- Collection:
- Georgia Government Publications
- Title:
- Mineralogy and heavy-mineral resource potential of surficial sediments on the Atlantic continental shelf offshore of Georgia
- Creator:
- Grosz, A. E. (Andrew E.)
- Publisher:
- Atlanta, Ga. : Dept. of Natural Resources, Environmental Protection Division, Georgia Survey
- Date of Original:
- 1993
- Subject:
- Marine mineral resources--Georgia
Continental shelf--Georgia
Marine sediments--Georgia
Continental shelf
Marine mineral resources
Marine sediments - Location:
- United States, Georgia, 32.75042, -83.50018
- Medium:
- state government records
- Type:
- Text
- Format:
- application/pdf
- Description:
- Includes bibliographical references (p. 30-31)
- External Identifiers:
- OCLC 34599482
NZ MMS ID 9910167883902931
Call Number N200.G4 S1 P7 no. 19
Call Number TN264 - Metadata URL:
- https://dlg.galileo.usg.edu/id:dlg_ggpd_s-ga-bn200-pg4-bs1-bp7-bno-p-b19
- Digital Object URL:
- https://dlg.galileo.usg.edu/do:dlg_ggpd_s-ga-bn200-pg4-bs1-bp7-bno-p-b19
- Language:
- eng
- Extent:
- iv, 31 p. : ill., maps ; 28 cm.
- Holding Institution:
- University of Georgia. Map and Government Information Library
- Rights:
-
MINERALOGY AND HEAVY-MINERAL RESOURCE
POTENTIAL OF SURFICIAL SEDIMENTS ON THE ATLANTIC CONTINENTAL SHELF OFFSHORE OF GEORGIA
By Andrew E. Grosz
Department of Natural Resources Environmental Protection Division
Georgia Geologic Suney
PROJECT REPORT 19
MINERALOGY AND HEAVY-MINERAL RESOURCE POTENTIAL OF SURFICIAL SEDIMENTS ON THE ATLANTIC CONTINENTAL SHELF OFFSHORE OF
GEORGIA
By Andrew E. Grosz
Prepared in cooperation with U.S. Minerals Management Service and the
U.S. Geological Survey U.S. Departtnent of the Interior underMMS Agreement No. 14-12-<XX>1-30496
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey or Georgia Geologic Survey editorial standards and stratigraphic nomenclature.
DEPARTMENT OF NATURAL RESOURCES Joe D. Tanner, C001missiouer
ENVIRONMENTAL PROTECTION DIVISION Harold F. Reheis, Assistant Director GEORGIA GEOLOGIC SURVEY
WUiiam H. McLemore, State Geologist
Atlanta, Georgia 1993
PROJECT REPORT 19
CONTENTS Page
ABSlRACf .............................................................................................................................................................. 1 INTRODUCTION ..................................................................................................................................................... 1
Background ........................................................................................................................................................... 1 Physiography ............................ .......................... ...................... ... .. ................... ............ ......................................... 1 Previous work ....................................................................................................................................................... 4
PRESENT WORK..................................................................................................................................................... 4
San1ple acquisition ................................................................................................................................................ 4 Laboratory procedures ........................................................................................................................................... 6
RESlJLTS .................................................................................................................................................................. 15 Texture .................................................................................................................................................................. 15 Carbonate content.................................................................................................................................................. 15 Feldspar content .................................................................................................................................................... 15
Heavy minerals ...................................................................................................................................................... 23 Heavy-mineral content ...................................................................................................................................... 23 Heavy-mineral resource potential ..................................................................................................................... 23
CONCLUSIONS ....................................................................................................................................................... 30 ACKNOWLEOOMENTS ......................................................................................................................................... 30 REFERENCES .......................................................................................................................................................... 30
iii
ll.LUSTRATIONS
Page Figure 1. Spatial dislribution of S801ples from the Georgia shelf................................................................................ 2
2. Spatial distribution of 18 transect surface grab samples from the Georgia shelf.......................................... 3 3. Distribution of heavy minerals in surficial sediments of the U.S. Atlantic Continental Shelf...................... 5 4. Contour plot of the mean grain size of sediments in 65 grid surface grab samples from the
Georgia shelf............................................................................-...........................................................21
5. Contour plot of the CaC0:3 content of sediments in 65 grid surface grab samples from the
Georgia shelf..............................................................................................................................................22 6. Contour plot of the feldspar content of the sand fraction in 65 grid surface grab samples
from the Georgia shelf................................................................ ................................................................24 7. Contour plot of the pen:entage of heavy minerals in 65 grid surface grab samples from
the Georgia shelf ........................................................................................................................................ 25 8. Plot of the EHM/1' (economic heavy minenllslbulk S801ple) vel'SUS water depth for the 65
grid surface grab samples from the Georgia shelf ....................................................................................... 26 9. Contour plot of the EHM/1' of sediments in 65 grid swface grab samples from the Georgia shelf ..............27 10. Contour plot of the percentage of ilmenite in 65 grid surface grab samples from the Georgia shelf ............28 11. Plot of the mean grain size versus the percentage of heavy minerals ........................................................... 29
TABLES Page
Table 1. Location coordinates and lithologic descriptions of the 65 grid surface grab samples from the Georgia shelf.............................................................................................................................................. 7
2. WaJtr deplh, sampling equipment, texture, carbonate content, and gamma radiation activity data for the 65 grid surface grab samples from the Georgia shelf ....................................................................... 9
3. Feldspar and heavy-mineral data ((I the 65 grid surface grab samples from the Georgia shelf ................... 11 4. Location coordinates, water depth, gravel content, and heavy-mineral data for the transect
surface grab samples from the Georgia shelf .............................................................................................. 16 5. Texture and heavy-mineral content of the TACI'S samples ........................................................................ 17 6. Textme and heavy-mineral content of the Tybee and Skidaway Island borehole samples ........................... 19
lY
MINERALOGY AND HEAVY-MINERAL RESOURCE POTENTIAL OF SURFICIAL SEDIMENTS ON THE ATLANTIC CONTINENTAL SHELF OFFSHORE OF
GEORGIA
By
Andrew E. Grosz U.S. Geological Survey
ABSTRACT
Textural and mineralogical data for 83 grab samples from the Georgia shelfare used to detennine the potential forplacer heavy-mineralresources in the surficial sediments. The distribution ofcoarse-grained, feldsparrich, immature, terrigenous, clastic sediments shows that the Piedmont-draining Savannah and Altamaha Rivers controlled shelf-wide sedimentation; common shallowwater processes such as sea-level changes, bottom currents, and major storms have not substantially modified this shelf-wide pattern. The relative abundance ofheavy minerals that weather quickly outside the marine environment reflects either modern depositional loci of Piedmont-draining rivers or their seaward extension during times of lower sea level. Analyses of an additional 65 subsurface samples from offshore and onshore boreholes provide supporting data on the immature nature of the heavy-mineral suite provided to the Georgia shelf. Sealevel stillstands of significant duration are not supported by the mineralogic data except for one near the 14-m isobath.
The potential for deposits of heavy mineral placers is very low because the mineral suite provided from the Piedmont source terrane is immature. The bK:k of heavy-mineral placers is further indicated by the absence of beach-complex sediments, which tend to have mature assemblages, and the abundance of fluvial sediments, which tend to have immature assemblages.
INTRODUCTION
Background
Concentrations of heavy minerals, including those containing titanium, zirconium, and rare-earth elements, on the Atlantic Continental ShelfoffshoreofGeorgia (the Georgia shelf) have been known for some years. A tract about 60 km long, extending from about Tybee Island to about Jekyll Island, and about 15 km wide,
extending from the shoreline to about the 20 m isobath, was identified by U.S. Geological Survey scientists as prospective for heavy-mineral concentrations (Mining Journal, 1985). Exploration permits were subsequently granted to companies mining heavy minerals onshore in northeastern Florida; however, results of their sampling programs have not been made public.
The bK:k ofadequate geologic, grade, and compositional data for the swficial sediments of the Georgia shelf have hindered analyses of heavy-mineral resource potential on the Georgia shelf. This study was conducted attherequestoftheStateofGeorgia- U.S.Departmentof the Interior Task Force for the Offshore to provide an assessment of the potential for commercial deposits of heavy minemls within a geologic, textwal, and compositional framework. Surface sampling for heavy minerals may be effective only in locating swficial a::cumulations and may miss the more important non-eroded relict deposits. Geophysical techniques are required to locate buried pbK:ers, which must be confmned by coring or relatively deep dredging. This study is based only on surface and core samples.
Physiography
The Georgia shelf is approximately 120 km
wide; the shelf break is near the 60-m isobath. The shelf
surface isgenerally smooth andoutcropsofhardrocks are rare. Bathymetricexpressionsofsoutheast-trendingremnants of the Savannah and Altamaha River channels are discernible on the shelf even though they are now submerged and have been modified by depositional and erosional processes. High-resolution seismic data for this region show the presence of fluvial channels in the shallow subsurface. The degree offluvial sedimentation on the shelf can be inferred by the extensive "scalloping" of the 10-, 20- and 40- m isobaths shown in Figures 1and 2. Supporting evidence for this interpretation is given by seismic stratigraphic studies ofa feature called the Tybee Trough (located between sample sites 2295 and 1485 in
1
~
1
i
-') ~ '~"")~\~1 \,)...:..:~.:........:.. . \'sc t..
3
3
EXPLANATION OF SYMBOLS
.1682
.683 1698
.LOCATIONS OF SKIDAWAY & AND TYBEE ISLAND (T)
BOREHOLES
1680
LOCATION AND NUMBER OF GRAB SAMPLE
* LOCATION OF TACTS BOREHOLE
SCALE
25 ---====-==-- 0 NM
25
- - o Ml
251!!!!!1C:=-:::::&ii0 0 KM
Figure 1.--Spatial distribution of samples from the Georgia shelf. Bathymetry in meters.
2
31.5
81.00
E .0.,..
~41
10m
31.2
1495
81.00
0
<>cf?
0
1704
1680 80.75
SCALE
25F3 F3 eao Ml
25H H HOKM
25&3 ea E30NM
Figure 2.-Spatial distribution of 18 transect surface grab samples from the Georgia shelf. Transect samples indicated by solid circles; grid surface grab samples by stars. Latitude and longitude in hundredths of a degree to facilitate comparison with Table 4.
3
Figure 1) by Kellam and Henry (1987). Uchupi (1968) showed northeast- and southeast-trending sand swells radiating from near the mouth of the Altamaha River; he suggested that these features may be a response to waveinducedoscillatorycmrentsgeneratedduringintensestonns. Some of these features, however, may be fluvial levees (Uchupi, 1968). Seven escarpments thought to represent both accretional and erosional shorelines are approximately coincident with isobaths at 14, 20, 25, 30, 40, 45, and 60 m; they are identified on the basis of detailed bathymetric and high-resolution seismic transects (VJ. Henry, Jr., GSU, Atlanta, 1989, written communication).
Previous work
Previous studies of the surficial and shallow-su~ surface sedimentsofthe Georgia shelfhavebeen regional in scope. Although they address small-scale textural distribution patterns and general compositional trends (Pilkey and Fr.wnkenbe~.1964;~. 1972;llo~. 1973)only limited heavy-mineral analysis was done in attempts to outline petrographic provinces. Pilkey (1963) and Gorsline (1963) referred to heavy minerals in eight very widely spaced samples (described by Moore and Gorsline, 1960) from the Georgiashelfand gave mineralogyonlyfor narrow size fractions (<0.25 mm) of small samples.
Neiheisel (1965)studied the dispersion ofAltamaha River sediments near Brunswick Harbor, GA, by use of hornblende separated from the sand-size fraction of the sediments. Carver and Kaplan (1976) discussed the distribution of hornblende on the Georgia shelf and concluded that the Altamaha and Savannah Rivers are the dominant sources of sedimenL
Placer heavy-mineral distribution patterns in surficial sediments of the U.S. Atlantic Continental Shelf were discussed by Grosz and others (1987), and an assessment ofthe economic heavy-mineral resource potential was givenbyGrosz(1987)(Figure3). Neitherthesenortheother studies, however, provide mineralogic data for the Geo~ shelf.
Themostrecentanalysis of heavy-mineral data for theGeorgiashelfwasdonefortheTaskForcebytheZellars-
Williams Company (1988). The analysis was conducted on
non-opaque heavy-mineral data (from Hathaway, 1971) whichareexpressedaspercentagesofthesand-sizefraction from which they were separated.
Thus, available literature provides heavy-mineral data that were generated for regional studies or for sitespecific surficial sediment distribution patterns. Analyses limited to non-opaque mineral species of narrow size frac-
tions of small sediment samples do not provide adequate information for an assessment of detrital mineral resource
potentialbecause many ofthe economic heavy minerals are
opaque. In addition, the useofbulksamples weighing on the order of tens of grams creates a particle-sparsity-effect (Cliftonandothers,1969)thatmakesitdifficulttodetermine concentrations ofscarce buthighly valuable heavy minerals such as monazite accmately.
Gorsline (1963) and Henry andHoyt(1968) identified two textural domains on the Georgia shelf: one characteristically fine grained in the nearshore and another coarser grained further offshore. Pilkey and Fr.wnkenbe~ (1964) placed the boundary between the two textural domains althe 11-misobath; Henry and Hoyt(1968)proposed the 15-m isobath. Studies by Pilkey (1963), Neiheisel and Weaver (1967), and Bigham (1973) suggest that modern sedimentdeposition islimited~elytothisnarrow nearsloe zone, where sediment is dispersed longshore in a southerly direction; little sediment is transported seaward.
PRESENT WORK
This study is based on 116 offshore sediment samples [83 surface grab samples and 33 samples from 8 Tactical Air Command Test Site (TACTS) lo'eholes] and 32 onshore sediment samples (from 2 onshore boreholes on Tybee and Skidaway Islands) (Figure 1). The 83 grab
samples are located by a grid on the Georgia shelf with a sample density ofabout 1per 250 kfn2. This spacing allows
only the definition of regional patterns. To expand coverage, 20 samples from areas north and south of the Geo~ State line were included. Two types of grab samples were
utilized in the study: (1) 65 surface grab samples collected
on a grid (grid samples) and (2) 18 surface grab samples collected on transects of bathymetric features (transect samples). Sample coverage extends from the 6-m to the64m isobath, the approximate edge of the Georgia shelf. The variety of samples ~as assembled f<r this study to allow small- and ~e-scaie surficial coverage~ well as to probe patterns of mineral distribution in older, subsurface sediments both onshore and offshore.
Sample acquisition
The 65 grid samples are part ofabout 3600 ocean-
floor sediment grab samples collected from the Atlantic Continental Shelf through the joint efforts of the Woods Hole Oceanographic Institution and the U.S. Geological Survey (Hathaway, 1971). The sample collection was done between 1955 and 1970 by using several types of bottom samplers, including Campbell, Smith-Mcintyre, and Van Veen. The samples used in this study were collected during
4
PERCENT HEAV'f-MINERAL CON1ENl Of
SURfACE SED\MENlS
s 4.00% 1.00 - A.OO%
<tOO%
surficialse<funell~S F1gute 3.-Distriblltion of bea\'Y 1Jlinelals in
of the U.S. Atlantic Continellull
Shelf. From Grosz and othen (1987).
5
May and June of 1964 and May of 1965. Sample sites are approximately on a 20-km grid (Figure 1) the precision of the sample locations is estimated to be within about 2 Ian. However, these samples may not accurately represent bulk ocean-floor sediments, because part of the fine-grained material may havebeenlostfrom coarse-grainedorgravelly sediments dming collection.
The 18 ttansect samples were collected dming June of 1985 by the U.S. Geological Survey from the R/V
Jobo Wesley PQwell by use of a VanVeen grab sampler.
They were acquired dming sampling transects made on probable fonner fluviodeltaic deposits of the Altamaha Riveratwhatappeartobeshorelinedepositsnearthe 10-and 20-m isobaths. The precision of the locations of these samples (Figure 2) is estimated to be within about 30 m of the reported coordinates. The samples probably accurately represent the upper 10 to 15 em of ocean-floor sediment becausecompleteclosure ofthe samplingdevice (no loss of fines) was noted for each of the samples. Bulk samples of about 10literseach werecollected in singledropsofthe Van Veen grab sampler.
Samples from eightTACTS boreholes (sites A-H; Figure 1) were drilled for the U.S. Navy for foundation evaluation purposes. The TACTS drill cores do not representcontinuouscoverageofpenetrated strata (about 100m). axe materials exist in three forms: pint Mason jars of artificially consolidated material left from physical properties tests such as biaxial compressive strength; intact core sections of a few to about 33 em in plastic tubes of 6.5 em inner diameter; and bags of loose material, generally from near-SUiface sections. The33 samplesfrom theTACI'S drill holes are widely spaced, are generally ofsmall volume, and represent sediment shallower than 25.5 ft (7.8 m) (Pleistocene and Holocene) beneath the ocean floor. Lithologic descriptions and phosphorite pelletcontentofTACTS cores B, D, and H were given by Manheim and others (1989).
The 32 onshore borehole samples were provided
by the Georgia Geologic Survey. Boreholes on Tybee and Skidaway Islands were drilled to 167 and 191 feet, respectively. Samples representing approximately every 5-foot
interval were collected from the Tybee Island borehole to a
depth of86.5 feet and from the Skidaway Island borehole to a depth of 71 feeL Complete sample (core) recovery ofa 5 foot section yielded between 11 and 23 kg of sediment dependingon textureand watercontent However,asshown by the bulk weights in Table 7 complete recovery was seldom achieved and in sample recovery was genernlly poor.
Laboratory procedures
Each of the 65 grid samples was split and sieved into three size classes: (1) gravel and very coarse sand(> 16 mesh,>1.18 mm), (2) coarse to very fine sand (from <16 to >325 mesh, <1.18 ->0.045 mm), and(3) silt and clay (<325 mesh, <0.045 mm). The heavy-mineral fraction of the coarse to very fine sand fraction was separated with bromofonn. After the ferromagnetic minerals were removed from heavy-mineral concentrates heavier than 1.9 g by using a hand-held magnet, the heavy-mineral concentrates were further separated into three magnetic subfractions on a Frantz lsodynamic Magnetic Mineral Separator (0.0 0.5, 0.5 - 1.0, and >1.0 A). Each of the four magnetic separates was weighed and studied microscopically by transmitted and reflected light The identification of some minerals was also confirmed by X-ray diffraction. Comparison charts for the visual estimation of percentage composition (Terry and Chillingar, 1955) and point-counting were done to estimate mineral abundances in each magnetic subfraction. The identification of zircon and monazite was aided by using long- and short-wave ultraviolet illumination. Abundances of individual mineral species in each magnetic subfraction were summed and calculated as weight percentages of the total heavy-mineral fraction without compensation for differences in densities of individual mineral species. The lithologic descriptions, results of the mineralogic determinations, and textural and limited mineralogic data compiled by Hathaway (1971), are given in Tables 1, 2, and 3. The mineralogic analyses are incomplete with respect to heavy minerals in the gravel and very coarse sand and thesilt and clay fractions. Phosphorite is probably the only heavy mineral ofimportancein the coarse fraction. Silt and clay contents are very low except in one sample where this fraction is 8 percent; thus any heavy mineral in this size fraction would not substantially alter the ovecall mineralogic makeup of the heavy-mineral assemblages.
For the 18 transect samples, the procedures were different from those used for the grid samples. Only a brief description is provided here as details are given in Grosz and others (1990). An approximately 12.5 kg sample was wet sieved through a 10-mesh U.S. Standard stainless steel sieve to remove the gravel fraction. The entire sand-silt-clay fraction was then processed through a tJu"ee..turn spiral concentrator to preconcentrate the heavy minerals. Heavy minerals were recovered from the preconcentrate by use of acetylene tetrabromide and subsequently were separated into five magnetic subtractions (magnetic at 0.20, 0.40, 0.60,1.80,andnonmagneticat 1.80 A)on a Frantz Magnetic Barrierlaboratory Separatorafterremoval ofthe ferromagnetic particles by l.JSC of a Frantz lsodynamic Mineral
6
Table !.--Location coordinates and lithologic descriptions of the 65 grid surface grab samples from the Georgia shelf. [Data from Hathaway (1971). Lithologic descriptions are modified)
SAMPLE LONGITUDE LATITUDE LITHOLOGIC NUMBER (WEST) (NORTH) DESCRIPTION
==~-
:::===---=-================:=====---=.x~----==========
========-- -
1483 -80.22500 32 . 33334 GRAY, CLEAN, \JELL-SORTED FINE SAND WITH SHELL FRAGMENTS.
1484 -80.26834 32 . 16000 GRAY-GREEN, FINE TO MEDIUM SAND, WELL SORTED, ABUNDANT DARK MINERALS, SHELL HASH.
1485 -80.24667 31.98002 BROWNISH-GRAY-GREEN, FINE TO MEDIUM VERY SHELLY SAND, ABUNDANT DARK MINERALS.
1487 -80.46001 31.85002 LIGHT-GRAY, POORLY SORTED, MEDIUM TO COARSE CLEAN SAND, LUMPS OF GRAY CLAY.
1489 -80.75002 31.68335 LIGHT GRAY, FINE TO MEDIUM, UNIFORM SAND.
1490 -80.76668 31.49001 GRAY, CLEAN, MEDIUM SAND WITH MANY SHELL FRAGMENTS.
1491 -80.98835 31.51168 LIGHT-GRAY, WELL-SORTED, F1NE SAND WITH MANY SHELL FRAGMENTS.
1492 -81.01667 31.34001 LIGHT-BROWN, MEDIUM SAND, WITH APPRECIABLE MATERIAL IN FINE AND VERY COARSE SIZES.
1494 -80.99669 30.99169 LIGHT-BROWN, MEDIUM TO COARSE. CLEAN SAND. WORM TUBES, MANY SHELL FRAGMENTS.
1495 -81.22500 30.99169 LIGHT-GRAY, MEDIUM TO COARSE, CLEAN SAND WITH SHELLS.
1496 -81.22334 30.83502 BROWN, VERY FINE, UNIFORM SAND.
1497 -81.00000 30.83335 LIGHT-GRAY, MEDIUM TO COARSE, QUARTZ SAND WITH FEW SHELLS.
1498 -81.00333 30.67001 GRAY, FINE SAND, CLEAN AND WELL SORTED, WITH SHELL FRAGMENTS.
1499 -81.22834 30.66001 BROWN, VERY FINE SAND, WITH MUD BALLS OF VERY SOFT BLACK CLAY AND SILT.
1500 -81.25501 30.49334 LIGHT-GREENISH-GRAY, MEDIUM TO COARSE SAND WITH BLACK SILTY LUMPS, SHELL FRAGMENTS.
1501 -81.00000 30.48334 GRAY-GREEN, FINE SAND WITH SHELL FRAGMENTS.
~
1660 -79.96669 31.16834 BROWN, WELL-SORTED, CLEAN, COARSE, QUARTZ SAND.
1661 -80.00667 31.32667 LIGHT-GRAY, CLEAN, MEDIUM TO COARSE, QUARTZ SAND.
1663 -79.99502 31.67835 LIGHT-BROWNISH-GRAY, MEDIUM TO COARSE SAND.
1664 -80.24334 31.67335 LIGHT-BROWN TO YELLLOW-GRAY, MEDIUM TO COARSE SAND, SOME SHELL FRAGMENTS.
1665 -80.51001 31.68501 MEDIUM QUARTZ SAND.
1666 -80.34167 31.85002 MEDIUM QUARTZ SAND.
1667 -80.19167 31.84002 LIGHT-GRAY, MEDIUM SAND WITH SHELL FRAGMENTS.
1668 -80.01833 31.82335 LIGHT-BROWNISH-GRAY COARSE SAND WITH SHELLS.
1669 -79.98002 32.00833 GREEN-GRAY, VERY COARSE CLEAN SAND, SHELL FRAGMENTS, GLAUCONITE, HEAVY MINERALS.
1675 -80.32501 32.22500 GRAY, WELL-SORTED, FINE SAND.
1676 -80.47334 32.12667 GRAY, WELL SORTED, FINE SAND.
1677 -80.62001 31.94835 GRAY-GREEN, MEDIUM TO FINE SAND.
1678 -80.77168 31.34001 GRAY, COARSE SAND, SOME SHELLS.
1679 -80.76002 31.16000 LIGHT-GRAY, FINE SAND.
1680 -80.74668 31.00000 FINE, WELL-SORTED SAND, PELECYPODS.
1681 -80.75002 30.83002 FINE TO COARSE SAND, 20 X SHELL FRAGMENTS .
1682 -80.78668 30.66668 GRAY, FINE TO COARSE SAND, SOME SHELLS, ABUNDANT HEAVY MINERALS.
1683 -80.73335 30.49668 GRAY, FINE TO MEDIUM SAND, SHELLS, FORAMS.
1698 -80.47834 30.49168 GRAY-GREEN SAND WITH 20 X SHELL FRAGMENTS.
1699 -80.49668 30.66668 FINE SAND WITH BLACK SPECKS.
1700 -80.49668 30.83335 MEDIUM TO COARSE CLEAN SAND.
1701 -80.49168 31.00333 BROWN TO GRAY, FINE TO COARSE, QUARTZ SAND.
1702 -80.53334 31.18667 BROWN, MEDIUM TO VERY COARSE SAND.
1704 -80.50001 31.51334 GRAY-GREEN, MEDIUM TO COARSE SAND.
1705 -80.27501 31.50168 GREEN, FINE TO COARSE SAND.
1706 -80.23167 31.33334 LIGHT-GRAY, WELL SORTED, MEDIUM TO COARSE CLEAN SAND.
1707 -80.21000 31.15667 LIGHT-GRAY-BROWN, FINE TO COARSE, CLEAN SAND.
1708 -80.25001 31.00000 BROWN, FINE SAND.
:::=::=:::.=
Table 1.--Continued.
SAMPLE LONGITUDE LATITUDE LITHOLOGIC NUMBER (WEST) (NORTH) DESCRIPTION
:-::-.-:u:z:====,= = = = = == = = --
--
---=
==~=--====--==~===--=~===== =======---=--:=~=-
r====-==
1709 -80.25501 30.83335 COARSE SAND WITH PHOSPHATE ROCK AND SHELLS.
1710 -80.22500 30.67501 TAN SHELL HASH, 60 X, WITH FINE, BROWN SAND, 40 X.
1711 -80.22834 30.49668 TAN SAND, WITH SHELL HASH.
1751 -79.77002 31.49834 GREEN, MEDIUM, CLEAN SAND, ABUNDANT HEAVY MINERALS.
1754 -79.75335 31.65668 LIGHT-GRAY MEDIUM TO COARSE, CLEAN QUARTZ SAND.
1755 -79.75668 31.83168 LIGHT-BROWNISH-GRAY, COARSE TO VERY COARSE, WELL SORTED, CLEAN QUARTZ SAND.
1758 -79.75335 31.99502 BROWNISH-GREEN, MEDIUM SAND WITH SOME SHELLS.
2280 -81.28167 31.09667 MEDIUM OLIVE GRAY, VERY WELL SORTED, VERY FINE CLEAN SAND, 1 X SHELL FRAGMENTS.
2281 -81.31501 30.93002 VERY WELL SORTED, VERY FINE SAND, FEW (<1%) SHELL FRAGMENTS, UPPER 3-4 CM MEDIUM OLIVE GRAY, MEDIUM BLACK-GRAY BELOW.
2282 -81.36834 30.81168 MED IUM-OLIVE-GRAY, WELL SORTED SILT OR VERY FINE SAND, FEW SHELL FRAGMENTS .
2283 -81.40501 30.64335 WELL-SORTED, VERY FINE SAND, FEW SMALL SHELL FRAGMENTS, SOME LARGE, UPPER 4 CM MEDIUM OLIVE GRAY, GRAY BELOW.
2288 -81.18667 31.24167 LIGHT-OLIVE-GRAY. MEDIUM SORTED, MEDIUM SAND.
2289 -81.19667 31.32501 LIGHT-OLIVE-GRAY, WELL-SORTED, VERY FINE SILTY SAND, SOME SHELL FRAGMENTS.
2290 -81.06500 31.52001 LIGHT-OLIVE-GRAY, MODERATELY WELL SORTED, FINE SAND, FEW SHELL FRAGMENTS.
2291 -81.02167 31.67835 LIGHT-GRAY, WELL-SORTED, VERY FINE SAND.
2292 -80.89002 31.76502 MEDIUM SAND, MEDIUM-GOOD SORTING.
2293 -80.87335 31.86835 DARK GRAY, CLAYEY SANDY SILT.
2294 -80.75168 31.97169 DARK-GREENISH-GRAY, POORLY SORTED, COARSE SAND, MANY SHELLS, APPROACHING SHELL HASH.
00
2295 -80.62501 32.08500 WELL-SORTED, FINE SAND.
2296 -80.45001 32.26167 LIGHT-OLIVE-GRAY, MEDIUM TO WELL SORTED, FINE SAND.
2297 -80.22167 32.46668 LIGHT-GREENISH-GRAY, WELL-SORTED, FINE, QUARTZ SAND.
Table 2.--Water depth, sampling equipment, texture, carbonate content, and gamma radiation
activity data for the 65 surface grab samples from the Georgia shelf. [Sampling equipment:
1, campbell grab with camera; 2, Campbell grab without camera; s, Van Veen grab. NA, not
applicable, not separated; NO, not determined; HM, heavy minerals; CPM/g, counts per minute
per gram. Gravel, sand, silt, clay, CPM/g, and carbonate data from Hathaway (1971)]
WATER SMPL GRAVEL SAND
SILT
CLAY BULK WT X WT X WT X NUMBER MEAN WT X HM IN
WT WT WT WT GAMMA WT X
SAMPLE DEPTH EQPT >2.00 2.00 TO 0.0625 TO <0.0039 WT >16 <16->325 <325 OF SIZE WHOLE CARBONATE- X X X X ACTIVITY CARBONATE
NUMBER (m) TYPE mm (X) 0.0625 mm 0.0039 mm mm (g) MESH MESH MESH SIZE (mm) SAMPLE FREE F. MAG. 0-.SA .5-1A >1.0A (CPM/g) OF
(X)
(X)
(X)
~===========--=:====-==::= ===---====-====-==z:~'
MODES
SAMPLE
:.=z=::a===== -==z:r==~m
=-==-
SAND
=============-s~
1483 13 2 0.0
100.0
0.0 0.0 252.6 4.8 95.2 0.0 1 0.19 2.13
2.37 11.98 6.65 49.43 31.94 1.60 10.24
1484 15 2 0.0
100.0
0.0 0.0 272.2 7.3 92.7 0.0 1 0.27 1.90
2.86 18.43 13.14 27.45 40.98
ND 33.48
1485 21 2 0.0
100.0
0.0 0.0 238.6 3.5 96.5 0.0 1 0.26 0.58
0.71 NA NA NA NA
0.80 18.11
1487 18 2 0.0
100.0
0.0 0.0 254.8 8.1 91.9 0.0 1 0.35 1.13
1.36 2.81 13.33 33.33 50.53
NO 17.20
1489 17 2 0.0
100.0
0.0 0.0 257.3 4.8 95.2 0.0 1 0.27 1.71
1.81 5.09 19.68 44.44 30.79
ND 5.69
1490 20 2 0.0
100.0
0.0 0.0 231.6 2.8 97.2 0.0 3 0.30 1.14
1.26 0.38 8.78 24.81 66.03 0.95 9.48
1491 13 2 0.0
100.0
0.0 0.0 242.7 13.3 86.7 0.0 1 0.32 1.25
1.39 9.97 15.28 34.55 40.20
NO 10.22
1492 15 2 0.0
100.0
0.0 0.0 221.1 16.0 84.0 0.0 1 0.49 0.38
0.40 NA NA NA NA
0.34 5.01
1494 19 2 0.0
100.0
0.0 0.0 292.1 17.0 83.0 0.0 1 0.37 0.88
0.90 18.75 26.56 21.48 33.20 1.65 2.39
1495 16 2 0.0
100.0
0.0 0.0 249.2 6.6 93.3 0.1 1 0.45 0.17
0.19 NA NA NA NA
ND 10.20
1496 15 2 0.0
100.0
0.0 0.0 276.4 0.2 99.8 0.0 1 0.14 2.42
2.51 5.74 24.02 40.79 29.46 2.06 3.42
1497 18 2 0.0
100.0
0.0 0.0 251.1 3.3 96.7 0.0 1 0.27 0.71
0.75 0.58 58.48 11.70 29.24
NO 5.34
1498 20 2 0.0
100.0
0.0 0.0 238.3 1.0 99.0 0.0 1 0.19 0.79
0.85 0.58 64.33 11.70 23.39 0.77 6.93
1499 19 2 0.0
100.0
0.0 0.0 187.1 1.1 98.9 0.0 1 0.13 1.85
1.97 2.33 26.16 46.51 25.00
NO 6.25
1500 17 2 0.0
100.0
0.0 0.0 207.0 5.7 94.3 0.0 1 0.34 0.48
0.54 5.43 41.30 10.33 42.93 0.48 11.41
"'
1501 26 2 0.0 1660 46 2 1.0
99.0 99.0
1.0 0.0 253.4 1.9 98.0 0.1 1 0.22 1.52 0.0 0.0 255.3 8.5 91.5 0.0 1 0.44 1.09
1.86 3.98 14.59 24.93 56.50 1.19 8.24 26.97 48.69 16.10
NO 18.09 0.82 8.31
1661 41 2 0.0
100.0
0.0 0.0 241.0 1.0 99.0 0.0 1 0.38 0.33
0.35 NA NA NA NA
0.22 6.12
1663 36 5 0.0
100.0
0.0 0.0 244.7 5.9 94.1 0.0 1 0.36 0.48
0.51 0.94 84.91 4.72 9.43 0.33 5.63
1664 28 5 0.0
100.0
0.0 0.0 301.0 6.1 93.9 0.0 1 0.43 0.70
0.73 3.85 24.04 60.58 11.54 0.37 3.94
1665 20 5 0.0
100.0
0.0 0.0 208.2 4.5 95. 5 0.0 1 0.26 1.23
1.35 4.82 20.88 46.59 27.71
NO 8.92
1666 20 5 0.0
100.0
0.0 0.0 242.6 3.9 96.1 0.0 1 0.41 0.34
0.36 ~A NA NA NA
0.80 5.11
1667 22 5 0.0
100.0
0.0 0.0 274.2 15.8 84.2 0.0 1 0.40 0.92
1.04 10.53 12.15 24.29 53.04 1.58 11.19
1668 30 5 1.5
98.5
0.0 0.0 211.1 25.4 74.6 0.0 1 0.55 0.77
0.82 NA NA NA NA
0.70 6.42
1669 27 5 0.0
100.0
0.0 0.0 242.9 9.7 90.3 0.0 1 0.43 0.54
0.62 NA NA NA NA
0.35 12.44
1675 14 1 0.0
100.0
0.0 0.0 243.1 0.7 99.3 0.0 1 0.19 2.02
2.15 5.02 24.69 47.28 23.01
NO 6.00
1676 14 1 0.0
100.0
0.0 0.0 220.4 0.8 99.2 0.0 1 0.19 1.43
1.53 8.52 19.24 42.90 29.34 0.91 6.68
1677 17 1 0.0
100.0
0.0 0.0 249.1 3.6 96.4 0.0 1 0.31 1.28
1.44 3.72 18.58 47.68 30.03
ND 11.13
1678 22 1 0.0
100.0
0.0 0.0 252.1 12.5 87.5 0.0 1 0.49 0.74
0.80 0.53 32.62 13.37 53.48
ND 7.49
1679 19 1 0.0
100.0
0.0 0.0 255.0 5.9 94.1 0.0 1 0.36 0.58
0.61 2.03 50.00 11.49 36.48 0.41 5.04
1680 24 1 0.0
100.0
0.0 0.0 230.5 2.7 97.3 0.0 1 0.20 1.36
1.51 8.21 17.20 28.66 45.93 1.06 9.71
1681 24 1 0.0
100.0
0.0 0.0 218.8 12.6 87.4 0.0 1 0.38 0.84
0.96 1.65 40.98 13.11 44.26 0.68 12.67
1682 26 1 0.0
100.0
0.0 0.0 213.4 8.8 91.2 0.0 1 0.36 1.02
1.16 0.53 11.23 56.15 32.09 0.65 11.81
1683 32 1 0.0
100.0
0.0 0.0 253.8 3.2 96.8 0.0 1 0.21 0.57
0.69 2.08 57.64 11.81 28.47 0.74 17.82
1698 35 1 0.0
100.0
0.0 0.0 262.3 3.5 96.5 0.0 1 0.37 0.26
0.33 1.45 52.17 17.39 28.99 0.32 21.43
1699 38 1 0.0
100.0
0.0 0.0 217.8 11.8 88.2 0.0 1 0.40 0.78
1.01 1.78 47.93 14. 79 35.50 0.50 22.88
1700 33 1 0.0
100.0
0.0 0.0 232.3 4.8 95.2 0.0 1 0.37 0.87
0.98 9.64 13.20 35.53 41.62 0.43 11.55
1701 31 1 0.0
100.0
0.0 0.0 285.2 10.9 89.1 0.0 1 0.40 0.88
0.97 9.54 11.20 33.61 45.64 0.58 9.69
1702 31 1 0.0
100.0
0.0 0.0 249.1 10.6 89.4 0.0 1 0.37 0.33
0.36 3.66 73.17 6.10 17.07 0.30 7.82
1704 24 1 0.0
100.0
0.0 0.0 260.5 7.6 92.4 0.0 1 0.41 0.74
0.79 1.56 69.43 10.88 18.13 0.41 6.52
1705 32 1 0.0
100.0
0.0 0.0 244.3 6.4 93.6 0.0 1 0.40 0.34
0.35 3.62 75.90 8.43 12.05 0.34 3.56
1706 36 1 0.0
100.0
0.0 0.0 213.8 5.6 94.4 0.0 1 0.35 0.94
1.01 13.57 20.60 45.23 20.60 0.40 7.10
1707 36 2 0.0
100.0
0.0 0.0 192.5 13.1 86.9 0.0 1 0.48 0.31
0.32 8.48 66.10 8.47 16.95 0.35 4.34
1708 36 2 0.0
100.0
0.0 0.0 193.0 2.6 97.4 0.0 1 0.44 0.42
0.44 3.66 74.39 7.32 14.63 0.30 5.56
Table 2.--Continued.
WATER SMPL GRAVEL SAND
SILT
CLAY BULK WTX WTX WT X NUMBER MEAN WT X HM IN
WT WT WT WT GAMMA WTX
SAMPLE DEPTH EQPT >2.00 2.00 TO 0.0625 TO <0.0039 WT >16 <16->325 <325 OF SIZE WHOLE CARBONATE- X X X X ACTIVITY CARBONATE
NUMBER (m) TYPE 11111 (X) 0. 0625 11111 0.0039 11111 11111 (g) MESH MESH MESH SIZE (11111) SAMPLE FREE F. MAG. 0-.SA .5-1A >1.0A (CPM/g) OF
(X)
(X)
(X)
MODES
SAMPLE
SAND
======c=::::====--======::a:a:==--==--=-==::::t=:=:::========::::====-- -===-=~===~=
- rm
= :z:==::~aa:ata:
1709 37 2 0.0
100.0
0.0 0.0 186.9 11.7 88.3 0.0 1 0.26 0.44
0.54 3.66 78.05 4.88 13.41 0.35 18.97
1710 42 2 0.0
100.0
0.0 0.0 171.6 9.3 90.7 0.0 1 0.30 0.23
0.37 2.56 48.72 5.13 43.59 0.24 38.51
1711 43 2 0.0
100.0
0.0 0.0 245.6 11.1 88.9 0.0 3 0.54 0.31
0.53 0.69 7.48 36.73 55.10 0.32 42.04
1751 64 2 0.0
99.0
1.0 0.0 223.7 2.5 97.4 0.1 1 0.31 0.29
0.32 NA NA NA NA
0.21 9.10
1754 45 2 0.0
100.0
0.0 0.0 203.7 0.6 99.4 0.0 1 0.39 0.28
0.30 NA NA NA NA
0.28 5.71
1755 40 2 0.0
100.0
0.0 0.0 215.6 13.3 86.7 0.0 1 0.56 0.24
0.25 NA NA NA NA
0.21 5.13
1758 32 2 0.0
100.0
0.0 0.0 269.2 4.8 95.2 0.0 1 0.40 0.49
0.53 NA NA NA NA
0.36 7.14
2280 6 2 0.0
95.0
5.0 0.0 186.9 0.6 99.2 0.2 2 0.12 4.17
4.27 5.00 25.90 48.72 20.38 2.00 2.29
2281 7 2 0.0
93.0
7.0 0.0 182.7 2.0 97.6 0.4 2 0.14 4.28
4.41 7.16 28.90 37.98 25.96 4.83 3.02
2282 8 2 0.0
95.0
5.0 0.0 149.4 0.5 99.1 0.4 2 0.11 2.26
2.32 3.79 24.63 53.71 17.87 1.73 2.67
2283 8 1 8.0
90.0
2.0 0.0 323.0 9.0 90.8 0.2 2 0.15 2.03
2.09 1.23 23.66 46.56 28.55 0.51 2.81
2288 10 1 0.0
100.0
0.0 0.0 179.2 1.6 98.4 0.0 1 0.28 0.45
0.46 1.61 80.65 8.06 9.68
ND 2.30
2289 7 1 0.0
97.0
3.0 0.0 218.4 1.0 98.8 0.2 2 0.12 4.26
4.38 26.20 10.20 43.50 20.10 2.39 2.75
2290 9 1 0.0
100.0
0.0 0.0 196.6 4.6 95.2 0.2 2 0.22 1.17
1.26 20.09 9.82 40.63 29.46
ND 6.83
s
2291 8 1 0.0 2292 13 2 0.0
92.0 100.0
8.0 0.0 198.0 0.4 99.3 0.3 1 0.10 3.84 0.0 0.0 225.0 0.8 99.2 0.0 1 0.24 0.67
4.09 27.89 8.82 48.55 14.74 1.80 6.08 0.70 0.74 80.88 3.68 14.71 0.56 3.98
2293 9 2 0.0
94.0
6.0 0.0 139.6 0.0 92.0 8.0 2 0.15 3.15
3.33 27.10 6.50 46.34 20.05 2.10 5.27
2294 10 2 26.0
74.0
0.0 0.0 192.2 37.6 62.3 0.1 4 0.59 0.55
0.67 NA NA NA NA
0.47 18.34
2295 8 2 0.0
100.0
0.0 0.0 147.2 0.2 99.8 0.0 1 0.14 2.62
2.68 21.04 15.84 41.30 21.82 1.19 2.17
2296 11 2 5.0
90.0
5.0 0.0 172.6 4.7 94.9 0.4 3 0.18 2.00
2.21 33.14 6.69 43.02 17.15 1.08 9.59
2297 11 2 0.0
100.0
0.0 0.0 202.1 1.4 98.6 0.0 1 0.17 3.95
4.13 18.68 18.56 37.11 25.65 3.20 4.35
Table 3.--Feldspar and heavy-mineral data for the 65 surface grab samples from the Georgia
shelf. [SG, specific gravity; T; trace, less than 0.1 %]
POTASSIUM PLAGIOCLASE TOTAL f ILMENITE MAGNETITE GARNET STAUROLITE EPIDOTE PYROBOLEf ALUMINO- iOURMALINE LEUCOXENE If
SAMPLE FELDSPAR' FELDSPAR' FELDSPAR
SILICATES
NUMBER AS A PERCENTAGE OF THE NON-
-= - - - :;::c:#C:-
CARBONATE -
0.125-.250 mm FRACTION ----------------EXPRESSED
-----=-=----==-- ... ..-.=n -
AS
W-E-IG-HT
PERC-ErNmTAmGE-S=O=F=T=HE=-SG=
>2.85 FRACTION----------------
- -.==::::::r-r==::z:== -======
1483
5.0
8.0
13.0 27.0
1.3 0.9
2.8 20 . 1
9.9
10.5
6.9
6.3
1484
4.0
4.0
8.0 25.2
1.7 1.2
3.2 15.6
4.1
11.1
13.6
2.9
1485
4.0
2.0
6.0 44.0
1.0
T
3.0 15.0
5.0
7.0
15.0
5.0
1487
5.0
5.0
10.0 15.8
0.2 1.1
3.4 10.4
7.0
4.9
14.9
6.0
1489
6.0
4.0
10.0 20.0
0.3 0.7
4.3 19.4
5.9
11.3
7.7
2.6
1490
5.0
5.0
10.0
6.8
0.1 0.2
1.7
9.5
5.0
9.3
12.8
13.7
1491
3.0
3.0
6.0 19.9
1.2 1.1
3.8 14.1
8.5
9.5
5.7
4.7
1492
3.0
3.0
6.0 54.0
T 3.0
5.0 10.0
7.0
2.0
15.0
2.0
1494
6.0
2.0
8.0 36.7
0.8 2.4
4.4 10.4
3.2
9.6
5.4
3.0
1495
6.0
4.0
10.0 45.0
T 1.0
3.0 20.0
10.0
5.0
10.0
3.0
1496
8.0
2.0
10.0 16.0
1.6 1.3
4.7 20.5
13.0
12.7
3.7
3.8
1497
3.0
5.0
8.0 32.1
0.6 1.8
3.3 10.0
5.8
9.6
5.8
3.0
1498
3.0
3.0
6.0 20.0
0.7 1.3
2.3 18.0
16.3
8.7
4.7
1.7
1499
7.0
4.0
11.0 14.2
0.7 0.8
6.5 22.9
17.6
11.9
6.7
3.5
1500
3.0
3.0
6.0 17.9
0.5 2.2
3.1 20.0
2.9
7.2
7.5
4.7
1501
2.0
3.0
5.0 17.8
0.6 0.8
2.9
7.4
3.0
7.6
5.7
6.4
1660
5.0
5.0
10.0 26.8
1.1 6.0
12.2 16.0
3.2
4.2
8.4
3.9
..........
1661
4.0
4.0
1663
4.0
2.0
8.0 25.0 6.0 26.4
T 2.0 0.9 2.5
5.0 25.0
10.0
6.3 31.5
8.5
7.0
15.0
2.0
4.6
5.1
1.7
1664
4.0
5.0
9.0 22.3
0.6 0.4
6.1 23.5
18.2
6.4
8.3
4.1
1665
4.0
5.0
9.0 11.0
0.7 1.1
5.1 24.1
17.1
10.6
6.8
3.2
1666
4.0
4.0
8.0 39.0
1.0
T
3.0 20.0
5.0
7.0
10.0
10.0
1667
2.0
2.0
4.0 12.2
0.7 1.7
5.0 13.6
7.9
6. 0
4.5
10.9
1668
5.0
2.0
7.0 42.0
T 5.0
7.0 15.0
3.0
5.0
10.0
7.0
1669
4.0
3.0
7.0 34.0
T 5.0
7.0 15.0
7.0
10.0
7.0
10.0
1675
2.0
4.0
6.0 11.9
0.5 0.3
5.2 21.7
24.0
8.5
3.9
7.0
1676
4.0
2.0
6.0 14.1
0.6 0.4
4.0 20.5
18.4
10.1
4.5
5.9
1677
3.0
2.0
5.0
9.8
T 0.6
4.4 17.3
21.8
9.3
8.3
8.9
1678
3.0
1.0
4.0
6.1
0.3 1.6
2.3
6.7
1.0
2.9
3.6
9.0
1679
3.0
2.0
5.0
5.8
T 2.5
3.5 14.0
5.0
6.3
3.7
3.1
1680
5.0
2.0
7.0 10.5
0.4 0.6
4.1
9.2
13.8
6.8
7.9
9.9
1681
3.0
0.5
3.5
8.8
0.9 2.0
4.1
9.5
2.9
5.8
2.9
2.5
1682
2.0
0.5
2.5
9.6
T 0.6
4.7 12.4
7.3
3.9
6.3
6.0
1683
4.0
4.0
8.0 12.3
1.3 4.0
5.8 13.3
4.1
10.0
7.2
1.7
1698
5.0
3.0
8.0
5.9
0.6 2.6
8.0 12.4
2.8
7.2
2.9
7.8
1699
4.0
4.0
8.0
4.8
T 4.8
7.5 13.5
3.4
5.3
2.8
6.1
1700
3.0
3.0
6.0 12.3
0.1 0.9
5.0 12.6
11.0
2.7
4.8
12.9
1701
3.0
5.0
8.0 14.0
0.2 1.1
6.3 13.7
4.6
1.4
7.1
9.8
1702
3.0
1.0
4.0
7.9
0.9 7.5
5.2 18.4
11.1
13.3
7.7
2.0
1704
3.0
5.0
8. 0 11.6
0.7 2.1
7.2 17.4
5.1
7.6
4.9
1.3
1705
5.0
3.0
8.0 10.6
0.9 1.6
11.5 16.3
11.8
10.2
6.3
1.6
1706
3.0
4.0
7.0 21.9
0.4 1.3
5.1 22.2
9.6
6.8
7.1
4.0
1707
3.0
1.0
4.0 17.0
1.6 3.5
7.3 21.8
6.8
9.0
4.2
1.7
1708
4.0
3.0
7.0 13.9
0.9 3.8
7.7 19.0
11.2
10.3
6.0
1.5
Table 3.--continued.
SAMPLE
POTASSI!!'1 PLAGIOCLASE FELDSPAR FELDSPAR'
TOTAL ILMENITE MAGNETITE GARNET STAUROLITE FELDSPAR#
EPIDOTE
PYROBOLES2 ASILLUIMCAINTOE-S1TOURMALINE LEUCOXENE~
NUMBER AS A PERCENTAGE OF THE NON-
CARBONATE 0.125-.250 mm FRACTION ----------------EXPRESSED AS WEIGHT PERCENTAGES OF THE 56 >2.85 FRACTION----------------
~========::mrmr .m::z=-~=-==
ua== rm-========:s-=
~-~-=-~u--===--=z
1709
3.0
1.0
4.0 18.5
1.7 5.5
8.0 22.7
7.9
10.4
4.3
1.7
1710
2.0
2.0
4.0
5.3
0.1 1.5
5.0 21.0
4.9
29.2
3.5
4.1
1711
4.0
4.0
8.0
1.7
T 0.5
2.2
3.9
1.6
33.5
2.2
5.7
1751
4.0
4.0
8.0 34.0
T 2.0
3.0 15.0
7.0
5.0
15.0
15.0
1754
5.0
5.0
10.0 28.0
T 3.0
5.0 25.0
5.0
7.0
20.0
5.0
1755
4.0
3.0
7.0 33.0
T 3.0
5.0 30.0
3.0
7.0
15.0
3.0
1758
6.0
5.0
11.0 31.0
T 3.0
7.0 25.0
5.0
10.0
10.0
5.0
2280
3.0
2.0
5.0 12.2
1.1 0.9
5.3 27.6
21.3
11.7
5.5
4.7
2281
4.0
3.0
7.0 12.1
0.3 0.9
4.3 20.2
25.5
15.0
5.3
3.4
2282
4.0
2.0
6.0
5.6
0.9
T
2.8 24.7
34.1
14.2
5.3
3.4
2283
2.0
1.0
3.0 15.0
T 4.5
1.0 35.0
12.0
21.0
2.5
0.5
2288
6.0
3.0
9.0 13.9
T 0.8
2.9 20.3
34.1
10.7
2.5
0.2
2289
9.0
5.0
14.0
9.1
0.5 0.6
3.5 25.3
23.5
16.5
3.6
6.6
~
2290
5.0
4.0
9.0 15.9
0.5 0.9
2.8 22.6
15.4
10.2
4.7
4.5
2291
6.0
5.0
11.0 15.7
2.0 0.3
2.6 23.0
20.4
18.5
2.4
5.9
2292
7.0
5.0
12.0 17.8
0.8 2.4
4.1 24.3
20.5
8.1
4.2
1.8
2293
NO
ND
NO 22.2
0.4 0.4
2.5 10.9
23.5
16.8
3.0
13.3
2294
4.0
5.0
9.0 27.0
1.0 3.0
5.0 25.0
5.0
7.0
20.0
3.0
2295
6.0
5.0
11.0 19.9
0.6 0.6
4.4 15.4
19.7
11.7
4.7
6.6
2296
10.0
5.0
15.0 15.9
1.0 0.4
5.0 19.7
21.1
10.1
4.3
8.0
2297
8.0
5.0
13.0 13.1
1.3 1.1
6.0 15.4
23.8
14.8
4.4
7.2
Table 3.--continued.
RUTILE ZIRCON MONAZITE PHOSPHORITE OTHERS5"
WTX
SAMPLE
WT X WT X EHM/T
WT X ~ ZT~0 ILMENITE/
NUMBER ------EXPRESSED AS WEIGHT PERCENTAGES------ EHM/Cii EHM/T 1- CARBONATE- LABILE IND LEUCOXENE
OF THE SG >2.85 FRACTION = = = = = = = = - -===c:=::::a:::c:::==;= =
-
-
FREES -===:::==----==- = - -,- -
1483
T 0.3
0.5
11.2 2.3 44.6 0.95
1.06 32.2 13.9
4.3
1484
T 0.4
0.3
20.4 0.3 39.9 0.76
1.14 22.6 28.3
8.7
1485
T
T
T
2.0 3.0 56.0 0.32
0.39 21.0 33.3
8.8
1487
T
T 0.7
35.6
T 27.4 0.31
0.37 18.7 35.1
2.6
1489
T 0.3
1.3
26.2
T 35.5 0.61
0.65 26.3 15.7
7.7
1490
T
T 0.7
40.2
T 30.5 0.35
0.39 14.8 32.7
0.5
1491 1.2 1.2
1.0
28.1
T 37.5 0.47
0.52 24.9 17.6
4.2
1492
T
T
T
T 2.0 58.0 0.22
0.23 20.0 35.7
27.0
1494 1.7 10.0
1.7
10.7
T 62.7 0.55
0.56 16.8 35.0
12.2
1495
T
T
T
T 3.0 53.0 0.09
0.10 31.0 20.4
15.0
1496 2.1 0.9
3.5
16.2
T 39.0 0.94
0.97 36.4 10.7
4.2
1497 0.9 0.6
T
26.5
T 46.2 0.33
0.35 18.2 19.3
10.7
1498 0.7 0.2
T
24.8 0.6 31.3 0.25
0.27 36.3 10.7
11.8
1499 0.8 0.5
1.4
10.7 1.8 32.3 0.60
0.64 42.0 11.6
4.1
1500 0.9
T
T
32.7 0.4 30.7 0.15
0.17 25.6 19.2
3.8
1501
T 2.8
0.7
42.5 1.8 35.3 0.54
0.66 11.8 27.5
2.8
,_
1660 0.3 0.5
1.5
1661
T
T
T
15.9
T 37.2 0.41
0.45 26.3 17.6
6.9
5.0 4.0 34.0 0.11
0.12 37.0 23.4
12.5
w
1663 0.7 0.5
T
11.3
T 33.9 0.16
0.17 43.4 10.6
15.5
1664 1.2 0.3
1.2
7.4
T 35.5 0.25
0.26 42.7 14.9
5.4
1665 0.3 0.8
1.4
17.7 0.1 27.3 0.34
0.37 43.0 11.7
3.4
1666
T
T
T
3.0 2.0 56.0 0.19
0.20 26.0 22.2
3.9
1667
T 1.1
0.7
35.7
T 30.9 0.28
0.32 23.9 13.8
1.1
1668
T
T
T
3.0 3.0 54.0 0.42
0.45 23.0 22.2
6.0
1669
T
T
T
2.0 3.0 54.0 0.29
0.33 27.0 13.7
3.4
1675 0.2 1.2
0.9
14.5 0.2 29.7 0.60
0.64 46.5 8.0
1.7
1676 0.6 1.3
2.1
16.8 0.7 34.1 0.49
0.52 39.9 10.3
2.4
1677
T 0.3
1.4
17.6 0.3 29.7 0.38
0.43 39.7 13.6
1.1
1678
T
T
T
66.5
T 18.0 0.13
0.14
9.6 19.9
0.7
1679
T
T 1.5
54.5 0.1 16.7 0.10
0.11 21.5 10.1
1.9
1680 0.9 0.5
1.4
32.9 1.1 30.0 0.41
0.46 24.0 20.6
1.1
1681
T 3.1
2.0
54.2 1.3 22.2 0.19
0.22 15.3 18.6
3.5
1682 0.6
T 1.7
46.8 0.1 21.8 0.22
0.25 20.3 18.4
1.6
1683 2.0 2.0
4.0
28.1 4.2 32.0 0.18
0.22 22.7 21.4
7.2
1698
T 0.9
5.2
43.7
T 27.0 0.07
0.09 18.4 9.0
0.8
1699
T 1.8
2.4
46.5 1.1 20.4 0.16
0.21 21.7 11.1
0.8
1700
T
T 2.5
35.2
T 30.4 0.26
0:29 24.6 12.2
1.0
1701
T
T 1.0
40.8
T 26.2 0.23
0.25 19.6 20.2
1.4
1702 1.8 1.2
5.6
17.3 0.1 31.8 0.10
0.11 37.9 14.9
4.0
1704 0.5 0.9
3.8
36.9
T 25.7 0.19
0.20 25.3 12.7
8.9
1705 0.8 0.8
5.3
22.2 0.1 29.3 0.10
0.10 30.6 12.2
6.6
1706 0.6 0.4
2.3
18.1 0.2 36.0 0.34
0.37 33.5 14.6
5.5
1707 1.7 2.5
2.5
20.3 0.1 34.4 0.11
0.11 33.7 14.2
10.0
1708 1.6 3.1
6.3
14.7
T 36.7 0.15
0.16 34.9 15.5
9.3
Table 3.--continued.
RUTILE ZIRCON MONAZITE PHOSPHORITE OTHERS;
WT"
SAMPLE NUMBER
------EXPRESSED
AS
WEIGHT
PERCENTAGES------
WT " EHM/C6
WT ~ EHM/T
EHM/T CARBONATE-
WT " ~ LABILES
INZDTREX0LILEMUCEONXIETNEE/
----- = OF THE SG >2.85 FRACTION
= = - - - =-=====--=-=-::_.-=====~===
FREES ::=o--====-
--
- =
1709 1.0 0.7
6.0
11.2 0.4 38.3 0.17
0.21 37.8 9.0
10.9
1710 3.1 4.4
4.6
13 .3
T 50.7 0.12
0.19 27.5 14.2
1.3
1711 2.8 1.7
2.4
32.6 9.2 47.8 0.15
0.26
6.0 13.2
0.3
1751
T
T
T
3.0 1.0 54.0 0.16
0.1B 24.0 31.9
2.3
1754
T
T
T
T 2.0 40.0 0.11
0.12 33.0 30.8
5.6
1755
T
T
T
T 1.0 43.0 0.10
0.10 36.0 23.8
11.0
1758
T
T
T
1.0 3.0 46.0 0.23
0.25 33.0 16.7
6.2
2280 1.4 0.4
2.4
5. 4 0.1 32.8 1.37
1.40 50.9 9.5
2.6
2281 1.8 0.8
1.1
9. 0 0.3 34.2 1.46
1.50 46.9 10.5
3.6
2282 0.2 0.9
1.6
5.9 0.4 25.9 0.59
0.61 59.7 7.6
1.6
2283 2.0 3.0
T
3.0 0.5 41.5 0.84
0.86 51.5 9.3
30.0
2288 0.3 0.3
T
14.0
T 25.4 0.11
0.11 55.2 4.3
69.5
2289 0.6 0.4
2.2
7.1 0.5 35.4 1.51
1.55 49.9 6.0
1.4
2290 0.8 0.3
1.2
20.2
T 32.9 0.38
0.41 39.4 9.8
3.5
2291 0.3 0.4
1.4
6. 7 0.4 42.2 1.62
1.73 45.7 4.5
2.7
2292 0.3 0.3
T
15.4
T 28.3 0.19
0.20 48.0 7.5
9.9
2293 0.5 0.3
0.4
4.5 1.3 53.5 1.69
1.79 35.2 6.5
1.7
......
~
2294
T
T
T
T 4.0 37.0 0.20
0.24 34.0 30.8
9.0
2295 1.5 1.1
0.8
12.2 0.8 41.6 1.09
1.11 36.3 12.2
3.0
2296 1.2 0.5
2.2
10 . 2 0.4 37.9 0.76
0.84 42.2 9.3
2.0
2297 0.5 1.3
1.1
9.6 0.4 38.0 1.50
1.57 41.6 9.1
1.8
1 Modified from Hathaway (1971).
2 Undifferentiated pyroxenes and amphiboles.
3 Sillimanite, kyanite, and andalusite.
4 Altered ilmenite.
5 May include undifferentiated opaque minerals, non-opaque minerals, glauconite, mica, apatite, spinel, corundum, gahnite(?), quartz.
6 EHM/C = the sum of the economic heavy minerals ilmenite + leucoxene (altered ilmenite) + rutile + zircon
+ monazite + aluminosilicates expressed as a percentage of the heavy-mineral fraction.
7 EHM/T = the sum of the economic heavy minerals expressed as a percentage of the bulk sediment sample.
8 EHM/T on a calcium-carbonate-free basis. 9 sum of the labile minerals magnetite + epidote + pyroboles expressed as a percentage of the heavy-mineral
fraction.
10 ZTR index = sum of the resistant minerals zircon + tourmaline + rutile expressed as a percentage of the non-
opaque heavy minerals.
Separator modified to allow free-fall separation. Magnetic fractions of the transect samples were weighed and studied
in the same manner as the magnetic fractions of the grid
samples were.
Use of heavy liquids, if properly done, results in the recovezy of almost all the heavy minerals in a sample, whereas spiralconcenttationdoesnot Onaverage, about85 percent of the heavy minerals in a sample are recovered by the spiral; minerals with poor hydrodynamic shapes such as pyroboles (undifferentiatedpyroxenesandamphiboles) and micas, and those with lower densities, such as phosphorite, highly altered ilmenite, and glauconite,compose the bulk of the heavy mineral rejected by the spiral. Location, texiUral, and mineralogic data for the transect samples are given in Table4.
The TACTS borehole samples were weighed and wet sieved through a 10-mesh U.S. Standard stainless steel screen (>2.00 mm) toremove the gravel fraction. The sandsilt-clay (<2.00 mm) fraction was repeatedly washed to decanttheclay-sizefraction;asmallamountofsiltmayhave been lost during this procedure. The heavy-mineral fraction of the sand-silt fraction was separated in acetylene tettabromide. The separates were fractionated magnetically and analyzed optically in the same manner as the transect samples. Textural and mineralogic data for the TACTS samples are given in Table 5.
Samples from Skidaway and Tybee Islands were dried, weighed, and wet sieved through a 10-mesh sieve to remove the gravel fraction. The clay fraction was elutriated from the sand-silt fraction, and large samples were processed by the spiraJ/heavy-liquid process described for the transect samples. Smaller samples were processed in heavy liquid after clay removal. Heavy minerals were recovered in acetylene tettabromide and then were magnetically fractionated and optically analyzed in the same manner as the transect samples. Textural and mineralogic data for the Skidaway and Tybee Island borehole samples are given in Table6.
RESULTS
Texture
The surficial sediments on the Georgia shelf are predominantly unimodal and well-sorted sands (data in Hathaway,1971). The sand-size fraction (2.00-0.0625 mm) in the grid samples ranges from 74 to 100 pezcent by weight (henceforth %) and averages about 99%; gravel and silt contents average 0.6% and 0.7%, respectively. The sand fraction is dominantly quartz, which averages about 90% (range from 67%-96%). The mean grain size ofthe surficial
sediments is 0.31 mm (medium sand) in a range from 0.10 to 0.59 mm (vezy fine to coarse sand).
A trend of increasing grain size from inner to outer shelf is shown in Figure 4. A narrow belt of largely fmegrained sediment occurs in a zone (7 to 15 km wide; defmed by the 0.2-mm contOur) extending from near the Savannah River south to the St Marys River, where it broadens about 50 km seaward The zone extends north of the Savannah River also. Lobate seaward extensions of the fine-grained sedimentzoneare also locatedoffshoreofthe Ogeecheeand St Marys Rivers; each has headwaters in the Coastal Plain. This pattern may reflect southward nearshore sediment dispersal. Coarse grained sediment ttains (outlined by the 0.4-mm contour) extend due eastward from the Savannah and Altamaha Rivers and probably outline drowned ancestral river channels that spanned the shelf when sea level was near the shelf edge.
The change in sediment texture at the 11-m isobathisproposedbyPilkey(1963),PilkeyandFrankenberg (1964),andBigham (1973) to be the modem/relict sediment boundary. Henry and Hoyt (1968) proposed the 15-m isobath as this boundary. If the lobes of fme-grained sediment are derived from the Savannah and Altamaha Rivers (Figure 4) then modern sediment is not limited to a narrow nearshore zone as suggested by Pilkey (1963), NeiheiselandWeaver(1967),andBigham(1973). Neither is the boundary at Pilkey and Frankenberg's (1964) 11-m isobath, or Henry and Hoyt's (1968) 15-m isobath. Instead it is outlined by the 1.0% or 1.5% heavy-mineral isopleth of this study (Figure 7); both are irregularly shaped and range from water depths less than about 10m todepthsofabout26
m.
Carbonate content
Although the sediments are dominantly quartz, carbonate content, principally in the fonn of shells, shell fragments, foraminiferal tests, andphosphaterock, averages about 10% of the sand-size fraction. The gravel fraction is composed entirely of carbonate. A general increase in carbonatecontent ofthe sand-size fraction with waterdepth is evident in Figure 5. The high cmbonate content (exceeding 16%) at the 40-m isobath near the St Marys River may represent an area ofhigh shell productivity, but the presence ofphosphaterockin the samplesuggests that carbonate-rich Miocene(?) outcrops may be present at or near the surface in this area.
,Feldspar content
The total feldspar content of the sand fraction of the sediments averages about 8% (ranges from about 3% to
15
Table 4.--Location coordinates, water depth, gravel content, and heavy-mineral data for the transect surface grab samples from the Georgia shelf. [Column heads as in Table 3]
WATER BULK WTX WEIGHT WTX WTX WTX WTX WTX WTX
" SAMPLE LONGITUDE LATITUDE DEPTH WEIGHT GRAVEL
ILMENITE MAGNETITE GARNET STAUROLITE EPIDOTE PYROBOLES
NUMBER (WEST) (NORTH)
(m)
(g) >2.0mm RHM
:====
==--===-rm...m-======:c:=:======--===- -====
_.....,.=m------ -
======
1316 -81.15600 31.18450
5.8 10559
2.9 0.37
34.1
0.7
1.4
4.5 16.8
6.0
1317 -81.15717 31.18050
5.4 12392
3.9 D.51
16.4
0.1
0.6
4.9 17.9
5.7
1318 -81.16117 31.17917
6.8 14011
3.4 0.34
25.9
0.2
1.1
4.2 15.8
12.9
1320 -81.16434 31.17500
12.3 10190
2.6 0.73
33.2
0.0
1.4
4.9 13.3
6.6
1321 -81.17750 31.17284
6.7 12968
3.8 0.61
29.9
1.3
1.0
5.0 13.6
8.9
1322 -81.18767 31.16917
6.5 9561
2.1 0.67
21.5
1.3
1.4
5.5 19.8
10.5
1325 -81.18400 31.15667 1326 -81.17517 31.16300
5.0 11972
1.6 0.59
18.2
2.0
0.6
6.2 10718
2.7 0.70
27.3
0.9
0.9
5.9 4.5
2u0..s9
13.3 6.6
1328 -81.17500 31.15134
5.0 10315
2.8 0.58
25.4
1.7
1.4
5.1
8.9
8.1
1329 -81.15167 31.15384
6.8 13286
4.0 0.19
29.0
0.8
1.7
6.6
7.2
11.0
1330 -80.80018 31.06733
16.7 13044
4.2 0.41
26.1
0.9
3.1
7.7 10.2
7.1
...
1332 -80.86252 31.09734
14.3 13204
3.6 0.29
23.8
1.1
3.5
5.7
8.5
9.5
1335 -80.83785 31.12967
14.3 14793
5.7 0.42
21.0
0.8
3.5
8.4
8.0
8.9
0\
1337 -80.77735 31.12850
16.1 14555
3.8 0.29
23.6
0.7
3.2
11.0 10.8
7.7
1339 -80.76285 31.11567
20.0 13644
1.2 0.18
17.0
1.1
0.3
5.7 20.7
18.5
1341 -81.09334 31.38601
7.6 12064
0.7 0.57
19.4
0.8
0.4
8.6 13.2
5.6
1343 -81.03917 31.51401
5.0 14774
5.9 l.DO
18.4
1.8
1.4
10.7 12.3
6.3
1345 -81.03117 31.61701
5.0 20216
0.9 3.27
21.2
3.2
1.7
4.4 11.1
8.7
WTX
WT X WTX
WTX WTX WTX WTX WTX
WTX ILMENITE/ ZTR
WTX
SAMPLE ALUMINO- TOURMALINE LEUCOXENE RUTILE ZIRCON MONAZITE OTHERS EHM/C EHM/T LEUCOXENE INDEX LABILES
NUMBER SILICATES
-=
-==
===.----~===========~-e:=:c;::=:=========-~~===-_;_-==,===~:=:c=============
1316
25.9
6.4
2.5
0.7
0.3
T
0.9 63.4 0.23
13.5 11.9
24.8
1317
42.0
8.5
2.8
0.3
0.4
T
0.5 61.8 0.32
6.0 11.3
24.3
1318
28.2
6.2
1.0
3.5
0.3
T
0.7 59.0 0.20
25.9 13.9
29.9
1320
31.3
5.1
1.6
1.3
0.3
T
1.0 67.7 0.49
21.0 10.5
21.3
1321
31.9
4.3
2.4
1.2
0.3
T
0.3 65.6 0.40
12.6
8.7
24.8
1322
29.2
7.9
1.4
1.3
T
T
0.3 53.4 0.36
15.0 12.1
33.0
1325
27.0
9.0
1.4
1.5
T 0.0
0.2 48.1 0.28
12.9 13.4
36.8
1326
33.6
7.1
3.8
3.7
T 0.0
0.1 68.5 0.48
7.1 16.0
19.9
1328
28.5
8.7
6.7
4.5
0.3 0.1
0.5 65.6 0.38
3.8 20.7
20.1
1329
24.3
7.2
5.9
5.5
0.3
T
0.5 65.1 0.12
5.0 20.4
20.7
1330
21.6
11.3
7.5
3.9
0.3 0.4
0.1 59.7 0.24
3.5 23.7
21.2
1332
16.0
14.7
11.0
5.1
0.3 0.1
0.9 56.2 0.16
2.2 31.9
22.5
1335
16.7
18.0
9.2
4.1
0.3 0.4
0.9 51.7 0.22
2.3 32.9
21.2
1337
17.4
11.4
6.6
6.6
0.3 0.0
0.6 54.6 0.16
3.6 26.7
22.4
1339
13.9
15.8
5.6
1.0
0.1
T
0.5 37.5 0.07
3.1 22.3
40.4
1341
25.9
18.3
4.1
2.6
0.4
T
0.8 52.3 0.30
4.8 28.3
20.1
1343
7.5
32.6
5.4
2.5
0.1 0.4
0.7 34.3 0.34
3.4 47.8
21.7
1345
20.0
17.5
5.1
5.7
0.7 0.1
0.7 52.7 1.72
4.2 34.3
24.7
Table 5.--Texture and heavy-mineral content of the TACTS samples. [Heads as in Table 3 except: WT % HM, SG greater than 2.96; Fe-OXIDES, limonite-goethite]
SAMPLE BULK WTX WTX WTX WT WTX WTX WTX WTX WTX
" - SAMPLE DEPTH BORE- INTERVAL (m) WEIGHT GRAVEL SAND+ CLAY
MAGNETITE ILMENITE GARNET PYROBOLES STAUROLITE
NUMBER (m) HOLE FROM TO (g) >10 MESH SILT
HM
=--======:t:.:=:===:=====:c:=::=========-:::::_--:--=:=======-=-====
-
----=:==~==========
A3.2 3.2? A 3.2
? 1520.1 28.8 54.2 17.0 0.12
17.1
6.2 1.9
7.1
2.4
A5.8 5.8 A 5.8 6.1 110.5 20.8 65.7 13.5 0.18
20.0
4.4 0.6
6.6
0.8
A8.5 8.5 A 8.5 9.1 1106.8 24.2 56.4 19.4 0.05
1.5 22.7 2.7
6.2
11.9
A16.1 16.1 A 16.1 16.8 1017.0 22.1 56.3 21.5 0.08
12.4 11.1 1.2
3.4
6.6
B3.2 3.2 B 3.2
? 652.9 5.1 87.0 7.9 1.39
0.8
9.9 2.2
12.5
8.5
B5.5 5.5 B 5.5 5.9 386.2 43.1 43.0 13.9 0.18
7.9 10.2 1.8
5.0
3.5
B12.2 12.2 B 12.2 12.4 222.6 4.0 87.4 8.5 0.22
2.0 17.8 2.0
17.4
1.7
Cl.5 1.5 C11.0 11.0 C17.7 17.7
c c
1.5 11.0
2.1 1732.1 11.6 565.9
c 17.7 17.9 640.8
4.5 95.0 0.5 0.70 51.2 44.2 4.6 0.19 0.0 3.4 96.6 0.02
1.3 17.7 1.6
72.0
0.8
T
49.5
T T
24.4 T
0.5
3.7 T
0.5
tj
01.5 1.5 D 1.5 3.5 220.8 5.6 85.4 9.0 0.50
1.8 13.6 0.6
6.4
2.1
09.4 9.4 D 9.4 9.6 1467.1 13.4 72.3 14.2 1.02
11.8
3.2
T
5.7
0.8
010.8 10.8 D 10.8
? 482.9 17.4 58.4 24.2 0.31
56.0
2.1 0.2
2.4
0.4
E4.6 4.6 E 4.6 5.2 585.5 3.2 88.4 8.4 0.60
2.8 24.7 3.3
6.0
3.5
F3.4 3.4 F 3.4 <5.8 294.2 4.9 93.0 2.2 0.41
4.1 17.4 0.8
13.8
2.6
F5.8 5.8 F 5.8
? 601.4 5.4 85.2 9.5 0.28
6.1 20.8 1.2
7.3
3.3
F6.7 6.7 F 6.7 6.9 149.0 3.2 91.3 5.6 0.40
6.3 15.0 1.1
12.9
2.8
Fl0.1 10.1 F 10.1 <12.0 207.9 0.0 68.4 31.6 0.10
0.2
0.4 0.2
3.0
8.0
F12.0 12.0 F 12.0 12.4? 232.4 11.2 67.9 20.9 0.04
24.8 24.3
T
2.5
1.5
F18.9 18.9 F 18.9 <20.6 315.7 0.0 3.3 96.7 0.03
19.8 12.4 0.2
1.6
0.4
F20.6 20.6 F 20.6 <23.8 472.4 0.0 24.6 75.4 0.17
4.7 10.4
T
3.1
1.3
G0.9 0.9 G 0.9 2.5 292.7 3.1 90.1 6.7 0.51
1.7 20.5 0.4
6.3
3.7
G2.7 2.7 G 2.7 4.8 403.6 2.7 92.5 4.9 0.82
0.2 20.0 1.5
9.3
5.1
G5.0 5.0 G 5.0 <5.2 820.3 0.0 33.2 66.8 0.73
0.1 27.0
T
11.1
2.3
65.6 5.6 G 5.6 6.3 234.9 12.8 53.4 33.8 0.51
0.6 29.8 4.7
5.0
3.9
67.6 7.6 G 7.6 8.4 308.5 16.9 64.5 18.6 0.32
2.5 26.2 1.8
8.0
4.5
68.5 8.5 G 8.5 11.2 310.0 24.3 66.5 9.2 0.39
5.0 24.6 2.5
6.3
3.0
G11.3 11.3 G 11.3 17.0 218.1 0.0 83.5 16.5 0.78
0.5 31.7
T
5.2
4.5
G17.1 17.1 G 17.1 19.7 184.7 0.0 85.7 14.3 0.65
6.6 28.8
T
2.7
4.8
619.8 19.8 G 19.8 22.8 232.7 0.0 96.0 4.0 0.86
0.6 23.1
T
4.3
6.5
H1.2 1.2 H 1.2
? 948.6 1.6 96.7 1.7 0.53
1.5 13.9 2.5
5.5
6.1
H14.6 14.6 H 14.6 <15.8? 350.3 31.3 64.0 4.7 0.17
15.0 15.2 1.0
2.8
4.7
H18.9 18.9 H 18.9 25.5 115.5 18.4 64.8 16.7 0.26
30.0
3.0
T
4.7
2.0
Table 5.--Continued.
WTX
WTX WTX WTX
WTX WTX WTX WTX WTX WTX WTX WT X ILMENITE/ ZTR WTX
SAMPLE ALUMINO- LEUCOXENE EPIDOTE TOURMALINE MONAZITE RUTILE ZIRCON PHOS- Fe- OTHERS EHM/C EHM/T LEUCOXENE INDEX LABILES
NUMBER SILICATES
PHORITE OXIDES
===========a=a:am:.==-==-- -:C-aB1Pc:a:z=========~=========~===-===-maam=--=~~
- --===
m=:z:::=:a:
A3.2
5.4
T 3.8
1.3
T
T T 47.3 6.2 1.4 11.5 0.014
NA 5.9 34.6
A5.8
5.0
T 7.4
1.8
T
T T 26.2 17.0 10.2 9.4 0.017
NA 8.1 26.9
A8.5
9.2
2.6 16.5
1.0
T
T 0.2 14.1 0.5 10.9 34.6 0.016
8.8 2.5 24.7
A16.1
12.0
15.3 7.7
0.8
T
T T 24.1 0.8 4.7 38.4 0.030
0.7 2.6 34.8
83.2
9.9
1.6 19.3
85.5
4.1
0.3 12.7
812.2
17.6
0.2 14.0
1.2
0.1 0.2 0.2 23.8 0.2 9.6 21.9 0.305
6.4 3.1 27.5
2.9
T 0.6 0.6 39.5 0.2 10.6 15.8 0.029
39.2 13.3 35.4
1.6
T 0.2 0.4 21.5 1.2 2.4 36.2 0.081
89.0 4.0 45.9
Cl.5
14. 2
0.1 18.7
1.7
T 0.1 0.8 14.1
T 1.7 32.9 0.232 147.6 3.9 72.0
Cll.O
T
T
T
T
T
T T
T 25.3 1.9 0.8 0.002
NA N/A 50.0
....
C17.7
T
T
T
T
T
T T
T 39.5 10.0 0.0 0.000
NA 0.0 25.6
00
D1.5
7.3
T 16.8
1.1
T
T 0.2 47.1 1.8 1.2 21.1 0.105
NA 3.8 34.2
D9.4
5.0
0.1 16.7
2.8
T
T 0.1 21.5 21.8 10.4 8.5 0.086
46.1 9.4 67.3
D10.8
3.8
0.1 8.8
0.6
T
T T 6.0 15.9 3.8 6.0 0.019
19.5 3.8 44.0
E4.6
7.4
0.2 31.9
1.9
T
T 0.6 15.0 0.3 2.6 32.8 0.196 145.1 4.5 51.0
F3.4
14.3
0.6 32.3
3.3
T
T 0.1 9.5
T 1.1 32.3 0.132
27.6 5.0 44.4
F5.8
14.3
0.7 29.8
1.8
T
T 0.6 11.9 0.1 2.3 36.3 0.103
30.1 4.1 46.4
F6.7
11.8
T 26.2
1.2
T
T 0.8 15.8 0. 1 6.1 27.7 0.111
NA 3.5 5.4
F10.1
2.5
T 2.0
2.0
T
T T 11.5 11.7 58.6 2.9 0.003
NA 11.3 28.0
F12.0
T
T 0.8
2.5
T
T T 10.0 33.8 0.0 24.3 0.010
NA 34.5 21.6
Fl8.9
6.0
T
T
0.8
T
T T 8.4 36.0 14.4 18.4 0.006
NA 8.9 33.2
F20.6
20.1
0.9 25.4
1.6
T
T 0.5 11.1 15.9 5.0 32.0 0.054
11.0 4.0 39.6
60.9
13.9
1.3 31.3
1.3
T
T 0.9 17.7 0.2 0.8 36.7 0.188
15.4 3.9 38.3
62.7
13.0
0.8 27.4
1.1
T
T 0.9 16.8 0.5 3.7 34.7 0.283
24.4 3.3 36.3
65.0
17.7
2.3 25.1
0.6
T
T T 8.9 0.6 4.4 46.9 0.343
11.6 1.0 35.7
65.6
11.8
6.4 25.4
0.7
T
T 0.4 10.6 0.8
T 48.4 0.247
4.6 2.1 38.5
67.6
10.8
6.9 26.2
1.7
T
T 0.7 9.5 0.9 0.3 44.6 0.145
3.8 4.5 41.3
68.5
6.1
0.3 27.5
1.4
T
T 0.6 20.3 1.6 0.8 31.5 0.122
98.3 4.2 32.1
611.3
14.0
6.3 26.4
0.8
T
T 0.7 9.1 0.9
T 52.7 0.411
5.0 2.7 35.1
617.1
9.4
12.9 25.7
0.8
T
T 0.2 7.3 0.7
T 51.3 0.333
2.2 2.3 37.5
619.8
6.0
16.6 32.6
0.7
T
T T 7.6 0.3 1.7 45.7 0.393
1.4 1.5 43.7
H1.2
18.5
1.4 34.2
1.2
T
T 0.5 14.2 0.1 0.6 34.2 0.180
10.2 2.4 47.7
H14.6
11.5
1.7 28.8
1.5
T
T 0.5 15.0 0.7 1.7 28.8 0.049
9.1 3.9 34.7
H18.9
T
T
T
T
T
T
T
T 1.0 59.3 3.0 0.008
N/A 0.0 0.0
Table 6.--Texture and heavy-mineral content of the Tybee (GAT prefix) and Skidaway Island (GAS prefix) borehole samples. [Column heads as in Tables 2, 3, and 5]
DEPTH
SAMPLE INTER- BULK WTX WTXWTX WTX WT% WT X WTX
WTX WTX
NUMBER VAL WEIGHT GRAVEL CLAY HM ILMENITE GARNET PYROBOLES STAUROLITE ALUMINO- EPIDOTE
(ft) (g)
SILICATES
==:.:==-- --
-=::::::r::c:::-----==--=======- -
- ------- ===
GAT- 1 0-5 5044 1.2 NO 1.06 11.5
T
13.5
1.5
9.3 23.4
GAT- 2 5-10 5109 1.2 NO 0.86 11.3 1.8
14.1
2.8
7.9 43.0
GAT- 3 10-15 6568 1.2 NO 0.46 11.2 0.3
20.8
1.6
11.5 37.1
GAT- 4 15-20 7873 1.8 NO 0.49
7.2 0.2
27.1
1.7
8.0 34.3
GAT- 5 20-25 1343 3.0 NO 0.93
8.7
T 38.8
1.2
4.5 24.7
GAT- 6 25-31 578 14.5 63.9 0.81
3.8
T 18.4
GAT- 7 31-36 303 14.1 30.3 0.56
6.7
T 24.0
GAT- 8 36-41 388 5.5 11.1 0.98
7.0
T
22.3
GAT- 9 41-46 486 13.4 70.3 0.37 11.7 0.2
18.3
GAT-10 46-51 918 6.0 10.3 1.17 12.8 0.5
16.6
T 19.2 29.2
T 10.5 36.4
T
7.5 41.2
T 13.8 33.6
1.5
4.3 33.1
tD
GAT-11 51-56 808 3.4 11.5 0.80 12.1 0.1
15.1
GAT-12 56-61 2135 2.6 NO 0.71 18 . 7 1.9
11.3
1.6
13.6 27.1
6.0
9.2 20.6
GAT-13 61-66 383 7.7 13.1 0.57 18.8 2.5
11.4
4.5
7.5 22.4
GAT-14 66-71 2425 2.4 NO 0.75 25.2 1.5
5.4
3.9
7.2 11.8
GAT-15 71-76 2943 4.6 NO 0.93 24.8 2.1
1.6
6.9
4.4 9.7
GAT-16 76-79 1755 14.8 NO 0.48 27.4 1.5
2.9
GAT-17 82.5-84 1076 1.9 17.4 0.17 24.8 1.9
0.4
GAT-18 84-86.5 1726 2.2 NO 0.15 22.9 1.6
0.3
~=--====,=:======:e======---=----===-::::::::a:===:==
GAS- 1 0-5 6849 0.3 NO 0.77 18.5 0.5
5.7
GAS- 2 5-10 22856 0.4 NO 0.70 18.7 0.6
10.4
GAS- 3 10-14 11330 0.2 NO 0.59
8.9 0.6
18.1
GAS- 4 16-21 2291 27.2 48.2 0.27 27.7 0.5
5.9
GAS- 5 21-26.5 3286 1.9 NO 1.05 22.8 1.2
6.5
10.5
1.5 9.7
12.5
5.0 11.3
8.9
7.7 10.5
==~=~:::=
5.5
13.2 38.3
3.9
11.2 33.5
2.1
5.8 34.5
1.7
7.3 33.0
2.9
15.6 30.2
GAS- 6 26.5-30 895 7.8 28.7 0. 55 26.5 1.5
5.8
GAS- 7 30-35 1680 8.8 NO 0.60 19.1 1.3
5.5
GAS- 8 35-39 844 6.1 19.4 0.90 16 . 2 1.4
2.8
GAS- 9 39-40.5 929 24.8 NO 0.49 13 . 1 0.3
2.7
GAS-10 40.5-44 1088 11.4 13.9 0.88 29 .3 1.6
4.1
3.6
9.7 30.2
3.9
9.0 30.1
1.1
17.2 21.0
1.0
5.9 10.9
2.7
6.7 27.7
GAS-11 44-50 2138 1.4 NO 0.97
6.8 0.1
2.2
GAS-12 50-55 2734 2.5 NO 0.51 12 .9 0.3
13.9
GAS-13 55-62 776 0.2 58.2 0.49 18.5 0.2
12.0
GAS-14 64-71 3083 11.2 NO 0.86 13.1 3.1
0.4
0.9
13.5 19.4
0.4
6.6 23.2
0.9
6.5 18.2
4.7
2.9 6.1
Table G.--Continued.
SAMPLE WTX WTX WTX WTX WTX WTX WTX WT X WT X ZTR WTX
NUMBER TOURMALINE MONAZITE RUTILE ZIRCON PHOS- Fe- OTHERS EHM/C EHM/T INDEX LABILES
PHORITE OXIDES ::o:==== --- =====---===---:=:---::=:a-=::====,==:--====:===--=~
GAT- 1
0.1
T 2.1 3.8
T 17 .1 17.6 26.8 0.28 11.2 36.9
GAT- 2
0.5
T 1.4 2.1 0.1 2.5 12.4 22.7 0.20 5.5 58.9
GAT- 3
0.4
T 1.2 2.0 1.0 0.2 12.7 25.9 0.12 4.7 58.3
GAT- 4
0.2
T 1.1 1.3 1.8 0.1 16.8 17.6 0.09 3.5 61.7
GAT- 5
0.1
T 0.5 0.6 0.6 0.1 20.1 14.3 0.13 1.6 63.5
GAT- 6
T
T 0.2 2.2 0.2
T 26.9 25.4 0.21 3.5 47.5
GAT- 7
T
T 2.3 3.7
T T 16.4 23.1 0.13 7.7 60.4
GAT- 8
T
T 1.3 2.9 0.7
T 17.1 18.7 0.18 5.5 63.5
GAT- 9
0.6
T 1.7 3.9
T T 16.1 31.1 0.12 8.6 52.2
GAT-10
1.6
T 1.1 0.9
T T 27.5 19.2 0.22 6.1 50.2
~
GAT-11 GAT-12
T
T 0.1 6.0 1.1 0.1 23.0 31.8 0.26 9.6 42.3
0.6
T 2.2 1.6 15.8 0.4 11.9 31.6 0.23 8.2 33.8
GAT-13
0.1
T 4.1 2.7 1.0 0.1 25.2 32.9 0.19 12.4 36.3
GAT-14
1.0
0.1 2.6 6.0 22.2 0.3 12.8 41.1 0.31 24.2 18.7
GAT-15
1.2
0.1 6.6 1.4 19.1 0.4 21.5 37.4 0.35 27.2 13.5
GAT-16
1.5
T 2.1 3.0 24.4 0.5 14.9 34.1 0.16 20.2 14.0
GAT-17
1.7
0.1 1.9 7.6 23.2
T 9.7 39 .5 0.07 26.5 13.5
GAT-18
4.2
T 0.8 2.5 24.5 0.7 15.4 34.0 0.05 20.5 12.4
=~==-----==:a======--=~====-== ======:====
--------=----==
GAS- 1
2.6
T 2.5 2.8
T 0.7 9.7 37.0 0.28 11.1 44.5
GAS- 2
0.3
T 1.8 2.9
T 0.5 16.2 34.6 0.24 7.7 44.5
GAS- 3
0.5
T 0.6 1.0 3.4 0.6 23.9 16.3 0.10 3.3 53.2
GAS- 4
0.5
T 2.4 3.4
T 0.4 17.2 40.8 0.11 11.5 39.4
GAS- 5
2.3
T 6.6 1.0
T 0.1 10.8 46.0 0.48 14.9 37.9
GAS- 6
1.5
T 3.4 3.6 3.7
T 10.5 43.2 0.24 14.3 37.5
GAS- 7
0.6
T 2.0 2.7 15.5 0.1 10.2 32.8 0.20 9.6 36.9
GAS- 8
3.1
T 1.4 3.9 17.1
T 14.8 38.7 0.35 16.2 25.2
GAS- 9
0.7
T 0.2 1.6 28.0 0.9 34.7 20.8 0.10 10.7 13.9
GAS-10
1.1
T <0.1 1.7 10.8
T 14.3 37.7 0.33 6.1 33.4
GAS-11
0.3
T 0.2 0.3 27.9 0.4 28.0 20.8 0.20 2.2 21.7
GAS-12
0.9
T 1.1 1.9 21.1
T 17.7 22.5 0.11 8.1 37.4
GAS-13
0.4
T 0.2 1.1 12.1 0.1 29.8 26.3 0.13 4.3 30.4
GAS-14
0.2
T 1.5 3.3 53.7 0.1 10.9 20.8 0.18 22.5 9.6
3
Figure 4.---Contour plot of the mean grain size of sediments in 65 surface grid samples from the Georgia shelf. Contour interval 0.1 mm.
21
3
Figure 5.-Contour plot of the CaC03 content of sediments in 65 grid surface grab samples from the Georgia shelf. Contour interval 8 percent. 22
15%); potassium feldspar is somewhat more abundant than plagioclase. Feldspar concentrations occur in two zones perpendicular to the coast as defined by the 8% contour interval (Figure 6). The northern coast-perpendicular zone is a continuation of the Savannah River, and the southern zone is a seaward continuation of the AltamahaRivez. Both rivez-associatedfeldspar-richzonesextend to theshelfedge. Although locally diffuse, thepattern offeldspar disttibution emphasizes the enduring effects offluvial sedimentation on the Georgia shelf.
Heavy minerals
Mineralogic data are reported and discussed as weightpercentagesoftheheavy-mineralassemblageunless otherwise noted. The heavy-mineral data in this report do not include the <325-mesh and the >16-mesh fractions; however, only 13 ofthe65 grid samples had any <325-mesh size fraction and only 15 of the samples had >16-mesh fractions in excess of 10%. In general, the frequency of occurrence (in decreasing order of abundance) of heavy minerals in the sample population are phosphorite, ilmenite, epidote, pyroboles,aluminosilicates, tourmaline,leucoxene, staurolite, monazite, garnet, zircon, rutile, and magnetite.
Heavy-mineral content
ThesurfJCialsedimentsavezage 1.21_1.06%heavy minerals on a bulk sample basis. Inner shelf samples average 1.86_1.24% heavy minerals, middle shelf samples average0.73_0.32% heavyminerals,andoutershelfsamples average 0.40_0.29% heavy minerals. A contour plot of these data (Figure 7) reveals that the high heavy-mineral values are restticted to inner shelf sediments as previously shown elsewhere on the Atlantic Continental Shelfby Grosz (1987). However, two lobes correspond to the fme-grained texturallobesoffshoreoftheOgeecheeandSt Marys Rivers (Figure 4). These results suggest that the fine-grai.I;led sediments contain the larger concentrations ofheavy minerals.
Transect samples from the 10- and 20-m isobaths show the same trend of decreasing heavy-mineral content with depth; the nearshore (10 m) and midshore (20 m) groups average 0.78% and 0.32% heavy minerals respectively. However, it should be noted that values vary widely, particularly within the nearshore group. The distribution of heavy minerals on the Georgia shelf appears to be related to the disttibution of fine-grained sediment lobes associated with fluvial deposition extending offshore from the Savannah-Ogeechee and Satilla-St Marys River pairs.
Heavy-mineral resource potential
The detrital minerals (exclusive of sand and gravel) of
commercialintereston theGeorgia shelfconsistofilmenite, leucoxene (altered ilmenite), rutile, zircon, monazite, and aluminosilicates (sillimanite, kyanite, and andalusite). The variable EHM{f (sum of the economic heavy minerals mentioned above expressed as a percentage of the bulk sample, 1) is used as a measure of economic viability of heavy-mineral deposits.
For the grid samples, EHM/1' averages 0.44_0.42% and exhibits an inverse relationship to water depth (Figure 8). Data for the transect samples show that within the inner shelf the nearshore samples have a higher, but much more variable average EHM{f (0.43_0.39%) than the midshore samples (0.17_0.06%). The distribution pattern ofEHM/f values (Figure 9) is similar to that of total heavy minerals (Figure 7). High EHM/1' values are confmed to nearshore sediments and to lobate seaward extensions near the mouths of the rivers from th~ Savannah south to the Satilla (Figure 9). The 20-m-isobathregion offshoreofthe AltamahaRiver (Figure 2) is notably depleted in economic heavy minerals; however, ilmenite, the most abundant economic heavy mineral, is preferentially concentrated there (Figure 10). The abundance of ilmenite is also high offshore of the Altamaha River and in a broad zone trending south-southeastacross theshelffrom neartheEdistoRiver. Theilmenite concentration near the Altamaha River is approximately coincident with what is probably a 14-m sea-level stillstand beach-complex deposit
High-resolution seismic data show that, in places, at least theupper20 mofsedimentcontainsextensivechannels to the shelf edge and that channel thalwegs have migrated considerably ovez time. Cross-shelf-trendingcoarse-grained fluvial sediments (Figure 4) are not coincident with anomalous EHM/T concenlrations (Figure 9) as predicted by the inverse relationship between mean grain size and heavy mineral content (Figure 11).
Factors limiting the potential for significant concentrations of economic heavy minerals in channel deposits include (1) the aooence of significant amounts of heavymineral-bearing, fme-grained sediments in channels (see the relationship in Figure 11), (2) the juvenile nature of the heavy-mineral assemblage provided by the rivers, and (3) the low overall abundance of heavy minerals in the sediments on the Georgia shelf. The potential for placer deposits of heavy minerals in beach-complex deposits seems to be equally limited because (1) the heavy-mineral assemblage provided to the Georgia shelf is ubiquitously juvenile, (2) upgrading of the assemblages by weathering does not appear to be significant or areally extensive, and (3) textural and mineralogic data do not provide supporting evidence for significant sea level stillstands (necessary for the formation oflarge placerdeposits) at waterdepths other than the 14-m
23
3
Figure 6.--Contour plot of the feldspar content of the sand fraction in 65 grid smface grab samples from the Georgia shelf. Contour interval 2 percent
24
3
SCALE:
~--==--==--o~m.
Figure 7.-Contour plot of the percentage of heavy minerals in 65 grid surface grab samples from the Georgia shelf. Contour interval 0.5 percent
25
1.8
+
1.6 +
++ +
1.4 +
1::: 1.2
~
Jw: 1
(fl.
.....
J:
0.8
-~ w
~ 0.6
0.4
0.2
0 0
+
++
+ + +
+
+ ++ +
+
++
+
+ ++
*=q.
+
+
++ \ +
+++ +++ + ++++
++ +++
~-l:t+
+*++
I
I
I
I
I
10 20 30 40 50
WATER DEPTH (m)
+
I
60 70
Figure 8.-Plot of the EHM/f (economic heavy minerals/bulk sample) versus water depth for the 65 grid smface grab samples from the Georgia shelf.
26
3
Figure 9.-Contour plot of the EHM/f of sediments in 65 grid surface grab samples from the Georgia
shelf. Contour interval 0.2 percent
27
3
~
~
lq
(J
0
'S'()
0
R "' 1-...
<"
~
.._J
1-...
25
~
25
SCALE:
25
0 Noutic.ll """ 0-
o~.
Figure 10.-Contour plot of the percentage of ilmenite in 65 grid surface grab samples from the Georgia shelf. Contour interval 10 percent.
28
0.7...--------- - - - - - - - - ,
0.6 +
+ +
+
-E
..E........
w
0.5
l +
+ +++
+
N
-en
z
a<C:
C!l
z
<w (
~
0.4 0.3 0.2
t+ 4
.fl +++ ++.+++
l
++++
+"4+
++
+ +
+
+ + ++
t+
0.1
+ +
++ +
+
+ +++
+
0
T
I
I
I
0
1
2
3
4
5
WEIGHT% HEAVY MINERALS
Figure 11.-Plot of the mean grain size versus the percentage of heavy minerals.
29
isobath. As marine lranSgreSSions may be effective dispersing agents ofbeach-complex sands, the preservation potential of beach-complex-associated deposits of heavy minerals on the Georgia shelfis very low. Itis possible that small remnants of basal pmions of larger deposits (beach-complex and fluvial) may exist; however, their expression would be difficult to detect with regional grab sampling grids; sampling at depth is necessary.
Greenwood and Arjun R. Gadgil, Volunteers for Science at the USGS in Reston, VA, helped with the compilation of data and the drafting of figures. This study was conducted under a joint funding agreement between the Georgia Department of Natural Resources and the U.S. Geological Survey.
REFERENCES
CONCLUSIONS
The terrigenous clastic component of smficial sediments on the Geagiasbelfhas been derived predominandy
from Piedmont Province source rocks and carried to the sea
by rivers having headwaters extending into the Piedmont The Altamaha and Savannah Rivers are important conduits for these mineralogically immature sediments, and, along with the St Marys River, they have had apronounced effect on the texture and mineralogy of the surficial sediments. Beach-complex sediments are not important, except locally at the outeredgeoftheinner shelfapproximatelycoincident with the 14-m isobath.
The heavy-mineral resource potential of the surficial sediments on the Georgia shelf is limited by a number of factors, the most profound and controlling one being the immature heavy-mineral suite that has been~ vided from the Piedmont Additional constraints are the absence ofbeach-complex sediments, which tend to have a lll8IUreassemblage, andtheabundance offluvial sediments, which tend to have immature assemblages.
Indications are that the best potential,low as it is, for
titanium-bearingplacerdeposits ofheavy minerals occurs in
a zone between the 14 and 20 m in depth offshore of the Altamaha River where concentrations are coincident with a pobable sea- level still stand.
ACKNOWLEDGMENTS
Jolm C. Hathaway of the U.S. Geological Survey (USGS) at Woods Hole, MA, supervised the heavy-liquid separationandmagneticfractionationofsomeofthesampJes. RicardoLopezoftheUSGS,Reston,VA,perfonnedheavyliquid and magnetic fractionation of the transect samples and conducted mineralogic determinations of individual magnetic fractions. JamesR. HerringoftheUSGS, Denver, CO, provided samples from the TACI'S cores for analyses. Kathleen Farrell of the Georgia Geologic Survey collected the samples from the Tybee Islar)d borehole. W. Jason
Bigham, G.A, 1973,Zone ofinfluence-inner continental shelfoffGeorgia: Journal of Sedimentary Petrology, v.43,no.4,p.207-215.
Carver, R.E., and Kaplan, D.M., 19761 Distribution of hornblende on the Atlantic continental shelf off Georgia, United States: Marine Geology, v. 20, no. 4, p. 335-343.
Clifton, H.E., Hunter, R.E., Swanson, FJ., and Phillips, RL., 1969, Sample size and meaningful gold analysis: U.S. Geological Survey Professional Paper 625-C, 19p.
Gorsline,D.S., 1963,BottomsedimentsoftheAtlanticshelf andslopeoffthe southeasternUnited States: Journal of Geology, v. 71, no.4,p. 422- 440.
Grosz, A.E., 1987, Nature and distribution of potential heavy-mineral resources offshore of the Atlantic Coast of the United States: Marine Mining, v. 6, p. 339-357.
Grosz, A.E., Hathaway, J.C., and Escowitz, E.C., 1987, Placer deposits of heavy minerals in Atlantic Continental Shelfsediments: Proceedingsofthe 18thAnnual Offshore Technology Conference, Houston, Texas,
arc May 5-s. 5198, p; 387-394.
Grosz, A.E., Berquist, C.R.,Jr., and Fischler, C.T., 1990, A procedure for assessing heavy-mineral resources potential of continental shelf sediments.in Berquist, C.R., Jr., ed., Heavy- mineral studi~Virginia Inner Continental Shelf: Virginia Division of Mineral Resources Publication 103, p. 13-30.
Hathaway, J.C., 1971, Data file, Continental Margin Program, Atlantic coast of the United States, v. 2, Sample collection and analytical data: Woods Hole Oceanographic Institution Reference Number 71-15, 486p.
Heruy, VJ., Jr., and Hoyt, J.H., 1968, Quaternary paralic and shelf sediments of Georgia: Southeastern Geology,no.9,p. 195-214.
30
Hollister,C.D.,1973,Atlanticcontinentalshelfand slqJeof the United States-Texture ofsurface sediments from New Jersey to southern Florida: U.S. Geological Survey Professional Paper 529-M. 23 p.
Kellam,J.A., and Henry, VJ.,1987, Seismic investigation of the Tybee Trough area Georgia/South Carolina: Southeastern Geology, v. 28, no. 2, p. 65-80.
ofthe United States-Physiography: U.S. Geological Survey Professional Paper 529-C, 30 p.
Zellars-Williams Company, 1988, Georgia offshore mineralsassessment: GeorgiaGeologic SurveyProject Reportno.14,291 p.
Manheim,F.T.,Huddlestun,P.F.,andDaSilva).L.,1989.Lithology of TACTS cores B, D, H, and AMCOR
drillhole 6002, in Manheim, F.T., ed., Phosphoote
potential in the continental shelf offGea'gia; Results of the TACTS core studies: U.S. Geological Survey Open-File Report 89-G 559, p. 25-33.
Milliman,J.D.,1972,Atlanticcontinentalshelfandslopeof the United States-Petrology of the sand fraction of sediments, northern New Jersey to southern Florida: U.S. Geological SurveyProfessionalPaper529-J,40p.
Mining Jomnal, 1985, The U.S.Geological Survey has found titanium and zircon off east coast: Mining Journa!,v. 71,no. 13,p. 11.
Moore, J.E., and Gorsline, D.S., 1960, Physical and chemical data for bottom sediments, South Atlantic Coast of the United States: U.S. FISh and Wildlife Service, Special Scientific Repm 366, 84 p.
Neiheisel,James, 1965, Source and distribution of sedimentsatBrunswickHarborand vicinity, Georgia: U.S. Army Corps of Engineers, Coastal Engineering Research Center, Technical Memorandum no. 12,49 p.
Neiheisel,James, and Weaver,C:E., 1967, Transport and deposition of clay materials in southeastern United States: Journal of Sedimentary Petrology, v. 37, p.
1~1116.
Pilkey, O.H., 19(;3, Heavy minerals of the U.S. South Atlantic continental shelf and slqJe: Geological Society of America Bulletin, v. 74, no. S, p. 641-648.
Pilkey, OH., and Frankenberg, D., 1964, The relict- recent boundary on the Georgia continental shelf: Bulletin of the Georgia Academy of Sciences no. 2201, p. 37-40.
Terry,R.D.,andChillingar,G.V.,19SS, Comparisoncharts for visual estimation of percentage composition: Journa! of Sedimentary Petrology, v. 25, p. 229-234.
Uchupi, Elazar, 1968, Atlantic continental shelf and slope
31
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