c. 4

SRT-EST-97-193

Subsurface Geology of the A and M Areas of the Savannah River Plant, Aiken, South Carolina(U)

by D. Jackson (Contact) E. 1. du Pont d e Nemours and Company Savannah River Site Aiken, South Carolina 29808 W. C. Fallaw

K. A. Saraent

~ S T F I I B ~ ~ ~ O N OF THIS DOCUMENT IS U N L I M ~ ; ~ ~

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1 , * , I I ' -

/ . .A

I .- - - ---. SRT-EST-97-193 - .... ."I. ..

SUBSURFACE GEOLOGY OF THE A AND M AREAS

AT THE SAVANNAH RIVER PLANT, AIKEN, SOUTH CAROLINA

. by

W.C. Fallaw

and

K.A. Sargent

June 1986

Submitted i n par t ia l fulfillment

o f Contract AX 715063

f o r .

E.I. duPont de Nemours & Company

. Savannah River Plant-.. ~

Aiken, South Carolina 29808

Geological Consulting Services

R t . 7, 12 Kensington Road

Greenvi 11 e, South Carol ina 29609

,

*TABLE OF CONTENTS

LIST OF ILLUSTRATIONS. . . . . . . . . . . . . . . . . . .

LISTOFTABLES. . . . . . . . . . . . . . . . . . . . . .

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . .

GEOLOGY.

. REFERENCES CITED. . . . . . . . . . . . . . . . . . . . . .

LITHOLOGIC AND GEOPHYSICAL LOGS. . . . . . . . . . . . . . . , .

Page

iii-v

vi

- 1

2

55

Appendix

'

LIST OF ILLUSTRATIONS

PAGE

5 Figure 1. Location map of borings used i n geologic study.

Figure 2. Structure contour map of t o p surface, Black

Creek Formation. On a l l maps, wells w i t h o u t

l e t t e r designations a re MSB wells. 11

Figure 3. Structure contour map of t o p surface, Ellenton

Formation.

Ellenton are missing i n places, the surface is

Because the higher units o f t he

i n 4 of the 5 Ellenton u n i t s . . 13

Figure 4. Isopach map o f the e n t i r e Ellenton Formation. 14

Figure 5. Structure contour of t o p surface, lower Ellenton-

cl ay. 15.

Figure 6. Isopach map, lower Ellenton clay. 1 6 .

Figure 7. Structure contour map o f t o p surface, lower

Ellenton sand. 18

Figure 8. Isopach map, lower Ellenton sand. 19

Figure 9. Structure contour map o f t o p surface, middle

E l 1 enton cl ay. 20

Figure 10. Isopach map, middle Ellenton' cl-ay. 21

Figure 11. Structure contour map of t o p surface, upper

E l 1 enton sand. 22

Figure 12. Isopach map, upper Ellenton sand.

Figure 13. Structure contour map of t o p surface, upper

E l l enton clay.

Figure 14. Isopach map, upper Ellenton clay.

Figure 15. S t ruc ture contour map of t o p surface, lower

Congaree sand.

Congaree is missng i n the south , the Congaree

Formation is not subdivided there.

Because the clayey zone of the

,

Figure 16. Isopach map, lower 'Congaree sand.

Figure 17. S t ruc ture contour map o f t o p surface, Congaree

clayey zone.

Figure 18. Isopach map, Congaree clayey zone.

Figure 19. S t ruc ture contour map of t o p surface, Congaree

Formation.

Figure 20. Isopach map, upper Congaree sand. Because. the

clayey zone is missing i n the south, the e n t i r e

thickness of the Congaree Formation is mapped

there .

Figure 21. S t ruc ture contour map of t o p surface, McBean

Formation.

Figure 22. S i l t and clay percentage map, McBean

Formation.

- i v -

23

25

26

28

30

31

32

33

34

36

*37

/

Figure 23. Isopach map, McBean Formation.

Figure 24. Structure contour map of top surface, Dry Branch

Formation (lower upit of the Barnwell Group).

Figure 25. Isopach map, Dry -Branch Formation.

,Figure 26. Structure contour map of top surface, Tobacco Road

Formation (upper unit of the Barnwell Group).

Figure 27. Isopach map, Tobacco Road Formation.

Figure 28. Isopach map, Upland unit. Only ground elevations

at wells were used in making the map. The existing

topography is the t o p surface of the Upland unit

except in the south, where the Tobacco Road and Dry

Branch Formations are exposed on the surface.

Figure 29. Map showing,lines of cross-section (Figs. 30-34)-.

Figure 30-34. Cross-sections. Dips are not as steep as

shown because of a 12-to-1 vertical exaggeration of

the sections.

based on structure contour maps of the stratigraphic

The configuration between wells is

units. Rock types are generalized, with no details

shown.

- v -

38

39

43

44

45

46

48

50-54

LIST OF TABLES

Tab1 e

1 Data Used i n Geologic Study

- 2 Elevations of Strat igraphic Units

3 Ellenton Size Analysis Date

. * . ' ,

. . .

4 Lower Congaree Size Analysis Data

5 Upper Congaree Size Analysis Data

6 Average Clay and S i l t Content from Visual Analysis

7 McBean Size Analysis Data.

- v i -

Page

6

24

24

24

40

41 *

i

INTRODUCTION

A study of the subsurface geology o f A and M areas at the Savannah River

Plant was begun in the summer of 1984 with the establishing o f a sedimen-

tological 1 aboratory at Building 704-U. Here, core samples, recovered during

the drilling of selected A and M area monitoring wells, we examined by trained

geologists under the supervision of Dr. W.C. Fallaw.

tinued during the summer of 1985. The results of these studies were used,

along with available borehole geophysics, to delineate the subsurface geology.

This report is based on these investigations.

tained are summarized,by monitor well as a lithologic l o g and are presented

along with the borehole geophysics in the Appendix.

This project was con-

The sedimentological data ob-

The geological interpretation is presented in the form of structure con-

( . tour maps,. isopach maps, and cross-sections. The study is limited t o existing data from A and M areas, and the interpretation may change as additional data

become avai 1 ab1 e.

STRATIGRAPHIC SECTION

GEOLOGY

The Cretaceous and Cenozoic sediments ' o f ' the Coastal Plain are approxi-

mately 700 ft thick in A and M Area and regional dip is t o the southeast (Si-

ple, 1967; Colquhoun et. al., 1983). The sediments are mostly loose and par-

tially indurated sands and clays, and they overlie Precambrian or Paleozoic

metamorphic rocks of the Appalachian Province.

occur between the Coastal Plain sediments and the Appalachian crystal1 ine

rocks in a part of the Savannah River Plant, but none are known in A'and M

Newark-type Triassic sediments

areas. The Cretaceous and Cenozoic deposits appear t o have formed i n f l u v i a l ,

d e l t a i c , and shallow marine environments.

Terminology used f o r the strata var ies among the studies done i n the SRP

area. Among the more per t inent publications a re Sloan (1908), Cooke (1936),

S ip l e (1967), Nystrom and Willoughby (1982), Carter (1983), and Colquhoun e t

a1 . (1983). The terminology of t h i s report , shown below, . i s based on a review of these s tud ies , and on the usage of DuPont employees concerned w i t h subsur-

face s t ra t igraphy. Further study may r e s u l t i n revision.

Upland u n i t Age unknown

Barnwell Group Unconformi ty?

Late Eocene (and younger?) Tobacco Road Formati on Dry Branch Formation

Unconformi t y

Unconformi ty? Middl e Eocene McBean Formation

Congaree Formation Unconformi t y

E l l enton Formation Unconformi ty

Unconformi t y B1 ack Creek Formation

Middendorf Formation

Middl e Eocene

Paleocene

Late Cretaceous

Late Cretaceous

METHODS

The core samples were acquired us ing e i the r a sp l i t spoon o r phosphate

barrel sampler.

runs up t o 24 i n long.

diameter core i n runs up t o 10 f t i n length b u t more commonly i n unconsoli-

dated sediments is r e s t r i c t ed ' t o less than 5 f t . Upon recovery, the cores were

wrapped i n aluminum f o i l o r a polyvinyl p l a s t i c sheet and stored i n core boxes

marked t o record the sampling interval and t o d i s t i n g u i s h top and bot tom of

The s p l i t spoon sampler re t r ieves a 1 7/8 in-diameter core in

The phosphate barrel sampler r e t r i eves a 3 7/8 i n -

- 2 -

the core samples. Storage boxes were normally of waxed corrugated cardboard

'construct ion b u t on occasion wood boxes were used. Long-term storage was e f -

fected i n a locked building.

The cores were examined megascopically and w i t h binocular microscopes , and these propert ies were recorded:

Depth Recovery Color Clay co lor Sedimentary s t ruc tu res Percentages of pebbles, granules,

sand, s i l t , and clay Percentage carbonate (detected

by HCI) Rock name ' Maximum gra io size

Modal grain size Sorting Roundness Presence of sul phides Percentage muscovite Percentage glauconite Percentage l i g n i t e

Presence o f f o s s i l s Fluorescence under .ultra-

v io l e t l i g h t ( fo r heavy mineral s)

Grain sizes were estimated by comparing the core samples w i t h sieved f rac t ions

o f known s i z e , and percentages were estimated by comparing the core samples

w i t h diagrams showing how various percentages would appear under the micro-

scope (Terry and Chilingar, 1955). The Wentworth-Udden sca l e was used f o r

grain sizes. T h i s is shown below, and on the f a r r i g h t is shown the cor-

responding d sca l e terminology, d being the negative of the logarithm t o t h e base 2 of t he 'grain s i z e diameter. -The d u n i t s were used i n parameters (Folk

and Ward, 1956) of size frequency d i s t r ibu t ions f o r samples w h i c h had been

s i z e analyzed by s ieve and hydrometer:

Grain Size Pebbles Granules , Very coarse sand Coarse sand Medium sand Fine sand Very f i n e sand S i l t C1 ay

Diameter i n mm 4

2 - 4 1 - 2

1/2 - 1 114 - 112

1/16 - i/a 118 - 114 - .

11256 -1/16 11256

- 3 -

d Scale -2

-1 - -2 0 - -1 1 - 0 2 - 1 3 - 2 4 - 3 4 - a

8

,

In t h e formation descriptions, the average s i ze f rac t ion percentages and

In the presentation o f the r e su l t s f o r sor t ing a re based on visual analysis.

t h e few samples which were sieved and analyzed by hydrometer, the sand per-

centage a l so includes granules and pebbles, these being present i n only minute

amounts i n those samples.

Sorting, a measure o f the degree t o which a l l grains i n a sample approach

the same size, was estimated f o r sands according t o this scale:

Well sor ted 90% o f sample w i t h i n 2 sand size classes Moderately sorted 90% o f sample w i t h i n 3 sand size classes Poorly soted 90% o f sample w i t h i n 4 sand s i z e c lasses Very poorly sor ted 90% o f sample w i t h i n more than 4 s i z e c lasses

In general , t h e core data were recorded a t 2 f t - i n t e r v a l s , b u t where

there was an obvious l i t ho log ic break w i h i n the in te rva l , smaller intervals

were recorded.

were prepared from the coded data. Major features recorded on the logs are

modal grain s i z e , maximum grain s i ze , pebble p l u s granule percentages, sort-

ing, carbonate zones, dominant color, sedimentary s t ruc tures , -fossils, and

Lithologic logs (see Appendix) on a sca le of 1 i n t o 10 f t

content of muscovite, glauconite, l i g n i t e , and heavy minerals.

O f t he 47 borings used i n the s t ra t igraphic study, 33 were cored. Some

borings were’cored continuously and some were cored 2 f t i n every 5 f t of

depth. Figure 1 shows the locat ions of the borings and Table 1 shows the

amount o f data available. In making correlat ions and describing formation

l i t h o l o g i e s , g rea t re l iance was placed on 13 borings which were cored con-

t inuously a t l e a s t throughthe Eocene section: ASB-8, MSB-IO, -11, -12, -13,

-21, -29, -30, -31, -36, -40, -41, and -42..

- 4 -

I . c

d

i

!

llOBo00

96ooo

2000

\ \

+ a i 2 9

i A

0 2000

4

Geoloqical Consulting Services

4000 Ft 1

Figure 1. Location map o f borings used in geologic study.'

- 5 -

Table 1.

Elevations of Thickness of Core Elevations of Thickness Well Intervals Cored Interval Cored Spacing" Intervals Logged of Intervals C1 uster ft ft ft ft AC2 343-139 204 2/5 337-143 194

Data Use'd in Geologic study. Elevations relative to mean sea level CORES GEOPHYSICAL LOGS

ASB 7 ASB 8 ASB 9 MSB 9 MSB 10 MSB 11 MSB 12 MSB 13 MSB 14 MSB 15 MSB 16 MSB 17 MSB 18 MSB 19 MSB 20 MSB 21 MSB 22 MSB 23 MSB 24 MSB 25 MSB 26 MSB 27 MSB 28 MSB 29 MSB 30 MSB 3 1 MSB 32 MSB 33 MSB 34 MSB 35 MSB 36 MSB 37 MSB- 38 MSB-39 MSB 40 MSB 41 MSB 42 MSB 43 MSB 44 MSB 45 MSB 46 RWM 4 RWM 5 RWM 6 RWM 7 RWM 8

351-211 349-11 306-216 357 - 263 353-104 363- 123 346-(-313) 343-99 346-143 365-163 365- 163 266-154 248- 141 298-96 262-150 354-16 357-155 370-54 379-127 365-113 359-156 374-171 252-151 364-47 253-27 246-12

381 - (-279) *

340-38 382-260

321-9 323-18 376-36

140 338

90 9 4.

249 240 659 244 203 202 202 112 107 202 112 338 202 316 252 252 203 203 101 317 226 23 4

660

302 382

312 305 340

2)5 Continuous

Continuous Con t i n uous Continuous Continuous Continuous

2/5 2/5 2/5 2/5 2/5 2/5 2/5

Continuous 2/5 2/ 5 2/5

2/5 2/ 5 2/5

Continuous Continuous Continuous

2/5

2/5

2/ 5

Continuous Cuttings

Continuous Continuous Continuous

349-19

348-1 12 357- 123 338-(-309) 337-98 340-147 359-165 359-167 350-156 332-138 292-98 346-152 354-10

370-44

372-60

364-52 348-33

247-40 251 -7 375- (-279) 348-34 338-40

352-32 338-40 319-23 323-12 371 -25 355-41 370-118 374-120 368-122 360-126 361-103 347- 138 345-141 346-1 00

374- (-4)

330

23 6 234 647 23 9 193 194 192 194 194 194 194 344

326

312

312 315

207 244 654 214

. 298 3 78 320 298 296 311 346 314 252 254 246 23 4 258 209 204

* 246

* 2/5 indicates well was cored 2 ft of every 5 ft

f :'

,

I I

Table 2. Elevations of Tops of Strat igraphic Uni t s . r e l a t i v e t o mean sea level.

Elevations given are f.

Upper Congree Lower (

Ground Tobacco Dry We1 1 E l evati on Road Branch McBean Congree c l ay Congree Cluster f t f t f t f t f t f t :ft

AC 2 343 305 25 1 206 183 ASB 7 351 ASB 8 349 ASB 9 306 MSB 9 357 MSB 10 353 MSB 11 363 MSB 12 346 MSB 13 343 MSB 14 346 MSB 15 365 MSB 16 365 MSB 17 356 MSB 18 338 MSB 19 298 MSB 20 352 MSB 21 354 MSB 22 357 MSB 23 370 MSB 24 379 MSB 25 365 MSB 26 359 MSB 27 376 MSB 28 353 MSB 29 365 MSB 30 353 MSB 31 346 MSB 34 253 MSB 33 254 MSB 34 381 MSB 35 350 - MSB 36 340 ' MSB 37 382 MSB 38 356 MSB 39 341 NSB 40 321 MSB 41 323 MSB 42 376 MSB 43 357 MSB 44 375 MSB 45 379 MSB 46 370 RWM 4 364 RWM 5 365 RWM 6 347 RWM 7 347 RWM 8 346

328 328 274 317 315 307 300 291 308 312 308

290 276

316 315 343 350 3 18 331 336

345 306

356 3 26 324 332 338 324 321 295 348 339 352

346

266 23 1

269 227 253 220 248 210 260 223 264 218. 260 223 265 227 246 197 243 210 266 213 255 207 246 196 255 220 270 233 267 234 279 23 5 266 269 233

264 220 259 205

222 236 204 245 215 262 220 259 214 266 226 266 224 264 220 258 226 261 226 255 2 23 266 23 2 270 234 255 214 278 23 1 275 233 263 224 277 23 2 265 220 263 218 252 220

- 7 -

197

198 197 184 195 194 198 197 177 189 186 184 162 201 215 214 212

212

198 185 198 187 193 201 190 202 224 - 196 205 198 205 210 213 192 204 208 194 216 201 200 198

-- 169

183 161 156 177 154

175

136

167 149 169

158-

167 133 152

. ... 150 152

202 150 153

175 179 159 152 173 152 150 174 154 157 183

146

158 155 136 146

124

152

138

154 123 146

.. . 138 150

175 149 148 150 - 159 136 141 144 152 148 142 169 150 154 142

Table 2. (continued)

ELLENTON BLACK CREEK Upper Upper Middl e Lower Lower

We1 1 cl ay sand cl ay - sand cl ay C1 uster f t f t f t f t ft

112 110

114

118 147

143

140 142 126

119

I112

125

114 141

140

137 137 125

117

102 95 71 55

147 148 106 127

138 143 101 109

118 129 73 34

133

107

122

123

129

133 117 140 112 13 2

140 134 130 140 132 135 123 120 128 -130 134 144

134

AC 2 ASB 7 ASB 8 ASB 9 MSB 9 MSB 10 MSB 11 MSB 12 MSB 13 MSB 14 MSB 15 MSB 16 MSB 17 MSB 18 MSB 19 MSB 20 MSB 21 MSB 22 MSB 23 MSB 24 MSB 25 MSB 26 MSB 27 MSB 28 MSB 29 MSB 30 MSB 31

- MSB 32 MSB 33 MSB 34 MSB 35 MSB 36 MSB 37 MSB 38 MSB 39 MSB 40 MSB 4i HSB 42 MSB 43 MSB 44 MSB 45 MSB 46 RWM 4 RWM 5 RWM 6 RWM 7 RWM 8 112

- 8 -

d

130

86

111

110

64

95

35

66

116

129 113 128 110 113 116 134 114 123 124 119 13 1 121 118 126

139

104 62

113 93

114 97 82

103 117 90

104 114 101 99 81 98

108

101 37 - 68 53 55 67 67 80 87 67 86 47 62 74 72

120

. . I FORMATION DESCRIPTIONS

I I

Middendorf Formation

The two deepest borings i n M area, MSB-12 and MS-34, cored i n t o the Mid-

dendorf b u t did not d r i l l through it. MSB-l2,the deeper of the two, reached

an elevat ion of -313, The top of the formation was picked a t the t o p of a

thick clay a t -113 i n #34 and -118 i n #12. The assignment of this clay t o the

Middendorf rather than the Black Creek is arb i t ra ry .

The Middendorf cons is t s mostly o f medium- and coarse-grained, moderately

. and well-sorted quartz sand, averaging 17% s i l t and clay. Pebbly layers a r e common. Muscovite is common i n some places, bu t not a s abundant as i n t he

overlying Black Creek Formation. Tan is the most common color , w i t h gray,

white, purple, orange, and yellow occurring. In addition t o the clay a t t he

top of t he u n i t , c lay and s i l t layers a re interbedded w i t h .the sand.

20% of the sand sect ion underlying the upper clay is composed of s i l t and clay

beds. These fine-grained beds appear t o be discontinuous, b u t the thick upper

c lay seems t o be extensive w i t h i n SRP. The upper c lay is 38 f t thick i n MSB-

Roughly

34.

l aye r o f sand.

In MSB-12, the upper c lay is divided in to two par t s by a 14 f t ' t h i c k

The upper layer of c lay is 9 f t and. the lower 10 f t thick.

The deposit ional u n i t s appear t o be discontinuous, except perhaps the

t o p clay. The i r r e g u l a r bedding, var ia t ion i n sor t ing , and clay ba l l s sug-

ges t t h a t t he Middendorf was deposited i n f luv ia l environments. Most of the

sands a r e probably point bar and channel deposits. The t h i n clays and s i l ts

were probably formed i n overbank environments.

B1 ack Creek Formation

Thirteen.A and M borings are cored in to the Black Creek Formation and

seven others were logged geophysically.. 0.nly MSB-12 and MSB-34 d r i l l e d

through i t .

The upper contact is picked a t the bottom o f a thick clay immediately below

The formation is 152 f t th ick i n #12 and 180 f t thick i n #34.

- 9 -

'. I

t h e poorly sor ted, dark sands of the Ellenton Formation. The boundary is d i s -

t inct on both l i t ho log ic and geophysical logs. Figure 2 is a s t ruc ture contour

map of the top surface of the Black Creek Formation.

picked a t the upper surface of the thick clay a t the top of the Middendorf.

Both contacts are probably unconformable (Col quhoun e t a1 . , 1983).

The lower contact is

Most o f the Black Creek consis ts of medium and coarse sands. Sorting is

qu i t e var iable , ranging from well sorted t o very poorly sor ted, w i t h .the

former being more common. Pebbly beds occur throughout, and c lay b a l l s a r e

common. The sands are generally micaceous, more so than i n the Middendorf,

and fe ldspar and pyrite a r e rare. Tan, white, and yellow sands a re most com-

mon, and the top o f the sand is black i n several borings, perhaps s ta ined by

the overlying Ellenton i n some cases. Sands average 18% s i l t and clay. The

upper p a r t o f the sand is 'massive, but c lay beds occur i n the lower pa r t i n

t h e two deep,borings. About 5% o f the sect ion is composed o f s i l t and c lay

beds.

borings, 22% of the sediment i s c lay and si l t .

those o f the Middendorf and appear t o be f luv ia l .

Within the upper 30 f t , a zone penetrated by 10 continuously cored

The deposi ts are s imi la r t o

E l 1 enton Formation

Parts o f the Paleocene Ellenton Formation a r e dark gray o r black, poorly

sor ted, f i n e t o coarse, clayey, s i l t y sand and dark, k a o l i n i t i c c lay and

clayey si l t . Muscovite, fe ldspar , iron su l f ide and l i g n i t e are common i n

these sediments.

c lays are t an , purple, o r orange, a r e be t t e r sorted, and tend t o lack the sul-

f i d e and l i g n i t e found i n the dark sediments.

In other places j n the A and M areas the Ell'enton sands and

Both dark and l i g h t deposi ts

contain pebbly zones.

crude pa t te rn seems t o exist, however.

northeastern p a r t o f the study area which i s s t ruc tu ra l ly low, and near a

Some borings have both dark and l i g h t sections. A

Light deposits tend t o occur i n the

I

$H112000 5

I

2000

\

4 \

L - - J \ t

cmtw Interval = la Ft I 0 2000

\

Eeoloqical Consultinq Ser

4000 Ft

Figure 2. S t ruc ture contour map of t o p surface, Black Creek Formation

- 11 -

I

/ . -

s t ruc tu ra l high which is located near MSB-11.

1 igh ter sediments were deposited i n .post-Ellenton time.. Their muscovite and

fe ldspar content i s more s imi la r t o t h a t of the typical Ellenton than t o the

Eocene sands, and the shape of the modal size curves is s imi la r t o t h a t of t h e

dark Ellenton. The l i g h t color may have developed secondarily by leaching and

I t is possible t h a t some of t h e

oxidation of su l f ides , and l i g n i t e . For the Ellenton as a whole, clay and

s i l t beds make up 59% of the u n i t , and 62% of a l l sediments a r e clay and si l t .

Table 3 gives the results of size analysis of some of the l i g h t e r , be t t e r

sor ted sands. The lower boundary of the El len ton is picked a t the contact

between a t h i c k c lay and the t h i c k Black Creek sand section. The upper con-

t a c t is picked a t the base of a t h i c k Eocene sand section which is usually a

l i g h t e r color and much be t t e r sorted than the Ellenton. An indurated i r o n

oxide layer marks this boundary i n several borings. In Figure 3 is a struc-

ture contour map of t he top.surface of the Ellenton.

Thickness of t he Ellenton i n A and M area borings is from 32 t o 95 f t .

(See Figure 4). The upper pa r t of the Ellenton is absent i n some bor ings

which a r e general ly i n a' zone trending northisouth through A and M areas.

(See Figures 11 and 13) T h i s zone corresponds crudely t o s t ruc tu ra l ly h i g h

t rends , b u t some 'borings w i t h a missing section occur of f s t ruc ture . In a

complete sect ion, t he Ellenton cons is t s of five u n i t s . .These are , from bottom

t o top: a t h i c k c lay, a t h i c k sand, a medium-thickness clay, a t h i n sandj

and a t h i n clay. The clay a t the bottom, of the formation i s from 10 t o 56 f t

th ick , and general ly t h i n s toward s t ruc tura l highs. (See Figures 5 and 6 ) .

I n most borings, t he clay is gray, greenish gray, o r black.

oxidized colors a r e common, such as red, purple, 'orange, and yellow.

borings which have dark clay also have an oxidized zone a t the t o p , and some

borings have interbedded l i g h t and dark layers.

In other borings

Some .

. .

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F i g u r e 3 . S t r u c t u r e con tour o f t o p s u r f a c e , E l l e n t o n Formation.

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1 1 ( ( 1 1 1 1 I J I I Figure 4 . Isopach map o f the e n t i r e Ellenton Formation.

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Figure 5. S t ruc ture contour map o f t o p surface, lower Ellenton clay.

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F i g u r e 6. Isopach map, lower E l l e n t o n clay.

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’ A sandy zone from 2 t o 8 f t t h i c k was encountered i n a few bor ings about

Iron su l f ide occurs i n some borings, 15 t o 20 f t above the base of the clay.

l i g n i t e i n a few, and f i s s i l i t y was observed i n a small section of core i n one

boring. In MSB-36, a sect ion of core from the base of the clay layer was seen .

t o expand i n diameter by perhaps 25% when removed from the core barrel .

analysis revealed only kaol in i te and quartz i n this material .

X-ray

Pebbles occur

i n parts of t h e clay, b u t i n general t he la rges t pa r t i c l e size is medium or

coarse sand.

Dinoflagel la tes and pollen from the lower clay yielded Eocene(?) dates

from MSB-12 and MSB-34, Paleocene(?) i n MSB-42, and Early Paleocene i n MSB-36.

S t ee l e (1985) assigned this c lay i n M a rea ’ to the Paleocene, using a gamma ray

k ick a t the base as a Cretaceous-Paleocene Contact.

The lower Ellenton sand is generally coarse t o very coarse, micaceous,

fe ldspa th ic , and poorly sor ted, although light-colored, cleaner sands occur i n

some borings. Average s i z e f rac t ions o f this sand a re 77% sand s i z e and

l a rge r , and 23% s i l t and clay. Several clay beds, 1 t o 2 f t . thick, a r e ( * interbedded w i t h t he sand i n most borings. The sand is from 10 t o 40 f t thick

and t h i n s toward structural highs (See Figures 7 and 8 ) .

The middle c lay a t t a i n s a thickness of more than 20 f t of f s t ruc ture and

tends t o t h i n toward highs (See Figures 9 and 10)

MSB-34, allowing the lower Ellenton sand t o be i n contact w i t h Eocene sand.

Dinoflagel la tes and pollen ind ica te an Eocene age f o r the c lay i n MSB-21.

I t appears t o be missing i n

The upper Ellenton sand is up t o 9 f t thick and tends t o be missing i n

some borings (See Figures 11 and 12). I t is medium and f ine grained, s i l t y

and clayey, poorly sor ted, and micaceous. Size f rac t ions average 66% sand

s i z e and l a rge r , and 34% s i l t and clay. Dinoflagellate and pollen dates from

this u n i t a r e Early Paleocene i n MSB-23 and MSB-36.

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Figure 7. Structure contour map o f t o p surface, lower Ellenton sand.

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Figure 8. Isopach map, lower Ellenton sand.

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- Fig. 9 . Struc ture contour map of t o p surface, middle Ellenton clay.

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Figure 10. Isopach map, middle Ellenton clay.

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Figure 11. S t ruc ture contour map o f top surface, upper Ellenton sand.

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Fig. 12. Isopach map, upper Ellenton sand. 6

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Table 3. Ellenton Size Analysis Data (be t t e r sorted sands) Well Elevation Sand S i l t Clay Median Mean Sorting Skewness

MSB-IO 119 . 65 20 15 2.7 3.5 2.5 0.4 MSB-11 132 88 6 6 1.4 1.6 2.5 0.3 MSB-11 130 91 6 3 1.2 1.3 1.9 0.2 MSB-19 117 95 2 3 0.5 0.7 1.3 0.4

C1 uster ft % % % b b b

Table 4. Well Elevation Sand S i l t Clay Median Mean Sorting Skewness

MSB-IO 152 88 7 5 2.6 2.7 1.5 0.37

MSB-13 134 89 2 9 2.4 . 2.5 2.1 0.45 MSB-13 132 88 6 6 0.9 1.5 2.9 0.47 MSB-13 130 89 5- 6 1.2 1.5 2.3 0.38

Lower Congaree Size Analyses Date

C1 uster ft % % % z d b

MSB-10 150 88 11 1 2.2 2.2 1 .o 0.02

Table 5. Well Elevation Sand S i l t Clay Median Mean Sorting Skewness

Upper Congaree Size Analysis Data

Cluster f t % % % d Q d MSB 11 178 56 20 1' 24 3.5 4.8 4.1 0.42 - MSB 11 163 ~ 89 MSB 11 162 30 MSB 12 183 92 MSB 12 181 93 MSB 12 179 93 MSB 12 161 92 MSB 12 159 84 MSB 12 157 55 MSB' 14 190 92 MSB 17 160 86

4 7 27 43 5 3 6 1 6 1 6 2 1 15 7 1 7 1 9 3 11

2.1 2.4 7.0 7.1 0.7 1.1 0.5 0.9 0.5 0.8 0.9 13 2.4 2.6 3.3 6.0 2.3 2.2 1.8 2.1

1.6 4.1 1.5 1.4 1.4 1.6 2.7 ' 4.9 1.2 2.1

0.73 0.05 0.52 0.48 0.20, 0.44 0.44 0.65 ' 0.01 0.61

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Figure 13. Structure contour map o f top surface, upper Ellenton .clay.

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Figure 14. Isopach map, upper Ellenton clay.

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I 1 The upper c lay is up t o 6 f t t h i c k and i s missing i n some borings (See

Figure 14). An Eocene age determination was made from microfossils i n MSB-21.

The contradictory paleontological age determinations from Ellenton sam-

ples i n A and M areas may be caused by the paucity of f o s s i l s and by ignorance

of the true s t r a t ig raph ic ranges of t he taxa. The lower clay had one Early

Paleocene da te and two questionable Eocene dates. The middle clay yielded one

Eocene da te . The upper sand had two Early Paleocene determinations, and the

upper c lay had a s ing le Eocene date. Pollen dates from boring FC-5, several

miles southeast o f the study area, were Early Paleocene i n deposits s imi la r t o

the Ellenton i n A and M areas.

on A and M cores.

Further paleontological study is i n progress

The dark color , py r i t e , and l i g n i t e , jndicat ive of a reducing environ-

ment, suggest a d e l t a i c o r 'lagoonal environment for the Ellenton. The de-

crease i n grain s i z e upward o f t he lower El len ton sand would be expected i n a

d e l t a i c d i s t r i b u t a r y channel. The El len ton clays may have

quie te r environments between d i s t r i b u t a r i e s and seaward of

shore1 i ne.

Congaree Formation

The Middle Eocene Congaree- Formafion

i n the lower middle p a r t i n most borings.

been deposited i n

t h e d e l t a

i s 2 sandy u n i t w i t h a 'c layey zone

The lower unconformable contact is

picked where the dark clays of t he Ellenton Formation meet t h e clean, yel-

lowish sands o f the Congaree. An iron oxide-cemented zone marks the contact

i n s o m borings. MSB-36 displays the contact very well. Gamma ray readings

a re general ly h i g h i n t he Ellenton and low i n the Congaree. The upper bound-

ary of the Congaree is picked where the Congaree sands meet t he clay beds and

c l ay ie r sands of the McBean Formation.. .

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Figure 15. S t ruc ture contour map of top surface, lower Congaree sand.

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/

The lower Congaree sand (Figure 15) is brown, tan, and yellow; medium-

grained;. and moderately well sorted. An average of .17% of the en t i re u n i t is

composed o f clay and s i l t , and 6% of the section ‘is made up of clay and s i l t

beds. Clay laminae and heavy mineral zones occur i n places. Pebbly layers

are common, especially near the base. Thickness is from 4 t o 44 ft. (See Fig-

ure 16) . Table 4 gives data from size analyses.

The clayey zone i n the Congaree (Figure 13) is a clay layer i n some

borings, and i n others occurs as alternating sands and clays. A moderate gam-

ma ray high and a low r e s i s t i v i t y are usually logged through the interval.

The’zone is very t h i n o r missing i n the southern part of A and M areas (See

Figures 17 and 18). The clayey zone appears t o vary i n s t ra t igraphic posi-

t ion, sometimes appearing very low i n the Congaree and sometimes higher.

is possible t h a t there is more t h a n one clayey zone. The interval i s gray,

tan, and, rarely, green, orange, brown, o r purple. An average of 70% o f the

zone is composed of clay and s i l t beds, and 72% of a l l sediments are clay and

silt. The sands i n the zone are medium- t o fine-grained and well sorted.

Thickness varies from 0 t o 43 ft. (See Figure 18). Middle Eocene pollen oc-

curs i n MSB-18.

I t

The upper Congaree sand (Figure 19) is yellow, tan, and brown, medium-

and fine-grained, well-sorted sand. Heavy mineral zones are common, as a re

pebbly zones and clay bal ls . Clay and s i l t beds make up an average of 7% of

the section, and 16% o f a71 material i n the u n i t is clay and si l t .

nae occur i n most borings and micaceous zones occur i n some.

14 t o 60 ft t h i c k .

data.

Clay lami-

The u n i t is from

(See Figure 20) Table 5 shows size frequency dis t r ibut ion

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F i g u r e 16. Isopach map, lower Congaree sand

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Figure 17. S t ruc ture contour map of t o p surface, Congaree clayey zone.

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Figure 18. Isopach map, Congaree clayey zone.

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Figure 19. Structure contour map of t o p surface, Congaree Formation

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1 1 1 1 f 1 l f f 1 1 1 J F’igure 20. Isopach map, upper Congaree sand.

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1

McBean Formation *

t i o n across the Savannah River i n Georgia.

the Middle Eocene sect ion above the Congaree i n many SRP bor ings . MSB-40, on

the southern edge of A and M areas contains 7 f t of limestone i n a 28 f t sec-

t i o n composed mostly of glauconi t ic , poorly-sorted sand, w i t h a t h i n c lay a t

the top.

limestone, b u t a gamma ray high i n MSB-40, corresponding t o the sect ion of

g lauconi t ic sand, limestone,and clay, can be found i n most borings. S i l i c i f i e d

mollusks were found i n MSB-11.

c lay, e i t h e r as clay layers o r as matrix i n sands, than i n t h e underlying up-

per Congaree sand and the overlying Dry Branch Formation (Table 6). I t a l so is

more micaceous.

Congaree.

Limestone occurs a t t he type l o c a l i t y of the Middle Eocene McBean Forma-

Calcareous deposits a re found i n

(See Appendix Figure A36). Other borings i n the study area lack the

In most borings, the- sect ion contains more

An unconformity may separate the McBean from the underlying

The McBean sect ion is usually orange and yellow. Clay and s i l t beds

average 14% of the u n i t , and c lay and silt make up 25% of a l l sediments. In the northern pa r t , the formation appears t o be more permeable than elsewhere

i n A and M areas (Figure 22). The sands a re fine-grained and well, moderate-

l y , . and poorly sor ted. ' Pebbles and clay ba l l s occur i n some borings, and mus-

covi te is found i n most. There does not apepar t o be an extensive, continuous

l aye r of green clay a t the bottom nor a tan clay a t the top, as has been re -

ported elsewhere i n SRP, b u t c lay layers o f gray, green, tan , and other colors

occur a t various s t r a t ig raph ic horizons w i t h i n the McBean. Thickness of the

formation is from 16 t o 34 f t i n borings (See Figure 23). Dinoflagellates and

pollen from MSB-19 yielded a Middle Eocene date. Table 7 shows s i z e data from

sieve and hydrometer analysis.

,

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F i g u r e 21. S t r u c t u r e c o n t o u r map o f t o p surface, McBean Formation-'

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Figure 22. Percentage of s i l t and clay i n the McBean Formation.

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Figure.23. Isopach map for the McBean Formation.

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Figure 24. Structure contour map of t o p surface, Dry Branch Formation.

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Table 6. Average Clay and S i l t Content from Visual Analysis

S t ra t igraphic U n i t

As matrix i n sands and as beds

%

As beds

%

52 49 Upland u n i t

Tobacco Road

Dry Branch

McBean

Up p e.r Con g a r e e

Congaree clayey zone

79

54

71

. 47

85

13

18

25

16 ~

72

2

11

14

7 .

70

17 6 Lower Congaree

El-1 enton

Black Creek (upper 30 f t )

-

62 ' 59

22 5

Table 7. McBean Size Analysis Data

Well Elevation Sand S i l t Clay Median Mean- Sorting Skewness C1 us ter f t

MSB 10 210 77 10 13 2'.8 3.1 3.2 0.29

MSB 10 208 82 10 8 1.7 2.1 2.5 0.46 0.27 MSB 10 206

MSB 11 208 16 5 3.4 3.7 1.3 0.57 0.39 MSB 11 206 38 8 3.8 0.29 MSB 11 204

0.39 ' MSB 17 190

MSB 17 185 4 11 2.0 2;6 2.8 0.58

% % % d d d

93 6 1 1.5 1.6 1.2

4.3 2.1

21 8 3.1 3.3 2.5

43 10 4.2 4.7 2.1

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Dry Branch Formation

The Dry Branch (Figure 24) is the lower formation i n the Late Eocene

Barnwell Group and unconformably overl ies the McBean. The sands of t he Dry

Branch a re coarser and cleaner than those i n the McBean, and a pebbly layer

occurs a t t he base i n some'borings.

yellower sands w i t h c lay laminae meet the redder sands of t h e Tobacco Road

The top of the u n i t is picked where the

which tend t o lack c lay laminae. .The Dry Branch is composed of orange, brown,

and yellow, medium-grained, moderately- and well-sorted sand.

beds compose an average of 11% of the formation, and clay and s i l t cons t i t u t e

18% of a l l the sediments. Clay laminae are common. There does n o t appear t o

be an extensive layer o f tan c lay anywhere i n the formation. Clay layers ,

Clay and -si l t

however, usual ly tan, occur a t various s t ra t igraphic horizons w i t h i n t he Dry

I Branch. Pebbly l aye r s a r e common, Thickness of the formation is from 30 t o

55 f t (See Figure 25).

Tobacco Road Formation

,

26) is character ized i n many outcrops by a concentration o f f l a t quartz peb- bles a t i t s base.

The upper u n i t of the Barnwell Group, t he Tobacco Road-Formation (Figure .

In MSB-15 and -24, (See Appendix Figures A l l and Al9) f l a t

quartz pebbles were'round a t an obvious l i tho logic change, A gamma ray k ick -

occurs there. The base of the formation was picked i n other borings e i t h e r by .

l i tho logy or by a gamma ray kick. The upper contact was picked where the

f a i r l y well-sorted sands of Tobacco Road change t o clayey, s i l t y , sandy, peb-

bly, and poorly-sorted beds of the Upland u n i t .

The Tobacco Road is brown, orange, yellow, red, and purp le . Medium and

f i n e sands, moderately and well sorted, compose nearly the e n t i r e formation.

An average o f 13% of a l l t he sediments are clay and s i l t . Clay and s i l t

layers make up only 2% of the section.

near t he base.

Pebbly layers are common, especial ly

Clay b a l l s occur i n some borings.

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The thickness, controlled pa r t ly by erosion accompanying deposition Qf

the overlying Upland u n i t , and pa r t ly by post-Upland u n i t erosion, var ies from

0 i n stream va l leys t o about 97 f t . (See Figure 27).

and the Dry Branch were probably deposited during the Late Eocene marine

t ransgression.

t ransgress ive phase and the younger Tobacco Road was deposited during .the

regressive phase.

Both the Tobacco Road

The l a t t e r formation w i t h i ts c lay layers formed during the

Upland U n i t

Capping the higher areas i n SRP is a deposit of coarse-,medium- and fine-

grained, poorly sor ted, pebbly and cobbly material with extreme l a t e r a l and

v e r t i c a l va r i a t ion , The South Carolina Geological Survey has been mapping i t

as the informally named "Up1 and u n i t . 'I It parti 'al ly corresponds t o sediments

previously mapped i n SRP as the Hawthorn Formation.

I n A and M areas, the u n i t is orange, brown, red, and tan. Sorting is

Clay and si l t make up about 50 % of the deposits. -Pebbly zones very poor.

are abundant. Feldspar gra ins occur i n places. Thickness is from 0 t o 57 f t .

(See Figure 28). I t was probably deposited i n high energy f l u v

point bars, f l ood plains , and abandoned channel s. The channel s cut down i n t o the Tobacco Road i n places, forming a very i r regu

i ts top .

a1 channels,

seem t o have .

a r surface a t

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Figure 25. Isopach map, Dry Branch Formation.

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Figure 26. Structure contour map of t o p surface, Tobacco Road Formation.

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Figure 27. I sopach map, Tobacco Road Formation.

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Figure 28. Isopach map, Upland unit.

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STRUCTURE

Cross-sections t h r o u g h the area (Figure 29) were prepared using the

structure contour maps as a guide. The highs and lows betwen borings on t he

cross-sect ions (Figures 30-34) were inferred from the s t ruc tu re contour maps.

Dips a r e up t o about 260 ft/mi (3') f o r the BlHck Creek Formation and general-

l y decrease going up t he s t r a t ig raph ic section. A plausible sequence o f

events leading t o the development of the structures is:

Deposition of sediment

Erosion during unconformi t y devel opment, probably

Deposition on i r regular erosion surface, w i t h th icker

Different ia l compaction causing th icker sediments and

caused by drop i n sea level

sediments being deposited i n topographic lows

clayey sediments t o subside more than thinner sediments and sandier sediments

/ Erosion during unconformity development G

T h i s process would be modified by l a t e r a l changes i n pat terns of sedimentation

during deposit ion of each formation. A bar r i e r island, f o r example, would.

cause sediments t o build h ighe r than the adjacent shallow sea f loor .

The s t ruc tu ra l grain (trends of h i g h s and lows) shown on the s t ruc tu re

contour maps (Figures 2,3,5,7,9,11,13,15,17,19,21,24,25) is generally

northwest-southeast, para l le l t o regional slope. An exception t o this i s the

top of t he Tobacco Road Formation which is also the lower surface of the Up-

l and u n i t (See Figure 26).

northeast-southwest.

toward the Savannah River ra ther than toward the Atlant ic Ocean.

-

T h i s surface shows a g ra in which generally trends

Erosion here may have been controlled by streams f lowing

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SUMMARY

The s t r a t ig raph ic u n i t s beneath A and M areas a re mostly sands. Exten-

s i v e c lays occur a t the top of the Cretaceous Middendorf Formation, w i t h i n the

Pal eocene El 1 enton Formation , the Eocene Congaree Formati on , the Eocene McBean Formation, and the Upland un i t (age unknown) Carbonates were found i n only

the southern p a r t o f the study area.

Cross-section-s, structure contour maps, and isopach maps show t h a t

s t r a t ig raph ic units change i n thickness, contacts a r e i r r egu la r ra ther than

planar, and local d ips vary i n direct ion.

The coring and geophysical logging t h a t will accompany future monitor

well i n s t a l l a t i o n i n the A and M areas w i l l g rea t ly a id i n the ref ining of the

s t r a t ig raph ic and s t ruc tu ra l model presented here. O f especial help would be

the expansion of the d r i l l i n g e f f o r t towards Tims Branch which would enable

this study t o be cor re la ted w i t h s tud ies i n the F and H areas.

Further de t a i l ed sedimentological invest igat ions of the available

cores and the obtaining o f additional age determinations should also. be con-

sidered. During t h e summer of 1986, an investigation of the so-called "cal-

careous zone" is being conducted a t SRP and should provide answers

questions concerning the age and correlat ion of these sediments.

L

t o many

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Figure 29. Location map for the cross-sections in Figures 30-34.

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REFERENCES CITED

Carter, J.G.. (ed.), 1983, Biostratigraphy newsletter, Gulf and Atlantic coasts of North America, correlation chart; Chapel Hill, N.C.

Colquhoun, D.J., Woolen, I.D., Van Nieuwenhuise, D.S., Fadgett, G.G., Oldham, R.W., Roylan, D.C., Bishop, J.W. , and Howell, P.D., 1983, Surface and subsurface stratigraphy, structure and aquifers o f the South Carolina Coastal Plain: South Carolina Department of Health and 'Environmental Control, Governor's Office, and University .of South Carolina, Columbia, S.C., 78 p.

Cook, C.W., 1936, Geology of the Coastal Plain of South Carolina: U.S. Geological Survey Bulletin 867, 196 p.

Folk, R . L . , and Ward, N.C., 1957, Brazos River barf a study in the sig- nificance of grain size parameters: Journal of Sedimentary Petrology, V . 27, p. 3-27.

Plystrom, P.G., and Willoughby, R.H., (eds.) 1982, Geological Investigations Related t o the Stratigraphy in the Kaolin Mining District, Aiken County, South Carolina: Carolina Geological Society Field Trip Guidebook, 1982, South Carolina Geological Survey, Columbia, S.C., p. 80-113.

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South

Reprinted by South Carolina Geological Survey, Columbia,

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I , ' : ,

Location map of borings used in geologic studyletter designations are MSB wells4 of the 5 Ellenton units

Isopach map of the entire Ellenton Formationay

Isopach map lower Ellenton clayEllenton sand

Isopach map lower Ellenton sandEl 1 enton cl ay

Isopach map middle Ellenton' cl-ayEl 1 enton sandData Used in Geologic Study3 Ellenton Size Analysis DateLower Congaree Size Analysis DataUpper Congaree Size Analysis DataAverage Clay and Silt Content from Visual Analysis

ACMSBMSBMSBMSBMSBMSBMSBMSBMSBMSB- MSBMSBMSBRWMRWMRWMMSB-IOMSB-13130MSBMSBMSBMSBMSBMSB'MSB