The stratigraphy of the Barnwell group of Georgia [1979]

THE STRATIGRAPHY OF THE BARNWELL GROUP
OF GEORGIA
by Paul F. Buddlestun and John B. Hetrick
OPEN FILE REPORT 80-1
Published by the Georgia Geologic Survey for the 14th Annual Field Trip of the Georgia Geological Society
DEPARTMENT OF NATURAL RESOURCES ENVIRONMENTAL PROTECTION DIVISION
GEORGIA GEOLOGIC SURVEY
Atlanta 1979

Georgia Geological Society

Officers 1.978-79

President Past President President-Elect Secretary Treasurer
Councilor Councilor

C. 0. Pollard
Thomas J. Crawford Norman Herz
Thomas Sanders James A. Whitney Harland E. Cofer Eugene Hartley

Officers 1979-80

President Past President President-Elect Secretary Treasurer Councilor Councilor

Norman Herz C. 0. Pollard Roger S. Austin Johnny A. Waters Alan Ortiz Harland E. Cofer Lin D. Pollard

Field Trip Committee

Doral S. Mills, Chairman

Daniel D. Arden

Paul F. Huddlestun

Field Trip Leaders Paul F. Huddlestun John H. Hetrick

ii

'

CONTENTS

Introduction o o o

Page
..... .. 1

Barnwell Group

0





6

Clinchfield Formation

9

Undifferentiated Clinchfield Sand . 10

Riggins Mill Member

11

Treadwell Member

12

Undifferentiated weathered and

leached Clinchfield east of

the Ocmulgee River

13

Albion Member

14

Utley Limestone Member
. . . . Dry Branch Formation
. . . . . . . Twiggs Clay Member

. 16 . 17
19

Irwinton Sand Member 23

. . . Griffins Landing Sand Member
Tobacco Road Sand

24 25

References Appendix

28
. . . . . . 32

Road Log

33

Measured and Described Sections Stop 1

. . .

Stop 2

Stop 4

Stop 5

Stop 6

Stop 7 Stop 8

. . . . .

Stop 9

Stop 10 Stop lla

...

Stop llb

43
47
52 . 55
. 59 64 68
72
76
83 88

iii

ILLUSTRATIONS
Figure 1. Location Map 2. Field Trip First Day 3. Field Trip - Second Day 4. Upper Eocene Correlation Chart 5. Explanation 6. Stop 1 7. Stop 2 8. Stop 3 . 9. Stop 4
10. Stop 5 11. Stop 6 and 7 12. Stop 8 13. Stop 9 14. Stop 10 15. Stop lla & b

Page 3 4 5 8
41 42 46 50 51 54 63 67 71 75 87

iv

THE STRATIGRAPHY OF THE BARNWELL GROUP OF GEORGIA by
Paul F. Huddlestun and John H. Hetrick
INTRODUCTION
This field trip presents some of the results of an investigation initiated in 1972 of the upper Eocene sandy deposits of eastern Georgia. Up to that time the stratigraphy of these deposits, largely called Barnwell, was poorly known in spite of the fact that the deposits had been observed and commented on as early as the 1840's by Charles Lyell (1845). The reasons for the lagging state of knowledge are many: (1) the sands of the Barnwell are typically unconsolidated, loose, very permeable, and have been altered considerably both mineralogically and chemically by ground-water conditions in the vadose zone; (2) the Barnwell deposits are thin and lie near the surface in the outcrop area, and as a consequence they commonly are weathered intensely to depths that may include the entire unit; (3) natural outcrops are rare and found only as scattered exposures along streams (human enterprise, on the other hand, has produced many excellent but temporary exposures in the kaolin mining area and along roads); (4) the Barnwell deposits originated in a marginal marine, coastal environment where facies change in short distances and a paucity of fossils makes internal stratigraphic correlation very difficult (the type of deposits that commonly attract reasearch workers and receive sufficient basic investigations are well stratified, richly fossiliferous deposits and are lithologically uniform over large distances); and as a result (5) it is very tedious and time consuming to try to develop consistent stratigraphic information and data with which to construct a consistent, reliable, and reproducible stratigraphic framework from these sorts of deposits.
It is important that the stratigraphic framework of the upper Eocene deposits of Georgia be understood. These deposits (mainly Barnwell) are important to the investigator of several different geologically related disciplines for the following reasons: (1) It is through these sediments that most of the principal artesian aquifer of southern and eastern Georgia is recharged. If the aquifer characteristics and parameters are to be understood in detail, then so must the stratigraphy of the recharge deposits also be understood in detail. (2) The Barnwell is a shallow aquifer in its own right; therefore, it is of value to have a good comprehension of the permeable sand/impermeable clay relationships within the aquifer . (3) There are numerous sanitary landfills and one proposed hazardous waste site in the Barnwell outcrop area. The geologist, engineer, and technician should have as thorough an understanding as possible of the potential impact of such sites on the aquifer system.
1

(4) The Barnwell has been of some commercial or economic value in that fuller's earth has been mined from the unit in Georgia. (5) The Barnwell is overburden for the kaolin industry and it would be of great bene~it to the industry to understand in detail both the systematic thickness variation and the systematic lithologic variation on a small scale in order to predict costs and time for the removal of these sediments. In addition, electrolytes leached from the overlying Barnwell are critical to the viscosity and other physical characteristics of the underlying kaolin.
In this redefinition of the upper Eocene deposits of central and eastern Georgia, we are raising the Barnwell to group ranking and we are recognizing three formations of the Barnwell Group. These are in ascending 'order, the Clinchfield Formation, the Dry Branch Formation (new name), and the Tobacco Road Sand. We recognize four formal members of the Clinchfield Formation: the Riggins Mill Sand Member (new name), the Treadwell Sand Member (new name), the Albion Member, and the Utley Limestone Member (new name). The Dry Branch Formation is subdivided into the Twiggs Clay Member, the Irwinton Sand Member, and the Griffins Landing Sand Member (new name). The Sandersville Limestone is a formal member of the Tobacco Road Sand. In all, we are proposing five new names, i.e., one new.formation and four new members.
We do not claim to have answered all the questions concerning the Barnwell Group in Georgia. However, this investigation has been continuing since 1972, and the basic Barnwell stratigraphic framework has been more or less defined since 1975. Since then, we have been field testing the model and making improvements and adjustments in the model to accommodate new field and core information. This evaluation has continued to the present time, and we see no reason that it should not continue in the future. Nevertheless, four years of field testing have confirmed the .basic stratigraphic framework as described in this field trip; and, therefore, we believe that we are submitting a solid and reliable stratigraphic framework for the Barnwell that the interested professional community can use and build upon.
2

t9
w
""'

0

10

20

30 MILES

0

10

20

30

40

50 KILOMETERS

~.

LOCATION MAP- OUTCROP BELT JACKSONIAN DEPOSITS WITH LOCATIONS OF FIELD TRIP STOPS

FIGURE

FIELD TRIPFIRST DAY
~
0 I 2 3 4 5 Ml LES
FIGURE 2

------ ~ .............. - ~

/
FIELD TRIPSECOND DAY

HOLI()A Y INN

'

0

~ 4 5MILES

FIGURE 3

5

THE BARNWELL GROUP
We propose that the Barnwell Sand (formation) of earlier usage be raised in lithostratigraphic rank to that of the Barnwell Group. This reranking is needed to accommodate the first order and second order stratigraphic subdivisions (formations and members) of the Barnwell Group. These formations are in ascending order, the Clinchfield Formation, the Dry Branch Formation (new name), and the Tobacco Road Sand.
There is no adequate or useful reference section of the Barnwell Group in Barnwell County, South Carolina. The typical Barnwell Sand in Barnwell County is a deep red residuum (moderate reddish-brown, 10 R 4/6), the original unit having been restricted to late Eocene age by Cooke (1936, p. 89). This kind of material is of little use in terms of stratigraphic correlation and is of no use in paleogeographic and peleoecologic reconstruction.
The railroad cut one mile (0.6 km) east of the railroad station at Barnwell has been used as a reference locality (Cooke, 1936) and a type locality (Connell, 1968). However, we agree with Cooke and McNeil (1952) and Doering (1960) that the deposit under question is Neogene in age, and is not Barnwell by original designation or by present usage.
We have preserved the earlier concept of the Barnwell in that we understand the Barnwell Group to be -dominantly a sand deposit of late Eocene age. In this respect the Barnwell Group is a sand lithesome of the southern Atlantic Coastal Plain that is fully equivalent to the Yazoo Group (the upper Eocene clay lithesome of the northern and eastern Gulf Coastal Plain) and to the Ocala Group (the upper Eocene carbonate lithesome of the Florida "platform" or "banks"). These three lithosomes-sand, clay, and carbonate--interfinger in the central and east-central Georgia outcrop belt. The Clinchfield Formation, the Irwinton and Griffins Landing Sand Members of the Dry Branch Formation, and the Tobacco Road Sand are simply subdivisions of the sandy Barnwell lithesome. Although we consider the Twiggs Clay to be part of the Barnwell Group, we recognize that it is probably an easternmost tongue of the Yazoo clay lithesome. The Twiggs Clay is practically identical lithologically, paleontologically, and in stratigraphic position to the lowest subdivision of the Yazoo Group., the Northtwistwood Creek Clay of Alabama and Mississippi. The Tivola Limestone, Ocmulgee Limestone (Cooper Marl of earlier usage), and possibly the Utley Limestone Member (new name) of the Clinchfield Formation represent the interfingering of the downdip Ocala carbonate lithosome with the updip sand and clay lithosomes.
It is desirable for identification and correlation purposes to have at least a reference locality for a lithostratigraphic unit, even at group rank. We therefore propose the large roadcut on Windsor Springs Road in
6

Richmond County, Ga. to be the principal reference locality of the Barnwell (see Fig. 11, p. 63). This locality was chosen because it is the nearest completely exposed upper Eocene section to the type area in Barnwell Courity, S.C. For eastcentral Georgia, a good but incomplete reference section is the roadcut on Linton Road in the southern valley wa;ll of Little .Keg Creek, 6.2 mi (10 km) northwest of the Sandersville city limits in Washington County (see Fig. 6). A description of these two reference sections is given in the Appendix on pages 59 and 43, respectively.

The lithology of the Barnwell Group is dominated by quartz sand;

other mineral components are subordinate. In the western area, however,

montmorillonite clay (Twiggs Clay) may dominate the lithology of the

group. Minerals or lithologies that are normally subordinate may

do~inate the lithology of particular beds or lenses in the group. These

include clay (both montmorillonite and kaolinite), limestone, glauconitite

(greensand), lignite, opal-cristobalite, chert, sandstone, and gravel.

Shells, locally

mica, very

choyndspraicteudouisr.onOothxeidr easc, caensdsomryanlgiathneosleogoixcidecom(Mpno0n2e)ntms aoy fbethe

Barnwell include aragonitic shells, pyrite, flecks of carbonaceous matter,

siliceous microfossils (diatoms and sponge spicules), small marine

Vertebrate phosphatic bone debris (fish teeth, scales, and bones), and

gorceixite (a hydrated phosphate).

The quartz sand of the Barnwell Group ranges in grain-size from very fine to pebble size, and the sorting of the sand component ranges from very well-sorted to very poorly-sorted. In general, the fine and very fine sands are very well-sorted. Commonly, as the upper limit of the
grain-size of the quartz sand increases, the lower limit of the grain-size decreases (becomes finer). As a result, with increasing grain-size within the Barnwell Group, the sorting deteriorates, producing very poorly sorted sediments. The extreme of this situation results in lithologies consisting of clayey, fine to medium to coarse to granully and pebbly sand. This relationship is not invariable, however, in that some beds or lenses of well-sorted, coarse or very coarse sand may be locally common.

Typical Barnwell lithologies display prominent bedding that ranges from horizontal (thick-bedded, thin-bedded, rudely bedded, laminated) to cross-bedded of various kinds and degrees. Some deposits, however, may show little apparent bedding. These include the typical Clinchfield, some of the Twiggs Clay (west of the Ocmulgee River) and Griffins Landing Members of the Dry Branch Formation, the Tobacco Road Sand, and the Sandersville Lim~stone Member of the Tobacco Road Sand. Although the above sounds like a formidable list of exceptions, all of the above contains bedding with various degrees of development, locally or regionally.

7

UPPER
PRIABONIAN

EOCENE

- - - -BARTONIAN
-

JACKSONIAN

LOWER

UPPER

PANVILLENSIS

_

~ERROAlULENaiS COCOAC:N81S

" .

.ll t#.t ll ll lllflwj~tAIIi loll. Ollol~'-\l t AIUtllt ll IIIIAIN!'ILI Mf.MII~U
n '"''"'"' '' ,,,,,w,_,.,..,
Ill~[ Y ll~lfllt!Nf MfMDiFI

OCALA LIMESTONE

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BARNWELL GROUP

l> r l> lD l> 3: l>
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FIGURE 4

BARNWELL GROUP
8

CLINCHFIELD FORMATION
The Clinchfield Sand of present usage had earlier been recognized and correlated with and referred to as the Gosport Sand (MacNeil, 1947; Herrick, 1961; LeGrande, 1962). Pickering (1966, 1970) formally defined the Clinchfield Formation and Herrick (1972) discussed its age and correlation. The original description of the formation is as follows (Pickering, 1970, p. 7,8):
The Clinchfield Sand is a medium-grained, well-sorted, poorly consolidated quartz sand. The sand is massive and no bedding or cross~bedding may be observed. Accessory minerals present are detrital carbonate, ilmenite, leucoxene, muscovite, hornblend, zircon, staurolite, epidote, and monazite. The total content of heavy minerals is less than one percent. The Clinchfield Sand grades upward into the Ocala Limestone, through a zone of sandy limestone lenses and sand beds approximately five feet thick. In this report, the top of the Clinchfield Sand is placed at the highest bed of unconsolidatated s.and.
The type locality of the Clinchfield Sand is at the pit of the Medusa Portland Cement Company at Clinchfield, Houston County. The formation at this site, however, is only intermittently exposed during quarry operations because it is the overlying Tivola Limestone that actively is being quarried. Therefore, no specific exposure in the quarry at Clinchfield can be named or designated. Because the authors have correlated the Clinchfield Sand with deposits in eastern Georgia that have hitherto been referred to simply as Barnwell, we are, therefore, expanding the original definition and concept of the Clinchfield to include these deposits.
The Clinchfield Formation is the basal sand deposit of the Barnwell Group. In central Georgia, it is predominantly a quartz sand, but in the far updip areas near the Fall Line and in eastern Georgia east of the Ogeechee River, the Clinchfield may be conspicuously less sandy.
We find it convenient to discuss the Clinchfield Formation under six subdivisions:
(1) the typical and undifferen.tiated Clinchfield Sand of its type area west of the Ocmulgee River.
Between the Ocmulgee and Ogeechee Rivers the Clinchfield consists of:
(2) a lower Riggins Mill Member,
(3) an upper Treadwell Member,
9

..
{4) . an undifferentiated, weathered and leached Clinchfield Formation.
East of the Ogeechee River the Clinchfield Formation consists of: {5) an updip, nearshore, spiculitic Albion Member in Glascock and Richmond Counties, Ga., and Aiken County,
s. c. '
{6) a downdip, offshore Utley Limestone Member in Burke and subsurface Screven Counties.
Undifferentiated Clinchfield Sand
In general, the unweathered exposures of the Clinchfield Formation west of the Ocmulgee River consist of fine- to medium-grained, wellsorted, calcareous, fossiliferous sand. Typically, small-scale primary sedimentary structures are lacking. The only bedding appears to be scattered, moderately thin to moderately thick beds of sandy limestone or calcareous sandstone. The undifferentiated Clinchfield Sand is typically very well mixed in terms of the lithologic components, but bioturbation and burrowing may be locally intense.
In most places the quartz sand is soft and unconsolidated, so that recovery in coring operations is very poor. In some places, such as in the quarry at Clinchfield, the massive-bedded sand is locally cemented and indurated and contains abundant shell molds. Consequently, in the past, this particular lithology in the Clinchfield has led to miscorrelation with the shelly Gosport Sand in western Alabama that occurs in a similar stratigraphic position, i.e., between the Claibornian Lisbon Sand and the Jacksonian Mo~dys Branch Formation {MacNeil, 1947; Herrick, 1961; LeGrand, 1962).
The Clinchfield Formation west of the Ocmulgee ranges in thickness from 9 to 35ft {2.75 to 10.5 m) (Herrick, 1972, p. 6) but is generally between 10 and 20 ft (3 and 6.1 m) thick.
The undifferentiated Clinchfield Formation west of the Ocmulgee River contains the "Scutella" bed (Periarchus lyelli bed) of the eastern Gulf Coastal Plain. Locally, P. lyelli is abundant in these sands but more commonly it occurs in moderate to low frequencies.
10

Riggins Mill Member of the Clinchfield Formation
The Riggins Mill Member of the Clinchfield Formation is named for Riggins Mill Road which passes 0.75 mi (1.2 km) northeast of the type
locality. The type.locality is in the Georgia Kaolin Company Pit so.
at the intersection of two kaolin haul roads. 0.75 mi (1.2 km) southwest of the community of Treadwell. Twiggs County; 1.4 mi (2.25 km) southeast of the Bibb/Twiggs County line on Riggins Mill Road. Georgia Kaolin Pit 50 is approximately 10 mi (16 km) southeast of Macon. Bibb County. Ga. The type description of the Riggins Mill Member is on p. 78 in the Appendix (see also Fig. 14, p. 75).
The Riggins Mill Member of the Clinchfield Formation is the basal deposit of the Clinchfield Formation over much of the outcrop area between the Ogeechee and Ocmulgee Rivers, and at some sites the entire Clinchfield interval consists of the Riggins Mill Member. In general, in the type area in western Twiggs County, the Riggins Mill consists of a basal, poorly sorted, pebbly, argillaceous fine-to coarse-grained sand that is locally calcareous and macrofossiliferous. Primary sedimentary bedding structures are not obvious and the deposit is typically massive-bedded. Lithologic components appear fairly well mixed. On closer inspection, where the grain-size is less coarse, this poorly sorted, pebbly sand can be seen to contain rude and vague stratification. The poorly sorted. pebbly, fossiliferous Riggins Mill lithofacies is easily identifiable even in deeply weathered exposures because weathering does not significantly effect the characteristic grain size (ranging from clay to pebbles) and high degree of mixing of the sediments.
Calcareous concretions or nodules of varying sizes, approximately 0.5 to 6 in . (1 to 15 em), and of roughly spherical shape, are characte~istic of relatively unweathered Riggins Mill. The smaller nodules have the appearance of "popcorn". Where these calcareous nodules or concretions are exposed on a weathering surface, the surface appears knobby. These nodules probably originated during sedimentation because they commonly contain concentrations of shell molds and the sand distribution. in them is different from that of the surrounding matrix
.In a few places where the Riggins Mill has been deeply weathered, the macrofossil hard parts have been replaced by silica. As a result, the siliceous pseudomorphs of the fossils lie scattered on the weathering surface in profusion. The degree of replication of the detail of the fossil shells may be very high. The fossils include gastropods, pelecypods, scaphopods, corals, bryozoans, and echinoids.
In the type area of the Riggins Mill Member. in western Twiggs County, the middle part of the unit consists of a sandy, fossiliferous limestone that is virtually identical lithologically to the stratigraphically equivalent Utley Limestone Member of the Clinchfield Formation in Burke
11

and Screven Counties. Although widespread in southeastern Bibb, northern Twiggs, and northwestern Wilkinson Counties, this limestone bed has not been observed east of the type area. Similarly, the upper bed of the Riggins Mill Member in northern Twiggs County, .which consists of a finer grained, somewhat better sorted, clayey, very calcareous, massive-bedded, nodular, fossiliferous, fine-to medium-grained sand, appears to be restricted to the type area. However, if this b.ed were completely leached of calcite, it would probably appear as a finer textured, crudely layered variation of the typical poorly sorted and pebbly Riggins Mill.

Chlamys cocoana (sensu Glawe, 1974, p. 6-7, pl. 2, figs. 3,5,10,11)

is characteristic of the Riggins Mill Member and can be considered a

guide fossil for the unit. Although C. cocoana occurs in other Eocene

deposits .in the Coastal Plain, the only other occurrence of the fossil in

the state of Georgia is a trace occurrence in the McBean Formation at

Shell Bluff in Burke County. Crassostrea sisantissima, which occurs as

scattered shell fragments, individuals, and in small oyster bioherms, also

is characteristic of the Riggins Mill Member in its type area. Periarchus

lyelli occurs only in the upper part of the Riggins Mill, but it occurs

only in low frequencies as scattered individuals or more commonly as

scattered fragments. We have observed that f gigantissima does not occur

ih the member where there is an abundant molluscan fauna, and that P.
lYelli neither occurs with f gisantis!!!! nor with an abundant and-diverse molluscan faunas. It is our general observation that abundant c. gigan-

tissima, P lyelli, and rich and diverse molluscan faunas are three

mutually exclusive faunal assemblages in the Jacksonian deposits of Georgia.

It also is of interest to note that, although the limestone bed in the

Riggins Mill Member is virtually identical lithologically and in strati-

graphic position to the Utley Limestone Member of the Clinchfield Formation

in eastern Georgia, the Utley Limestone contains the "Scutella" bed (P.

lyelli bed) and the limestone in the Riggins Mill does not.

-

Microfossils are common locally in the Riggins Mill Member and the member may contain a diverse suite of benthonic foraminifera. Two species of benthonic foraminifera that occur in the Riggins Mill Member that are characteristically Jacksonian are Discorbis hemisphaerica and Discorbis globulospinosa. Unfortunately microfossil preservation is very poor at the type locality.

The known thickness of the Riggins Mill ranges from 0 to 17 ft (0 to 5.2 m).

Treadwell Member of the Clinchfield Formation
The Treadwell Member of the Clinchfield Formation is named for the community of Treadwell, 1.4 mi (2.24 km) southeast of the Bibb County/Twiggs County line on Riggins Mill Road in northern Twiggs County, Ga. The type

12

locality is the Georgia Kaolin Company Pit 40, at the intersection of two

~aolin haul roads, 0.75 mi (1.2 km) southwest of the community of Treadwell.

The type description of the Treadwell Member is on p. 76 in the Appendix

(see also Fig. 14, p. 75).



The Treadwell lithology typically ranges from a very calcareous sand to a sandy limestone. It is generally deficient in clay and therefore tends to be more indurated by calcite than the underlying Riggins Mill Member or the overlying Tivola Limestone. The quartz sand component of the Treadwell is fine~to medium-grained and well-sorted. The Treadwell Member is generally well-stratified and may be thin-bedded or thick-bedded, and horizontal-or cross-bedded. Lenses or thin layers of almost pure limestone or noncalcareous, well-sorted quartz sand may be interlayered with more typical lithologies.

The Treadwell Member of the Clinchfield Formation in central Georgia contains the "Scutella" bed (or Periarchus lyelli bed) of the eastern Gulf Coastal Plain. Periarchus lyelli is generally common to abundant in the Treadwell, and may be the only macrofossil present. In this member~
Aequipecten spillmani replaces f cocoana of the Riggins Mill.

The contact between the Riggins Mill and the Treadwell Members appears to be gradational at some sites (as at the type locality) and very abrupt at other sites, suggesting a discontinuity. The presence of (1) diverse foraminiferal s.uites, (2) diverse molluscan suites, and (3) fairly intense bioturbation and biological mixing of the sediments in the Riggins Mill as compared to (1) no known foraminiferal suites, (2) a meager molluscan fauna, and (3) primary bedding generally undisrupted through faunal mixing in the Treadwell Member suggests that the Treadwell was deposited in shallower water and represented a biologically more restricted environment than that of the Riggins Mill. It is possible that the Treadwell sediments represent a minor and subtle regressioa in the upper part and at the top of the Clinchfield, which at other locations may be represented only by a diastem. This is consistent with the observation that the Treadwell is known definitely only in northern Twiggs county and appears to be much more limited in its geographical occurrence than the Riggins Mill.

Undifferentiated, Weathered and Leached Clinchfield
In many weathered exposures the Clinchfield cannot be readily separated into either Riggins Mill or Treadwell. Where the deposit has not been completely weathered to nondescript residuum, the sediments generally range from rude to well defined, horizontally bedded, fine-to medium-grained, generally moderate to well-sorted quartz sand. The clay content of these sands. ranges from only slightly argillaceous (with scattered clay partings

13

or laminae) to thin to moderately thick beds of relatively pure, wellbedded clay. There.is no definite evidence at this time that any of these sands correlate with the Treadwell Member, but there is a clear relationship with the Riggins Mill. In places, e.g., Stop 1 of the 1974 Southeastern GSA Fieldtrip (Huddlestun, Marsalis, and Pickering, 1974, Fig. 5 (referred to as Tivola equivalent), these sands contain
a silicified, Riggins Mill molluscan assemblage including f cocoana,
and in other places, e.g., at the Central of Georgia railroad cut at Mountain Springs, Jones County (referred to by LaMoreaux, 1946, as channel sands), typical Riggins Mill lithology grades up into rudely layered, medium-grain~d sand of moderate sorting.

Sands of this lithology are not included in the Riggins Mill Member

at this time as not enough is known of the geographic distribution of

these sands to warrant recognition as a separate member of the Clinch-

field Formation. As a result, we currently refer to these bedded sands

only as undifferentiated, weathered and leached sands of the Clinchfield

Formation.



Albion Member of the Clinchfield Formation
Carver (1972, p. 163-164) formally defined the Albion Member of the Barnwell Formation. The type locality of this unit is at the Babcock and Wilcox Albion Kaolin mine, approximately 1 mi west of Hephzibah, Richmond County, Ga. His thorough description of the Albion is as follows (ibid., p. 163164):
The Albion Member of the Barnwell Formation was informally defined in Sandy, Carver and Crawford (1966). The type section of the Albion Member is here designated as the section exposed in the Albion Kaolin Mine approximately 1 mile west of Hepzibah, Richmond County, Georgia (Section 12 of this report). The Albion Member consists of discontinuous lenses of spiculite, spiculitic clay and mudstone and opal-cemented sandy spiculite and spiculitic sandstone (Buie and Oman, 1963; Carver, 1968, 1966). Typical exposures of spiculite and spiculitic clays occur in the section along Windsor Spring Road a mile north of the Tobacco Road in Richmond County (Sandy, Carver and Crawford, 1966; Herrick and Counts, 1968). Opalcemented rocks occur in the Albion Mine, in the abandoned Harbison~ Walker Co. flint-kaolin pit near Gibson, Glascock County (Sandy, Carver and Crawford 1966), and as float along Brier Creek at the crossing of U.S. Highway 1 on the west boundary of Richmond County.
Fine~grained sediments of the Albion Member normally are massive to poorly bedded and megascopically structureless, but intraformational conglomerates (with 1 to 4 mm diameter fragments) occur in the Windsor Spring and Gibson sections. X-ray diffraction indicates that the underlying Middendorf Formation consists of mixtures of kaolinite and quartz, but the spiculitic clays and mudstones of the Albion Member

14

are mixtures, in varying proportions, of opal, montmorillonite, quartz and kaolinite, with opal and montmorillonite dominant in most cases. The change in clay mineralogy across the MiddendorfBarnwell Formation boundary in the Albion Member outcrop area is evidence for a significant change in source materials, perhaps the introduction of volcanic ash, or a change in weathering conditions in the source area, and substantiates the importance of the unit as a stratigraphic marker.
The mudstones and clays of the Albion Member contain abundant sponge spicules, which are one source of opal in the sediment. Separation and low-power microscopic examination of the coarser fractions of the spiculitic clays reveals that the tripartite spicule terminations of class Hyalospongia are common. Hyalospongia are an entirely marine class of sponges, and the presence of hyalospongia firmly establish the marine character of Albion Member sediments.
Opal-cemented units of the Albion Member are dominantly opal with varying amounts of clastic quartz and minor amounts of montmorillonite and kaolinite. One lense of opal-cemented sandstone in the Albion Mine grades laterally into marcasite-cemented gravel with montmorillonite fragments, pinching-out within a few feet of the lateral change in grains size. Silicified (opalized) plant fragments and carbonaceous matter are abundant in lower parts of the unit. Taken together, the thin, discontinuous nature of the units, the abundance of plant fossils, and the abrupt lateral transition to marcasite-cemented gravels strongly indicate an extreme near-shore, perhaps tidal pool, origin for the opal-cemented clastics and spiculites of the Albion Member of the Barnwell Formation. This interpretation confirms the observation of Cavaroc and Ferm (1968) that richly spiculitic sediments are indicators of shoreline environments.
The Correlation of the Albion with the Clinchfield Formation is a probability rather than a certainty. No calcareous fossils are present in the Albion that can be used for establishing correlation within the rest of the Jacksonian deposits. Only radiolarians, which have not been employed for correlation purposes in the Upper Eocene, sponge spicules, and very poorly preserved diatoms have been reported from the Albion. The reasons for correlating the Albion with the Clinchfield are as follows:
(1) Stratigraphic position - both the Clinchfield Formation and the Albion occur beneath perimarine deposits of certain Jacksonian age and above kaolinitic sand deposits of early Tertiary age (Huber Formation).
(2) Facies - both the Clinchfield Formation and the Albion are very shallow-water, nearshore deposits that occur at the base of a major marine transgression.
15

(3) Both the Clinchfield Formation and the Albion are quite variable in thickness and locally (commonly in the case of the Albion) may be absent. The ab.sences appear to be due to initial Jacksonian sedimentation in topographic lows on an earlier, pre-Jacksonian surface of some relief. The Dry Branch Formation does not exhibit this style of thickness variability, suggesting that a surface with topographic relief did not develop between Dry Branch time and Clinchfield/Albion time. This suggests that the Albion is not an updip, nearshore facies of the underlying Claibornian, Lisbon/McBean Formation in that we would expect the upper surface of a nearshore Claibornian deposit to exhibit moderate relief.
(4) Finally, in the case of the Albion, there is a very uniform, abrupt change in lithology between the Albion and the overlying . Dry Branch Formation, suggesting that the Albion is not a basal facies of the Dry Branch.
The Albion Member of the Clinchfield Formation is present only in Glascock and Richmond Counties, Ga, and in Aiken County, S.C. Its geographic occurrence, therefore, is only in the updip nearshore facies of the Jacksonian in easternmost Gerogia and western South Carolina.
Utley Limestone Member of the Clinchfield Formation
The name Utley Limestone Member of the Clinchfield Formation is taken from Utieys Cave, the type locality at the upper end of Mallard Pond. This location is on the property of Georgia Power Company's Plant Vogtle site, 1.3 mi (2.1 km) immediately south of east of the intersection of Hancock Landing Road and River Road, Burke County, Ga. The only other exposure of the limestone known to the e11thors is at Utley Point (also see Cooke, 1943, p. 57) on the Savannah River, 0.9 mi (1.5 km) eastnortheast of Utleys Cave, also on the property of Georgia Power Company. Because the Plant Vogtle site has been proposed to be a nuclear facility, the security and restrictions of movement on the property is high and, therefore, access to the type locality is difficult. Unfortunately, there are only two known exposures of the member.
The Utley Limestone Member is typically a sandy, glauconitic, slightly argillaceous, fossiliferous limestone of varying degrees of induration. In places the sand content is high enough to be a very calcareous sandstone. Although there are few known surface exposures of the Utley, and these only on the property of Plant Vogtle, the Utley Limestone Member, however, can be identified in cores taken by the Georgia Power Company in southern Burke (Bl53, Bl56, 'B246) and northern Screven Counties, (B32, B33, B34). The Utley Limestone is not known to occur north of the vicinity of Hancock Landing. The stratigraphic interval of the basal Jacksonian at Shell Bluff
16

in Burke County is covered, but presumably the tough Utley Limestone is not present there.
Like the Albion Member farther north, and the rest of the Clinchfield Formation in east-central Georgia, the Utley Limestone. is locally absent in :Burke County. Part of the patchy distribution of the unit is almost certainly due to its being deposited only in topographic lows on a surface of low or moderate relief. However, the Utley is also known to be carvernous (as at the type locality) and part of its absence may be due to solution.
The Utley Limestone Member of the Clinchfield Formation locally contains abundant Periarchus lyelli and, therefore, contains the easternmost occurrence of the "Scutella" bed of the eastern Gulf Coastal Plain.
The Utley Limestone Member of the Clinchfield Formation will not be seen on this field trip.
Dry Branch Formation
The name Dry Branch Formation, a new stratigraphic unit, is taken from the community of Dry Branch, located on US 80, on the Bibb/Twiggs County line. The type locality of the Dry Branch Formation is in Twiggs County, on the north side of a disused kaolin haul road, 0.6 mi (1 km) from the junction of the kaolin haul road and US 80 (at the highway bridge where _ US 80 passes over the Seaboard Coast Line), 2.3 mi (3.7 km) south of Dry Branch. The type locality of the Dry Branch Formation is 0.6 mi (1 km) northeast of the old type locality of the twiggs Clay at the pit of the General Reduction Company, and 1 mi (1.6 km) northwest of the proposed reference locality of the Twiggs Clay along the Seaboard Coast line railroad tracks. The type description of the Dry Branch Formation is in the Appendix on p. 73 (see also Fig. 13, p. 71).
The Dry Branch Formation is a ne~.;r formation that consists of three distinct but interfingering and intergrading lithofacies, a marine, montmorillonite clay lithofacies (Twiggs Clay), a distinctly bedded sand and sand and clay lithofacies (Irwinton Sand), and a rudely bedded to massivebedded, calcareous, fossiliferous sand lithofacies (Griffins Landing Sand). In the areas of extreme development of these lithofacies, they generally constitute the entire Dry Branch section. It is in such areas that it is useful to recognize these lithofacies as distinct,, formal members of the Dry Branch Formation. In many areas of Georgia, however, a fine distinction between the lithofacies, due to complex interfingering and intergradation, is not possible. In these areas, for mapping purposes and purposes of discussion, it is best to distinguish only the formation and to recognize the facies subdivisions as informal lithofacies, lithosomes, or lithostromes.
17

In general the Twiggs Clay is characteristic of the entire Dry Branch Formation west of the Ocmulgee River with the exception of the single Jacksonian outlier at Rich Hill in Crawford County where the Irwinton Sand (Roberta Sand of Connell, 1958) overlies the Twiggs Clay. East of the Ocmulgee River the Twiggs Clay is characteristic of the downdip and/or the lower part of the Dry Branch Formation.
The Irwinton Sand, on the other hand, is characteristic of the updip, outcropping Jacksonian in the areas near the Fall Line of eastern Georgia and western South Carolina. It does not extend very far downdip in the subsurface
The Twiggs Clay lithology and the Irwinton Sand lithology in the outcrop belt are very closely and intimately related spacially and in origin. The silty fine sand along the bedding planes of Twiggs Clay is essentially Irwinton "sand", and the clay laminae, thin layers, lenses, and detrital chips so characteristic of the Irwinton Sand are essentially Twiggs "clay". Curiously, sedimen~ary processes over large expanses of the late Eocene coastal area of eastern Georgia effectively and almost exclusively separated the fine and medium sand components of the incoming terrigenous clastic sediments from the almost pure clay component.
Although there are scattered layers or lenses of Griffins Landing lithofacies in the Dry Branch Formation west of the Ogeechee River, this unit is for the most part restricted to the area east of the river. The Irwinton and Griffins Landing lithofacies are so intimately intermixed in much of the Jacksonian outcrop belt in northwestern Burke County that regional separation of the two is impractical. One lithofacies may dominate the Dry Branch section at one site whereas, nearby, the other facies dominates.. In southeastern Burke County, however, the Griffins Landing lithofacies consistently dominates the lower part of the Dry Branch section and, except for a thin, fairly consistent bed of Twiggs Clay near the base of the unit, the entire formation in the shallow subsurface in Screven County Ga. consists of the Griffins Landing Member.
The stratigraphic pattern that is apparent within the Dry Branch Formation in Burke and Screven Counties is as follows:
(1) the Twiggs Clay lithofacies is commonly, but not invariably, present near the base of the Dry Branch Section,
(2) the Griffins Landing is thickest and constitutes a greater proportion of the Dry Branch Formation, downdip,
(3) the Griffins Landing thins and is restricted to the lower part of Dry Branch section updip,
18

(4) the Irwinton is thickest and constitutes a greater proportion of the Dry Branch Formation updip, and
(5) the Irwinton thins and is restricted to the upper part of the Dry Branch downdip.
Therefore, it appears in a general way that the Twiggs lithofacies represents a transgression (offshore deposit); the Griffins Landing lithofacies appears to be regressive over the Twiggs; and the Irwinton, being non-fossiliferous, is regressive over the Griffins Landing (also see Herrick, 1964) and represents the most restricted marginal marine environment in the Dry Branch Formation.
The general lithofacies patterns within the Dry Branch Formation in central and eastern Georgia are listed below.
(1) The greatest probability of encountering Twiggs Clay is near or at the base of the Dry Branch Formation.
(2) Irwinton scour and fill structures (tidal channels?) are most commonly encountered near the middle of the Dry Branch; some are found near the top of the section whereas others extend all the way to the base, having removed even the previously deposited Twiggs Clay.
(3) There is a discontinuous lensical development of Twiggs lithofacies in the upper part of the Dry Branch, above the main concentration of scour and fill structures.
(4) The Irwinton lithofacies is most commonly developed very near the top of the Dry Branch Formation.
(5) There is a discontinuous but common occurrence of thinly bedded clay and thinly interbedded clay and fine sand at the very top of the Dry Branch in most of eastern Georgia and is therefore a useful marker bed. However, the bed does not occur in eastern Burke County and may not occur east of the Ogeechee River.
The thickness of the Dry Branch Formation varies from over 180 ft (54 m) to less than 30ft (9 m). In eastern Georgia and western South Carolina the Dry Branch appears to thin systematically toward the Fall Line, being consistently thinnest in that area.
Twiggs Clay Member of the Dry Branch Formation
The Twiggs Clay was named by Shearer (1917, p. 165-172) for a clay deposit being mined for fuller's earth near Pikes Peak Station in Twiggs County, Ga. The type locality is in the pit of the defunct General Reduction
19

Company, adjacent to US 80 and on the east . side of the intersection of Riggins Mill Road and US 80, 2.0 mi(3.2 km) south of Dry Branch, Twiggs County. A section exposed in the pit described by Shearer (1917, p. 166, 167) and coordinated with the authors' experience.of the area and with the exposures still extant in the pit is shown with Stop 9 (Fig. 13) in the Appendix on p. 71.
The original type locality of the Twiggs Clay, in the abandoned fuller's earth or montmorillonite open pit of the General Reduction Company, is no longer usable as a critical reference locality because the pit is overgrown by a first generation forest. As a result, we are designating the railroad cut called "map locality E" by Shearer (1917, p. 171, 172) the main reference locality for the Twiggs Clay (also see Connell, 1966a). This exposure was described by Shearer (ibid.) and is still in an excellent state of preservation. The exposure is on the north side of the Seaboard Coast Line railroad tracks 3.3 mi (5.3 km) southeast of Dry Branch; 1.0 mi (1.6 km) southeast of former site of original type locality of the Twiggs Clay at the fuller's earth pit of the General Reduction Company, and about 0.6 mi (0.97 km) southeast of the US 80 overpass of the Seaboard Coast Line. The railroad cut is about 260 ft (80 m) southwest of the railroad crossing of an unimproved dirt road which is 0.25 mi (0.4 km) south of jet with US 80. This location is listed as map locality E of Shearer (1917, p. 171, 172), and he (ibid.) supplies a measured and described section of the site. This location is on the southeastern flank of the hill known in former days as Pikes Peak. The railroad station called Pikes Peak station in the early literature has long since been destroyed and the site is now a forest with fairly large trees.
Our description of this main reference locality of the Twiggs Clay and the measured sections from the type area of the Twiggs Clay, including that from the General Reduction Pit, the type locality of the Dry Branch, and the reference locality of tr.e Twiggs Clay, are given in the Appendix on p. 72
and p. 71 (Fig. 13) respectively.
It is apparent on examining our sections of the type area of the Twiggs Clay and the Dry Branch Formation (see Fig. 13, p. 71) that the Irwinton Sand is an integral part of the type deposits of the Twiggs Clay. It is also clear that:
(1) the type minable deposits of the Twiggs, fuller's earth clay, is overlain by Irwinton Sand;
(2) there is a thick section of Irwinton Sand underlying the type Twiggs Clay; and
(3) the type Twiggs Clay occurs near the top of the Dry Branch Formation, just below the Tobacco Road Sand.
20

Thi~ is in revel:'se order of the sequence as postulated by LaMoreaux (1946, p. 58) for the typical Twiggs/Irwinton stratigraphic relationships and that of the experience of most subsequent investigators. We emphasize the most persistent interval of stratigraphic occurrence of the Twiggs Clay is near the base of the Dry Branch Formation. Therefore, we conclude that:

(1) the type stratigraphic concept of the Twiggs Clay is not consistent with the concept of the Twiggs Clay that has been developed by a number of investigators over the years (LaMoreaux, 1946; Carver, 1966, 1972; Pickering, 1971); and

(2) the type deposit of Twiggs Clay is a local lens of Twiggs lithofacies in the upp.er part of the Irwinton Sand Member of the Dry Branch Formation.

The type bed of Twiggs Clay can be looked upon for formal purposes as "floating" lithostratigraphically in an Irwinton Sand deposit. It is not correlative with the principal, lower bed of Twiggs Clay that we conceive as the Twiggs Clay Member of the Dry Branch Formation.

In an effort to stabilize the stratigraphic terminology of the Dry Branch Formation and the concept of the Twiggs Clay, and to make the concept of the Twiggs clay consistent with established usage, we propose establishing the Twiggs Clay exposure in the pit of the Medusa Portland Cement Company at Clinchfield in Houston County as a key alternate type locality for the Twiggs Clay Member of the Dry Branch Formation. In this area the Twiggs Clay includes the entire Dry Branch stratigraphic interval and always has been recognized by various investigators as being of late Eocene age, and therefore, correlative with the type Jacksonian deposits farther west (Veatch and Stephenson, 1911; Shearer, 1917; Cooke and Sheare.r, 1918; Cooke, 1943; Cushman, 1945; Pickering, 1970; Schmidt, 1977). In addition the Twiggs Clay .in this area is underlain and overlain by other distinctive upper Eocene lithostratigraphic units that contain distinctive upper Eocene faunas. Therefore, the upper and lower stratigraphic boundaries of the Twiggs Clay are clearly definable at Clinchfield.

The Twiggs Clay is a pale greenish, olive green, bluish gray, dark

gray, or locally, almost black, silty clay with hackly, blocky, shaley,

.

subconchoidal to conchoidal fracture. Where the clay is almost pure and

unaltered by weathering, it commonly displays a combination of blocky and

conchoidal fracture, and where it is weathered, its fracture is pronouncedly

hackly. Where the Twiggs Clay is sandy or silty, and especially where

concentrations of fine to very fine sand occur on bedding planes, the

fracture can be fissile and shaley. The Twiggs Clay commonly displays

jointing and at some locations may be intensely jointed.

21

Some beds of Twiggs Clay may consist of almost pure montmorillonite clay with minor or trace amounts of illite and kaolinite. The kaolinite ~ontent (in unweathered Twiggs Clay) is always highest at the base of the Dry Branch. This kaolinite distribution is consistent with the concept of the Dry Branch being a transgressive unit in that the basal portion of the Twiggs was deposited nearest the shore where kaolinite is more readily deposited.
Characteristically the clay is impure. The impurities consist of quartz silt or sand, rarely pebbles; finely disseminated or biogenic calcite, occasionally preserved aragonitic mollusk shells; opal-cristobolite; glauconite; pyrite; mica; lignite and flecks of carbonaceous matter; and apatite in the form of small vertebrate bone debris, fish teeth and scales, and Zeuglodon bones. Minerals that are normally subbordinate may produce the dominant lithologies in specific beds or exposures in this unit. Sand, glauconite, chert, limestone, or lignite beds of varying thickness and extent may be present locally.
An eastern and western facies of the Twiggs has been recognized by some previous investigators. This regional division of the Twiggs Clay also applies to the clay that is updip or downdip, or upsection or downsection. The western, downdip, downsection facies of the Twiggs Clay is generally calcareous with some admixtures of sand, glauconite, mica, and finely disseminated pyrite. Sandy, glauconitic, fossiliferous (shelly fauna), thin limestone beds or layers, calcareous concretions, or calcareous, glauconitic, fossiliferous sandstone beds or layers are not uncommon within the section. Toward the base of the Twiggs Clay in the western facies, the clay becomes very calcareous and fossiliferous and is commonly ref~rred to as "marl". Glauconitite beds (greensand) are generally present near the top of the western-most Twiggs Clay, west of the Ocmulgee River. These greensand beds are only sparsely calcareous but are sandy and argillaceous and ~y contain scattered shall molds.
The eastern, updip, upsection facies of the Twiggs Clay is characterized by a paucity of calcite and glauconite and the almost universal presence of uni-dimensionally disordered cristobolite (opal claystone of Heron, Robinson, and Johnson, 1965). The opal-cristobolite in the clay is generally disseminated through the clay as fine particles. The source of this silica in the Twiggs Clay is siliceous microfossils, i.e., diatoms, radiolarians, and sponge spicules (Schmidt, 1977; Wise, Buie, and Weaver, 1972; Wise, Ciesielski, Schmidt, and Weaver, 1974; Wise and Weaver, 1974: Wise and Weaver, 1973). Evidently the eastern facies of the Twiggs Clay was conducive to proliferation of diatoms, radiolarians, and sponges during late Eocene time, whereas the western facies of the Twiggs was not conducive to the proliferation of these organisms but rather to that of calcareous organisms.
The Twiggs Clay is thickest in the western area, being as much as 100 ft thick at Clinchfield. East of the Ocmulgee River the Twiggs Clay inter-
22

fingers with the Irwinton Sand and although the entire thickness of the Dry Branch may be as much as 180 ft (54 m) thick, the combined thickness of the distinct beds of Twiggs Clay is less, e.g., only 86ft (26m) thick at the type locality as opposed to the reported thickness of 100 ft (30m) (Cooke and Shearer, 1918; Cooke, 1943). The Twiggs Clay pinches out east of the Savannah River where it becomes discontinuous and thin, being at the most 10 ft (3 m) thick. This thinning is not a function of dip position or nearness to the shore because the Twiggs does not thicken downdip in the Screven County area. In the Savannah River area, the updip Irwinton and Twiggs passes downdip into Griffins Landing and Twiggs, and thence into the Ocala Limestone in the ScrevenEffingham Counties area.
Irwinton Sand Member of the Dry Branch Formation
The Irwinton Sand was named by Lamoreaux (1946a, 1946b) for a soft, commonly loose, fine to medium, well-bedded sand that conformably overlies the Twiggs Clay in Wilkinson, Twiggs, and Washington Counties, Ga. The type locality of the Irwinton Sand is in gullies, now overgrown, on the west side of Ga. 29 (US 441), 0.3 mi (0.5 km) south of the courthouse in Irwinton, Wilkinson County, Ga. The type description of the Irwinton is as follows (LaMoreaux, 1946a, p. 17):
During this investigation it was noted that many dug wells throughout the "Red Hills" area obtained their water from a persistent bed of fine to coarse unconsolidated sand, the Irwinton sand member of the Barnwell formation, which lies conformably on the Twiggs clay member. It was also noted that the sand capped many of the uplands in the northern half of the area of outcrop of deposits of Jackson age (see Plate.l). The sand bed ranges in thickness from about lO feet along the northern margin of the Barnwell formation to a maximum of 52 feet in the vicinity of Irwinton.
In the type area of the Irwinton Sand in Wilkinson County and in east central Georgia, it typically consists of fine- to medium-grained, well sorted, almost pure quartz sand that shows well developed horizontal- and cross-bedding. The coarser beds of Irwinton Sand tend to become progressively more poorly sorted as the maximum grain size of the quartz sand increases. Most exposures of the Irwinton Sand contain some thick beds, thin beds or lenses, and laminae or disrupted clay clasts of Twiggs type montmorillonitic clay. In general, all the clay beds. within the Irwinton probably are lenses, but the thicker beds are areally more extensive than the thin beds, and the clay laminae are especially discontinuous laterally.
Accessory lithic components include clay that is mainly montmorillonite but contains minor amounts of illite and kaolinite. Some weathered beds of clay in the Irwinton are composed completely of kaolin, apparently altered from montmorillonite. All of the clay beds in the Irwinton, known
23

to the authors, are of Twiggs Clay-type lithology or aspect. Other

accessory minerals in the Irwinton Sand include heavy minerals (which

are locally very conspicuous), very minor mica, fossiliferous and

nonfossiliferous chert and chert-cemented sandstone, calcite, and

minor dispersions Sand known to the

aouf thMonors2

Almost all of the have been weathered

outcrops of the to some degree.

Irwinton However,

completely unweathered Irwinton is known from cores (GGS-3174 and GGS-

3175) and it has been found that completely unweathered Irwinton Sand

is typically slightly calcareous and microfossiliferous, thus accounting

for the scattered but common beds or lenses of sandy fossiliferous

chert on the weathering surface.

The Irwinton Sand is typically very well bedded. Only in scattered beds in any given section are there thin layers of Irwinton that have been clearly bioturbated ot burrowed, with observable mixing of the sand and clay components.

As noted above, the typical Irwinton Sand is fine- to ~edium-grained and well sorted. However, there are beds within . the Irwinton, and some sections are dominanted by medium to coarse, even pebbly, poorly sorted sand. It appears that as the maximum grain-size of the Irwinton Sands increases, the sorting gets poorer, and the minimum grain-size also
diminishes.

Typically the Irwinton Sand is soft and unconsolidated, in some places even loose. So, in general, the Irwinton is a "slope-former". However, there are beds of chert-cemented sandstone that are much more resistant to weathering and hold up ledges in roadcuts and old clay pits.

Fossils are generally rare in the Irwinton Sand. This is in part due to the usual leaching of the soft porous sands in the vadose zone. However, it is also due to the original sedimentary environment of the Irwinton where it is clear that no burrowing organisms lived to destroy the fine bedding characteristic of the unit. Scattered beds within the Irwinton are fossiliferous and a shelly, silicified molluscan fauna can be collected. Normally, however, the main fossil components of the Irwinton are shell fragments of clams and oysters. Fairly typical Irwinton Sand will be seen at Stops 6 and 8 (Figs. 11 and 12).

Griffins Landing Member of the Dry Branch Formation
The type locality of the Griffins Landing Sand Member of the Dry Branch Formation is at Griffins Landing on the Savannah River, 1.4 mi (2.25 km) north of the junction of Griffins Landing Road and River Road, and 5.2 airmiles (8.4 km) north of Girard, Burke County, Ga. A description and measured sections of the type locality of the Griffins Landing Member are given on p. 57 and p. 54 (Fig. 10) respectively of the Appendix.

24

In general the Griffins Landing Sand Member is a fairly well-sorted, massive to rudely bedded, calcareous sand. In updip areas thin limestone beds, clay beds or lenses, local oyster shell (Crassostrea gigantissima) beds and bioherms, and chert or silica-cemented sandstone (as at Stoney Bluff Landing) are common.
Subordinate lithic components include montmorillonite clay, calcite, shells, chert, mica, and dispersed Mno2
In many places in outcrop and in cores the Griffins Landing Sand shows little of any original primary sedimentary and biogenic structures. This is especially the case in the downdip, shallow subsurface in Screven County where the Griffins Landing Member consists of a massive-bedded, uniformly structureless, somewhat argillaceous, calcareous, microfossiliferous, medium-grained, well-sorted sand. Rude ' stratification is present, however, in outcrop, as at Griffins Landing, and in the shallow subsurface of Burke County.
One of the most characteristic features of the Griffins Landing Sand
in the outcrop area is the local abundance of f gigantissima, both in
living position, as at the type locality, and as oyster shell rubble. In
the past some investigators have attempted to use f gigantissima as a
guide fossil for specific deposits. We have observed that C. gigantissima is locally abundant in deposits of various Jacksonian ages in Georgia (Clinchfield, Dry Branch, and Tobacco Road). In addition, C. gigantissima occurs with Cubitostrea sellaeformis in the McBean of middle Eocene age at Shell Bluff in Burke County. Crassostrea gigantissima is a facies fossil and cannot be used for stratigraphic correlation except on an exceedingly broad scale.
Although the Griffins Landing Member is characteristically a sand, it does contain lenses of Twiggs-type montmorillonitic clay, and it is most
commonly with these clay beds or lenses that the f gigantissima bioherms
are associated. We have not observed oyster bioherms in the predominant, massive-bedded sand facies of the member.
TOBACCO ROAD SAND
The Tobacco Road Sand was named by Huddlestun and Hetrick (1978) for upper Jacksonian deposits that earlier had been called the upper sand member of the Barnwell (LaMoreaux, 1946a, 1946b). The type locality of the Tobacco Road Sand is located on the east side of Morgan Road, 0.35 mi (0.5 km) north of the junction of Morgan Road and Tobacco Road, Richmond County, Ga. The type description and measured section is presented on p. 64 and p. 63 (Fig. 11) in the Appendix.
25

The Tobacco Road is very predominantly a sand; all other lithic components--heavy minerals, clay mineral, chert, mica, calcite and limestone, glauconite, and Mn02--are minor and only locally significant. The sand 'in the Tobacco Road varies from fine-grained and well-sorted to very coarse-grained, granually, pebbly and very poorly sorted. The Tobacco Road is characteristically massive-bedded due to bioturba~ tion and burrowing but locally the formation may be very thinly and distinctly bedded, even laminated. Vague, crude bedding and disrupted thin~bedding is proba~ly the norm for the formation as a whole. Bedding ranges from horizontal-bedded to cross-or inclined-bedded of various kinds. Amplitudes of cross-bedding range from barely perceptible (less than 1 in~ (2.5 em) to as much as 6ft (1.8 m).
In eastern Georgia and western South Carolina, bioturbation and burrowing is especially characteristic of the Tobacco Road Sand (Siple, (1967) refers these deposits to the Hawthorne Formation). In this area, burrows of Callianassa major can almost be considered a "guide fossil" for the Tobacco Road Sand.
Since the publication of the Tobacco Road (Huddlestun and Herrick, 1978), field work has provided additional data that requires some adjustments to be made in some of the characterist;cs of the formation:
(1) Several sections have been measured since the writing of the initial paper where the formation is greater than 50 ft, thereby almost doubling the earler reported thickness. This in no way sig~ificantly effects the discussion on Tobacco Road sedimentation rates.
(2) Several areas have been identified where the lithology of the Tobacco Road varies significantly from the "norm":
(a) In eastern Twiggs and westernmost Wilkinson County the Tobacco Road is unusually fine-grained, with the bulk of the identifiable unit consisting of fine to medium grained, well-sorted sand;
(b) In central and eastern Washington County the Tobacco Road Sand is again unusually fine grained and siliceous. The base of the unit in this area consists of the Sandersville Limestone above which lie fine-to fine/medium-grained, wellsorted sands with considerable volumes of thinly bedded, laminated, interlayered clay and fine-grained sand. Lenses
of oyster shells (. gigantissima), where the shells are
normally silicified, are locally prominent. Thin to thick beds and lenses of chert and chert-cemented sandstone, resembling the "Altamaha" or "Ashburn" sands'tone found in the area, occur in the upper part of the Tobacco Road.
26

(c) In the vicinity of the Fall Line, some exposures of the

Tobacco Road Sand are very coarsely cross-bedded and

show little, if any, evidence of marine or perimarine

origin (Stop llb}. These deposits appear to be mainly

fluvial in origin.



Sandersville Limestone Member of the Tobacco Road Formation
The type locality of the Sandersville Limestone is in a sink on the south side of Sandersville, 0.8 mi (1.25 km) south of Washington County courthouse in Sandersville (Cooke, 1943, p. 65, 66}. An amended type description of the Sandersville Limestone and measured sections of the upper Eocene deposits in the Sandersville area are presented in the Appendix on p. 47 and p. 46 (Fig. 7}.
The Sandersville Limestone is a basal limestone phase of the Tobacco Road Sand that is restricted to central Washington County. Based on outcrop and core evidence, the Sandersville disappears either by facies change or by pinch-out no more than 1 mi (1. 6 km.} west and 2 mi (3. 2 km} southeast of Sandersville.

27

REFERENCES
Blow, W.H., 1969, Late ~iddle Eocene to Recent planktonic foraminiferal biostrat'igraphy: In: P. Bronnimann and H.H. Renz (Eds.), Proc. Int. Con. Planktonic Microfossils, 1st., Geneva, 1967, 1. E. J. Brill, Leiden, p. 199-421.
Buie, B.F., and Oman, C.H., 1963, Sponge spicules from Coastal Plain strata in Glascock and Richmond Counties, Georgia: Geol. Soc. Am. Spec. Paper 73, Abstracts for 1962, p. 2, (Abe.).
Carver, R.E., 1966, Stratigraphy of the Jackson Group (Eocene) in central Georgia: Southeastern Geology, v. 7, p. 83-92.
----------~' 1968, Facies relationships in the Jackson Group of
central and eastern Georgia: Geol. Soc. Am. Spec. Paper 101,
Abstracts for 1966, p. 352 (abe.).
----~--~--' 1972, Stratigraphy of the Jackson Group eastern Georgia: Southeastern Geology, v. 14, no. 3, p. 153-181.
Cavaroc, V.V., Jr., and Ferm, J.C., 1968, Siliceous spiculites as
shoreline indicators in deltaic sequences: Geol. Soc. Am. Bull.,
v. 79, p. 263-272.
Connell, J.F.L., 1958, The Jackson Group of Georgia-a preliminary report: Southwestern Louisiana Jour., v. 2, no. 4, p. 321-347.
----~----' 1966a, Twiggs Clay Member of the Barnwell Formation (u. Eocene); in catalogue of type localities: Trans., Gulf Coast Assoc. Geol~ Soc., v. 16, p. 387-388.
----~------' 1966b, Irwinton Sand Member of the Barnwell Formation (u. Eocene); in catalogue of type localities: Trans. Gulf Coast Assoc. Geol. Soc., v. 16, p. 389-390.
, 1966c, Sandersville Limestone Member of the Barnwell --~-F- o- rm-a=ti-o- n (u. Eocene); in catalogue of type localities: Trans.,
Gulf Coast Assoc. Geol. Soc., v. 16, p. 391-392.
----~~-----' 1968, Barnwell Formation; in catalogue of type localities: Trans., Gulf Coast Assoc. Geol. Soc., v. 18, p. 451-454.
Cooke, c.w., 1936, Geology of the Coastal Plain of South Carolina: U.S.
Geol. Survey Bull. 867, 196 p.
-------------' 1943, Geology of the Coastal Plain of Georgia: U.S. Geol. Survey Bull. 941, p. 53-77.
28

Cooke, C.W., and MacNeil, F.S., 1952, Tertiary stratigraphy of South Caroli~a:. U.S. Geol. Survey Prof. Paper 243-B, p. 19-29.
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 Clay of Georgia: Contr. Cushman Lab. Foraminiferal Res., v. 21, pt. 1, p. 1-11.
Doering, J.A., 1960, Quaternary surface formations of the southern part of the Atlantic Coastal Plain: Jour. Geology, v. 68, no. 2, p. 182-202.
Glawe, L.N., 1974, Upper Eocene and Oligocene Pectinidae of Georgia and their stratigraphic significance: Georgia Geol. Survey Inf. Circ. 46, 27 p.
Heron, S.D., Robinson, G.C., and Johnson, H.S., Jr., 1965, Clays and opal-bearing claystones of the South Carolina Coastal Plain: Div. of Geology, South Carolina State Development Board, Bull. 31, 66 p.
Herrick, S.M., 1961, Well logs of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 70, 462 p.
, 1964, Upper Eocene smaller foraminifera from Shell Bluff
--- an~ d~ G~ riffins Landing, Burke County, Georgia: u.s., Geol. Survey Prof.
Paper 501-C, p. C64-C65.
--~~~-' 1972, Age and correlation of the Clinchfield Sand in Georgia: U.S. Geol. Survey Bull. 1354-E, p. 1-17.
Huddlestun, P.F., and Hetrick, J.H., 1978, Stratigraphy of the Tobacco Road Sand-a new formation: Georgia Geol. Survey Bull. 93, p. 56-77.
Huddlestun, P.F., Marsalis, W.E., and Pickering, S.M., Jr., 1974, Tertiary stratigraphy of the central Georgia Coastal P~ain: Guidebook 12, Southeastern Sec., Geologic Soc. Am., 35 p.
LaMoreaux~ P.E., 1946a, Geology of .the Coastal Plain of east-central Georgia: Georgia Geol. Survey Bull. 50, 26 p.
--~~~-~ 1946b, Geology and ground-water resources of the Coastal Plain of east-central Georgia: Georgia Geol. Survey Bull. 52, 173 p.
LeGrand, H.E., 1962, Geology and ground-water resources of the Macon area, Georgia: Georgia Geol. Survey Bull. 72, 68 p.
29

Lyell, C., 1845, Observations on the white limestone and other Eocene or older Tertiary formations of Virginia, South Carolina, and Georgia: Geol. Soc. London Quart. Jour., v. 1, p. 429-442.
MacNeil, F.S., 1947, Geologic map of the Tertiary and Quaternary forma-
tions of Georgia: u.s. Geol. Survey Oil and Gas Inv. Prelim. Map 72.
Pickering, S.M., Jr., 1966, Stratigraphy and paleontology of portions of ' Perry and Cochran Quadrangles, Georgia: Masters Thesis, University of Tennessee, p.
----=---~-' 1970, Stratigraphy, paleontology, and economic geology of portions of Perry and Cochran Quadrangles, Georgia: Georgia Geol. Survey Bull. 81, 67 p., 14 pls.
------~---' 1971, Lithostratigraphy and biostratigraphy of the north-central Georgia Coastal Plain: Guidebook for the 6th Ann. Field Trip, Georgia Geol. Soc., pt. 2, 15 p.
Sandy, J., Carver, R.E., and Crawford, T.J., 1966, Stratigraphy and economic geology of the Coast~! Plain of the central Savannah River area, Georgia: Geol. Soc. Am., Southeastern Section, Guidebook for Fieldtrip 3, 30 p.
Schmidt, w., 1977, A paleoenvironmental study of the Twiggs Clay (upper
Eocene) of Georgia using fossil microorganisms: Master Thesis, Florida State University, 140 p.
Shearer, H.K., 1917, Bauxite and fullers earth of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 31, p. 158-259.
Siple, G.E., 1967, Geology ar.d ground water of the Savannah River Plant and vicinity, South Carolina: U.S. Geol. Survey Water-supply Paper 1841, 113 p.
Stainforth, R.M., Lamb, J.L., Lutherbacher, li., Beard, J.H., and Jeffords, R.M., 1975, Cenozoic planktonic foraminiferal zonation and characteristic of index forms: Univ. Kans. Paleontol. Contrib., Art. 62, 425 p.
Veatch, 0. and Stephenson, L.W., 1911, Preliminary report on the geology of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 26, p. 235-306.
Wise, S.W., Jr., Buie, B.F., and Weaver, F.M., 1972, Chemically precipitated sedimentary cristobalite and the origin of chert: Ecologae Geol. Helv., v. 65, no. 1, p. 157-163.
30

Wise, S.W., Jr., Ciesielski, P.F., Schmidt, W., and Weaver, F.M., 1974, Altered upper Eocene diatomite in the Coastal Plain of Georgia: Geol. Soc. Am. Southeastern Meeting Abets, p. 414.
Wise, S.W., Jr., and Weaver, F.M., 1973, Origin of cristobalite-rich Tertiary sediments in the Atlantic and Gulf Coastal Plain: Trans., Gulf Coast Assoc. Geol. Soc., v. 23, p. 305-323.
- - - - - - -, 1974, Chertification of oceanic sediments in pelagic sediments on land and under the sea: Spec. Pubis. Int. Assoc. Sedimentologists, v. 1, p. 301-326.
31

APPENDIX 32

ROAD LOG FIRST DAY

Mileage

Interval
o.o

Cumulative 0.0

3.5

3.5

8.0

11.5

1.3

12.8

8.4

21.2

3.7

24.9

3.3

28.2

2.4

30.6

1.5

32.1

3.9

36.0

0.4

36.4

0.4

36.8

0.1

36.9

Leave Holiday Inn in Milledgeville. Turn left (south) on U.S. 441.
Turn left on Ga. 24. Continue through Milledgeville and cross the Oconee River.
Jet. Turn left onto Deepstep Road.
Contact with Coastal Plain gravel overlying Piedmont metamorphic rocks.
Traffic light in Deepstep.
Jet. Turn left onto paved county road.
Jet, paved county road and Linton Road at fire tower. Turn right onto Linton Road.
STOP 1. Almost the entire, typical weathered, Upper Eocene Barnwell Group :f.s exposed here with the Riggins Mill Member of the Clinchfield Formation overlain by the Twiggs Clay Member of the Dry Branch Formation, Gverlain by the Irwinton Sand Member of the Dry Branch Formation, overlain by the Tobacco Road Sand with the typical basal, f1at-pebble bed.
Dry Branch (Irwinton Sand Member)/Tobacco Road exposed in roadcut on left, The basal, flat-pebble bed of the Tobacco Road is absent here.
Cross railroad tracks. Miocene "Altamaha" exposed in upper part of railroad cut. Entering Sandersville.
Jet. Bear to the right on Warthen Street in Sandersvill.e.
Jet. Turn left.
Intersl."!cti.on. Turn right at Harris St. (Ga. 15). Continue through Sandersville on Ga. 15 past Kaolin Plaza.

33

1.0

37.9

1.1

39.0

0.4

39.4

0.9
0.2 2.9
47.9 1.3 0.8 3.7 1.1 3.8

40.3
40.5 43.4
91.3 92.6 93.4 97.1 98.2 102.0

Jet, Ga. 15 and Koalin Raod. Turn right.
Jet, Kaolin Road and paved county road. Turn left.
STOP 2. For the Sandersville and eastern Washington County area, this stop shows (1) the typical Tobacco Road sequence with Sandersville Limestone Member of the Tob~cco Road Sand exposed in the old Lime pit (also see LaMoreaux, 1946b; Cooke, 1943) near the base of the section under the power lines about 100 yds. west of the paved road; (2) the typical oyster beds (bearing Crass'ostrea gigantissima) exposed in the road cut; (3) an upper silicified, irregularly fossiliferous sandstone; and (4) waxy, pale to pistachio green, montmorillonite clay beds at the top to the sequence. Oyster shells and sand dollars (Periarchus quinquefarius) can be collected at this site.
Jet, paved county road and Oconee Road. Turn left on Oconee Road.
Jet, Oconee Road and Ga. 15. Turn left on Ga. 15.
Jet, Ga. 15 and Ga. 24. Turn right onto Ga. 24 and continue towards Waynesboro.
Jet, Ga. 24 and Ga. 56. Continue on Ga. 24.
Waynesboro, Burke County. Turn right on Ga. 24.
Leaving Waynesboro. Turn left on Ga. 24.
Fitz Branch (creek).
Jet. Turn left onto Thompsons Bridge Road.
STOP 3. Former Hatchers Mill site. The top of the Dry Branch Formation (Irwinton Sand or Griffins Landing Member) and the base of the Tobacco Road Sand is exposed here. The very top of the Dry Branch and the Lower part of the Tobacco Road is siliceous (cherty) here. The basal Tobacco Road contains layers and blocks of very fossiliferous chert with abundant molds of Turritella and scattered silicified Periarchus quinguefarius. The bioturbated bed, which is typical for this area, occurs in the upper part of the Tobacco Road section here but it is recognizable only in scattered pockets where it has not been completely weathered to residuum.
34

0.6

102.6

0.6

103.2

0.2

104.0

2.8

106.8

1.5

108.3

4.2

112.5

3.7

116.2

1.3

117.5

0.8

118.3

1.3

119.6

4.7

124.3

The Tobacco Road/"Altahama" contact is exposed on the left where basal channel gravels and lenses overlie, disconformably the bioturbated bed of the Tobacco Road.
Tobacco Road/"Altamaha" contact exposed in roadcut on left.
Tobacco Road/"Altamaha" contact exposed in roadcut.
Turn left and continue to T jet.
Jet. Turn right on road to Girard.
In Girard, turn left on paved county road.
Jet, unimproved county road and River Road. Turn left onto River Road.
STOP 4. The top of the Dry Branch Formation (Irwinton Sand Member), the Tobacco Road Sand, and the basal part of the "Altall1aha" is exposed here.
Jet, River Road and Griffins Landing Road. Turn right onto Griffins Landing Road.
STOP 5. Griffins Landing. This is the type locality of the Griffins Landing Member of the Dry Branch Formation as recently proposed (Huddlestun and Hetrick, in prep.). At this site, the Griffins Landing Member is exposed down to low water level of the Savannah River. However, in cores taken by the Georgia Geological Survey (GGS-1172) and by Georgia Power Company(Bl56 and Bl52), the Griffins Landing Member is underlain by a thin bed of the Utley Limestone Member of the Clinchfield Formation (recently proposed by us, ibid.), which in turn is underlain by the Lisbon Formation of Claibornian age. Only the Griffins Landing Member of the Dry Branch is exposed along the river at this site. However, in the road ditch exposed above the parking area, what is evidently a lens of Twiggs clay lithology (which occurs higher in this section than the Griffins Member) is itself overlain, farther up the hill in the ditch, by the Irwinton Sand Member.
Jet, Griffins Landing Road and Ga. 23. Turn right onto Ga. 23.

35

18.0 1.3 0.7 5.6 8.1 2.4 0.9

142.3 143.6 144.3 149.9 158.0 160.4 161.3

0.7

162.0

2.0

164.0

1.0

165.0

0.5

165.5

Jet, Ga. 23 and Ga. 56. Turn left onto Ga. 56.
McBean Creek, Richmond County line.
Jet, Ga. 56 and Hephzibah-McBean Road. Turn left onto Hephzibah-McBean Road.
Jet, Hephzibah-McBean Road and US 25. Turn right onto US 25.
Jet, (first stop light), US 25 and Tobacco Road. Turn left onto Tobacco Road.
Jet, Tobacco Road and Windsor Springs Road (stop light). Turn right onto Windsor Springs Road.
STOP 6. Most of the Upper Eocene, sandy deposits (Barnwell Group) are exposed here. The Albion Member of the Clinchfield Formation disconformably ove~lies the Huber Formation. The Albion Member is overlain by the Dry Branch Formation, represented by the Irwinton Sand Member, and is overlain by the lower part of the Tobacco Road Sand. We (Buddlestun and H.etrick, in prep.) have recommended that this exposure, and the nearby road cut on Morgan Road, be the main reference locality for the Barnwell Group.
Jet, Windsor Springs Road and Meadowbrook Road. Turn left onto Meadowbrook Road,
Jet, Meadowbrook Road and U.S. 1 (Deans Bridge Road). Turn left onto U.S. 1.
Jet, u.s. 1 and Morgan Road. Turn left onto Morgan
Road.
STOP 7. This is the type locality of the Tobacco Road Sand. Exposed at this site is the upper part of the Dry Branch Formation (Irwinton Sand Member), the Tobacco Road Sand, and an upper bed that is very deeply weathered, but based on what can be observed of its lithology in its basal part, can be either "Altamaha" sands or regressive, fluvial Tobacco Road. Because this locality is so near the Fall Line, and therefore near the ancient shore line, either possibility may be correct.
This is the last stop of the first day. The field trip party will return to the Holiday Inn in Milledgeville.
36

0.0

o.o

3.1

3.1

0.5

3.6

0.1

3.7

0.2

3.9

0.3

4.2

0.3

4.5

0.9

5.4

2.2

7.6

0.8

8.4

2.2

10.6

1.3

11.9

0.4

12.3

1.5

13.8

0.6

14.4

0.4

14.8

1.6

16.4

0.2

16.6

1.3

17.9

0.2

18.1

0.7

18.8

20.7

0.1

20.8

SECOND DAY
Holiday Inn, Milledgeville. Turn left (south) on
u.s. 441.
Railroad crossing. Jet, U.S. 441 and Ga. 24 and Ga. 22. Turn left. Turn right. Jet. Ga. 49, stop light. Stop sign. Turn left. Stop light. Turn right. Leave Milledgeville; enter Hardwick. Camp Creek.
Jet, u.s. 441 and Ga. 243. Turn right on Ga. 243.
Huber-Cretaceous on left in roadcut. Huber-Cretaceous in road cut on left and right. Huber-Cretaceous in road cut on left and right. Huber-Cretaceous in road cut on left. Railroad crossing. Enter Wilkinson County. Ivey city limits. Huber-Cretaceous on right. Lake Tchukolaho. Commissioner Creek. Gordon City limits. Gordon. Jet. Ga. 243 and Ga. 18 spur. Turn left onto Ga. 18 spur. Turn right.
37

0.1

20.9

0.5

21.4

0.5

21.9

0.8

22.7

0.1

22.8

1.1

23.9

0.1

24.0

3.1

27.1

0.5

27.6

2.0

29.6

0.1

29.7

0.2

30.9

1.0

31.9

2.8

34.7

0.9

35.6

0.3

35.9

8.5

44.4

1.0

45.4

0.3

45.7

Turn left.
Jet. Ga. 18 and Ga. 18 spur. Turn left onto Ga. 18.
Leave Gordon.
Massey Hill. Jet. Ga. 18 and Ga. 57. Continue on Ga. 18.
Tobacco Road residuum in roadcut on left and right.
Shortwave relay tower on left.
Upper Eocene residuum in roadcut on left and right.
Deeply weathered Dry Branch Formation in roadcut on left and right. Twiggs Clay and Irwinton Sand present.
Twiggs Clay Member of Dry Branch Formation on right.
Big Sandy Creek.
Enter Twiggs County.
STOP 8. Dry Branch Formation with beds of Twiggs Clay lithofacies and Irwinton lithofacies. section consists only of the Dry Branch Formation and displays the interbedding of Twiggs and Irwinton lithologies.
Dry Branch Formation in roadcut on left and right.
Jeffersonville city limits.
Stop sign. Turn right.
Railroad crossing and jet. Ga. 18 and U.S. 80 in Jeffersonville. Turn right onto U.S. 80.
Railroad crossing.
Powerline.
STOP 9. This is the main reference locality of the Twiggs clay, "map locality E" of Shearer (1917) The lowest bed exposed here is equiV-alent to the "type" bed of Twiggs Clay still exposed in scattered outcrops in the abandoned open pit mine of the General Reduction Company 1.0 mi. (1.6 km) to the northwest. The Twiggs here is overlain by 10.5 ft. (3 m) of Irwinton Sand, which in turn is overlain by 24 ft. (7.3 m) of relatively fine textured Tobacco Road Sand that is typical for the area.
38

0.4

46.1

0.3

46.4

0.4

46.8

0.4

47.2

0.5

47.7

1.3

49.0

0.6

49.6

0.4

50.0

50.0

0.4

50.4

0.7

51.1

1.1

52.2

0.3

52.5

0.8

53.3

0.5

53.8

0.1

53.9

1.7

55.6

2.0

57.6

Crossing the crest of Pikes Peak.
Railroad crossing under U.S. 80.
Jet, Riggins Mill Road and U.S. 80. Turn left onto Riggins Mill Road.
Jet, Old Marion Road and Riggins Mill Road. Continue on Riggins Mill Road.
Stone r.reek Baptist Church on right, county road jet. on left. Continue straight on Riggins Mill Road.
Jet, kaolin haul road and Riggins Mill Road. Turn left onto haul road.
Turn right.
STOP 10. Georgia Kaolin Pit 50, the type locality for the Riggins Mill Sand and Treadwell Sand Members of the Clinchfield Formation. The Riggins Mill Member at this locality unconformably overlies the Huber Formation, which consists of an upper Callianassa burrow-bearing sand, and a lower leaf-bearing clay and fine sand. The contact here between the Riggins Mill and the Treadwell is sharp but gradational. The Treadwell in turn grades upward into the Tivola Limestone.
Turn around and go back the way we came.
Turn right.
Jet, Kaolin haul road and Riggins Mill Road. Turn left.
Power lines.
Bibb County line.
Huber Formation in roadcut on left.
Stone Creek.
Railroad crossing.
Airfield on left.
Jet, Riggins Mill Road and U.S. 23 and U.S. 129. Turn right (Jeffersonville Road).

39

0.2

57.8

0.5

58.3

0.7

59.0

0.5

60.5

0.8

61.3

2.1

63.4

0.7

64.1

Jet, Ga. 57. Continue straight.
Macon city limits.
Jet, Jeffersonville Road and Millerfield Road, stop light. Turn right onto Millerfield Road.
Jet, Millerfield Road and Ga. 49. Turn right onto Ga. 49.
Enter Jones County.
STOP lla. This stop, at Mattie Wells School, consists completely of the Dry Branch Formation. The Twiggs Clay lithofacies dominates the Dry Branch here despite the locality being essentially on the Fall line. Irwinton Sand lithofacies is interlayered with the Twiggs. The Dry Branch/Tbbacco Road contact may be in the uppermost residuum exposed here.
STOP llb. The elevation of the top of this hill is substantially higher then that at the previous stop 0. 7 mi. (1.1 km) away. As a result we see a younger part of the Dry Branch Formation and the Tobacco Road Sand. Of interest here is the apparent fluvial facies of the Tobacco Raod with only a trace, perhaps, of marine influence. In the middle part of the Tobacco Road sequence, above the strongly cross-bedded lower part, is a thin interval that appears to be bioturbated. The upper part of the Dry Branch is also of interest in that it consists of 32 ft (10 m) of massive-bedded, very poorly sorted, pebbly, clayey coarse sand, a lithology that has only been seen in the near vicinity of the Fall Line in the Jacksonian deposits.

End .of Field Trip, Return to Milledgeville.

40

EXPLANATION
u SAND

BEDDED SAND

GRAVEL

~ CARBONATE

~
D

IMPURE CARBONATE CLAY

LIMEY CLAY

l I ~= CLAY INCLUSIONS

~MICA

=-1

I MANGANESE OXIDE

lcr,;-~:::1 CHERT OR CHERT LENSES

0

GLAUCONITE

LIGNITE -FOSSILSBURROWS
~ CALLIANASSA BURROWS

SHELLY FOSSILS

BIOTURBATION

SPONGE SPICULES
w JOINTS

FIGURE 5
41

STOP I
ROAD CUT ON LINTON ROAD ON EAST SIDE OF LITTLE KEG CREEK, WASHINGTON COUNTY

.-.

-.,

.. I

:....-

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

I
I
I
I COVERED I
t
I
I
1.~.-

. .I...., .....~..~,
. .. ,.,_ I.;'?.

.-.-I....... - . )

..

'!....._..~

-
. f

, t ~ ...

/
/
{ _c '"Iii/
:. -=-,_:......~. '- -
}~I.~~~~~~~~~ __,..._

_- _- -- --..--- ..

-

..t! . .. -~--

-.- .. -- .... ,

.
- ......,

1_.- - - .

FIGURE 6

42

:;z:

;Qw ~
It!

0 ~
i
~

!5
0 D:
~

l: 0 0
fu

q0 :

10

0c::

quu0:

m g

9
r>!;!

7

rq0 z :

...J
w...J

wwuz

~qcz:::
m

0 w cw::
0..

0..

Cll

::J

g z
z

u:qzr::

6 ; g;

mc::

c>:-:

0

-
5

zww
u 0 w
'uwzw
0 w
q...J: 0..

STOP 1

ROAD CUT ON LINTON ROAD, ON TilE EAST SIDE OF LITTLE

KEG CREEK 6.2 MILES (10 km) NORTHWEST OF SANDERSVILLE,

WASHINGTON COUNTY

Lithostratigraphic unit and bed number

Description

Thickness

BARNWELL GROUP TOBACCO ROAD SAND
BED 10

Sand residuum: argillaceous, scattered limonitecemented sand nodules and irregular-shaped, submetallic, magnetic to nonmagnetic ironstone concre~ tiona or nodules (up to 1 em in size), scattered quartz pebbles; poorly sorted, medium-to-coarse grained sand with moderate-reddish-brown matrix; massive-bedded, no primary sedimentary or biogenic structures preserved; tough, dense, resistant, almost hard; color moderate reddish-brown (10 R 4/6).

25 feet (7. 6 m)

BED 9

Sand: mainly residuum, argillaceous, pebbly; (flat pebble bed), very poorly sorted, medium-to-coarse grained sand with rounded quartz pebbles and flat pebbles; pebbles up to 1.5 inches (4 em), most pebbles 1 inch (2.5) or less; no primary sedimentary or biogenic structures; appears well mixed; tough, resistant, dense, almost hard; color moderatereddish-brown (10 R 4/6).

DRY BRANCH FORMATION IRWINTON SAND MEMBER

BED 8

Clay, with silt and fine sand; tough but not resistant to weathering, forms a slight reentrant in outcrop; no distinct bedding observed; discontinuous.

1.3 feet (30-90 m)
0-0.5 feet (0-.15 m)

BED 7

Sand: with discontinuous clay laminae and thin dis-

continuous clay layers; variable medium-grained/well

sorted and coarse-grained/poorly sorted (poorly

sorted layers are more resistant to erosion than are

well-sorted layers); deeply weathered; well-bedded,

varying from very thin-:-bedded with layers highlighted

by thin clay laminae, to small-scale crossbedding/and

festoon-bedding where the amplitude of the sets

23 feet

of inclined bedding is as much as 3 to 4ft (90-120 em). (7 m)

43

BED 6

Sand: massive-bedded residuum where deeply weathered 1 but faint traces of bedding present where less deeply

weathered; bedding consists of rude horizontal layering

defined by contrasting sand-particle size that varies

from medium-grained to coarse-grained; a few scattered

discontinuous clay laminae still evident where the

sediment is not too deeply weathered; weathers massive,

even where bedding is evident; tough, hard and resis-

tant; uppermost part of bed less resistant; color is

moderate-reddish-brown (10 R 6/4); the scattered clay

laminae are pale-yellowish-orange (10 YR 8/6); due to 30.5 feet

rolling topography, part of the bed is not exposed.

(9.3 m)

BED 5

Sand: thin, wispy, undulatory clay layers and laminae; coarse-grained, poorly sorted sand with scattered quartz granules; deeply weathered but original horizontal bedding still evident due to thin clay layers and sand-size differences from layer to layer; tough hard, and resistant; quartz granules angular, some rounded; color moderate-reddish-brown (10 R 6/4).

6 feet (1.8 m)

BED 4

Sand: some undulatory clay laminae, a few cherted-ce-

mented sandstone blocks that appear to be out of place;

poorly sorted, medium to coarse sand; part of bed may

be slump of sand that has migrated downhill due to

3 feet

mass wasting; moderate-reddish-brown (10 R 4/6)

(90 m)

TWIGGS CLAY MEMBER

BED 3

Clay: weathered, ranges from fairly pure waxy clay to

silty and sandy, purest in the lower part; small amount 9 feet

of stratification noted; color light-olive-gray

(2. 7 m)

(5 y 6/1).

'

CLINCHFIELD FORMATION RIGGINS MILL SAND MEMBER

BED 2

Residuum: very poorly sorted, sandy, pebbly, limonitic, cherty, fossiliferous clay to clayey, limonitic, poorly sorted sand; with dispersed Mn02 ; quartz pebbles subangular to subrounded up to 1 in. (2.5 em) in diameter; most pebbly at base of unit; scattered limonitic concretions or iron stone-(limonite) cemented sand or clayey sand near or at base of bed; scattered pockets of chert of silicious pseudomorphs of mollusk shells and corals; MnOz staining along horizontal layers in some parts of the outcrop; where there are large con~ centrations of Mno2, silicified fossils are rare or absent; conversely, Mno2 is not prominent near large concentrations of silicified shells; bed varies from massive-bedded, and devoid of primary sedimentary structures in most places, to definite layering in other places; bedding where present is outlined by

44

HUBER FORMATION BED 1

wispy clay laminae or thin layers, or by Mn02-stained layers; color ranges from black (Nl) to very darkyellowish-qrange (10 YR 4/6-5 /6), to moderate-reddish-brown (10 R 4/6), to grayish-orange (10 Y 7/4), to yellowish-gray (5 Y 7/2); basal contact very irregular and undulatory.

1.5-4 feet (0.46-1. 2 m)

Kaolinitic clay: blocky, hackly, brittle kaolin near top of bed; massive-bedded, no apparent primary sedimentary structures.

11+ feet
(3.4 m)
114.5 feet (34.3 m)

45

WASHINGTON 10 (GGSII82) CORE

.... ....

TOBACCO ROAD SECTION EXPOSED IN "THE SINKS" SOUTH OF SANDERSVILLE

STOP 2
TOBACCO ROAD SECTIONS EXPOSED ALONG NEW PAVED ROAD SOUTH OF SANDERSVILLE

'NASH!NGTON 6 -6A
(GGS-!168) CORE ~

6 ~ :-.
----
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e

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TWIGGS LITHOFACIES

:....-_-
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SANDERSVILLE LS

I-. _. C:-:: TYPE LOCALITY ~

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FIGURE 7

STOP 2

TOBACCO ROAD SECTION EXPOSED ALONG NEW HIGHWAY

SOUTH OF SANDERSVILLE, WASHINGTON COUNTY,

INCLUDING OLD LIMEPIT

Lithostratigraphic unit and bed number

Description

Thickness

TOBACCO ROAD FORMATION

Bed 6

Clay and sand: clayey, fine silty sand to finely

micaceous, silty clay; thin-bedded; inclusions, clasts,

and lenses of waxy, pistachio-green clay, clay con-

tent increases upward in the bed; popcorn-shaped sili-

ceous concretions or nodules scattered here and there,

nodules up to 2 or 3 in. (5 to 7 em) in size; color

pale-green to pistachio-green with some maroon to

7 feet

brown-color mottles,

(2.1 m)

BED 5

Sandstone: chert-cemented; soft, friable, varying from

weakly cemented, very friable, to moderately hard fri-

able sandstone, to hard siliceous sandstone; fine- to

medlum-grained, well-sorted, but coarse sand grains and

granule-size quartz scattered throughout; generally

rudely layered but where the sandstone is freshly

exposed, layering is not obvious; generally non-fossi-

liferous but burrows present at some sites, and hori-

zontally oriented shell hash present at other sites;

oyster bed overlies, underlies, and occurs at the same 0.15 feet

elevations as the sandstone; thickness variable.

(0-4.5 m)

BED 4

Sand: clayey, cherty, richly fossiliferous with silicified (Crassostrea gigantissima); bed 4 is deeply weathered in outcrop and the matrix sediment is a residuum; no original sedimentary or biogenic structures, oysters' orientation in outcrop is random; most oyster shells are single valves, a few oysters are double-valved, therefore the deposit is a thanatocenose; oyster concentration varies from very closely packed to moderately closely packed; oyster bed in outcrop always contains well-rounded quartz pebbles up to 3 in. (7.5 em) across, most pebbles are up to 2 in. (5 em) across; thickness and stratigraphic position of oyster bed quite variable, ranging from the top of the Sandersville Limestone to near the top of the Tobacco Road section in Sandersville vicinity;

47

(Residuum/sandy, very abundant sil

clayey with icified oys

tdeirssp; ebrseedddinbglacapkpMean0rs2

and

massive and chaotic; oysters weather out and are strewn

over the surface of the outcrop; bed definitely a slope-

former; color irregularly mottled-brown, deep~red,

black (MnOz) with some pale-green clay pockets still 0-11.5 feet

intact).

(0-3.5 m)

BED 3

Sand: generally fine-to fine/medium-grained, well-sorted,

poorly exposed in outcrop; generally a slope-former;

in places has a 1 to 2 ft. (30-60-cm) bed of silici-

fied oyster shell and pebbles at base, some MnOz con-

centrations; in the vicinity of the road cut, this bed

is generally deeply weathered and little specific can

be said of it; horizontal layering is evident in a few

places; generally it is massive-bedded and argillaceous; 5-16 feet

thickness variable.

(1.5-4.9 m)

SANDERSVILLE LIMESTONE MEMBER

BED 2

Limestone: sandy, especially toward top of bed; sand

distribution patchy with some patches {up t .o a few em

in size) being a calcareous sand, and other patches or

zones being devoid of sand; irregularly indurated with

very sandy zones being soft and easily eroded, and

sand-free limestone being hard and moderately indurated;

very abundantly fossiliferous with oyster (Crassostrea

gigantissima) producing a coarse bioclastic texture

to the limestone; massive-bedded with the oysters

occurring in random orientation; no primary sedimentary 4 feet

or biogenic structures preserved.

(1.2 m)

BED 1

Limestone: scattered small clasts (1-2 mm) or inclu-

sionsof pistachio-colored clay, hard, tough, moderately

indurated and recrystallized limestone; varying de-

grees of recrystallization and hardness (on the order

of a few mm to 1 or 2 em) produces an uneven, hackly

fracture surface that resembles cottage cheese; mas-

sive-bedded, no primary sedimentary or biogenic struc-

tures observed; fossiliferous; in some places few

clearly distinguishable fossils; other places very

coarsely fossiliferous, imparting a coarse, bioclastic

texture to ~he limestone; casts and molds of ~1

mollusks, Turitella and bryozoans generally common,

solitary corals, stoney algae, very rare scallops, and

Periarchus quinquefarius observed; color very pale-

14 feet

orange (10 YR 8/2-9/2).

(4 m)

53 feet (16 m)

4.8

In general, in the Sandersville area, beds 3,4,5, and 6 occur in the order given. However, their thicknesses vary considerably and any one or two beds may be absent at a given site. Beds 3 and 6 appear to be the basic lithologies of the Tobacco Road overlying the Sandersville Limestone Member in central and eastern Washington County and the oyster bed or biostrome and the cherty sandstone appear to be local, but commonly occurring facies or lenses within the formation,
49

STOP 3
THOMPSON'S BRIDGE ROAD EXPOSURES

ROAD CUTS ON THOMPSON'S BRIDGE

ROAD,0.5 TO 2..0 MILES EAST OF

FORMER SITE OF HATCHER'S MILL,

BURKE CO.

w z

0:: 0

:I:
1-
~

:I:

I
/ / I I EXPOSURES AT FORMER I SITE OF HATCHER'S MILL I
I
. BURKE,CO.
Periarchus

FT M 10
3
2 5
0 0

FIGURE 8

50

0 <t
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0
(.)

(.)
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STOP 4
WEST SIDE OF LITTLE BEAVER DAM CREEK ON RIVER ROAD, .075 MILE (1.2 KM) SOUTHEAST OF JUNCTION OF RIVER ROAD AND GRIFFINS LANDING ROAD,
BURKE CO.

t~"'ff-17
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FIGURE 9

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51

STOP 4

IN ROAD CUT ON RIVER ROAD ON THE NORTH SIDE OF

LITTLE BEAVERDAM CREEK, 0.75 MILES (1.2 krn)

SOUTHEAST OF THE JUNCTION OF GRIFFINS LANDING ROAD AND RIVER

ROAD, 3.6 MILES (5.75 km) NORTH-NORTHEAST OF GIRARD,

BURKE COUNTY

Lithostratigraphic unit and bed number

Description

Thickness

HAWTHORNE/"ALTAMAHA"

BED 7
BARNWELL GROUP TOBACCO ROAD SAND

Sand and gravel: clayey, poorly sorted; contains crossbedded stringers of limonite-goethite pebbles; most of the bed is residuum, only basal few feet contain original sedimentary structures.

10 feet+ (3.0 m+)

BED 6

Sand to sandy clay: sand clayey, heavily bioturbated,

poorly mixed, burrowed; sandy clay heavily mottled

with purple, maroon, orange, and white; basal 1 ft.

is very clayey sand, middle 1 ft. (30 em) sandy clay,

upper part is bioturbated, fine-medium grained,

clayey sand; bed is strongly oxidized and leached

throughout; basal contact is sharp but gradational;

bed appears to be discontinuous due to very uneven 0-3.5 feet

upper, eroded surface.

(0-1 m)

BED 5

Sand: medium-grained, well-sorted; soft and loose

where freshly exposed, tough and coherent where case-

hardened; cross-bedded and festoon-bedded, very

strong bedding with many bedding planes outlined by

small, sand-sized white, clayey particles that may

originally have been fecal pellets; abundant, large

Callianassa burrows; bed thickens from 3 ft. (0.9 m)

at southeastern end of exposure to 6 ft. (1.8 m) at

northwestern end, over a distance of approximately

100 ft. (30.5 m); some liesegang bands on weathered

surface; basal contact very irregular and chewed.

up in appearance; common Callianassa burrows

3-6 feet

extend down into underlying bed.

(0.9-1.8 m)

52

BED 4

Sand: clayey; medium-grained with many coarse sand

grains, poorly-sorted, grain size ranges from clay-

. size to pebble-size; pebbles widely spaced; tough,

massive-bedded, holds up vertical walls; abundant

discontinuous, irregular, thin clay laminae; bio-

turbated, many burrows present; color pattern ir-

regular, purple and yellow; basal content irregular;

burrows extend downward 1 ft. (30 em) into underly-

ing sand.

Basal sand: coarser than that of overlying bed;

somewhat more pebbly in basal few inches (1 em), more

poorly sorted, flat discoidal clay clasts up to 6

13.75 feet

in. (15 em) across; bed is oxidized throughout.

(4.2 m) '

BED 3

Sand: clayey; fine-grained, incompletely mixed clay and sand; massive appearance, very thinly bedded, some bioturbation, some burrows present, some clay laminae; many layers waxy, discontinuous, approximately horizontal; unconsolidated but coherent; more clay in basal 6 in. (16 em), some clay clasts at base up to 3 in. (7.5 em) long; in other places clay beds or lenses are discontinuous; some clay layers roughly 1 mm thick, clay layers interlayered with sand; bed is oxidized throughout; color is purple to maroon; lower contact sharp but gradational.

4.5 feet
(1.4 m)

DRY BRANCH FORMATION IRWINTON SAND MEMBER

BED 2 BED 1

Sand: argillaceous; medium-grained, poorly sorted,

somewhat bioturbated and poorly mixed; tough, moderately

consolidated; massive, highly disrupted thin bedding;

a few rare burrows; bed is oxidized throughout;

color is yellow with thi~, light-gray to white linear

color mottles; lower contact very sharp but irregular 3.0 feet

on a small scale.

(0.9 m)

Sand: slightly micaceous, very slightly argillaceous;

fine- to medium-grained, fairly well-sorted; soft,

unconsolidated; massive, indistinctly to subtly

bedded; oxidized throughout; color is deep-yellow

6.5 feet+

to orangish-yellow.

(2 m+)

47.25 feet (14.5 m)

53

AT TOP OF BLUFF AT GRIFFINS LAND I NG

STOP 5 GRIFFINS LANDING

BURKE NO I (GGSI171l CORE

J:

IWAD CUT IN UPPER PART OF BLUFF

" 0
0.

AT GRIFFINS LANDING

"'

- ~-

- -..._ ...
- ....

- ... .L

- -... .L- -

-'-
~

--.'.:....

- -' .... '
-.....~ ,,""

;t -~

IN PARKING AREA AT GRIFFINS LANDING
BURKE NO~ (GGS-11721 CORF

FIGURE 10

I
I
I
I I
r I F .~- .
. .,:..-.:.:.~J.~...,_'_.~~."

Cz l
<{ Ul
z
0
1z ;ii !!:
BED 10
TYPE LOCALITY OF THE GRIFFINS LANDING MEMBER OF THE DRY BRANCH FORMATION,LOWER BLUFFS ON THE SAVANNAH RIVER

:I:

w

u

z

z _J _J
<{ w

w u 0

0:: ~ w

OJ z

0:: a::

>-
0::

<{ OJ

w
aa..

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::::J

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LISBON

g

FORMATION

~

54

Lithostragraphic unit and bed number

STOP 5 AT GRIFFINS LANDING ON THE SAVANNAH RIVER, BURKE COUNTY, GEORGIA
Description

Thickness

DRY BRANCH FORMATION IRWINTON SAND MEMBER

BED 14

Residuum: sandy, clayey; massive-bedded and devoid

of primary sedimentary and biogenic structures;

tough and hard when dry; tough and sticky when moist;

mottled maroon, orange and gray; lower contact in- 15 feet+

distinct due to severe weathering.

(4.6 m+)

BED 13

Sand: very deeply weathered, medium-grained, not

well-sorted, argillaceous with secondary interstitial

cementing agent (Fez03), and clay mineral of soil

origin?, wisps of disturbed clay or clayey, discon-

tinuous laminae, thin layers, or thin lenses; evi-

dently bioturbated; very tough; color purple to gray;

lower contact appears gradational but is very deep- 3.5 feet

ly weathered.

(1.1 m)

BED 12

Weathered sand and clay: interlayered, sand dominates;

sand fine- to medium-grained, fairly well-sorted;

clay occurs as discontinuous thin layers and lenses

up to 1 in. (2.5 em) thick; clay layers are partially

disrupted by scattered burrows and weak bioturba-

tion; some scattered clay clasts; in general, the

b~d is well layered; clay is white and probably kao-

linized; sand is orange in color; lower contact

2. 0 feet

gradational.

(0.6 m)

BED 11

Sand: deeply weathered, fine- to medium-grained,

moderately well-sorted; distinctly layered, some thin,

discontinuous clay layers, laminae, and lenses de-

fining bedding planes; tough due to secondary harden-

ing but nonindurated; color orange; grades down- 2.0 feet

ward into bed 10.

(0.6 m)

BED 10

Sand: residuum, massive-bedded, no original primary sedimentary or biogenic structures preserved; sand is fine- to medium-grained; interstitial material or matrix Fe203 and clay mineral of soil origin?; in general the bed is not resistant to weathering, and

55

BED 9 BED 8 BED.7

13 ft. (13.9 m) of the bed is very poorly exposed;

color moderate-reddish brown (10 R 4/6); grades

downward into underlying bed by becoming less in-

tensely weathered; one interval or lens in the middle

of the section is a white, well~sorted, fine- to

medium-grained, almost pure "sugar" sand that con-

tains only irregular concentrations of hardened

33.5 feet

matrix,

(10.2 m)

Sand: clayey, slightly micaceous, scattered MriOz dispersions; sand component fine- to. medium-grained, well-sorted; rudely layered with some incomplete mixing of sand and clayey sand etched ou.t on wea.thering surface; some intervals or zones display more or clearer bedding features; freshly scraped surface does not display layering clearly at all; some clay present as scattered, thin (up to 1/16 in. (1-2m) ), very discontinuous clay lenses, laminae, or chips highlighting or defining bedding planes; sand is unconsolidated, sticky, and clayey; lower contact gradational with underlying bed,

7.0 feet (2.1 m)

Clay and sand (Twiggs Clay lithofacies): domi-

nantly clay, some MnOz dispersions; thinly in-

terlayered to interlaminated, shaley, fissile tex-

ture with thin interlayers of fine-grained sand and

some fine-grained mica along bedding planes or

partings; finely micaceous thin sand and clay layers

generally well-separated texturally; lower part of

bed more clayey, grades upward into Bed 9 by increase

in thickness of sand layers, and by decrease in thick-

ness and number, and disappearance of clay layers;

Bed 8 appears to grade laterally and downward into

Bed 7; therefore one bed appears to thicken at the 7.5 to less

expense of the other bed.

than 4 feet

(2.3 to less

than 1.2 m)

Sand: clayey, some MnOz dispersions, scattered fine

mica; sand fine- to medium-grained, well-sorted; sand

and clay ~ell mixed, massive bedded; no visible pri-

mary sedimentary or biogenic structures; soft clayey

texture; appears to both underlie and grade lateral- 5.0-2.5 feet

ly into Bed 8, grades downward into Bed 6.

(1.5-0. 76 m)

56

. BED 6

Clay (Twiggs Clay lithofacies): interlayered with finely micaceous, silty fine sand, some Mn02 dispersions; fissile, blocky, hackly, shaley, thinly bedded to laminated; clay layers 1 in. (2.5 em) or less thick; most discrete clay layers (intervals between sand laminae) are~ in. (6 nun) or less thick; basal 1 ft. (30.5 em) of bed is less well-bedded and more poorly sorted, and is more coarsely sandy, with scattered quartz granules, than the rest of Bed 6.

Bed 6 gets steadily more sandy upward; gradational over approximately 1 ft. (30.5 em) with bed 7; uppermost 1 ft. (30.5 em) sandy and bioturbated; partially or incompletely mixed fine sand and clay;

Bed 6 appears to be, along the face of t~e outcrop, a thinly layered clay lens within a generally more massive-bedded clayey sand deposit (Beds 7 and 9); color yellowi~h-gray (5 Y 7/2)

5.5 feet
(1.5 m)

GRIFFINS LANDING MEMBER

BED 5

Sand: argillaceous, micaceous, calcareous, heavy minerals present; some discontinuous thin layers of waxy pure clay; some irregular calcareous nodules, fossiliferous; stratified but layering subtle except for thin clay layers; fine shell material and oyster fragments tend to be aligned horizontally and define bedding planes; gross appearance of bed is massive and structureless; quartz sand component medium-grained, fairly well-sorted; burrows present in some exposures; bed is soft and easily eroded; therefore exposures are intermittent and scattered along the face of the bluff.

Where weathered, bed 5 consists of rudely layered, me dium- to coarse-grained, well-sorted sand, layers about 1 in. (2.5 em) or less thick; unconsolidated and soft; color ranges from orange to brown:

Oyster shell beds or biostromes are scattered throughout the bed with some, especially higher up in the bed being noticeably discontinuous along the line of the bluffs; those 10 to 15 ft (3 to 4.5 m) above mean low water appear to be more continuous; some of the oyster shells in the beds occur in living position whereas shells in other beds appear to be jammed together in random orientation.

52 feet (15.8 m)

BED 4

Clay: very calcareous, finely sandy and micaceous with most of the fine grained mica and silty fine-grained sand along the partings or bedding planes; thin bedded, blocky, hackly clay with conchoidal to subconchoidal fracture between bedding planes; clay that displays conchoidal fracture is waxy, very finely laminated; grades downward into:

1.0 foot (30.5 em)

57

BED 3
BED 2
BED 1

Limestone: argillaceous, contains fine~grained sand and mica; tough, rubbly, but not heavily indurated; irregular fracture; no apparent sedimentary structures; color yellowish-gray (5 Y 8/1); grades downward over an interval of about 6 in, (15 ern) into:

1. 0 foot (30.5 em)

Clay: very finely sandy, very calcareous, micaceous,

fossiliferous; sand component fine~grained, well-sorted;

clay near the top of the bed massive-bedded with conchoi-

dal fracture; no apparent sedimentary structures; hard

and brittle when dry, plastic but tough when moist; oys-

ter shells (Crassostrea gigantissima.) present and in

living position; mussel shell impressions locally common;

softer than underlying and overlying beds, forms a reen-

trant; color ranges from yellowish-gray (5 Y 8/1) to

light-grayish-yellow (5 Y 9/4) to pale-greenish yellow 1-2 feet

(10 Y 8/2); grades downward into:

(30-60 em)

Clayey fine sand to very sandy clay: calcareous, mica-

ceous, fossiliferous; massive-bedded, no apparent fine-

scale bedding; sediment fairly well-mixed but some marb-

ling of sand and clay present which is probably due to

bioturbation; sediment unconsolidated but tough and com-

pact; some clay lenses appear to be scattered randomly

throughout the bed; oysters (C. gigantissima) very a-

bundant, tend to occur in concentrations and in living

position; some mussel impressions and barnacles present;

color greenish-gray (5 G 6/1) when freshly exposed;

where weathered the color ranges from yellowish-gray

(5 Y 7/2) to dark-yellowish-gray (5 Y 6/2) to light-

olive-gray (5 Y 6/1) to grayish-yellow (5 Y 8/4) to

7 feet+

dusky-yellow (5 Y 6/4).

(2.1 m+)

140.5 feet

(42.8 m)

58

STOP 6 ROADCUT ALONG WINDSOR SPRINGS ROAD, 1.1 MILES (1.8 km) NORTH OF THE JUNCTION OF WINDSOR SPRINGS ROAD AND TOBACCO ROAD,
RICHMOND COUNTY r GEORGIA

Lithostratigraphic unit and bed number

Description

Thickness

BED 14

Soil sand: argillaceous, unconsolidated but firm; massive-bedded; buff to tan color.

3.0 feet (0. 9 m)

TOBACCO ROAD SAND

BED 13

Residuum: argillaceous sand; very tough, resistant to erosion; massive-bedded, structureless; color moderate-reddishbrown (10 R 4/6).

5.5 feet (1. 7 m)

BED 12

Sand: argillaceous with clayey, wavy

laminae and wisps, pebbly with abundant

flat pebbles; quartz-sand component

appears to be medium-grained, moderately

poorly sorted; thin layering barely visible

with faint, p~rtially disrupted clayey

laminae; bioturbation evident; main concen-

tration of flat pebbles is in lower 1 ft

(0.3 m); quartz pebbles of various rounded

shapes up to 1.5 in. (4 em) along long axis;

pebbles display tendency toward horizontal

orientation; in spite of apparent layering,

bed is very massive in small and large-scale

fracturing; very tough and compact, almost

hard; color moderate-reddish-brown (10 R 4.4 feet

4/5).

(1.4 m)

DRY BRANCH FORMATION IRWINTON SAND MEMBER

BED 11

Sand with scattered wavy, wispy thin layers or laminae of sandy clay: sand medium-to fine/medium-grained, moderateto well-sorted, poorly to well-mixed; rude stratification; soft but coherent; sediment massive-bedded, does not fracture or separate along bedding planes.

1.5 feet (0.5 m)

59

BED 10 BED 9 BED 8 BED 7

Clay and sand: finely micaceous; thinly bedded to laminated; clay laminated, blocky, sticky, and plastic but firm; sand fine-to medium-grained, well-sorted; bedding wavy, lensical, and undulatory, sand/ clay about 50/50 over all; most clay in lower half of bed; grades downward into:

1.5-2.5 feet (0.5-0.7 m)

Sand: slightly argillaceous with scattered wispy, wavy thin layers or laminae of sandy clay; somewhat stratified; appears somewhat bioturbated; moderate-to well-sorted, well to poorly mixed, medium-to fine/mediumgrained quartz sand; grades downward into:

2.0 feet (0.6 m)

Clay: with sandy clay and clayey sand, micaceous; clay thinly layered to laminated; some few scattered bioturbated, well-mixed, thin, clayey micaceous sand layers or lenses up to 1 ft (30.5 em) thick; bed appears to be a clayey lens within the Irwinton; it is
3.5 ft (1.0 m) thick at the south end of the roadcut and it thins and pinches out northward.

0-3.5 feet (0-1.0 m)

Sand: with discontinuous thin clay layers, larr.inae, and lenses (less than 1 in. (2.5 em)), fine-grained mica, heavy minerals conspicuous; sand is fine-to medium-grained, generally wellsorted where not stirred by scattered bioturbation; bed in general is thinbedded with wavy and undulatory thin clay layers, some low-amplitude, planar crossbedding present; sand is typically loose and incoherent where freshly exposed but becomes firmer, more coherent and casehardened on long exposure; where freshly exposed, the sand layers form reentrants between more prominent clay layers; separation between clay layers ranges from less than 1 in. to 6 in. (2.5-15 em); some scattered burrows present and appear to occur together; bed is not present at north end of roadcut, either due to crosscutting stratigraphic relationship with underlying beds (see Fig. 11), or due to lateral facies change into bed 6.

10.0-6.5 feet (3.0-2.0 m)

60

BED 6.

Sand: some thin clay layers (up to 2 in. (5 em) and scattered, disrupted clay laminae; quartz sand ranges from fine-to medium-to coarse-grained, sorting ranges from well-sorted (fine-to medium-grained sand) to poorly sorted (coarse-grained sand in discrete layers or lenses); bedding prominent, varying from horizontal layering to planar crossbedding, scour and fill structures, and festoon crossbedding; crossbed sets range up to 3 ft (0.9 m) in amplitude; discontinuous zone of pebbly, poorly sorted coarse sand layer in basal ~ ft (15 em) of
bed; lower 1.5 ft (0.5 m) of bed slightly bioturbated with disrupted, scattered
clay laminae; somewhat case-hardened and resistant due to prolonged exposure; bed 6 is present only at north end of the roadcut; grades downward into:

6.0 feet (1.8 m+)

BED 5 (Twiggs Clay lithofacies)

Clay: very thinly layered to laminated with silty, finely micaceous, finegrained sand along bedding planes and interlayers; clay blocky, sticky, and plastic when moist, shaley and hard when dry; clay in outcrop has the appearance of etched wood, very wavy bedded; most clay concentrated in lower 2 ft (0.6 m) of bed, upper 2 ft (0.6 m) of bed has same bedding characteristics but consists of more fine-grained, well-sorted sand layers than clay layers (at south end of road-cut bed 5 separates into 3 clay layers with fine, well-sorted sand layers between); some rare scattered burrows; sand interlayers generally form thin reentrants between the projecting clay layers in outcrop; grades downward into:

4.0-3.5 feet
(1.2-1.0 m)

BED 4

Sand: discontinuous thin clay layers and laminae up to 1/16 in. (2 mm) thick; greater concentration of clay laminae in upper half of bed; some heavy minerals present; sand fine-to medium-grained, well-sorted, loose, almost incoherent; a thin layer of coarse, granually sand with scattered pebbles at the base of the bed; bedding distinct but rather rude except where defined by discontinuous clay laminae, some small-scale, planar cross-bedding with amplitudes up to 2 or 3 in. (5-7.5 em) observed; abruptly overlies:

7.0 feet (2 .1 m)

61

CLINCHFIELD FORMATION ALBION MEMBER

BED 3

Clay: waxy, blocky, tough, plastic and sticky when moist, almost pure clay in upper part, silty in lower part:

3.5 feet
{1.0 m)

BED 2

Spiculitic (see Sandy, J., et al., 1966) claystone, sandy, thinly disseminated pyrite?, some phosphatic grains?; upper 3/5 of bed contain the most clay; massivebedded except for crude organization into ledges; bed 2 divided into 2 parts: (2A) hard ledges that are concentrated toward the base and near the top, and are interlayered with a grade laterally into (2B), more argillaceous and less resistant to weathering than (2A);

19.0 feet (5 .8 m)

(2A) lowest ledge somewhat sandy, hard claystone with some undetermined dark grains; lendges in lower part massive with rough, irregular, hackly fracture; ledges are darker in color than (2B); coloring agent may be finely disseminated pyrite; ledges above base are silty but are not noticeably sandy; upper ledges are very dark-colored, clayey, spiculitic, and with small light and dark inclusions (intraformational clasts?) imparting appearance of porphyritic rhyolite or dacite; fracture of upper
ledges blocky, conchoidal to subconchoidal; lower contac: with Huber Formation very vague;

(2B) claystone, tough, clayey, finegrained, brittle with hackly and conchoidal fracture; moderately indura.ted but less resistant than (2A); massive-bedded, no apparent primary sedimentary structures; sparsely spiculitic.

Huber Formation

BED 1

Clayey (kaolinite) sand to silty, sandy clay; fining upward from kaolinitic, moderately well-sorted, medium/coarse-grained sand to silty, tough but unconsolidated kaolin at top; little indication of primary sedimentary structures; very massivebedded.

78 feet
(23.8 m)

62

STOPS 6 and 7

STOP 7
TYPE LOCALITY OF TOBACCO ROAD SAND

BED7
I" BleD 6
BED 3. ~-.ll"'f"'"''-l'r'~"~ ,,...BED 2

STOP 6
ROAD CUT ON WINDSOR SPRINGS ROAD BF.O 14
-'- BED 13

BF.fll

/ BF"D fi

::C:"
. -2 :o-.:~ -:7-.:: ...


f". . . .-..t.,: ~~~~r~~t'!_l _;_ .::...;. -~+-:.;"~\_.~ ~-..., ',:..._ :::S.-~~..~-~

BED 4

/'}.~::~,~}~~;'i~~i""" _:t~~X".'.~}.l,:::.::-J,._ .-;;-:: '.~.
. ~ ' _:-~.b- ,,;-.:;-_):~~ . -- ~~...

!:;$ . ~~,._f.~ ..\~,f..-.- -of-~ . ~}~~~~~~2-: ~

l!z.

:~~ ..... 1. '

- ..... -
BED I

FIGURE II
63

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c0r .
0 u u
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w
z ~

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cr
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acw r . a.

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3:

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cw r
CD
~
I

STOP 7 ROADCUT ON THE EAST SIDE OF MORGAN ROAD, 0.35 MILES (0.1 km) NORTH OF THE JUNCTION OF MORGAN ROAD AND TOBACCO ROAD, RICHMOND COUNTY, GEORGIA

Lithostratigraphic unit and bed number

Description

Thickness

BED 10

Sand: (surficial sand of the soil zone), medium-grained, loose, paletan color.

4.5 feet (1.4 m)

TOBACCO ROAD SAND

BED 9

Residuum: fine-grained sand, argillaceous, massive-bedded; soft but tough when moist, hard and brittle when dry; resistant to erosion; color moderate-reddish-brown (10 R 4/6).

10 feet
(3 m)

BED 8

Sand: very poorly sorted, medium to coarse to pebbly, quartz pebbles up to 1 iri. (2.5 em) in size, rounded to subangular, some pebbles crumble under pressure; clayey, with irregular-shaped clay clasts up to 1~ in. (3 em); massivebedded, no apparent sedimentary structures; very abrupt and irregular basal contact.

1.5 feet (0 .5 m)

BED 7

Sand: fine to medium-grained, mainly medium-grained and moderately poorly sorted in lower 1 or 2ft (0.3-0.6 m); rest of sand in bed 7 is fine-grained and wellsorted; bedding very distinct and undulatory; some small scale crossbedding in the sand layers; conspicuous thin clay layers range in thickness from less than 1/16 in. to 0.5 in. (0.5 mm to 1 em); a few clay clasts present; some clay layers disrupted and distorted; more closely spaced clay layers in upper 2 ft (0.6 m); where exposed sand is fresh, it is soft,

64

BED 6
BED 5 BED 4

slightly coherent, and pale-yellow to cream in color; where the sand is weathered and case-hardened, it is tough, resistant, and deep-red in color; lower contact of bed slightly undulatory and very abrupt, varying from a knife-edge contact to gradational over approximately 1/16 in (1-2 mm).

9.0 feet (2.75m)

Sand: medium-grained, somewhat argillaceous, micaceous, scattered quartz granules and thin clay chips; bedding varies from being distinct to being indistinct and disrupted; in some places the bed is bioturbated but the sediments are incompletely mixed; in other places bioturbation is not evident and the bedding is conspicuous, each layer varying from a few millimeters to less than a centimeter in thickness; moderately wellsorted; soft and coherent when moist and fres~ly exposed; weathers to a tough, resistant ledge-former; a few scattered burrows present; weathers gray to brownish-yellow; grades downward into:

1.5 feet (0.5 m)

Sand: medium-to-coarse-grained, some very coarse sand grains and quartz granules present; micaceous, discontinuous clay laminae and clayey sand layer~, a few clay clasts present; layering present but indistinct and subtle; clay laminae slightly undulatory; scattered Callianassa burrows present throughout; base of bed consists of 6 in (15 em) of finely interlayered sand and clay; sorting moderate to poor: grades doWnward into:

7.5 feet (2.3 m)

Sand: medium-grained, some coarse-grained quartz sand grains scattered throughout; some heavy minerals present, very slightly argillaceous, quartz grains subrounded to rounded and frosted; fairly well sorted; very soft and incoherent where fresh, slightly coherent on weathered surface; very well-bedded, consists of gently dipping (to the southeast) crossbed sets; individual layers vary from a few milli-

6 feet

65

meters to 2 em in thickness.

(1.8 m)

BED 3

Sand: tine-grained, slightly argillaceous, micaceous, heavy minerals common; scattered clay laminae and thin layers up to 2 millimeters thick; clay layers become closer spaced toward top of bed; sand well-sorted; soft but slightly coherent.

3.5 feet
(1 m)

BED 2

Gravelly sand with common flat quartz pebbles; pebbles well rounded to subrounded, up to 2.5 in. (6 em); orientation of flat pebbles not always horizontal; sand medium-to coarse-grained; scattered clay layers throughout bed, up to 1 em in thickness; sorting is poor to moderate; gravelly sand soft and lacking coherence; clay confined to clay layers and not present as matrix of sand; lower contact sharp but conformable.

0.5 feet (0.15 m)

DRY BRANCH FORMATION IRWINTON SAND MEMBER

BED 1

Sand: medium-grained, only very slightly coherent~ very slightly argillaceous, discontinuous clay laminae and thin layers scattered throughout bed, becoming closer spaced toward top of bed; some scattered clay clasts and chips quartz grar.ules and pebbles present but scattered throughout; pebbles up to 1 em in size; moderately well-sorted, a few clayey sand layers up to 5 em thick are present; bedding subtle but distinctly horizontal, bedding surfaces are short, discontinuous.

21+ feet (6.4+ m)
64.5 feet (19.8 m)

66

STOP 8
ROAD CUT ON GA.I8,1.2 MILES(I.9KM) SOUTH OF TWIGGS-WILKINSON COUNTY LINE, TWIGGS COUNTY

FT M 10 3 2 5 0 0
FIGURE 12
67

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w

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STOP 8 ROADCUT ALONG GA. 18, 1.2 MILES (1.9 km) SOUTH OF
THE WILKINSON-TWIGGS COUNTY LINE, AND 5.0 MILES (8.0 km) NORTH OF
THE CENTER OF JEFFERSONVILLE, TWIGGS COUNTY, GEORGIA

Lithostratigraphic unit and bed number

Description

Thickness

DRY BRANCH FORMATION

BED 5

Residuum: sand, clayey, massive-bedded, no primary sedimentary or biogenic structures preserved; tough and hard when dry, soft but coherent when moist; color mottled moderate-reddish-brown and gray.

3.5 feet
(1 m)

BED 4

Sandstone and unconsolidated sand: sandstone is siliceous (chert-cemented), flaggy, very well-layered with concentrations of horizontally oriented shells and shell fragments along and defining the bedding planes; the sand size in the sandstone layers ranges from medium-to coarse-grained with the coarser sand grains being noticeably better rounded than the finer sand; sandstone layers range from about 2 in. (5 em) to 1 ft (30 em) and are well jointed;

Interlayered with the sandstone are layers of weathered, tough but unconsolidated, fine-to medium-to coarse, grained welllayered sand; the sand in the lower part of the bed is fine-to medium-grained, wellsorted, slightly micaceous, and with very thin clay partings or laminae; higher in the bed, the sand interlayered with the sandstone becomes coarser, more poorly sorted, more crudely layered with more sandsize variability between layers or lenses.

68

aED 3 BED 2

The sandstone ledges comprise only a small fraction of the total thickness of the bed; however, the thicker beds of unconsolidated sand erode out from under the hard, thin, flaggy sandstone layers leaving a rubble of sandstone blocks strewn over the surface.

The whole mass of the bed dips systematically to the south as if it were a channel-fill deposit.

11-8 feet
(3.42.4 m)

Clay and sand: discontinuous, 0-1 ft

(0-30 em) bed of partially mixed,

bioturbated, clayey sand at base of

bed overlain by interlayered sand and

clay; ratio of sand to clay appears

about even; sand well-sorted, fine-to

medium-grained, incoherent (sugar sand);

clay layers slightly undulatory, blocky,

hackly, conchoidal to subconchoidal, waxy;

spacing between sand and clay layers no

more than 3 to 4 in. (7.6 to 10.2 em) apart,

some are less than 1 in. (2.5 em); therefore

sand layers and clay layers are up to 3 or

4 in. (7.6 or 10.2 em) thick but generally

are less; little or no mixing of the sand

and clay components; sand layers are pure

sand and clay layers are pure clay; clay

component increases upward in the bed and

dominates the lithology in the upper part

of the bed with clay layers more frequent

and thicker than sand layers; upper few

5.5-8.5 feet

feet (1 rn or less) very similar to Bed 1.

(1. 7-2.6 m)

Sand: scattered thin clay layers up to 2 in. (5 em) thick, heavy minerals very conspicuous; a thin layer of silicified shell fragments near the top of the bed leaves the surface strewn with the fragments; sand fine-grained, white, very well-sorted, loose and incoherent where freshly exposed (sugar sand); clay layers up to 2 in. (5 em) thick but most layers are 1 in. (2.5 em) thick or less and are discontinuous; clay layers are also interlaminated with silty, very fine sand; sand between the clay layers almost devoid of primary sedimentary structure,

69

BED 1

appears almost massive and structureless; grades abruptly upward into Bed 3 in some places, in other places it grades upward gradually by increase in clay layers in the upper 2 ft (61 em).
Clay: thin interlayers of sand, heavy minerals conspicuous in the sand layers, more clay than sand; clay is thin-bedded, fissile, shaley, blocky, hackly, with conchoidal to subconchoidal fracture; most clay layers almost pure, waxy; dry clay blocks, display very fine lamination; thin, brittle, paper-like shaley chips litter the surface of the outcrop; clay layers 2-4 in. (5-10 em) thick, sand layers about 1-6 in. (2.5-15 em) apart, mostly 2-3 in. (5-7.5 em) apart; sand fine-grained, well-sorted, soft; freshly e~osed sand white and incoherent; where sand is somewhat weathered, it stands out in relief relative to the clay layers; where the sand is freshly exposed and unweathered, the clay layers stand out in relief; sand layers usually about 1 in. (2.5 em) thick, rarely as much as 3 in. (7.5 em) thick; unweathered sand white; weathered sand moderate-reddish-brown (5 R 4/6).

6.5 feet
(2 m)
22.0 feet (6.7 m)
48.5 feet (14.8 m)

70

STOP 9
PROPOSED REFERENCE LOCALITY FOR TWIGGS CLAY (MAP LOCALITY E OF SHEARER,I917)

f5 g COMPOSITE SECTI ON OF TYPE

'I:

LOCALITY OF T WI GGS CLAY IN

GENERAL REDUCTION COMPANY"$ FULLERS EA RTH PIT

I~D

AFTER SHEARE R, (1 9 17 )

c

;::
c ~

STOP 9

TYPE LOCALITY OF ~ SEO G
DRY BRANCH FORMATION

:0::0.

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1-

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1:1:
0 0

~-
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.. _. ....:;::-
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~
~

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FIGURE 13
71

STOP 9 MAIN REFERENCE LOCALITY FOR THE TWIGGS CLAY, (SHEARER'S MAP LOCALITY E), SECTION EXPOSED ALONG RAILROAD CUT OF SEABOARD COAST LINE, 1.0 MILES (1.6 km) SOUTHEAST OF THE TYPE LOCALITY OF THE TWIGGS CLAY IN THE ABANDONED FULLERS EARTH PIT OF THE GENERAL REDUCTION COMPANY, IN TWIGGS COUNTY.

Lithostratigraphic unit and bed number

Description

Thickness

TOBACCO ROAD SAND

'

BED 6

Sand: deeply weathered residuum, tough

and resistant, case-hardened by secondary

interstitial cementing agent (Fez03 and

clay mineral of soil origin?); sand fine-

to medium-grained, well-sorted; no bedding

preserved; massive-bedded and structure-

less, holds up a vertical face; color

15.5 feet

moderate-reddish-brown (10 R 4/6).

(4.5 m)

BED 5

Sand: as above but nor as deeply weathered and case-hardened, interstitial cementing agent occurs irregularly, rather marbled; original stratified, sedimentary nature more apparent, rudely but distinctly layered; sand is fine-to medium-grained and well-sorted; sand is soft and loose (sugar sand) where interstitial cementing agent is lacking; color of pure sand is white (N 9) and sand with interstitial cementing agent is moderate-reddishbrown (10 R 4/6).

4.5 feet
(1. 4 m)

Bed 4

Sand: slightly argillaceous; very coarse and granully , a few scattered small pebbles, very poorly sorted; vague, rude bedding apparent on close inspection, generally giv~s the impression of being structureless

72

and massive; tough and resistant due to weathering and some case-hardening.

4.0 feet
(1.2 m)

In general, the Tobacco Road Sand, beds 4 through 6, are a fining upward sequence; due to case-hardening by secondary interstitial material, beds 4-6 are relatively resistant to erosion and hold up vertical facies in outcrop.

DRY BRANCH FORMATION IRWINTON SAND MEMBER

BED 3

Sand: coarse-grained, moderate-to wellsorted; unconsolidated, soft and loose; thinly bedded with horizontal layering and cross-bedding; some very thin, scattered, discontinuous clay layers, laminae, or chips.

2.0 feet (0.6 m)

BED 2

Sand and clay: thinly interbedded finegrained, clean, well-sorted quartz sand (layers equal to or less than about 1/8 in. (2 mm)), clayey fine-grained sand, and finely sandy clay; specific layers no more than about 1 in. (2.5 em) thick; sediment is tough but not resistant to weathering and erosion; 4.5 ft (1.4 m) of bed in lower part not exposed due to slump and tendency toward water seepage (springine~s) on the top of the Twiggs Clay.

8.5 feet (2.6 m)

TYPE TWIGGS CLAY BED OR LITHOFACIES

BED 1

Clay: finely sandy to silty and micace-

ous with fine-grained sand, silt, and

mica restricted mainly to bedding planes,

calcareous in lower 5 to 5.5 ft (1.5-1.7 m)

of -exposure; diatoms conspicuous on bedd-

ing planes in upper part above calcareous

zone, less conspicuous in calcareous clay;

some surfa

cMen0i2nsutapipneirngpaarntdabdoevnedrciatelcsaroeno

clay us

zone;

73

clay thinly bedded to laminated with silty fine-grained sand and mica concentrations along bedding planes (only a few quartz grains thick) enhancing thinly bedded nature of the deposit; layers and laminae range in thickness from about 9 in. (23 em) to less than 1/16 in. (1 mm), most layers less than about 1 in. (2.5 em) apart; thicker layers (4-9 in. (13-23 em)) display conchoidal to subconchoidal fracture; laminae of fine-grained sand are obscure near the base of the exposure but weathering causes them to become more pronounced upward; thus the clay becomes more fissile upward; very shaley aspect of vertical weathering face;

the whole mass of clay is very well-jointed with abundant vertical to near vertical joints, some joints less than 1 in. (2.5 em) apart;

dry clay is light-weight fullers earth-type clay;

microfossiliferous with poorly preserved foraminifera and ostracods occurring in lower calcareous part, diatom impressions common on bedding planes in upper part;

unweathered calcareous clay varies from

light-olive-gray to olive-gray (5 Y 6/1 to

5 Y 4/1), upper diatomaceous clay is yellow-

ish-gray (5 Y 7/2 to 5 Y 8/1); base of bed 16 feet

is not exposed in railroad cut.

(4.9 m)

50.5 feet

(15.4 m)

74

"'T1

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HUBER PALEOCENE/EOCENE

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6

CLINCHFIELD

TIVOLA

BARNWELL

OCALA

UPPER EOCENE

BED
TWIGGS CLAY I MEMBER DRY BRANCH I FORMATION
GROUP
EPOCH

-

STOP 10 GEORGIA KAOLIN PIT 50, AT THE INTERSECTION OF TWO KAOLIN HAUL ROADS, 1.4 MILES (2.25 km) SOUTHEAST OF THE BUB-TWIGGS COUNTY LINE IN TWIGGS COUNTY.

Lithostratigraphic unit and bed number

Description

Thickness

DRY BRANCH FORMATION TWIGGS CLAY MEMBER

BED 11

Clay: calcareous, silty; hackly, blocky, subconchoidal to conchoidal fracture.

OCALA GROUP TIVOLA LIMESTONE

BED 10

Limestone: almost a bryozoan coquina, medium/coarse-textured, bioclastic, calcarenitic; massive-bedded, only indication of original stratification is in very rudely layered, rubbly zones in top 2 or 3 ft (0.6 or 0.9 m) and basal 2ft (0.6 m); moderately consolidated and indurated, irregular fracture; lower 2 ft (0.6 m) gradational with underlying Clinchfield (Bed 9).

8.0 feet (2.4 m)

CLINCHFIELD FORMATION TREADWELL MEMBER

BED 9

Limestone: sandy, somewhat glauconitic; upper part with scattered concentrations of bryozoans resulting in a resemblance to the overlying Tivola,. with which Bed 9 is gradational; vaguely and very rudely bedded, stratification appears lensical and undulatory; generally rubbly and moderately indurated or recrystallized, irregularly alternating hard and less hard; hard ledges or lenses consist of sandy to

76

BED 8 BED 7

nonsandy, fairly well-crystallized limestone; sandy lenses or patches relatively unconsolidated; quartz sand is a minor constituent' patchy; some scattered small lenses of calcarenitic, glauconitic, well-sorted, fine-to medium-grained sand (glauconitic in more sandy patches); moderately foss~liferous with scattered patches of abundant Periarchus lyelli; Aeguipecten spillmani present.

3 feet (0.9 m)

Sand, calcareous sand, and sandy

limestone: sand and limestone beds ;well

segregated into sand beds and limestone

ledges; the hard ledges consist of sandy

to nonsandy, fairly well-recrystallized

limestone; ledges vary from 1 to 9 in.

(2.5 to 23 em) thick; the less indurated

to nonindurated sand layers and lenses

between the hard ledges consist mainly

of unconsolidated, calcareous, medium-to

fine/medium-grained, well-sorted quartz

sand; the softer sand forms recesses or

reentrants upon weathering, these ranging

in thickness from 1 in. (2.5 em) to 1.5

ft (46 em) thick; thicker sand lenses

occur toward the top of bed; sand shows

fine-scale layering or laminations; very

well-layered with inclined bedding

(crossbeddin~ and festoon bedding) high-

lighted by strong development of alternating

hard and soft layers; bedding somewhat

undulatory; all "beds" appear to be dis-

continuous and lensical except basal sand

bed that can be traced around the pit;

fossils relatively rare; no microfossils

5 feet

recovered from. this bed.

(1.5 m)

Sand and sandstone: calcareous, consists of alternating slabs or ledges of calcareous sandstone and tough, coherent calcareous sand; the hard sandstone ledges become less sandy and more calcareous upward in the section; the thinner ledges, especially the sandy ledges near the base of the bed, appear more as coalescing bands of calcareous

77

sandstone nodules; these "ledges" are very irregular in shape and degree of induration, being only a little more calcareous and resistant or
tougher than the adjacent, noni~durated, recessed sand; the quartz sand consists of medium-to fine-grained, well-sorted sand; sandstone fracture slabby to very irreg~lar; Periarchus lyelli is persistently common to abundant in this bed; Aeguipecten spillmani rare; grades downward into Riggins Mill Member (Bed
6) by appearance and increase in clay content downward, by breakup of sandstone/limestone bands of nodules into separate nodules, and by domination of noindurated clayey sand over nodules and bands of nodules; lithology change takes place over an interval of of about 6 in. (15 em).

RIGGINS MILL SAND MEMBER

BED 6

Sand: argillaceous, calcareous, some dispersed Mn02, irregular-shaped limestone nodules or concretions occur throughout; quartz granules and pebbles scattered throughout but not common; scattered tnacrofossils;

Sand-clay-calcite distribution irregular, patchy, and marbled with small irregular lensoid concentrations of dominantly sand, dominantly clay, or dominantly calcite (nodules); sorting is also irregular, ranging from well-sorted to poorly sorted; quartz sand component generally medium-to fine/medium-grained with some irregular, coarser concentrations;

The gross appearance of the bed gives the general impression of being
massive-bedded but closer inspection
shows a definite but rude and ir-
regular stratification;

5.5 feet (1. 7 m)

78

BED 5

The degree of coherence ranges irregularly from well-indurated (nodules or concretions) to compact but unconsolidated;
Moderately fossiliferous; macrofossils include scattered Periarchus lyelli and P. lyelli fragments, Chlamya cocoana sensu Glawe (1974, pl. 2, fig. 3, 5, 10, 11), and scattered, rare aragonitic, small molluscan. shells;
Color yellowish-gray (5 Y 8/1); grades downward into:
Limestone: sandy, some scattered quartz granules and small pebbles; very fossiliferous with a diverse assemblage of pelecypods and gastropods in molds and casts;
Quartz sand distribution somewhat patchy and irregular on a small scale; generally poorly sorted, scattered, irregular inclusions of dense, hard, fine-grained, conchoidal fracturing, almost pure limestone;
Massive-bedded, little or no indication of bedding; basal 6 in. (15 em) of bed consists of a very hard, dense, resistant, sandy limestone ledge, bed gets sandier, more argillaceous, and less indurated upward; grades upward into bed 6 by becoming more clayey, sandy, and less calcareous;
Richly fossiliferous i~ lower part, becoming gradually less fossiliferous upward; Periarchus appears for the first time in upper part of the bed along with Chlamys cocoana sensu Glawe (1974, pl. 2, fig. 3, 5, 10, 11):

5.5 feet (1. 7 m)
5.0 feet (1.5 m)

79

BED 4

Sand: clayey, calcareous, pebbly, fossiliferous; many sandy, "popcornlike" limestone concentrations up
to aboutl ft (30 em) across; many
small, aragonitic shells scattered throughout the bed but are especially well preserved and delicate in the basal 1 ft (30 em);
Bedding rude, not obvious, but i't is apparent on close inspection; stratification wraps around "pop corn" concretions; small shells are preferen;... tially aligned horizontally, and to a lesser extent, "popcorn" concretions tend to be aligned;
Generally unconsolidated but firm except for "popcorn" concretions; concretions appear to have formed on sea floor because they do not contain as much quartz sand as the adjacent sediment; in addition the .interior of the concretions contain coquinoid limestone, similar in lithology to the basal part of the overlying limestone bed;
Very poorly sorted; grain-size ranges from interstitial clay to rounded pebbles up to 1.5 in. (4 em), especially poorly sorted and pebbly in the basal 1 ft (30 em); sediment size decreases, abundance of pebbles decreases, and clay content increases upward; the upper 1 ft (30 em) of the bed is d.ecidedly clayey with irregularshaped clay inclusions;
Very fossiliferous; fossils inclued scattered shells and shell fragments of Crassostrea gigantissima, corals, small pelecypods, gastropods, and scaphopods, shark teeth and ray teeth;
Color ranges from dark-grayish-yellow (5 Y 7/4) to pale-moderate-yellow

80

(5 Y 8/6) where weathered;

Basal contact very irregular and undulatory with relief of between 5 and 6ft (1.5- 1.8 m); in places the contact appears conformable, in other places the contact appears to be a discontinuity.

3.0 feet (0.9 m)

I:{UBER FORMATION

BED 3

Sand and kaolin clay: quartz sand medium-to coarse-to very coarsegrained, well-sorted to moderately sorted, the clay present in sand beds concentrated along bedding
planes as thin layers and laminae and in burrows; sand unconsolidated, commonly loose; very well-bedded, inclined bedding, horizontal bedding; Callianassa burrows common; peculiar funnel-shaped structures present; in places the sand grades downward and along inclined bedding slopes into underlying bed; in other places it rests on underlying bed with fairly sharp contact; the basal bed consists of poorly to moderately sorted, medium-to very coarse-grained pebbly sand with clay clasts.

Lenses or pods of silty, finely micaceous

kaolinitic clay (with high montmorillo-

nite content) occur in upper part of

bed 3 on opposite sides of the pit; the

kaolinitic clay has hackly, blocky, con-

choidal to subconchoidal fracture, and

breaks into small blocks generally less

than 1 in. (2.5 em) in size; massive-bedded;

clay pods are part of Bed 3 in that

Callianassa-bearing sands lie adjacent to

and underlie the kaolin pods; basal Riggins

Mill overlies the lenses in the pit and is

draped over them, with the upper surfaces

of the pods riddled with animal borings

3-6 feet

from the above Bed 4;

(0.9-1.8 m)

81

BED 2

Sa~d and clay: finely micaceous; quartz sand generally very fine to fine-grained, some medium and rarely coarse-grained sand, well~sorted; sand and clay con-
centrated in discrete layers; clay thinbedded to laminated; clay relatively more resistant to weathering than sand; as a result the sand and clay are very finely etched or sculptured by weathering of the pit face; display very intricate and varied bedding (crossbedding of various kinds); prints of plant leaves and stems are commonly found along clay parting planes;

HUBER FORMATION.? CRETACEOUS?

BED 1

Kaolin: massive-bedded, breaks into large blocks with conchoidal fracture; pure; this is the bed being mined; "soft" variety of kaolin. Top of Bed 1 is very irregular and shows considerable relief; bed 2 is reciprocaily thin (5 ft (1. 5 m)) where the top of Bed 1 is high, and is thick (16 ft+ (4.9
m+ where the top of Bed 1 is low.

5-16 feet (1.5-4. 9 m)
8 feet+ (2.4 m+)
60 feet
(18 m)

82

STOP lla SECTION EXPOSED IN ROADCUT AT MATTIE WELLS SCHOOL ON GA. 49, JONES COUNTY,
GEORGIA

Lithostratigraphic unit and bed number

Description

Thickness

DRY BRANCH FORMATION

BED 12

Residuum with pockets of saprolite: residuum consists of massive-bedded, clayey sand that is mottled moderate-
reddish-brown, yellow, orange, and gray; very tough, resistant, breaks off in large blocks, may be a hard pan; the pockets of saprolite consist of fine-to medium-grained, wellsorted, argillaceous sand with thin, discontinuous stringers or laminae of clay; lithologically the saprolite is identical with that of the underlying bed.

7.5 feet
(2.3 m)

Tobacco Road-Dry Branch contact may occur within Bed 12.

BED 11

Sand: with thin, discontinuous clay stringers or laminae; sand is fineto medium-grained, well-sorted, unconsolidated but tough; no evident primary sedimentary or biogenic struc-
tures; bed is deeply weathered ~nd the
sand.is moderate-reddish-brown (5 R 4/6)
in color, the thin clay layers are almost white.

5.0 feet
(1.5 m)

BED 10

Clay with thin sand layers: clay fairly pure, with fine-grained mica and silt along bedding planes; bedding planes within the clay layers mainly about 1 in. (2.5 em) apart; individual layers of clay display very f ine lamination; blocky, 'hackly, conchoidal to subconchoidal fracture; clay weathers into brittle, paper-thin

83

BED 9 BED 8
BED 7 BED 6 BED 5

chips, opal-cristobolite present?; scattered,

thin layers of fine-to medium-grained sand;

sand layers up to 6 in. (15 em) thick but

most are between 1 and 2 in. (2.5 and 5 em) 7.5 feet

thick.

(2.3 m)

Sand~ conspicuously layered, very wellsorted fine-to fine/medium-grained sand, heavy minerals conspicuous, very soft, incoherent (sugar sand); some thin layers and laminae of clay; layers range in thickness from 3 in. (7.5 em) to 1/8 to 1/16 in. (a few mm); clay lithology as in Bed 10.

1.5 feet (0.45 m)

Clay: fairly pure with fine-grained mica, silty fine-grained sand, and heavy minerals concentrated along bedding planes; bedding planes about 1 in. (2.5 em) apart; individual layers of clay display very fine lamination; fracture is blocky, hackly, conchoidal to subconchoidal; in general appears shaley; weathers into brittle, paper-thin chips; jointed.

4 feet
(1. 2 m)

Sand: well-layered, very well-sorted, fine-to fine/medium-grained, heavy minerals conspicuous, soft and incoherent (sugar sand); some thin discontinuous layers of clay that range in thickness from 3 in. (7.5 em) to 1/16 in. ( a few mm)

1.5 feet (0.45 m)

Clay, identical to Bed 8.

4. 5 feet
(1.4 m)

Sandstone: chert-cemented (siliceous), scattered lenses or pockets of almost pure chert or opal, scattered greenishclay grains or clasts; irregular coarse black grains or inclusions, some thin layers or lenses of almost quartzite; sandstone very hard and resistant; thinbedded to medium-bedded; very fossiliferatis with shell impressions concentrated along bedding planes; because the fossiliferous horizons are zones of

84

BED 4
BED 3

mechanical weakness in the rock, the sandstone preferentially fractures along the bedding planes, thereby exposing the concentrations of shell fragments; the zones of shell concentration range from~ in. (0.6 em) to a little over 1 in. (3 em); some small scale crossbedding present and some thin lenses of unconsolidated fine-to mediumgrained sand are present; grain size in the sandstone ranges from fine to medium.

2.5 feet (0.75 m)

Clay and sand: clay very shaley, fissile, breaks into brittle paper-like chips when dry; conchoidal fracture; stiff but gooey and plastic when moist; slightly micaceous; divisible into 2 or 3 discontinuous layers that are discriminated only by difference in color; Sand is medium-grained, well-sorted, very soft and unconsolidated; contains thin discontinuous, clay layers up to 1 in. (2.5 em) thick. The main clay layer occurs at the base of the bed, the sand at the top. The thickness of the clay is 5-8 in. (12.518 em), the sand 4-6 in. (10-15 em).

1.0 foot (30.5 em)

Sand: argillaceous, with clay component occurring both as matrix and as irregular-shaped inclusions; moderate amount of heavy minerals; sorting moderate, sand size ranges from coarse to medium, mostly coarse/medium, (upper 6 in. (15 em) medium-grained, well-sorted, fairly pure); clay inclusions consist of irregular, small, clast-like bodies; burrow fillings; thin discontinuous, bedding plane layers and partly "chewed up"
layers; heavily bioturbated; incompletely mixed sand and clay with original bedding planes not completely obliterated; weathers rather massively; sediment does not part along the vague bedding planes during erosion.

2.0 feet (61.0 em)

85

BED 2
BED 1

Sand and clay: incompletely mixed, bioturbated, tends to have very crude interlayering about 6 in. (15 em) apart, sand layers with irregular shaped clay inclusions range from 1-3 in. (2.5-7.5 em) thick with some thinner sand layers up to 1 in. (2.5 em) thick; sand layers appear to be continuous, at least over the length of the exposure (6ft (1.8 m));
Clay layers are 1-3 in. (2.5 - 7.5 em) thick but tend to break up into layers of clasts where the clay layer is 1 in. (2.5 em) or less thick; clay layers not continuous but can be followed (persistent but discontinuous);
Sand is medium-to fine/medium-grained, well-sorted; heavy minerals fairly conspicuous; some very small, scattered, fragmentary fossil-shell impressions.
Cristobolitic Clay: fairly pure, some silty fine sand, heavy minerals, and fine-grained mica along bedding planes; bedding planes mainly 1 in. (2.5 em) or less apart, many bedding planes are as little as 1/16 in. (1 mm) apart, individual laye~s of clay show very fine lamination; clay fracture is blocky, hackly, conchoidal to subconchoidal, shaley; tough and plastic when moist, hard and brittle when dry; weathers into paper thin chips.

11 feet (3.4 m)
16 feet
(4.9 m)
64 feet (19.5 m)

86

STOP II MATTIE WELLS SCHOOL LOCATIONS
STOP 11-B
0 r MILES (II KM) EAST OF
MATTIE WELLS SCHOOL ON GA. 49 JONES CO

.. .... -- :..

.': .... -: ' l

' . .i:- :..

~ r.. . .~ t



_)liB~~ "".

.(~ l

, .;._ ~-;. :

!~
/
.. /

Cl <l 0 0:::

0

13

;uua

0 1--

STOP II-A MATTIE WELLS SCHOOL ON GA.49
JONES CO.

....J
.w...J z ~ ~
CD

:I:

u z

BED I

<l
m0:::

>-
0::: Cl

FIGURE 15
87

STOP llb 0.7 MILES (1.1 km) NORTHEAST OF STOP lla
ON GA. 49.

Lithostratigraphic unit and bed number

Description

TOBACCO ROAD SAND

BED 4

Residuum: sand, argillaceous; tough, resistant, massive-bedded, structureless;

BED 3

Sand: medium to coarse to very coarse, with lenses of gravel and pebbly, very coarse sand, moderately poorly sorted to very poorly sorted; variably slightly argillaceous (in upper part of bed) to nonargillaceous, except for scattered clastic clay balls and some clay laminae; extremely crossbedded, appears to be mainly of the scour and fill kind; crossbed sets small to moderate in scale, being no more than about 2 ft (61 em) in thickness at the most; appears to be mainly fluvial type of crossbedding with no indication of marine or perimarine origin, except for interval of 2 or 3 ft (60 or 90 em) at top of bed where there appears to be faint traces of bioturbation; generally resistant to weathering due probably to case-hardening and cementation in the weathering zone;

DRY BRANCH FORMATION

BED 2

Sand: clayey, with scattered quartz granules and pebbles; very poorly sorted and well-mixed; massive-bedded;

Thickness 17 feet
(5.2 m)
21 feet
(6.4 m)

88

BED 1

except for top few feet (1 m) and basal 2ft (60 em), there is no indication of bedding; sand at top of bed is rudely layered, mediumgrained, and moderately wellsorted; basal bed is very pebbly and coarse with rude stratification; very tough but nonindurated;
Sand: argillaceous, fine-to mediumgrained, moderately well-sorted; compact but nonindurated; thinly bedded.

32 feet (9.7 m)
2 feet (0.6 m)
72 feet
(21.9 m)

89