Georgia but are considered inactive today.
EARTHQUAKES FELT IN GEORGIA
The earthquakes felt within Georgia have epicenters both inside and outside of Georgia's borders. Numerous small events near Georgia's borders have been felt within Georgia at intensity level of V or less. Two great earthquakes, the Charleston, S.C. earthquake of August31 , 1886, and the three largest New Madrid, Mo., earthquakes of 1811 and 1812 were felt across Georgia. Within Georgia, earthquakes occur in three general areas which correspond approximately to the Coastal Plain, Piedmont, and folded Appalachian physiographic provinces (fig. 2). Earthquakes in these three provinces will be discussed separately by province since the crustal structures in each province influence the manner of stress release by earthquakes. With existing data, the three provinces can be characterized according to the earthquake mechanism for events that occur within their boundaries as well as according to the crustal structures that host the earthquake.
EARTHQUAKES IN THE COASTAL PLAIN
Coastal Plain sediments cover the southern half of Georgia and extend into the neighboring states: southeastern Alabama, Florida and the southeastern half of South Carolina. The crustal structure beneath the Coastal Plain sediments is characterized by remanent features of extension .during the early opening of the Atlantic ocean . That is, the crust is generally thinner as a consequence of the extension and is intruded by extensive mafic volcanic rock units characteristic of incipient rift zones. The thinning and intrusives distinguish the crust of the Coastal Plain from the thicker crust of the Piedmont Province. In particular, examination of magnetic anomaly maps show that the Piedmont Province lithologies do not extend indefinitely under the Coastal Plain sediments. The southern boundary of the Piedmont lithologies (Popenoe and others, 1978) is assumed to define the northern boundary of the seismically active part of the Coastal Plain.
Three or perhaps six small earthquakes are suspected to have occurred in the Georgia Coastal

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Plain. On May 23, 1928, an apparent seismic tremor was felt in the Valdosta area . On AprilS, 1958, about noon, small earth tremors were reported by several residents near Tifton . The third event is the December27, 1976, South Georgia earthquake (see fig. 3) which was felt throughout Toombs County (Lance and others, 1977) . The maximum intensity for the earthquake was V (MM). The intensity data in figure 3 suggest a felt configuration oriented northeast. The first-motion data indicate a focal mechanism with a nearly vertical fault plane striking N40 E. The southeast side moved up as a result of the earthquake.The three other Coastal Plain events are of questionable location and probably occurred near Savannah. A similar sparse distribution of earthquakes occurs throughout Florida and southern Alabama.
The Charleston area events appear to be an exception to the generally low level of activity. The August 31, 1886, earthquake near Charleston was followed by a sequence of over 400 felt events. The 1886 event is the largest to occur in the southeastern United States. It had a maximum intensity of X(MM) at its epicenter. In Georgia it caused intensity VIII effects near the Savannah River, decaying to intensity V in the western and northwestern portions of the State. Throughout most of Georgia it generated

204

EXPLANATION Not felt
-II Intensity (MM)
'f Epicenter
o Portable station


N

,_

Figure 3.

Intensity data for the December 27, 1976 earthquake near Reidsville, Ga. Solid circles show locations where the shock was not felt The Roman numerals indicate locations where the shock wa~ felt at the indicated intensity. The domain of possible pressure "P" axes and tension "T" axes are shown 1n the focal mechanism solution above.

the most severe intensity ever experienced from any earthquake . If the Charleston area activity is considered as one epicentral zone, then in the Coastal Plain approximately twenty epicentral areas have generated intensity IV or greater events in the last 100 years. However, many earlier events could have escaped detection and the completeness of the data may be questionable, as evidenced by the identification of five Of these epicentral areas in the last ten years . Except for the Charleston area events, the sparse occurrence of Coastal Plain earthquakes does not allow evaluation of rates of occurrence or completeness. Most of the Charleston events are assumed to be aftershocks of the main event, but continuing tectonic forces may contribute to the recent activity. Most organizations required to assess seismic risk have traditionally assumed that the Charleston area activity is unique and have assigned it a level of risk higher than the rest of the Coastal Plain. They recognize that whether it is an area of aftershock activity or one of continued tectonic involvement, the potential for large events poses a serious seismic risk for South Carolina and adjacent states.

The question of whether an event of intensity X or larger would only occur near Charleston or would occur anywhere in the Coastal Plain (including southern Georgia) has not been answered. The existence of tectonic involvement as an explanation for the Charleston area events would allow an hypothesis that such large events might not occur in the remainder of the Coastal Plain. On the other hand, if the Charleston area events prove to be purely an aftershock sequence in an area indistinguishable, except for seismicity, from the rest of the Coast~! Plain, then an intensity X event might be expected anywhere in the Coastal Plain, but with a rate of occurrence compatible with the low-level seismicity. One can test whether earthquakes are compatible with an aftershock sequence by plotting the number of events versus time. Aftershocks will generally follow Omori's equation and hence decrease in number inversely proportional to time. If plotted on a logarithmic scale, a slope of0.9 to 1.3 will include observations for most earthquakes (Scholtz, 1968). The earthquakes felt near Charleston (from Tarr, 1977) following the 1886 main shock indicate a slope of 1.16 (see fig. 4). This slope is

205

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almost identical to the value of 1.14 obtai ned for the Great Alaskan earthquake (Page, 1968). The fit to the Omori equation shows that the current rate of activity at Charleston is entirely consistent with an aftershock sequence. Hence, without other constraints, the possibility exists that the tectonic input at Cha rl eston is mi nimal , the Charleston area may not be un ique, and an intenstiy X earthquake might be ex pected anywhere in the Coastal Plain .
Ultimately, the statistical approach presented above will be modified when a mechanism for earthquakes in the Coastal Plain is accepted and proven correct. A uniform probability of occurrence is not realistic because the crust in the Coastal Plain is heterogeneous in composition, nonuniform in thickness and, as such, can not be expected to react uniformly to any applied stresses. A spat ial association of earthquakes with mafic intrusions has been noted, and explanations for such an association (based on stress amplification or the particular material properties of the intrusives) have been proposed (Long 1977; Campbell 1978) . If shown to be correct, this association could limit the probable location of significant events in the Coastal Plain to major centers of mafic intrusives.

EARTHQUAKES IN THE CENTRAL PIEDMONT
The central portion of the Piedmont extends northeast from central Georgia and generally follows the axes of the Carolina Slate belt and Charlotte belt. The seismicity follows a zone of thinner crust interpreted as a late Precambrian or early Cambrian rift (Long, 1979). The crust is on the order of 33 km thick (Kean, 1978) . The historical earthquake epicenters in this zone in Georgia are concentrated in two general areas: central Georgia and Clark Hill Reservoir area.
The most active area appears to be central Georgia, with eight felt events with intensities from Ill to VI. These historical epicenters show a possible northwest trend. Two events of intensity VI have been felt in the Clark Hill Reservoir area. In the central Piedmont an earthquake has been felt approximately once each 10 years for the past 100 years . The seismic activity in central Georgia and the Clark Hill Reservoir area has been monitored in detail by recently installed seismic recording stations. In central Georgia, the general northwest trend has been confirmed and additional epicenters of small unfelt events (often called microearthquakes) have been located about Lake Sinclair. In the Clark Hill Reservoir area the most obvious center of activity has been the aftershock zone of the August 2, 1974, earthquake. Two other microearthquake epicentral zones have been identified near the reservoir.
Through seismic monitoring from 1973 to the present and associated geophysical studies in the Clark Hill Reservoir area (Denman, 1975; Bridges, 1976; Marion , 1977; Guinn, 1978; Dunbar 1978) a general model for the Piedmont Province earthquakes has been developed. The observations are consistent with these earthquakes being caused by a release of stress along existing planes of weakness such as joints near the surface. The stresses could be derived from minor flexure of the crust, stress amplifi cation ln inh om oge neou s geolog ic units, erosion al un load lng o r thermal perturbati o ns . The strain rel ease cou ld be fac ilitated by strength deterioration thro ugh weath ering processes or (I n some areas) water-related changes caused by reservoir impoundment. The implication of this mechanism is that the fault area for these earthquakes will be limited by the depth penetration of joints or other planes of weakness and hence will be limited to depths less than about 4 km. A maximum magnitude of about 5.5 is implied by limitations on a reasonable fault radius and stress drop (Long , 1976) .

206

EARTHQUAKES IN THE SOUTHERN APPALACHIANS
The seismically active part of the Southern Appalachians affects only the northwestern corner of Georgia. The southeastern edge of this zone in Georgia has been defined by the southeastern extent of Paleozoic sediments or, equivalently, by the Cartersville or Great Smoky fault. Few earthquakes are documented in Georgia in this zone, but some have occurred just across the border in Alabama and Tennessee. The Conasauga, Tenn ., earthquake of November 4, 1976, was typical of these events. It had a maximum intensity ofV to VI. A focal mechanism for this event indicates a probable thrust-type movement on a northwest-trending fault plane. Similar focal mechanisms are obtained for other earthquakes in eastern Tennessee, implying that tne stresses are horizontal and compressional and trend NE-SW. Few depths of focus are available, but most are estimated to be in the range of 4 to 8 km. This depth range places the earthquakes below the Paleozoic sediments and in the crystalline basement. Considering the historical recording of about 10 events in the last 100 years, one event of intensity V or greater should be expected approximately each 10 years in northwestern Georgia and adjacent areas of Alabama and Tennessee.
SEISMIC SURVEILLANCE IN GEORGIA
All the seismic stations except AMG shown on figure 2 are maintained by the School of Geophysical Sciences at the Georgia Institute of Technology . Financial support from the Nuclear Regulatory Commission, the Corps of Engineers, Georgia Power and Georgia Tech have made this net possible. AMG is supported by Georgia Southwestern College. Data for the Georgia Institute of Technology stations are all recorded in the laboratories of the School of Geophysical Sciences by means of telemetry from the remote sites. Information on recent or local earthquakes can be obtained by contacting the School of Geophysical Sciences. The National Earthquake Information Service of the U.S. Geological Survey in Golden, Colo., normally provides information on large regional or worldwide earthquakes by issuing bulletins to the news services.
ACKNOWLEDGEMENT
The research which has made this paper possible was supported by the Nuclear Regulatory Commission through grant number AT (49-24)-0210. The Georgia Power Company and the U.S. Army Corps of Engineers have suported the operations of the seismic stations. Appreciation is extended to Carl W. Stover and G .A. Bollinger for their comments and assistance with the manuscript.

BIBLIOGRAPHY
Bollinger, G.A., 1973a,Seismicity of the southeastern United States: Seismological Soc. America Bull.,v. 63, p. 1785-1808.
- -- 1973b, Seismicity and crustal uplift in the southeastern United States: Am. Jour. Sci.,v. 273-A, p. 396-408.
_ _ _, 1975, A catalog of Southern United States earthquakes -1754 through 1974: Virginia Polytech. lnst. and State Univ. Res. Div.,Bull. 101, 68 p.
Bridges, S. R., 1976, Evaluation of stress drop on the August 2, 1974, Georgia-South Carolina earthquake and aftershock sequence: unpub. M.S. thesis, Georgia lnst. Tech., Atlanta, Ga., 103 p.
Campbell, D.L ., 1978, Investigation of the stressconcentration mechanism for intraplate earthquakes: Geophys. Res. Lett., v. 5, p. 477-479.
Denman, H.E., Jr., 1975, Implications of seismic activity at the Clark Hill Reservoir: unpub. M.S . thesis, Georgia lnst. Tech., Atlanta, Ga., 103 p.
Dunbar, D.M. , 1978, A seismic velocity model of the Clark Hill Reservoir area: unpub. M.S. thesis, Georgia lnst. Tech., Atlanta, Ga., 59 p.
Guinn , S.A., 1978, Earthquake focal mechanisms in the southeastern United States: unpub. M.S., thesis, Georgia Inst. Tech., Atlanta, Ga., 150 p.
lsacks, B.D., Oliver, J ., and Sykes, L.R., 1968, Seismology and the new global tectonics: Jour. Geophys. Res., v. 73, p. 5855-5899.
Kean, A.E., 1978, A refraction crustal study of the southeastern United States: unpub. M.S. thesis, Georgia lnst. Tech., Atlanta, Ga., 68 p.
Long, L.T., 1974, Bouguer gravity anomalies of Georgia in Symposium on the petroleum geology of the Georgia Coastal Plain, Georgia Geol. Survey, Bull. 87, p. 141-166.
- - - 1979, The Carolina slate belt--Evidence of a continental rift zone: Ge.ology, v. 7, p. 180-184.
_ _ _, 1977, Maximum "induced" earthquake, Clark Hill Reservoir Area: Design earthquake report, Geological and seismological evaluation of earthquake hazards at the Richard B. Russell Project, U. S. Army Engineer Dist. Corps of Engineers, Savannah, GA., Sect. B, 15 p.
_ _ _, 1976, Speculations concerning southeastern earthquakes, mafic intrusions, gravity anomalies, and stress amplification: Earthquake Notes, v. 47, no. 3, p. 29-35.
Marion, G.E., 1977, A spectral analysis of microearthquakes that occur in the southeastern United States: unpub. M .S. thesis, Georgia lnst. Tech., Atlanta, Ga., 154 p.
Page, Robert, 1968, Aftershocks and microaftershocks of the Great Alaska Earthquake of 1964: Seismological Soc. Am. Bull ., v. 58, p. 1131-1168.

207

Popenoe, P., and Zeitz, 1., 1977, The nature of the crystalline basement beneath the Coastal Plain of South Carolina and southeastern Georgia: U.S. Geol. Survey Prof. Paper, 1028-1, p. 119-137.
Richter, C.F., 1958, Elementary seismology: San Francisco, Calif., W.H. Freeman Co., 768 p.
Scholz, C. H., 1968, Microfractures, aftershocks, and seismicity: Seismological Soc. Am. Bull., v. 58, p. 1117-1130.
Stover, C.W., Reapor, B. G., Algermissen, S.T., Long, L.T., 1978, Seismicity map of the State of Georgia: U.S. Geol. Survey Misc. Field Studies Map.
Sykes, L.A., 1978, Intraplate seismicity, reactivation of existing zones of weakness, alkaline magnetism and other tectonism postdating continental fragmentation: Rev. Geophys. Space Phys., v. 16, p. 621-688.
Taber, Stephen, 1914, Seismic activity in the Atlantic Coastal Plain near Charleston, South Carolina: Seismological Soc. America Bull ., v. 4, p. 108-160.
Tarr, A. C., 1977, Recent seismicity near Charleston, South Carolina, and its relationship to the August 31, 1886, earthquake: U.S. Geol. Survey Prof. Paper, 1028-D, p. 43-57.
Wilson, J.T., 1971, Continents adrift: Readings from Scientific American, San Francisco, Calif., W.H . Freeman Co., 172 p.
APPENDIX 1: Modified Mercalli Intensity Scale of 1931 (Abridged)
I. Not felt except by a very few under especially favorable circumstances.
II . Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
Ill. Felt quite noticeably indoors, especially on upper floors of buildings, but many people do. not recognize it as an earthquake. Standing motorcars rock slightly. Vibration like passing truck. Duration estimated.
IV. During the day, felt indoors by many, outdoors by few. At night some awakened. Dishes, windows, and doors disturbed; walls make creaking sound. Sensation like heavy truck striking building. Standing motorcars rocked noticeably.

V. Felt by nearly everyone; many awakened. Some dishes, windows, etc., broken; a few instances of cracked plaster; unstable objects overturned. Disturbance of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.
VI. Felt by all; many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight.
VII. Everybody runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures. Some chimneys broken. Noticed by persons driving motorcars.
VIII. Damage slight in specially designed structures; considerable in ordinary substantial buildings, with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving motorcars disturbed.
IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken.
X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed (slopped) over banks.
XI. Few, if any (masonry), structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.
XII. Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air.

208

APPENDIX II

U.S. DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
EARTHQUAKE REPORT

Form Approved OMB No. 42-R1700

Please answer this questionnaire carefully and return as soon as possible.

1. Was an earthquake felt by anyone in your town or zip code area recently?

0 Not felt: Please refold and tape for return mail.

0 Felt: Date

Time _ _ __

DAM
0 PM

0 Standard time 0 Daylight time

Name of person filling out form _ _ __ _ __ _ _ __ _ _ _ _ _ __ _ _

Address--- - - -- - - -- - - - - -- - - - - - - - - - -- -

City State

C o u n r y ' - - - - - -- - - -- Zip code ___ _ __ _ _ _ _ __ _

If you felt the earthquake, complete the following section. If others felt the earthquake but you did not, skip the personal report and complete the community report.

PERSONAL REPORT

2a. Did you personally feel the earthquake? b. Were you awakened by the earthquake? e. Were you frightened by the earthquake?

10 Yes 10 Yes
30 Yes

0 No 0 No 0 No

d. Were you at

40 Home

SO Work

60 Other?

e. Town and zip code of your location at time of earthquake

f. Check your activity when the earthquake occurred :

10 Walking

80 Sleeping

90 Lying down

10 O Standing

g1\.)

II 0 Driving (car in motion)
g. Were you

12 0 Sitting 14 0 Inside or

llO Other 150 Outside?

h. If inside. on what floor were you?

1600

Continue on to next section which should include personal as well as reported obser\lations.

COMMUNITY REPORT

Check one box for each question that is applicable.
3a. The earthquake was felt by 0 No one 170 Few

180 Several

b. This earthquake awakened c. This earthquake frightened

0 No one 0 No one

210 Few 250 Few

220 Several 260 Several

190 Many 130 Many 170 Many

100 All?
140 All? 180 All?

4. What outdoor physical effects were noted in your community?

Parapets or cornices fallen

290 Yes

0 No

Trees and bushes shaken

300 Slightly 310 Moderately

Standing vehicles rocked Moving vehicles rocked

330 Slightly 360 Slightly

34 0 Moderately 37 0 Moderately

Ground cracks

390 Wet

40 0 Steep slopes

ground

Landslides

410 Small

430 Largo

Underground pipes

440 Broken

45 0 Out of service

32 0 Strongly
35 0 Strongly 380 Strongly 410 Dry and level
ground

Water splashed onto sides of lakes, ponds, swimming pools
Elevated water tanks

460 Yes 470 Cracked

0 No
480 Twisted

490 Fallen (thrown down)

Air coolers

500 Displaced 510 Rotated

510 Fallon

Railroad tracks bent Stone or brick fences Tombstones

530 SUghtly 550 Cracked 580 Displaced

540 Greatly 560 Fallon 590 Cracked

57 0 Destroyed 600 Rotated

Chimneys
Highways or streets Sidewalks

610 Fallen

62 0 Cracked 63 0 Twisted

640 Fallen

650 Broken at roof line

660 Bricks fallen

67 0 Cracked slightly 68 0 Large cracks 69 0 Displaced

70 0 Cracked slightly 710 Large cracks 72 0 Displaced

Continued on the reverse side

5. What indoor physical effects were noted in your community?

Windows, doors, dishes rattled

73 0 Yes

0 No

Buildings creaked

74 0 Yes

0 No

Building trembled (shook)

75 0 Yes

0 No

Hanging pictures

760 Swung

77 0 Out of place

780 Fallen

Water in small containers

790 Spilled 800 Slightly disturbed

Windows

810 Few cracked 820 Some broken

830 Many broken

6a. Did hanging objects, doors swing? 0 No

b. Can you estimate direction?

0 No

840 Slightly 86 0 V iolentiY
87 0 North/South
890 Other

850 Moderately
88 0 East/West

7a. Were small objects (dishes, knick-knacks, pictures} 0 Unmoved

910 Overturned

920 Fallen, not broken

b. Was light furniture 0 Unmoved
95 0 Overturned

94 0 Sh;fted
96 0 Fallen, not broken

c. Were heavy furniture or appliances

0 Unmoved
990 Sh;fted

900 Shifted
930 Broken?
970 Broken?
980 Overturned
1000 Broken?

8. Indicate effects of the following types to interior walls if any ~

Plaster

1010 Cracked

102 0 Fell

Dry wall

1030 Cracked

1040 Fell

Ceiling tiles

1050 Cracked

106 [J Fell

9a. Check below any damage to buildings or structures.

Foundation

107 0 Cracked

108 0 Destroyed

Interior walls Exterior walls

1090 Split llOO Fallen 1120 Hairline cracks

1110 Separated from ceiling or floor

1130 Large cracks

114 0 Bulged outward

1150 Partial collapse

1160 Total collapse

Building

117 0 Moved on foundation

I18 0 Shifted off foundation

b. What type of construction was the building that showed this damage?

1190 Wood 1230 Brick

1200 Stone
124 0 Cinderblock

1210 Brick veneer

12G Other

1250 Reinforced concrete

c. What vJas the type of ground under the building?

126 0 Don't know

127 rJ Sandv soil

128 0 Marshy

129 0 Fill

130 0 Hard rock

Ul 0 Clay soil

132 0 Sandstone, limestone, shale

d. Was the ground:

Ill 0 Level

134 U Slopmg 1350 Steep?

e. Check the appro;~C;imate age of the building: 1350 Built before 1935 1370 Built 1935-65

1380 Built after 1965

10a. What percentage of buildings were damaged?
Within 2 city blocks of your location 0 None

1400 Many(about 50%)

b. In area covered by your zip code

0 None

143 0 Many (about 50%)

119 0 Few (about 5~~-i 1410 Mc.st (about 75%) 141 0 Few (at:tout 5%)
144 LJ Most (ab o ut 75%)

11 a. Were springs or well water disturbed? b . Were ri\lers or lakes changed?

145 0 Level changed

147 0 Muddied

1480 Yes

0 No

145 0 Flow disturbed 0 Don't know
[ J Don't know

12a. Was there earth noise?

0 No

149 0 Faint

150 0 Moderate 151 0 Loud

b. Direction of noise

1510 North 113 0 South

154 0 East

155 0 West

c. Estimated duration of shaking

156 0 Sudden, sharp

1110 Long

(less than 10 sees)

(30-60 sees)

1580 Short (10-30 sees)

1590 Other

13. What is the approximate population of your city/town?

160 0 Less than 1,000

161 0 10,000 to 100,000

161 0 1,000 to 10.000

163 0 Over 100,000

Or are you in a
1~ 0 Rural area?

This community report is associated with what town or zip code?

Thank you for your time and information. Refold this card and tape for return mail.

APPENDIX Ill: Chronological Listing of Earthquakes for the State of Georgia (from Stover and others, 1978)

DATE YEAR MONTH DAY

1826 1872 1875 1875 1884 1885 1903 1909 1912 1912 1913 1914 1928 1933 1943 1958 1963 1964 1964 1964 1965 1965 1965 1965 1969 1969 1969 1971 1973 1974 1976

OCT 15 JUN 17 JUL 28 NOV 02 MAR 31 OCT 17 JAN 24 OCT 08 JUN 20 OCT 23 MAR 13 MAR 05 MAY 23 JUN 09 JUL 29 APR 08 OCT 08 FEB 18 MAR 07 MAR 13 APR 07 JUL 22 NOV 08 NOV 08 MAY 05 NOV 04 NOV 08 APR 16 OCT 08 AUG 02 DEC 27

ORIGIN TIME(UTC)
H Ms
20 00 23 05 02 55 . . 10 00 22 30 01 15 10 00
01 15 .. 05 . .
20 05 ' . 10 15
11 30 . .
04 30
17 . .
06 01 43.4 09 32 11 .6 18 03 00.1 01 20 18.1 07 41 10.2 23 55 33.3 12 58 01.0 13 04 11 .5
17 14 . .
18 58 23 01 52
07 31 ..
13 38 ..
08 52 09.8 06 57 13.9

LAT.

( N. ) 32.0 33.1 33.1 33.8 33.1 33.0 32.1 34.9 32.0 32.7 34.5 33.5 30.8 33.3 33.4 31.5 3 3 .9 34.8 33.9 33.2 33.9 33.2 33.2 33 .2 33.9 33.2 3 3 .9 33.9 33.9 33.87 32.22

( w .) 81.1 83 .3 83.3 82 .5 83 .3 83.0 81.1 85 .0 81.0 83.5 85 .0 83.5 83.3 83.5 82 .0 83.5 82 .5 85.5 82.5 83.4 82.5 83 .2 83.2 83 .2 82 .5 83.2 82 .5 82.5 82.5 82.49 82.46

*INST- instrumentally recorded unfelt event.

INTENSITY
MM
v
Ill VI Ill IV VI
v v
IV IV VI Ill IV Ill Ill INST*
v
INST*
v
INST INST INST INST INST INST INST INST INST VI
v

Savannah Central Georgia Central Georgia Clark Hill Reservoir Central Georgia Central Georgia Savannah Northwest Georgia Savannah Central Georgia Northwest Georgia Central Georgia Coastal Plain Central Georgia Augusta Coastal Plain Clark Hill Reservoir Northwest Georgia Clark Hill Reservoir Central Georgia Clark Hill Reservoir Central Georgia Central Georgia Central Georgia Clark Hill Reservoir Central Georgia Clark Hill Reservoir Clark Hill Reservoir Clark Hill Reservoir Clark Hill Reservoir Coastal Plain

210

HYDROCHEMISTRY OF FORMATION FLUIDS IN ONSHORE AND OFFSHORE STRATA IN THE SOUTHEAST GEORGIA EMBAYMENT
F.T. Manheim and C.K . Pauli U.S. Geological Survey
Woods Hole, Massachusetts

ABSTRACT
Investigations of formation-fluid salinites in a transect from western Georgia to the edge of the Blake Plateau off the Georgia coast show surprisingly similar hydrochemical features offshore and onshore. A fresh brackish wedge of ground water (<25 g/kg total dissolved solids) lies beneath the shelf to a depth of about 900 m. On land, brackish waters extend to a maximum depth of about 1.2 km below sea level in Lowndes County, Georgia . In deeper horizons, hypersaline brines ~?100 g/kg) occur in Lower Cretaceous (?) strata. These strata have a pronounced evaporitic (anhydritic) character in the offshore segment. Strong salinity gradients in interstitial waters signify buried evaporite deposits at drill sites beneath the Blake Plateau.
INTRODUCTION
Until relatively recently, hydrologists in the United States focused their main attention upon shallow ground waters containing potable and nearpotable waters. Petroleum exploration firms generally limited their interests in fluid-bearing strata to prospective petroleum-producing (reservoir) beds. Consequently, data on regional hydrochemical patterns, migration paths, permeability, and sources of chemical constituents in sedimentary basins as a whole were rare.
Increased interest in use of subsurface strata as waste-disposal sites, in problems involving seawater encroachment, and in extension of the concept of "freshwater resources" to water containing as much as 10 g/kg total dissolved solids (see Kohout, this volume) has increased interest in the composition and distribution of deeper saline fluids in sedimentary strata.
Manheim and Horn (1968) summarized subsurface hydrochemical data from a shoreline transect extending from Long Island to the Florida Keys and provided a map of inferred salinity distributions from surface to igneous-metamorphic basement. The southeastern Atlantic region from South Carolina to northern Florida was shown to be the site of some of the most complex hydrochemical features along the U.S. Atlantic seaboard. The deepest freshwater horizons extended more than 1000 m below sea level in the region of South Carolina north of Parris Island. In contrast, in southernmost Geor-

gia, hypersaline brines (i.e., brines containing at least 50-100 g/kg total solids) were found at depths below 700 m. The distribution of such hypersaline brines, which approached saturation in NaCI beneath much of Florida, was linked to the distribution of evaporitic strata (Manheim and Horn, 1968). Evaporitic facies mainly characterized by dolomiteanhydrite occur in Paleocene rocks in Florida and southern Georgia (Chen, 1965), and thicker strata including some salt are found in Lower Cretaceous and Jurassic evaporites in Florida on land. Salt also occurs in diapirs offshore north of the Blake Plateau (Grow and others, 1977) and has been sampled during oil drilling in the Baltimore Canyon Trough (Oil and Gas Journal, 1978).
Recently, Brown and others, (1979) evaluated in detai I the deep-well waste-storage potential of Mesozoic aquifers in Georgia and South Carolina. They estimated formation-fluid salinity ranges by using electrical-log analysis and water analyses. We have taken advantage of these data, have further analyzed some of the electrical logs, and have incorporated hydrochemical data from available offshore drill holes and other onshore drill holes to prepare cross sections of subsurface "salinity" (total dissolved-salt content). Table 1 contains a list of sites utilized; figure 1 shows their location in Georgia and Florida and offshore regions. Our purpose is not to determine fine-scale chemical variations, but to discern broad regional trends that might shed light on fluid history, fluid migration, and fundamental geochemical and hydrochemical processes.
METHODS
All available sources of information on the composition of formation fluids in the study area (fig. 1) were utilized. The most accurate data are potentially those obtained from analysis of (1) drill stem tests or other (for example, reverse flush) fluid tests on permeable strata in land wells (no oil-producing wells exists in the study area), and (2) pore water extracted (by "squeezing") from cores of unconsolidated and partly consolidated rocks at depths as great as 300 m beneath the sea floor (Manheim, 1967; Manheim and Horn, 1968; Kohout, and others, 1979). The validity of drill-stem test data is normally governed by the care used in sampling fluids to minimize the

211

TABLE 1. List of boreholes utilized in study.

Borehole No.
LOW-1 LOW-2 LOW-3 CAL-1 D0-1 Ml-1 COL-1 EC-2 EC-5 SCR-1 SAV JAX
ST.M . COLIS. SUN GE-1 T

Borehole Name
Hunt Petroleum, J.T. Stalvey, No. 1, Lowndes County, Georgia
Hunt Petroleum, Langsdale No. 1, Lowndes County, Georgia
Hunt Petroleum, E.N . Murray No. 1, Lowndes County, Georgia
Sowega Mineral, J.W. West No.1, Calhoun County, Georgia
J.R. Sealy, Reynolds No.1, Dougherty County, Georgia
Stanolind, J.H. Pullen No. 1, Mitchell County, Georgia
R.T. Adams, D.G. Arrington No. 1, Colquitt County, Georgia
Hunt Petroleum, Superior Pine Co., 2, Echols County, Georgia
Humble Oil, Bennett and Langsdale No. 1, Echols County, Georgia
Boenwell Drilling Co., McGain-Pryor No. 1, Screven County, Georgia
Savannah Port Authority, Chatham County, Georgia
Jacksonville Test Wells, USGS (U.S. Geological Survey), Duval County,Fiorida
St. Mary A. Oil/Hilliard Turpentine Co., Nassau County, Florida
Colonel's Island Test Well, USGS, Glynn County, Georgia
Sun Oil Co., Powell, Volusia County, Florida
COST (Continental Offshore Statigraphic Test) Well GE-1
Tenneco wildcat well

1 ,2,3, 4,5,6 6002
6004

JOIDES (Joint Oceanographic Institutions Deep Earth Sampling Project) sites
AMCOR (Atlantic Margin Coring Project) Site 6002
AMCOR Site 6004

*Reinterpreted in part from original logs.

Source of Information Brown, et. al., 1979*
Do .
Do.
Do .
Do.
Do .
Do.
Do.
Do.
Do.
Do.
Leve, 1961, cited in Manheim and Horn, 1968
Manheim and Horn, 1968
H. Gill, USGS, 1979, written commun .
Manheim and "Horn, 1968
Scholle, 1979
L. Poppe, 1979, written commun.
A. Johnston, USGS, Reston, 1979,
oral commun. Manheim, 1967; Manheim
and Horn, 1968 Kohout, et al., 1979
Do.

212

influence of drilling mud. A minimum criterion for "good" water-test samples is that chloride analyses on sequential fluid samples (either flowing water or successive pipe stands) reach a constant value asymptotically. The squeezing-and-analysis methodology was used extensively in Deep Sea Drilling Project studies (Manheim and Sayles, 1974; Manheim, unpub. data) . Wireline samples from which external drill-fluid-contaminated zones had been removed were squeezed through filter paper in a stainless steel press, and recovered fluids were analyzed by microchemical techniques. Data are available from all JOIDES (Joint Oceanographic Institutions Deep Earth Sampling) and AMCOR (Atlantic Margin Coring Project) sites (see fig . 1 and table 1).
Much less accurate but indispensable is the technique of estimating fluid resistivity and, through it, formation-fluid "salinity" by quantitative electricallog interpretation. For the older drill holes on the continent, the only available method is simple estimation from the spontaneous potential (SP) log, as has been done by Manheim and Horn (1968) and Brown and others (1979). The technique is described in standard logging references (Schlumberger Well Surveying Corp., 1978, and documents cited therein).

1) SSP= -K log Rmf/Rwe
where K is a constant dependent on temperature,
Rmf is resistivity of mud filtrate,
Awe is the apparent resistivity of formation fluid,
SSP is the static spontaneous potential (SP).
The SSP is derived from the departure in millivolt scale units from shale baseline of the SP curve: it is corrected where possible for the effects of thin beds, mud resistivity, and fluid invasion of the formation. "Salinity" or the salinity of NaCI solutions having resistivities corresponding to observed resistivities can then be calculated from Rwe We have used the Arps-Hamilton log analysis slide rule or calculator program (for example, Schoonover and Fertl, 1979).
The SP data are particularly useful in deposits containing fresh and brackish strata, as the errors (to 50%) are still smaller than the salinity variations; the salinity values vary by four orders of magnitude. In our study areas, the simpler SP methods give rise to serious errors for the deeper strata containing saline water and especially for those containing significant proportions of clay colloids. Further, these methods are not applicable in carbonate strata.
For the GE-1 well (Scholle, 1979) that reached 4004 m depth below sea floor about 140 km seaward of Jacksonville, Fla., we used alternative methods utilizing deep induction (resistivity) and porosity logs. The basis for such calculations is as follows:

Figure 1. Location of drill holes utilized in study.
Abbreviations as shown in table 1. Bathymetric contour interval, 200 m.

2) F = Rt/Rw

and

F a0m

3) where F is the "formation factor", Rt is the true formation resistivity, Rw is the true formation-fluid resistivity,
0 is porosity, and
a and m are constant for given types of strata .

213

An empirical formula (SchlumbergerWell Surveying Corp., 1978) for formation-fluid resistivity, given 100% water saturation, can be expressed as:
4)
where V sh is volume percent of shale within the formation,
Rsh is the "shale" resistivity.
The V sh and Rsh figures can be obtained from induction-, neutron-, and formation-density logs by cross-plot techniques described in Schlumberger Well Surveying Corp. (1978) and references cited therein.
We were most fortunate to have both porosity and interstitial-salinity values as well as resistivity values for AMCOR sites 6002 and 6004. These permitted direct calibration of equations 2 and 3 for Tertiary strata penetrated by nearby GE-1. For deeper strata, the estimations are based upon cross-plot data and equation 4.
The "salinity" data (NaCI-equivalents) are subject to variation in ionic ratios. These variations are not discussed here, but the error they introduce is less than the uncertainty attributable to log analysis.
STRATIGRAPHIC NOTES
The geologic cross sections upon which the salinity data are superimposed (figs. 2 and 3) are based on available literature (Toulmin, 1955; Herrick and Vorhis, 1963; Chen, 1965; Applin and Applin, 1967; Maher, 1971; Cramer, 1974; Hathaway and others, 1979, Schlee, 1977; Dillon and others, 1979; and Scholle, 1979). We divide the stratigraphy of southern Georgia into the units: Neogene to Holocene, Eocene and Oligocene, Paleocene, Upper Cretaceous, Lower Cretaceous(?), and igneous and metamorphic basement.
The Neogene to Holocene unit is composed of predominantly clastic sediments, and the carbonate content increases to the southeast. The Eocene and Oligocene unit is dominantly carbonate except f_or some of the lower Eocene in southwestern Georgia, where clastic deposits dominate. The Upper Cretaceous and Paleocene units are generalized as marl but carbonate (chalk) and evaporitic facies (anhydrite-dolomite) increase southeastward in the Paleocene. The lithologies of the Lower Cretace-

ous(?) are different in the Southeast and Southwest Georgia Embayments; the basins are probably connected only by a thin basal sand. The unit thickens to more than 800 m of unfossiliferous, immature sandstone in southwest Georgia, where its age is questionable (Gohn and others, this volume) but has historically been labelled as Early Cretaceous. The Southeast Georgia Embayment contains a thick and variable sequence of Lower Cretaceous limestone, anhydrite, sandstone, and shale over metamorphic basement (Scholle, 1979).
Paleoenvironment
Except for anhydrite in the Paleocene and traces of evaporite units in the lower Eocene, all sediments of the Upper Cretaceous and Cenozoic were deposited in normal marine conditions. The lack of distinguishing fossils in the Lower Cretaceous(?) of the Southwest Georgia Embayment renders paleoenvironment identification difficult. In the offshore Southeast Georgia Embayment, the presence of evaporitic strata including anhydrite probably indicates hypersaline deposition.
DISTRIBUTION OF FORMATION SALINITY
The main salinity features are delineated in figures 2 and 3 by lines of equal "salinity" (total dissolved-salt content), or isosalines, at concentrations of 1, 5, 25, 50, 100, and 200 g/kg. These values may be converted to parts per million by multiplying by 1000. The isosalines are superimposed on transects A-A' and B-B', whose locations are shown in figure 1.
In interpreting the diagrams, we note that the isosalines may be subject to error, particularly where salinity distributions are complex, as between Echols and Mitchell Counties, Ga., (between Ml-1 and EC-2, figs. 1, 3), or in the deeper parts of the offshore basin. There may be inliers of different salinity and complex microstructure that cannot be depicted at the scale used here. Moreover, the salinities derived from the SP log in the deeper Southeast Georgia Embayment may be in error because of clay coloids and may understate true formation-fluid salinity.
Major relationships are evident from figures 2 and 3:
1. Strata on land have been infiltrated by meteoric (fresh) water (identified as water having a salinity less than 1 g/kg) to depths between 350m in Colquitt County, Georgia (COL-1 ), to more than 500 m near Jacksonville, Fla. (JAX, fig. 3). Farther northward near the South Carolina-Georgia border

214

A

I

0:
(.)

~

(/)

(/)

N

A'
Q SEA lEVEl

..........
(/)
0::
w 1w -
~
0
2:::::! ~
I 1-
0w....
0
3

4

Figure 2.

Salinity-stratigraphy transect, A-A' (see fig. 1 for location). Contours are in total dissolved solids, g/kg. Abbreviations for wells are as in figure 1. Stratigraphic
intervals are NEO-HOL, Neogene to Holocene; EO-OLIGO, Oligocene and Eocene; Paleo, Paleocene; UK, Upper Cretaceous; LK?, units historically referred to as being Lower Cretaceous; Dev. met, Devonian metamorphic rocks; Paleoz met, Paleozoic metasedimentary rocks. Partial limestone symbols in Upper Cretaceous and Paleocene strata represent marls and some evaporitic (anhydritic) sediments. The Neogene to Holocene section is variable but is predominantly of clastic lithology.

B

I()

w I

I
I
c 0

N

w

I
g31:

I
g31:

I()
I
(w.)

.., N I (.)
w

:::E 1-'
(/)

X <[

0: 0 J:
(/)

..,

<!'

1-

., (/)
0 N
(.)

It)

8'

.,Ul

J4~

Q SEA lEVEl

PAlEOZ MET.

0

50

KILOMETERS

..L

..0..

(/)
0w:: 1w -
~
0
_j
2:;2
I 10....
w
0
3

4
Figure 3. Salinity-stratigraphy transect, 8-B'. For explanation, see figure 2. Depth of isohalines in area seaward of the shelf is estimated beneath drill holes partly by salinity gradients in JOIDES holes 4, 5, and 6.
215

(SAV, fig. 2), fresh waters extend deeper, to more than 900-m depth. Fresh waters mixed with brackish waters have salinities less than the salinity of seawater (35 g/kg) and extend to a depth of 1.2 km in Lowndes County, Georgia (LOW-1, -2, fig. 3).
2. A freshwater and brackish-water (significantly less saline than seawater) wedge extends under the Atlantic Ocean as far as 120 km from shore, down to depths greater than 600 m. This phenomenon was reported in papers cited earlier and is dicussed in considerable detail by Kohout (this volume). and Pauli and Dillon (this volume). The evidence suggests that boundaries are much smoother and more regionally continuous than on land. These boundary characteristics are consistent with predictions based on the mobility of water influenced by artesian circulation (land) relative to the mobility of water in largely diffusive fluxes (beneath the sea).
3. Only beneath the freshwater/brackishwater lens underlying the shelf do we find substantial thicknesses of formation fluids having salinities within the approximate range of seawater salinities. On the continent, salinities generally pass relatively abruptly from brackish to hypersaline levels (.::o;5Q g/kg) .
4. The presence of hypersaline brines in stratigraphic levels as young as Paleocene appears to be limited to those areas where the evaporitic rocks are present in the earliest Tertiary; in other words, Echols County, Georgia, and eastward.
5. More concentrated hypersaline brines (>100 g/kg) are limited to Lower Cretaceous(?) strata on land. A lens of such fluids appears to extend from Calhoun County to Lowndes County, Georgia, in transect B-B' (CAL-1 to LOW-5, fig. 3); below the lens is less saline water. However, at these depths, the SP values yield only semiquantitative "salinity" values, because the "greasy" (high-claycontent) nature of the varicolored micaceous sands reported in this zone affects the well logs.
6. Offshore, in the GE-1 well, very high salinities are identified in Lower Cretaceous strata, consistent with the presence of evaporitic rocks (anhydrite). Toward the base of the section, low permeabilities render interpretation of salinities more difficult and less reliable, even with the aid of the porosity methods.

7. Previous results (Manheim and Horn, 1968) have shown that along the Atlantic margin, salinity commonly decreases just above the basement. In this study, we have detected indication of this phenomenon at sites in eastern Georgia and possibly in COST GE1. On the other hand, indications in some sites (LOW-1 and St. Mary Hilliard, transect B-B') are that salinity levels of 50-100 g/kg continue into crystalline or metamorphosed sediments.
DISCUSSION
The existence of fresh water beneath the Atlantic Ocean, to the edge of the continental Shelf, has been well documented in the JOIDES and AMCOR drill holes (Manheim, 1967; Kohout and others, 1979; Kohout, this volume; Pauli and Dillon, this volume). New electrical-logging data from the COST GE-1 well confirm the existence of brackish water in the upper 900 m. Moreover, a special agreement by Tenneco Oil Co. permitted the U.S. Geological Survey to run a dri 11-stem test at about 350-m depth in a wildcat well (T, fig. 1) about 85 km seaward of Jacksonville, Fla . A drill-stem test confirmed presence of brackish water having less than half the salinity of seawater (R. Johnston, 1979, oral commun.).
The distribution of lithologic and stratigraphic units and formation-fluid salinities shows clearly that few if any "paleosalinities" remain in deeper subsurface porous strata. All surficial strata have had the original seawater solutions permeating the interconnected pores of marine sediments flushed out by fresher waters of meteoric origin. We suggest that in the depth range where freshwater influence diminishes sharply, the dominant salting influence is frequently not seawater, but brine of hypersaline origin. These brines once originated from seawater, but they have been modified by processes involving secondary interactions with solid phases (Braitsch, 1971; Carpenter, 1978) during deposition and burial. Evaporite brines may permeate not only contemporaneous sediments, but also underlying strata to depths of several kilometers or more (e.g., see Manheim and Schug, 1978). Another source of salt is inclusions and microlayers of rock salt that are associated with original anhydritic rocks and are later dissolved, thereby contributing to total formation-fluid salinity. Not infrequently, anhydritic strata are characterized by brine concentrations approaching saturation with respect to NaCI, even though no appreciable salt bodies occur in the strata.
In previous papers, the senior author and his coworkers (Manheim and Sayles, 1974; Manheim and Hall, 1976) pointed out that significant increases in salinity of interstitial waters as depth increases in oceanic strata nearly always point to

216

presence of evaporitic strata at depth. As the present data indicate, "evaporitic strata" need not mean massive halite. Anhydritic rocks also incorporate a sufficient reservoir of brine salt to permit upward diffusion to influence fluids of overlying strata during geologic time. The new information can be applied to the interstitial salinity gradients shown in figures 2 and 3 to infer the extension of Lower Cretaceous(?) evaporitic facies to JOIDES holes 4, 5, and 6 (fig . 1, 3). Pre-existing hypersaline concentrations (if any) in earlier, deeper strata would have merged with the saline-water concentrations contributed by the latest evaporitic sequence and would probably not be discernible in the study area.
A further inference may be drawn from the saline gradients. If inorganic ions (Na, Cl, etc.) can move upward through the strata in response to concentration gradients, then light hydrocarbons dissolved or otherwise entrained in pore fluids may likewise be able to migrate through the strata. More detailed delineation of saline gradients may help map zones of diffusive or other permeability and "calibrate" surficial hydrocarbon anomalies.
REFERENCES
Applin , P.L., and Applin, E.R., 1967, The Gulf Series in the subsurface in northern Florida and southern Georgia: U.S. Geol. Survey Prof. Paper 524-G, 24 p.
Braitsch, 0., 1971, Salt deposits: Their origin and composition : New York-Heidelberg, Springer-Verlag, 297 p.
Brown, P.M., Brown, D.C., Reid, M.S., and Lloyd, O.B., 1979, Evaluation of deep-well, wastestorage potential of Mesozoic aquifers in the southern part of the Atlantic Coastal Plain, Georgia and South Carolina : U.S. Geol. Survey Prof. Paper, in press.
Carpenter, A.B., 1978, Origin and chemical evolution of brines in sedimentary basins: Oklahoma Geol. Survey Circ. 79, in press.
Chen, C .S., 1965, The regional lithostratigraphic analysis of Paleocene and Eocene rocks of Florida: Florida Geol. Survey Bull . 45, 105 p.
Cramer, H.R., 1974, Isopach and lithofacies analysis of the Cretaceous and Cenozoic rocks of the Coastal Plain of Georgia, in Stafford, L.P., ed., Petroleum geology of the Georgia Coastal Plain Symposium: Georgia Geol. Survey Bull. 87 , p. 21-43.
Dillon, W .P., Pauli, C.K., Buttler, R.T., and Fail, J.P., 1979, Structure and development of the Southeast Georgia Embayment and northern Blake Plateau, Preliminary Analysis, in Watkins, J.S ., Montadert, L., and Dickerson, P.W.,

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THE EFFECTS OF CRETACEOUS AND YOUNGER FAULTING ON COASTAL PLAIN ROCKS AROUND AUGUSTA, GEORGIA
David C. Prowell U.S. Geological Survey
Reston, Virginia

Mr. Prowell's article, based on his symposium presentation and the following abstract, was published in GEOLOGY, 1978, val. 6, p. 681-684.

ABSTRACT

The Belair fault zone is a series of northeast-trending en echelon reverse faults that cut the inner margin of the Atlantic Coastal Plain near Augusta, Georgia. The effects of the faulting during the early Cenozoic have been evaluated by recent geologic mapping of the Coastal Plain strata. The mapping has shown that the fault zone is at least 15 miles (24 km) long. The Coastal Plain sediments around Augusta traditionally have been mapped as a basal fluvial unit (Tuscaloosa Formation) unconformably overlain by a sequence of nearshore marine sediments (Barnwell Formation). The Tuscaloosa consists of two distinguishable sedimentary sequences as far south of Augusta as Wrens, Georgia. The lower unit is characterized by a coarse basal gravel and an unusual heavymineral fraction, whereas the upper unit is characterized by thick kaolin deposits of commercial value. Palynological analysis indicates that the lower unit is Late Cretaceous (Santonian) in age, whereas the upper unit is middle Eocene (Claibornian) . Both units are considerably younger than the Tuscaloosa Formation (Cenomanian) of western Georgia and Alabama. The Barnwell Formation unconformably overlies the Tuscaloosa in the Augusta area; it can be divided into three mappable units, which are, from oldest to youngest: (1) Twiggs Clay Member; (2) Irwinton Sand Member; and (3) an unnamed sand member. The Twiggs Clay Member is a carbonaceous

clay that has been dated by palynology as late Eocene (Jacksonian). At Augusta, the Twiggs is a barrier lagoon deposit, but farther downdip it has offshore characteristics. The Irwinton Sand Member is a fine quartz sand that is the nearshore facies equivalent of the Twiggs . Transgression of the late Eocene sea has resulted in part of the Irwinton being conformably deposited on the Twiggs. Unconformably overlying the Irwinton is an unnamed medium to coarse marine sand whose base is marked by a thin layer of ovoid pebbles. Shark teeth in this unit date it as Oligocene to early Miocene.
Movement along the Belfair fault zone has caused about 100 feet (30 m) of vertical offset of the base of the Tuscaloosa Formation since initial deposition. The basal unconformity of the Barnwell Formation has been displaced about 40 feet (12m) since its formation in the late Eocene. The succession of fault movements along the Belair zone from the Late Cretaceous until the early Tertiary affected both the thickness and distribution of the Coastal Plain strata in the Augusta ,region. For example, the absence of certain sedimentary units on the upthrown block of the fault zone is probably the result of uplift and erosion . Such evidence indicates that faulting elsewhere in the Atlantic Coastal Plain has influenced the configuration of sedimentary strata and should receive attention by regional mappers.

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