THE LITHOSTRATIGRAPHIC FRAMEWORK OF THE UPPERMOST CRETACEOUS AND LOWER TERTIARY OF EASTERN BURKE COUNTY, GEORGIA
Paul F. Huddlestun and Joseph H. Summerour
GEORGIA DEPARTMENT OF NATURAL RESOURCES Lonice C. Barrett, CommissionerCommhioner ENVIRONMENTAL PROTECTION DIVISION Harold F. Reheis, Director GEORGIA GEOLOGIC SURVEY William H. McLemore, State Geologist
Atlanta 19961906
Bulletin 127 ABSTRACT
One new formation, two new members, and a reclefhitionredefinition of an established lithostratigraphic unit are formally introduced here. The Oconee Group is formally recognized in the Savannah River area and four South Carolina Formations not previously used in Georgia by the Georgia Geologic Survey are recognized in easterndrnBurke County. The Still Branch Sand is a new formation and the two new members are the Bennock Millpond Sand Member of the Still Branch Sand and the Blue Bluff Member of the Lisbon Formation. The four South CarolinaCarob formations recognized in eastern Burke CountyCountY include the Steel Creek Formation and Snapp Formation of the Oconee Group, the Black Mingo Formation (undifferentiated), and the Congaree Formation. The Congaree Formation and Still Branch Sand are considered to be lithostratigraphic components of the Claiborne Group. The Congaree Formation is included in the Claiborne Group because it extends westward to the Chattahoochee River area of Georgia and Alabama, and perhaps farther west into Alabama. In this area, the Congaree has been called the TallahatlaTallahatta Formation for many years and the Alabama and w-rnwestern Georgia "Tallahatta""Tallahatla" is an essential formation of the Claiborne Group. The age and correlation of all of the lithostratigraphic unitaunits are discussed. In addition, the Pen Branch fault is recognized in the vicinity of Hancock Landing in eastern Burke County.
i TABLETABLE OFOF CONrENTSCONTENlW
IN"TRODUCTIONINTRODUCTION ...... 1...... 1 PurposePurposeandSeopeand Scope ...... 11 LocationLocationofStudyAreaof Study Area ...... 11 PhysiographicPhysiographicsettingSetting ...... 11 PreviousPreviousWorkWork ...... 11 MethodsMethods ...... 33 AcknowledgementsAcknowledgements ...... 33
GEOLOGYGEOLOGY ANDAND HYDROLOGYHYDROLOGY ...... 5 5 GeologicGeologicSettingSetting ...... 5 5 HydrogeologicHydrogeologicSettingSetting ...... 66 StructuralStruch.lralFeature~sFeatures ...... 10 10
STRATIGRAPHYSTRATIGRAPHY ...... 12 12 OconeeOconeeGroupGroup ...... 12 12 SteelSteelCreekFormationCreek Formation ...... 1414 SnappSnappFormationFormation ...... 1717 Undift'erentiatedUndifferentiatedBLackMingoFormationBlack Mingo Formation ...... 2323 ClaiborneClaiborneGroupGroup ...... 3131 CongareeCongareeFormationFormation ...... 3333 StillStillBranchSandBranch Sand ...... 4343 BennockBennock MillpondMillpond SandSand Member.Member ...... 4848 LisbonLisbonFormationFormation ...... 5363 BlueBlue BluffBluff MemberMember ...... 5656 McBeanMcBean LimestoneLimestone MemberMember ...... 6262 BarnwellBarnwellGroupGroup ...... 6464 ClinchfieldClincMeldFomationFormation ...... 6666 UtleyUtley LimestoneLimestone MemberMember ...... 6666 DryDryBranchFormationBranch Formation ...... 6868 TwiggsTwiggs ClayClay LithofaciesLithofacies ...... 7070 GriffinsGriflins LandingLanding MemberMember ...... 7070 IrwintonIrwinton SandSand MemberMember ...... 7171 TobaccoTobaccoRoadSandRoad Sand ...... 7272
REFERENCESREFERENCESCITEDCITED ...... 73 73
FIGURESFIGURES
1. IndexIndex mapmap ofof easterneastern BurkeBurke CountyCounty ...... 22 2. IndexIndex mapmap ofof corecore samplessamples withinwithin thethe Trans-RiverTrans-River FlowFlow ProjectProject areaarea ...... 4 4 3. TritiumTritium ProjectProject stratigraphicstratigraphic andand hydrostratigraphichydrostratigraphic unitsunits ...... 7...... 7 4. CorrelationCorrelation chartchart forfor thethe TritiumTritium ProjectProject studystudy areaarea andand a ii 11. StructureStructure contourcontour mapmap ofof thethe toptop ofof thethe Undi1ferentiated.UndifferentiatedBlack Black MingoMingo FormationFormation ...... 28 28 12. Undi1ferentiated.UndifferentiatedBlack BWsMingo/Snapp Mingo/Snapp FormationsFormations isopachieopach mapmap ...... 2929 13. CongareeCongarseFomtioniaopaCnmapFormation isopach map ...... 3939 14. StructureStructure contourcontour mapmap ofof thethe toptop ofof thethe CongareeCongaree FormationFormation ...... 4040 15. StillStiLlBranchSandiaopachmapBranch Sand isopach map ...... 4646 16. StructureStructure contourcontour mapmap ofof thethe toptop ofof thethe StillStillBranch Branch SandSand ...... 4747 17. LisbonLisbon Formationc or mat ion isopach'bopach mapmap ...... 5767 18. StructureStructure contourcontour mapmap ofof thethetop top ofof thethe LisbonLisbon FormationFormation ...... 6868 19. GeologicGeologic mapmap showingshaKingextent extent ofof BarnwellBarnwell GroupGroup ...... 65 66 TABLESTABLES 1. CoreCoredatafmmstudyareadata from study area ...... 5...... 6 2. CoreCore datadata fromfmm outsideoutside studystudy areaarea ...... 66 3. SteelSteel CreekCreek FormationFormation referencereference sectionssectionsin in easterneastern BurkeBurke Coun~County ...... 1516 4. ThicknessThicknessvariationsforvariations for SteelSteel CreekCreekFormationFormation ...... 1717 5. SnappSnapp FormationFormation referencereference sectionssections inin thethe SavannahSavannah RiverRiver areaarea ...... 1919 6. Undi1ferentiatedUndifferentiated BlackBlack MingoMingo FormationFormation referencereference sectionssections inin ...... 25 26 7. CongareeCongaree FormationFormation referencereference sectionssections inin easterneastern BurkeBurke Coun~County ...... 3536 8. CongareeCongaree FormationFormation referencereference sectionssections inin GeorgiaGeorgia westwest ofof BurkeBurke Coun~County ...... 36 36 9. StillStill BranchBranch SandSand referencereference sectionssections ...... 4546 10. BennockBennock MillpondMillpond SandSand MemberMember referencereference sectionssections ...... 49 49 11. BlueBlue BluffBluff MemberMember referencereference sectionssections ...... 6060 12. ThicknessThicknessvariations variationsfor for McBeanMcBean LimestoneLimestone MemberMember ...... 6464 APPENDICESAPPENDICES 1. DescriptionsDescriptionsof of corecore sitesite locationslocations ...... 7979 2. HistoricalHistorical reviewreview ofof BlackBlack MingoMingo andand EllentonEllenton FormationsFormations ...... 8383 3. HistoricalHistorical reviewreview ofof CongareeCongaree FormationFormation ...... 9090 4. HistoricalHistorical reviewreview ofof thethe McBeanMcBean FormationFormation ...... 9191 PLATESPLATES 1. CorrelationCorrelation chartchart ofof easterneastern BurkeBurke Coun~County stratigraphicstratigraphic unitsunite withwith adjacentadjacent regionsregions ofof thethe southernsouthern AtlanticAtlantic andand easterneastern GulfGulf CoastalCoastal PlainsPlains ...... JacketJacket iii INTRODUCTION Plain sedimentary units outside the Burke County study area. The Georgia Geologic Survey (GGS) Tritium Project was initiated to investigate the Location of Study Area nature and distribution of tritium in aquifers in eastern Burke County, Georgia (Summerour, et Burke County is located along the al, 1994). This investigation began following Georgia-South Carolina border (Figure 1). The discovery of measurable tritium in a public northern boundary of the county (McBean(McBeah water supply well (DeLaigle Mobile Home Park, Creek) is approximately 15 miles southeast of Figure 1) in January and July, 1991. Core Augusta, Georgia and the southeastern boundary drilling for the project began at the TR92-1 site of the county is approximately 70 miles (Figure 2) in December, 1991. In March, 1992, northwest of Savannah, Georgia. The Savannah the U. S. Department of Energy (DOE) provided River Site (SRB)(SRS) is located directly across the the Environmental Protection Division (EPD) of Savannah River from Burke County. the Georgia Department of Natural Resources The Tritium Project study area is located with $800,000 to conduct the project. in the eastern third of Burke County from thE:the In July, 1991, DOE entered into an Savannah River on the east to Brier Creek on agreement with the United States Geological the west and from the Richmond-Burke County Survey (USGS) for an investigation of the line (McBean Creek) on the north to the Burke•Burke- conditions under which ground water from the Screven County line on the south (Figure 1). Savannah River Site (SRB)(SRS) in South Carolina The study area is 12 to 19 miles south of the could migrate beneath the Savannah River into Fall Line, which separates the Coastal Plain and Georgia aquifers. This study, originally referred Piedmont physiographic provinces. to as the Underflow Project, is now knownknmas the Trans-River Flow Project (Clarke, et al, Physiographic Setting 1994). Both the Tritium and the Trans-River Flow projects were initiated due to The Tritium Project study area is within environmental concerns arising from radioactive the Louisville Plateau of Cooke (1925),(19251, releases from the Savannah River Site (SRB)(SRS) characterized by broad, very gently rolling nuclear weapons and research facility, operated uplands that contain deeply incised streams. The by DOE, in South Carolina. Louisville Plateau is moderately dissected, with 100 to 150160 feet of topographic relief. McBean Purpose and Scope Creek definesddnes the northern boundary of the Louisville Plateau as well as formingfodng the The nature of local ground-water RichmondjBurkeRichmond/Burke County line in the$ldythe study area conditions is important to both the GGS Tritium (Figure 1). The Fall Line hills district lies and USGS Trans-River Flow Projects. In order directly across McBean Creek to the north. The to properly evaluate these conditions, an ScrevenjBurkeScreven/Burke county line approximates the understanding of the geology and stratigraphy is southern boundary of the Louisville Plateau in needed. The objective of this report is to lay a the study area, to the south of which is the lithostratigraphic foundation, baaedbased on the North Vidalia Upland district (Clark and Zisa, 1976). American Stratigraphic Code (1986),(19861, upon which further geologic studies and stratigraphic Previous Work refinements may be made. Lithologic descriptions of core samplessample8 and outcrops in Prior to the present investigations, areas to the east (South Carolina) and to the detailed subsurfacesubsur&ce geology (both litho•litho- west (central and west Georgia) were included to stratigraphy and hydrogeology) of eastern Burke provide information concerningthe lateral extent County was poorly understood. Exploratory of described units and correlation wi"'..hw-kh Coastal drilling results in northern Burke County were described by LeGrand and Furcron (1956).(1966). 1 SavannahSavannah RiverRiver SiteSite milesmiles 5 o 5 1 ...... "".". .. ."..... ---- FigureFigure1. 1. IndexIndex mapmap ofof easterneasternBurke Burke County,County,Georgia. Georgia. Modified Modifiedfrom from SummerourSummerour andand others others(1994). (1994). SubsurfaceSubsw4hce studiesstudiw of Burke Count;y County and well, e.g., TR92-1TRB2-1 (Tritium hject),Project), USGS adjacentacljacent areas were conducted by Herrick (1961) Millers Pond (Trans-River(TrnneRiver Flow Project),Prqject), VG-1 and Herrick and VorhisVorhia (1963).(1983). ReconnaissanceReconnAinnnnce (Bechtel Corp., for Georgia Power), etc. is used. mapping was conducted by John Sandy for a Core samples from other Georgia Coastal Plain study of mineral reso-resources in the Central sites are included in Table 2. Lithologic SavannahSadRiver area (Hurst,Wurst, et al,4 1966). descriptionsdeacriptiona from these cores are included for Huddlestun and Hetrick (1979, 1986) provided the purpose of describingdeecrib'hg the lateral extent and a definitiondelinition of the Barnwell Group in Burke correlationcordation with other units. Appendix 1 givesgivw Count;y,County, as well as areasareaa to the west and a physical description of the drill site locations southwest. Huddlestun (1988) defineddedned the as well as other designationsdwignations for these core Altamaha Formation in Burke Count;y.County. samples, including GGS numbers. The cores Structural studies in Burke Count;y County were used in this report are stored in the following conducted by Faye and Prowell (1982) and locations: GGS cores (McBean, Tritium Project) Bechtel Corporation (1982). Aquifer studies and USGS Millers Pond core are stored at the included Upper Three Runs (Vincent, 1982); GGS warehouse in Atlanta, Ga.; the Bechtel Gordon (Brooks, et al,4 1985; Gorday, 1985); and cores (VG-1(VG1 through VG8VG-8 and VSC-3 and VSC-VSC• Dublin and Midville (Clarke, et al, 1985). 4) are stored at Georgia Power Plant Vogtle, Prowell and others (1985) produced a cross• cross- east of Waynesboro, the USGS Albany core is section of the upper Coastal Plain in eastern stored at the USGS warehouse in Reston, Georgia and western South Carolina. Virginia, and the USGS Girard core is stored at Outside the study area, extensive the South Carolina Geological Survey warehouse subsurface studies were conducted at SRS and in Columbia, South Carolina. Core B-246 was the western South Carolina Coastal Plain to the inadvertently destroyed while in storage on east (Siple, 1967; Nystrom and Willoughby, Plant Vogtle property in the late 1970's. Cores 1982) and the Georgia Coastal Plain to the west P-18, P 21TA, and P 22TA (Table 1) are in and northwest (Huddleston,(Huddlestun, 1988; Huddlestun storage in a warehouse at SRS. and Hetrick, 1986, 1991). Fallaw and Price Initially, the core samples were (1995) named a number of new formations at recovered in order to determine well screen SRS, some of which are adopted in this report, intervals for the Tritium Project and Trans• Trans- and presented a very thorough listing of River Flow Project monitoring wells. previous work in the area. Subsequently, the cores were analyzed to evaluate the subsurface lithostratigraphic and Methods hydrostratigraphic framework of the local aquifers (Figure 3). During this study, approximately 9244 In addition to lithostratigraphic analysis, feet of core were examined and described. The micropaleontological identifications were core samples studied (Figure 2, Table 1) were conducted by the senior author, Lucy Edwards collected from the six GGS Tritium Project sites and Norm Frederiksen (both of the USGS) for (TR92-1 through TR92-6),TR92-61, two USGS sites chronostratigraphic and correlation purposes. (Millers Pond and Girard), and one core drilled by Georgia Power Company at Plant Vogtle (B•(B- Acknowledgements 246). Eight cores were drilled in 1982 by Bechtel Corporation (VG-1 through VG-8) in We wish to extend our appreciation to southeastern Burke Count;yCounty along River Road, as property owners of the drill sites in Burke and well as several across the Savannah River in Screven Counties for their cooperation and South Carolina, two of which were used in this assistance. We also gratefully acknowledge Lucy study (VSC-3WSC-3 and VSC-4). Other cores from Edwards and Norm Fredericksen of the USGS SRS in South Carolina were examinedPsrnmined in the for their time and efforts. OutsideOutaide reviews were interest of correlation and comparison. Within conducted by John Clarke (USGS), Tom the text of this report, the field name of each Temples (DOE), and Lucy Edwards (USGS).CUSGS). 3 Savannah River Site N VSC-4 • Figure 2. Index map of core sites within the Trans-River Flow Project area (used in this report). Additional information is within the text, Table 1, and Appendix 1. Modified from Summerour and others (1994). Table 1 Core data from studystudv area. CoreCora SiteSk USGS gridgr# GGSOGSmcore Northlkrthhtllud.IaUIucIe mkngmwe.t Iongllude SurfaceSurfllce ElevaUon-featElevation-feet number number (est.)(-1 (-1(est.) ~~OV~M..~~~~ISVOIDove Mean Sea 1A¥eI TR92-1Tm2-1 31Z0383121038 37643784 33°09'33' w 3r37 81'81° 49' 19"1Q 235 0 TR92·2 31Z047 3762 33 09'U 81° 47' 23" 285 TR92-3 31Y017 3781 33° 06' 35" 81° 48' 54" 195 TR92-4 31ZD50 3782 33° 11' 30" 81° 48' 34" 192 TR92-5 31Z089 3792 33°06' or 81° 4T 03" 235 TR92-6 31Z1OS 3794 33° 10' 42" 81° 47' 10" 240 McBean 3OZD18 3757 33° 13' 38" 81° 55' fJl1' 297 MillersMillen 3OZD16302016 3758 33°33' 13' 48"48' 81'81° 52' 44'44" 245 Pond Girard 32Y02O32Ym njan/a 33°33' 03' 54"54' 81'81° 43' 13"18 250 I I VG-1 32Y027 nja 33° 04' 45" 81° 38' 39" 155 VG-2 32Y017 nja 33° OS' OS" 81° 40' 31" 253 VG-3 32Y016 nja 33° 04' 54" 81° 39' 32" 165 VG-4 32Y018 nja 33° 04' 28" 81° 41' 38" 150 VG-5 33YOO8 nja 33° 04' 06" 81° 37' U 94 VG-6 33YOO7 nja 33° 03' 11" 81° 36' 4r 217 VG-7 32Y028 nja 33° OS' 54" 81° 42' 30" 250 VG-8 33Y011 nja 33° 02' 06" 81° 35' 00- 102 VSC-3VSG3 njan/a njan/a 33°33'07'28'07' 28" 81'81° 35' 42'42" 177 VSC-4V-SC-4 njan/a njan/a 33°06'29"33' 06' s 81'81° 34' 05'OS" 116565 8-2468246 njan/a njan/a 33oOS'53"33' 08' s 81'81° 46' 22'22" 220 P21TAP 21TA njan/a njan/a 33°33' OS'08' 48"48' 81'81° 36' 27'27" 207 P 22TA njan/a njan/a 33°33' 11' 28"28' 81'81° 30' 48'48" 21215 5 P-18 njan/a njan/a 33°33' 15' 11"11' 81'81° 40' 21'21" 354 "nja"-not"n/aM-notaV81lableavailable or not applicable This project was supported, in part, GEOLOGYANDHYDROLOGYGEOLOGY AND HYDROLOGY throughthrough Cooperative Agreements with the United States Department of the Interior (U. S. Geologic Setting Geological Survey) (Cooperative Agreement Number 1434-92-A-0959) and the U. S. Subsurface stratigraphy of the Tritium Department of Energy (Cooperative Agreement Project study area consists of a southeast Number DE-FG-09-92SR12868). dipping package of Upper Cretaceous, Paleogene, and Neogene siliciclastic and carbonate rocks (Figures 3, 4, and 5 and Plate 1). Regional dip 5 Table 2 Core data from outsideoutslde study area. Core Site USGS GGS North IetItucIe (eat.) WMt longitude Surface ElevatIon grid core (eat.) ·feet-fad above MeanM8an number number Sea Level GGS Pulaski 3 n/a 3111 32° 15' 51" 83° 28' 4T 300 USGS Albany nfa 3187 31° OS' 36" 84°06'50" 195 GGS Sumter nfa 3366 32° 04' 03" 83° 59' 23" 270 9A GGS Pulaski 5 nfa 3511 32° 22' SO" 83° 29' 1T 355 GGS LaurensLauren8 1 nfan/a 3523 32°32O30'5W30' 59" 83°63O 02'M' 43"43' 285 GGS ColquittColqultt nfan/a 3545 31°31' 17' 53"53' 83°63O 53' 55"55' 350 11 0 GGS Houston I nfaa 1 3629ZBZI 1 3232030.~39'2Jj'' I 83°d37'4237' 42" 310 9 I I I I I "n/a"-not?/aM-notavailable or not applicable on the top of the Claiborne Group (typical for Hydrogeologic Setting the area) is approximately ten feet per mile to the southeast. The Upper Coastal Plain sediments of The fluvial, coastal marine, and shallow the study area are included in the Southeastern inner neritic marine deposits which compose the Coastal Plain hydrogeologic province (Aadland, subsurface of the study area lie within a et al, 1992). The aquifers of interest in the transitional"zone"transitional "zone"between the Atlantic and Gulf Trans-River Flow study area are (in descending Coastal Plain provinces. Within this zone, order): 1.) Upper Three Runs (unconfined) abrupt lateral variations in lithofacies (Aadland, et al, 1992; Summerour, et al, 1994); characteristics are common. The Cape Fear 2.) Gordon (confined)(con6ned) (Brooks, et al, 1985); 3.) Formation, Steel Creek Formation, Millers Pond (confined) (Falls and Baum, 1995); undifferentiated Black.Black Mingo Formation, and 4.) Dublin (confined) (Clarke, et al, 1985); and Snapp Formation, McBean Member of the 5.) Midville (confined) (Clarke, et al, 1985). The Lisbon Formation and the IrwintonIMinton and GriffinsGfina hydrostratigraphic units discussed in this report Landing Members of the Dry Branch Formation include the Upper Three Runs, Gordon, and and Tobacco Road Sand of the Barnwell Group Millers Pond aquifers. are southern Atlantic Coastal Plain stratigraphic Downdip, the siliciclastic and carbonate units (Figure 4 and Plate 1). The Still Branch sediments of the Upper Three Runs aquifer Formation and Bennock.Bennock Millpond Sand Member, become part of the predominantly carbonate undifferentiated Lisbon Formation, Blue Bluff Upper Floridan aquifer system (Clarke, et al, Member of the Lisbon Formation, and Twiggs 1994) and the siliciclastic sediments of the Clay lithofacies of the Barnwell Group are Gordon aquifer become part of the eastern Gulf Coastal Plain stratigraphic units. predominantly carbonate Lower Floridan aquifer The Pio Nono Formation, Gaillard Formation, (Clarke, et al, 1994). The siliciclastic sediments and Congaree Formation occur both in the Gulf of the Millers Pond aquifer grade downdip into Coastal Plain and the southern Atlantic~tlhicCoastal the clays of the Meyers Branch confiningconhing system Plain (Figure 4 and Plate 1). (Falls, personal communication, 1995) (Figure 3). 6 Formation/Formation1 Burke Co. SASSRS Lithology Member Hydrologic Units Hydrologic Units ~ .::::•• e ••••••••••••••••••••.::::.::.: .:.. :::::::: : :.:: ::: . Tobacco Road Sand Upper Three ~ :.:~: Runs Aquifer :.::: ::::.::~::: ::: a. :.:•••••••••••: .••• ••••::::.::: (updip) ~ :::: .....::::::;:::::.::::: Irwinton Sand Mbr. (; :-.::::::. :-::.:.:.:.-.::-::::... .. - .. . Dry Branch Fm. Upper Three l··~~·~~·:~·~~ Runs Aquifer ~.~~. ~*:~~~~ Griffins Landing Mbr. ai Dry Branch Fm. Floridan Aquifer III •••• '. • •• Floridan Aquifer system •C Utley Ls. Mbr. (downdip) U •o Clinchfield Fm. W -LA- McBean I Blue Bluff P --LT LTATLT Mbr. Mbr. 3 OTTTT Lisbon Fm. Gordon L Aquitard Confining unit Bennock StilStill Branch Millpond Sd. Mbr. Sd. Gordon Aquifer Floridan Aquifer Congaree Fm. system ------. e ------. c ~::.:;::;._:::.;·t;·:·;:·;.;·::;~:;{;;;f:::~?f~~~:IT;{~~:{~y~~~~:~:::::;;:~;!:~ Snapp Fm. Aquitard •u Meyers Branch o ••:::.::••••::.:. -:-•• -7- Confining system !it •••• ••••••••• ~'-;- -:-.-; 'i• o •••. :.:.:.•::: ..•••.•. o--~7_~ Q. ~ -;-.~ Undiff. Black Mingo Fm. Millers Pond aquifer : :::::: .•.:: ~.-=- .:.. ... 7--:.•. r---- "••••• ••••••...•••••.•••••• ;••'-="=='=5'=::i=r------+------! itU~g:;~:f~~~~~~i$ Steel Creek Fm. Aquitard =i ~. ~'::.::;:.~.;:.;.::.;=;.;.::.=r=;. Q. () j :•: •••••• : •• iI------If------t------t I..£.L •• •• ••••• •• • ••••••• ~ ~ :~.:.~~ ~: : :.~ ~. ~:::::: ...... GaiHardGaitlard Fm. Dublin Aquifer Dublin Aquifer o ...... :::.::::::.::::.:.:.:.... ~...... Coarse sand ~ Limestone~imestone b-=-J Clayaay Marl and clay are [Zill Medium sand ~ Marl dotted where sandy. Figure 3. Tritium Project stratigraphic and hydrostratigraphic units for Burke County and SRS area. SASSRS terminology from Aadland and others (1992), Millers Pond aquifer from Falls and Baum (1995). Modified from Summerour and others (1994). 7 European Provincial Eastern Georgia Eastern Georgia Western Georgia South Carolina Stage Stage Prowell & others, 1985 this report W E Jacksonian Ocala Limestone Cooper Group Gl 00 • rane ormation 1iii Priabonian ...J Barnwell Group Bartonian Q) c: Q) ~ Claibornian Lisbon Formation lisbon/McBean Formation (J Bennock 0 :5! W ~ Millpond Sd. StiD Branch Sd Lutetian Congaree Formation Congaree Formation Congaree Formation >- Fourmile Fm. Fishburne Fm. ~ Ypresian w Huber Formation Sabinian Thanetian ili\\'i'~llllllfIIIJI~~::~l::;~,\:'t~ 2!Q) ~ (J ...J ap ormation Snapp Fm. .- Q. 0 Selandian t----==c....:...:==.:....--+=:::....:...:;.:....------1:::E ;:, j! Midwayan Undiff. Black e >- C!J ~ ~ Rhems Formation 13 w Danian Clayton Formation Mingo Fm. ffl co03 Navarroan Maastrichtian Ripley Formation Steel Creek Formation Steel Creek Fm . I------t"---t-----!....-~---; Unnamed Cusseta Sand Gaillard Formation Black Creek Group Campanian Tayloran III Black :;, BluffBlufftowntown Formation Creek ~ CII I-----~t_------I Formation p======:;:.;:; ~ &l 1:,;,"'::,"';:::"",:.....:':...::.....:..:"":.:.:"".,::"":::',"".:::.,.,.".""'•• ,:.""',',',.""::.:....:.::"".::,:""';::':"":....."'•••:.-.1" ~ Sentonian Austinian () Coniacian Turonian Eaglefordian Tuscaloosa Formation ape Fear Formation Cenomanian Woodbinan Figure 4. Correlation chart for the study area and adjacent regions. Shaded areas inidicate missing stratigraphic intervals. Modified from Prowell and others (1985) and Summerour and others (1994). A more detailed chart is shown in Plate 1. GGSGGS 37823782 GGSGGS 37943794 GGS 3762 GGS 3792 GGS 3781 TR92-2 TA92-5 TR92-4TR92-4 TR92-6TR92-6 TR92-2 TR92-5 % TR92-3TA92-3 192'lQ2' 252'252' 285' 235' 194' 300' ---l,.....------~- 200' Irwinton Sand Mbr. So ..,.:s.-41-----I------\--+----""" Griffins Landing Mbr. "C!., 100' un , undlff.•and f. sand Lisbon Fm. Utley Mbr., Clinchfield Fm. Blue Bluff Mbr. Bennock MiNpond Sand Mbr. Still 8fanch Sand Sea Congaree Fm. level Undlff.Undiff. BlackBlack MlngaMinw Fm.Fm. .__------100' ------. Unditf. Black M' ------:------:. SteelSteel Creek Creek Fm.Fm. 'ngo Fm. ------200' ---. GaillardGaiWard Fm.Fm. -----. -300' TOTD o0 1 mile TO 505505 B Kaolilitic strata 507 TOTD ...... Unconformity 10101010 -- Urit Ixuldaries I 1 I FigureFigure 5.5. North-southNorth-south stratigraphicstratigraphic cross-sectioncross-section betweenbetween core holes TR92-4 and TR92-3. Modified from Summerour and othersothers (1994.)(1994.) StrocturalStructural FeaturesFeaturea Late Eocene Dry Branch Formation. These relationships yield e8timatedestimated slip rangesmnges from 0 The most important basement structural to 1.5 m/my. with an avemgeaverage of about .4 m/my. feature in the study area is the buried Triassic over the last 85 mymy.... extensional Dunbarton graben basin (Marine The down-to-the northwest movement and Siple, 1974; Snipes, et al, 1992, 1993) sense forfor the Pen BmnchBranch fault is intriguing in (Figure 6). Based on simultaneous gravity and that early MesozoicMe8ozoic deposition of fluvial magnetic modeling (Cumbest, et al, 1992), the sequences in the Dunbarton basin indicates that dimensions of the Dunbarton basin are the base surface must have been lower that the approximately 30 miles (48 km) long, 5,500 feet erosional surface of the crystalline terrain to the (1,700 m) deep, and 8 to 10 miles (12.8 to 16 northwest. However, this paleoerosional surface kIn)km) wide (Snipes, et al, 1993). is presently about 80 to 100 feetfeet (24 to 30 m) The basement rocks adjacent to the below the basin surface at the location of the Dunbarton basin consist primarily of Paleozoic fault. This relationship has led to speculation greenschist facies metavolcanic rocks and that the Pen BmnchBranch fault is a Dunbarton basin amphibolite facies schists and gneisses (Snipes, border fault reactivated in a reverse sense due to et al, 1993). Red bed sediments and compressional stresses or that it is an antithetic conglomerates were deposited within the graben basin fault."fault. " (Siple, 1967; Marine and Siple, 1974; Cumbest, Based on core data, the presence of the et al, 1992; and Snipes, et al, 1993). In Georgia, fault in Georgia is suggested by structure core TR92-6, north of the basin (Figure 2) contour and thickness anomalies along the terminates in weathered biotite schists, whereas projected Pen Branch fault in eastern Burke the USGS Girard core (Figure 2) terminates in County. The anomalies become more Triassic red beds of the Dunbarton basin. pronounced with depth, suggesting continuing The southeastern boundary fault (or fault movement with time. Movement on the fault zone) of the Dunbarton basin is believed to Pen Branch fault does not appear to have be the Martin fault (Figure 6) (Snipes, et al, occurred since the end of the Middle Eocene 1993). The northwestern boundary fault (or because there areire no anomalies associated with fault zone) of the Dunbarton basin appears to be the fault for sediments deposited after the coincident with the known location of the Pen Middle Eocene (Snipes, et al, 1992, 1993). There Branch fault (Snipes, et al, 1992, 1993). Based is also a lack of historic seismic activity near the on data provided by 57 wells on SRS (Snipes, et fault and an apparent lack of recognizable al, 1992, 1993),1993)) the Pen Branch fault is slightly earthquake-produced liquefaction structures in sinuous with an average strike of N 55°55' E. If any of the Tertiary sediments near the fault. the Pen Branch fault extends into Georgia, as Additional information has been provided by a projected, it would lie beneath the Savannah shallow seismic reflection survey conducted River channel near Hancock Landing, north of during June, 1995, by University of South Georgia Power Plant Vogtle (Snipes, et al, 1993). Carolina personnel. This seismic survey was According to Snipes and others (1993, p. 195): conducted along a line between cluster sites "Stratigraphic relationships and seismic studies TR92-1 and TR92-5 (Figure 2) and indicated the indicate that the Pen Branch faultfault is a possible existence of a river or scour channel (of subverticalsubvertical growth fault with down-to-the unknown orientation) overlying the Pen Branch northwest movement sense. Near the center of fault (zone) (Mike Waddell, University of South SRS, the thickness of the Upper Cretaceous Carolina, personal communication, 1995). As clastic strata is about 670 feetfeet (201 m) on the indicated by the seismic survey data, the channel downthrown side, in contrast to 610 feetfeet (185 m) has a width of approximately 0.75 miles (1.2 km) on the up-thrown side. The throw decreases in and a depth of approximately 750 feet (250 m) successively younger beds from 80 to 100 feet (24 below current surface level, and has cut as deep to 30 m) at the base of the LuteLate Cretaceous Cape as the Middendorf Formation of Prowell and Fear Formation to 30 feetfeet (9 m) at the top of the others (1985) (Waddell, personal communication, 10 Savannah River Site miles 5 o 5 Figure 6. Map showing location of Dunbarton basin and Pen Branch and Martin faults on SRS and projected extensions into Georgia. Fault data from Snipes, et ai, 1993. 1995). A re-examination of the shallow seismic8eismic Type Locality survey of the Savannah River channel (Henry, 1994) shows the possible existence of a buried The name Oconee was taken from the channel feature near Hancock Landing (John Oconee River in Georgia, that flows through the Clarke, USGS, personal communication, 1995; heart of the Georgia kaolin mining district. The Waddell"Waddell, - personal communication, 1995). type area extends from near the Ocmulgee Structure contour and isopach anomalies shown River, in the west, into Washington County, in this report (based on core data), north of Georgia, in the east. In outcrop, formations that Plant Vogtle, may be due to the influence of constitute the Oconee Group in its type area both the Pen Branch fault zone and the buried include the Pio Nono Formation, Gaillard channel feature. Detailed results of this survey Formation, and Huber Formation. will be provided in the Tritium Project Phase IIIT Huddlestun and Hetrick (1991) did not report (Summerour, et al, in prepdon).preparation). select a type locality for the Oconee Group because all good exposures of the soft sands and STRATIGRAPHY kaolins are transient. Oconee sediments are best exposed in sand pits and kaolin mines (that Oconee Group will be reclaimed) and are rarely well-exposed in roadcuts. Natural exposures are either too small Definition or too weathered to observe the wide variation in lithologies present within the Oconee Group. The Oconee Group was introduced Two cores from the Deepstep area of informally by Huddlestun (1981) and Schroder Washington County include parts of the Oconee (1982), and was formally proposed as a new Group, whereas core GGS Houston 9 (Table 2), group by Huddlestun and Hetrick (1991). The though not in the "type area",arean, contains a more Oconee Group includes all pre-Upper Eocene, or complete Oconee Group section. pre-Barnwell Group kaolin and kaolinitic sand deposits of fluvial origin in the Fall Line Hills Lithology districts of the Coastal Plain of Georgia, South Carolina, and North Carolina (Cooke, 1925; Typical Oconee Group deposits consist of Fenneman, 1938; Cooke, 1936; Clark and Zisa a series of fining-upward sequences. Basal (1976),(19761, excluding the Cape Fear Formation. The sediments generally consist of crudely cross•cross- named formations that constitute the Oconee bedded, poorly sorted, pebbly to gravelly, Group in Burke County include from oldest to kaolinitic sand with variable quantities of kaolin youngest: Pio Nono Formation, Gaillard clasts and kaolin cobbles (rarely bauxite or Formation, Steel Creek Formation, and Snapp pseudo-bauxite cobbles). These basal sand units Formation of Price and others (1992). The first are prominently and, in many places, three formations above are Late Cretaceous in dramatically stratified with horizontal to age whereas we consider the Snapp to be Late undulatory bedding, and planar and trough cross Paleocene, Selandian, late Midwayan age (Figure bedding on small to large scales. 4). Prior to this report, only the Gaillard Above the basal beds, sands generally Formation had been recognized in the study fine upward and become better sorted, more area (Gorday, 1985). The Black Creek thinly bedded, and more finely micaceous. The Formation (downdip equivalent of the Gaillard middle and upper parts of the fining-upward Formation) and the Cape Fear Formation (basal sequences generally consist either of heavy Coastal Plain unit in the area) are not mineral-rich, moderately to well-sorted, considered to be part of the Oconee Group. undulatory to horizontally bedded, fine- to medium-grained sand or of small to large lenses of finely sandy and micaceous to relatively pure kaolin. 12 The tops of fining-upwardfininp-upward sequences however, the kaolins of the Pio Nono Formation, have uneven surfaces,sdms,indicating some scour and SteelSteal Creek.Creek Formation, and Snapp Formation erosion prior to deposition of the overlying t3'Picallytypically are strongly pigmented (weathered) fining-upward sequence. Fining-upward over most of their surface and subsurface extent.extent sequences generally cannot be traced across This suggests that the high pigmentation of the largelarge pits and, therefore,therefore, are not laterally formationsformations was penecontemporaneouspenemntemporaneous with continuous. Channel cut-and-fillcut-and-5U structures of deposition of thethe formations.formations. Numerous sand variable scale are commonly well-exposed inin intervalsintervals inin the the Steel Creek.Creek Formation have kaolin pits. littlelittle pigmentation and lithologicallylithologically resemble Sands of thethe Oconee Group are kaolinitic thethe Gaillard Formation. toto some degree, micaceous and feldspathic.feldspathic. Some formations and bedsbede are more feldspathic Stratigraphic Relationships thanthan others. The sands are laminatedlaminated toto thicklythickly bedded, finelyfinely toto coarsely micaceous, with The outcrop belt of thethe Oconee Group common micaceous bedding planes. Dark extends from eastemeastern Alabama throughthrough South minerals are locallylocally abundant and occur both Carolina intointo North Carolina. Because therethere are scattered throughthrough thethe sands or as thin dark locallocal outliers ofofthethe group north of thethe Fall line, layenllayers or lenseslenses thatthat appear toto be carbonaceous thethe Oconee Group probably exten,dedextended some or manganiferousmangan&rous wad (Mn0(MnO,).2). distance north of thethe present Fall Line. The All thethe formations of thethe Oconee Group Oconee Group inin Burke County isis a subsurface are kaolinitic (rarely(rarely smectitic or bauxitic), and unit. It grades downdip or seaward intointo various contain clasts and cobbles of kaolin, small to Upper CretaceousCremusand lowerlower Tertiary formations largelarge lenseslenses and irregular-shapedirregular-shaped masses of coastal marine toto marine formations inin Burke kaolin, small toto largelarge lenticularlenticular massesmassea of and Screven Counties,Countieg Georgia. micaceous, sandysandykaolin kaolin toto relativelyrelatively pure kaolin. InIn Burke County,County, thethe OconeeOconee GroupGroup TheThe lenseslenses ofof kaolin range inin thicknessthickness fromfrom a disconformablydisconformably overliesoverlies thethe CapeCape Fear fewfew feetfeet aess(less thanthan 11m) toto approximatelyapproximately 7070 feetfeet Formation.Formation. The uppermost formation ofof thethe (21(21 m), andand inin extentextent fromfrom several several hundred OconeeOconee GroupGroup inin Burke County,County, thethe SnappSnapp squaresquare yards (approximately(approximately several several hundred Formation,Formation, isis disconformably overlain by thethe squaresquare meters) toto severalseveral hundred acres.acres. CongareeCongaree Formation. The CongareeCongaree appears toto SmallSmall toto largelarge lenseslenses ofof variably pinch outout updip inin Richmond CountyCounty carbonaceouscarbonaceous and ligniticlignitic sandssands and and ~scleys immediatelyimmediately north ofof McBean Creek. commonlycommonly areare scatteredscattered throughoutthroughout thethe OconeeOconee OnlyOnly threethree corescores penetrate thethe entireentire Group.Group. The organicsorganics occur as finelyfinely OconeeOconee GroupGroup inin Burke County:County: thethe USGS disseminateddisseminated carbonaceous material, chiefly as MillenlEJIillers Pond core, thethe GGS TritiumTritium Project corecore ligniticlignitic oror carbonaceouscarbonaceous flecksflecks ofof uncertain TR92-6,TR92-6,andand thethe USGS GirardGirard corecore (Figure(Figure 2). origin,origin, discrete carbonizedcarbonized fragmentsfragments of woody TheThe totaltotal cumulativecumulative thicknessthickness ofof thethe OconeeOconee material (lignite),(lignite), andand carbonized impressionsimpressions of GroupGroup inin thethe USGS MillenlMillers Pond corecore isis 525525 vegetation.vegetation, Generally thethe carbonaceouscarbonaceous lenseslenses feetfeet (160(160 m), inin corecore TR92-6TR.92-6 thethe cumulativecumulative gradegrade inin allall directions intointo noncarbonaceous thicknessthicknees isis 517617 feetfeet (158(168 m), and inin thethe GirardGirard sand,sand, kaolinitic sand,sand, or kaolin. Organic Organic contentcontent corecore thethe OconeeOconee GroupGroup isis 522522 feetfeet (159(159 m). ofof thethe lenseslenses rangerange fromfrom minor (based(based onon graygrey ThereThere isis no apparentapparent thickeningthickening ofof thethe OconeeOconee colorationcoloration ofof thethe sedimentsediment due due toto finelyfinely GroupGroup southeastwardsoutheastward throughthrough BurkeBurke CountyCounty disseminateddisseminated carbonaceouscarbonaceous materialmaterial inin thethe sandsand becausebecause thethe GaillardGaillard FormationFormation gradesgrades downdipdowndip andand kaolin)kaolin) toto lenseslenses ofof almostalmost purepure intointo 155165 feetfeet (47(47 m)m) ofof BlackBlack Creek.Creek FormationFormation carbonaceouscarbonaceous kaolinkaolin andand lignite.lignite. inin thethe southemsouthern partpart ofof thethe countycounty andand thethe PioPio InIn thethe GaillardGaillard Formation,Formation, MiddendorfMiddendorf NonoNono gradesgrades downdipdowndip intointo anan unnamedunnamed Formation,Formation, SteelSteel Creek.Creek Formation,Formation, Snapp Snapp formationformationin in centralcentral andand southemsouthern BurkeBurke CountyCounty Formation,Formation, andand HuberHuber Formation,Formation, thethe sandsand isis thatthat isis notnot OconeeOconee Group.Group. characteristicallycharacterbtically whitewhite toto lightlight graygray inin color;.color;. 13 Sedimentary features such as formation that crops out in Richmond County bioturbation and herring-bone crosscmbedding, south of Augusta.Augusta and lithic components such as limeatone,limestone, calcite, In the past, the Steel Creek Formation dolostone, dolomite, glauconite, phasphate,phosphate, and was included in the Tuscaloosa Formation of marine fossils characteristic of coastal and near-near• Siple (1967) and BechtelBechtel(1982),(1982), undi£ferentiatedundifferentiated shore marine deposits are absent in the Oconee Oconee Group by Huddlestun (1981),(19811, Gaillard Group. Fossils include palynomorphs and plant Formation by Gorday (1982) and Black Creek fossils. Land vertebrate fossilsfoesile and associated Formation (?) by Faye and Prowell (1982). The trace fossils such as animal trails have not been lithology ofofthethe Steel Creek Formation resembles reported from Oconee Group deposits. that of the Pio Nono Formation more than any Similarly, shallow water sedimentary structures other formation of the Oconee Group. such as symmetrical ripple marks or mud cracks also have not been reported from the Oconee Type LocalityLocallty Group in Georgia. Considering the above observations, the The Steel Creek Formation is named for Oconee Group appears to have been deposited in Steel Creek, a small tributary of the Savannah an area of rapidly shifting river channels and River, approximately 3 miles (0.9 km) northwest currents such as in a continuously-saturated, of the AUendale/BarnwellAllendale/Barnwell Counties line and 1.3 braided river system. miles (0.4 km) northeast of S.C. Hwy. 125 in southern Barnwell County. The site of the core Age P 2121TATA in the Savannah River Site is the type locality of the formation. The coordinates of the In Burke County, Georgia, the age range site of the core P 21TA is 3333'0 08' 48" North of the Oconee Group is Late Cretaceous, Latitude and 8181'0 36' 27" West Longitude. The probably Austinian (early Santonian) through core site is on the Girard NE, USGS 1:24,000 early Navarroan (early Maastrichtian),Maashichtian), to Late topographic quadrangle sheet. The type section, Paleocene, late Midwayan, Selandian. In or unit-stratotype (holo-stratotype), of the Steel southern Richmond County the upper part of Creek Formation is in the interval from 453 feet the Oconee Group is Maastrichtian, Danian, and to 594 feet in the core. The Paleocene Sawdust Selandian in age (see Huddlestun and Hetrick, Landing Formation overlies the Steel Creek·Creek at 1991 for more discussion of the age of the 453 feet in the type core and the Black Creek Oconee Group). Formation.Formation underlies the Steel Creek at 594 feet. Three GGS Tritium Project cores, TR92-2, Steel Creek Formation TR92-4, and TR92-6 (Figure 2) are designated as reference localities for the Steel Creek Definition Formation in Georgia.Georgia The core siteaite localities are described in Appendix 1, and the coordinates The Steel Creek Formation was named are listed in Table 1. The core intervals for by Fallaw and Price (1992, 1995) for a these reference sections (hypostratotypes) for the subsurface, interbedded, varicolored and mottled, Steel Creek Formation are listed in Table 3. kaolin and light-gray sand formation in the The Steel Creek in core TR92-2 is Cretaceous part of the Oconee Group in SRS in typical for the formation in eastern Burke Barnwell County, South Carolina. In eastern County and consists of several fining-upward Burke County, Georgia, the Steel Creek sequences. In core TR92-4, the Steel Creek Formation overlies the Gaillard Formation and consists mostly of highly pigmented kaolins to disconformably underlies the unMerentiatedundifferentiated sandy kaolins with minor light gray sand and is Black Mingo Formation. Although the Steel disconformably underlain by the Gaillard Creek is a subsurface formation in Burke Formation. In core 7392-6,TR92-6, the Steel Creek County, it may be the uppermost Cretaceous Formation interval is Lithologicallylithologically typical of the unit and is conformably or panwonformablyparaconformably 14 Table 3 Steel Creek Formation reference sections In eastern Burke County. Core Site,Sb, GGS Site Top of formatlon-formcltlon- I Bottom~mofof see6ee figureFlgure 2 core ElevationElavolion feet below formlltlon-fonnatlon- Table 1 numbernumbof aboveabow MeanM.M Sell!ih .usurface....ce feeth* below .urf8cesurface LevelLwd TR92-2 GG8-3762 285 402 537 (core bottom) TR92-4 GG8-3782 192 386 501 TR92-6 GG8-3794 240 324 415 underlain by the Gaillard Formation. The Steel coherent sand, and scattered concentrations of Creek is disconformably overlain by the dark minerals define some crude bedding planes. undifferentiated Black Mingo Formation in all The colors of most sand intervals range three cores. In the USGS Girard core, the from light-gray to white. Where the sands are Gaillard grades downward into the Black Creek pigmented, the colors range fromfroni shades of Formation. reddish brown, purple, pale orange, brown, and gray.gray- Lithology Kaolin beds are generally silty to sandy, variably and finely micaceous, and contain The Steel Creek Formation commonly is varying amounts of dark minerals. Some beds made up of a series of fining upward sequences. appear to contain a trace of interstitial silica. Kaolin and sand are the dominant lithic "Hematitic" spherules or "ooids" occur within the components of the formation. Kaolin occurs kaolin in one core (TR92-4). Sand content interstitially and, more commonly, as thin to within the kaolin beds is variable, some intervals thick beds or lenses. Some beds of sand appear are almost barren of sand whereas other to be almost devoid of kaolin. Scattered kaolin intervals are very sandy. Sand size within clasts are rare. Minor lithic components include kaolin beds ranges from very fine-grained and sparse to common, finely to coarsely grained well-sorted, to coarse-grained and very poorly mica. The Steel Creek is more micaceous than sorted. overlying formations. Gypsum- and sulphur•sulphur- The kaolin beds are commonly massive•massive- bloom occurs in some thin intervals on the bedded and structureless. The kaolin is dense, cores; carbonaceous intervals and lignitic tough, brittle and hard, breaking with an fragments are rare; pyrite is rare and occurs as irregular, hackly fracture reminiscent of the dustings along partings or within the kaolins commercial "hard" kaolins. Some kaolin is waxy and dark minerals are common. Quartz pebbles to the touch and slickensided joints are common. are rare, and scattered throughout beds of Kaolin withwitl? subsubconchoidalconchoidal fracture occurs in coarser sand. some rare and scattered thin intervals. The sand ranges from very fine grained Individual kaolin beds may be as much as 69 and well-sorted (especially in the upper part of feet (21 m) thick. fining upward sequences) to coarse, granular, Kaolin in the top several feet of the pebbly, and very poorly sorted in the lower part formation is commonly "bleached" veryvery.light.light gray of a fining upward sequences. The quartz sand to very pale orange and may contain finely is variably coherent to incoherent, probably disseminated pyrite. Kaolin beds in general are depending on the amount of interstitial kaolin. highly and complexly pigmented throughout Sand beds generally are massive-bedded and with extremely irregular mottles, blotches, and structureless. However, crude bedding i~is almost microscopic root-like streaks. Colors commonly seen in some of the intervals of range from white to varying shades of gray 15 where carbonaceous and pyritic. Other colors burrows in the underlying sediment. Where the include shades of red, pink, reddish brown, basal Black Mingo and uppermost Steel Creek purple, orange, yellowish brawn,brown, yellow, gray, are coarsely sandy, micaceous, and poorly sorted, and yellowish green. the contact between the two formations is difficult to discern. In this situation, the Black Stratigraphic Relationships Mingo/Steel Creek contact appears to be only a minor bed change. The Steel Creek Formation is known to The Steel Creek Formation is underlie eastern Burke County and has also distinguished from other formations of the been identified in Bechtel Corporation cores Oconee Group in that; 1.) the kaolin beds are from Allendale County, South Carolina. Neither numerous and may constitute more than half of its known western nor southern limits have the Steel Creek section in any particular core; been identiiiedidentified in Georgia. However, its 2.) the kaolins (and some sands) are generally downdip limit is probably in Screven County. highly pigmented and mottled (generally the The Steel Creek Formation is not known associated sands are not pigmented or only to crop out in the kaolin mining district in mildly pigmented); and 3.), the Steel Creek Georgia. Farther west, the coastal marine kaolins are tough, waxy, commonly slickensided Nakomis Formation of Huddlestun and Hetrick and break with a hackly, uneven fracture. We (1991) is the most updip lower Navarroan know of no soft, conchoidally fracturing kaolin formation that occurs in the Steel Creek beds in the Steel Creek Formation that resemble stratigraphic position. Either early Navarroan the soft kaolins of the Gaillard Formation fluvial deposits were eroded prior to the (especially the Buffalo Creek Kaolin Member). Paleocene or were not deposited in central and Only five cores have penetrated the southwestern Georgia. entire Steel Creek Formation; therefore, the In all sufficiently deep cores in Burke regional or local thickness distribution patterns County, the Steel Creek Formation conformably cannot be clearly defined. However, assuming or paraconformably overlies the Gaillard the upper and lower contacts of the formation Formation. The contact relationships between have been correctly identified, there appears to the Gaillard and the Steel Creek are generally be no systematic thickness changes in the ambiguous due to several factors including: 1.) formation in the Savannah River area. The poor core recovery; 2.) the frequent lithologic thickness of the Steel Creek Formation ranges similarity of uppermost Gaillard and lowermost from 68 feet (21 m) thick in the USGS Millers Steel Creek sands or Gaillard sands underlying Pond core, to more than 135 feet (41 m) thick in lithologically similar Steel Creek sands; or 3.) the Bechtel core VSC-4 near the Savannah River massive reworking of Gaillard sediments into in northern Allendale County, South Carolina basal Steel Creek sediments during initial (Table 4). deposition of the Steel Creek. In southernmost There is a relatively consistent southeast Burke County, south of Girard, the Steel Creek dip of the upper surface of the Steel Creek, Formation probably directly overlies the Black except where influenced by the projected Creek Formation, the downdip equivalent of the location of the Pen Branch fault, northwest of Gaillard Formation. Plant Vogtle (Figure 7). The Steel Creek Formation in Burke The environment of deposition of the County is disconformably overlain by the Steel Creek Formation was fluvial, and the undifferentiated Black Mingo Formation. This formation was probably deposited by a system of contact is especially dramatic where braided streams draining the adjacent Piedmont carbonaceous clays or fine sands of the Black Province. Mingo lie directly on Steel Creek kaolins. In those examples, the top few feet of the Steel Creek Formation is "bleached" of pigment and fine-grained pyrite has formed in joints or 16 Table 4 Thickness variations for Steek Creek Formation. Core SlteSite GGS number thicknessThickness Inin feet USGS Millers Pond GG5-3758GGS-3758 68 TR92-4 GG5-3782GGS-3782 119 TR92-6 GG5-3794GGS-3794 90 USGS Girard n/anla 78 VSC-4 n/anla 135+ "n/a%/a"-not"-not applicable Age Formation appears to consist of one fining upward sequence capped with a strongly The Steel Creek Formation is mostly pigmented, hard, hadslyhackly kaolin with irregular nonfossiliferous. Samples from the few, thin fracture. The mottled kaolin is found in carbonaceous intervals of the formation in eighteen out of nineteen cores from Burke, Georgia are barren of pollen so no direct Richmond and Jefferson Counties, Georgia, and biostratigraphic information is available. western Barnwell and Allendale Counties, South However, in terms of stratigraphic position and Carolina. The kaolin bed, therefore, appears to physical correlation, the Steel Creek Formation be a useful marker bed across that entire area. stratigraphically overlies the Campanian The Snapp Formation is included here in the (Tayloran) Gaillard Formation which suggests Oconee Group. that the Steel Creek may be early Maastrichtian The Snapp Formation in Georgia has (early Navarroan) in age. According to Fallaw not generally been recognized as a separate and and Price (1995);(1995): ''Wood'Wood fiagnents,fragments, spores, distinct lithostratigraphic unit. LeGrand and pollen, and rare dinoflagellates have been found Furcron (1956) and Herrick.Henick (1961) included it in in the SRS wells. Dinoflagellates and pollen the Tuscaloosa Formation and Huddlestun yield a Maastrichtian age. If the Steel Creek is (1981) and Bechtel (1982) included it in the the same age as the redefined Pee Dee (Sohl(Soh1 and Huber Formation. In South Carolina, the Snapp Owens, 1991), it correlates with the middle and has been called the Williamsburg Formation by upper Ripley and Providence Formations of Colquhoun and others (1983), Steele (1985) and Georgia and Alabama."Alabama." McClelland (1987). The Steel Creek Formation is overlain disconformably by the Paleocene (Midwayan) Type Locality undifferentiated Black.Black Mingo Formation and, therefore, is older than Paleocene age. The Snapp Formation is named for an old railroad stop in the southeastern part of SRS Snapp Formation (Fallaw and Price, 1992). The type locality of the Snapp Formation is the site of the core (and Definition water well) P 22TA in SRS (Fallaw and Price, 1992,1995).1992, 1995). The type section, or unit-stratotype The Snapp Formation was named by (holostratotype), of the formation is the interval Fallaw and Price (1992, 1995) for a distinctive, 310 feet to 360 feet in core P 22TA. Three subsurface, lower TertiaIyTertiary kaolin and sand Georgia cores and one South Carolina core formation that underlies SRS. It is recognized (Table 5) have been designated as reference in Burke, Screven, and Jefferson Counties, localities for the Snapp Formation in the Georgia. In eastern Burke County, the Snapp Tritium Project study area (Figure 2). 17 Savannah River Site N Contour interval 20 feet Core site • Figure 7. Structure contour map of the top of the Steel Creek Formation. Elevations are in feet relative to mean sea level. Modified from Summerour and others (1994). Table 5 SnappS~DD. . Formation reference sections in the Savannah River area. Core SIteSlts GGS Site Top of Bottom of core Elevation formation-formatlon- formdon-formation- numbers aboveabOve Mean Sea feetfed below feet below surface Level (feet) surfacesurhlce USGS Millers Pond GG5-3758GGS-3758 245 165 236 TR92-2 GG5-3762GGS-3762 285 330 386 TR92-4 GG5-3782GGS-3782 192 231 282 ------ VSWVSC-4 nfan/a 165 322 3n.S377.5 "n/a'n/aU-not-not appllcaDleapplicable The USGS Millers Pond core was chosen of the Black Mingo Group). Core recovery as a reference section because it contains typical between the Williamsburg and the Snapp is Snapp lithologies and is clearly overlain 100%. There is no evidence for disconformity. disconformably by the Congaree Formation and is underlain with apparent disconformity by the Lithology undifferentiated Black Mingo Formation (to be discussed in the following section). Core TR92-2 The Snapp Formation commonly consists is chosen as a Snapp Formation reference of one fining upward sequence in Georgia. In all section because: 1.) it displays the typical single cores but one in Burke County (GGS McBean), fining upward sequence; 2.) the highly there is a bed of kaolin of varying thickness in pigmented kaolin and the "bleached"'%leacheduzone at the the upper part of the formation, the top several top of the formation is present; 3.) the lower feet of which are "bleached". In two cores kaolinitic, micaceous, poorly sorted coarse sand (TR92-4) in Georgia and VSC-4 in South in the lower part is well-developed; and 4.) there Carolina) the entire section consists of kaolin. was moderately good (72%) core recovery within Elsewhere, the lower part of the formation is a the formation. Core TR92-4 is chosen as a sand. The kaolin is variably silty and finely reference section because: 1.) it displays well the micaceous. Fine-grained pyrite commonly occurs "bleached" zone with burrows at the top of the in burrows, along joints or in irregular kaolin; 2.) spherical "ooids" or "pellets" that are concentrations near the top of the Snapp. Very locally common within the kaolin component of fine grained pyrite is found elsewhere scattered the formation; 3.) the entire Snapp section is in the formation. Fine "limonite-hematite"limonite-hematite" and distinctive and consists of kaolin without any kaolin "ooids" or "pellets" (about 1 mm to 2 mm sand beds; 4.) Planolithes are present at 228 to across) are scattered throughout the upper part 229 feet (also see Schroder, 1982); and 5.) the of the kaolin in several cores. contact with the underlying undifferentiated The kaolin generally is massive-bedded Black Mingo Formation is apparently and structureless but some intervals are crudely gradational. In the Bechtel core VSC-4, from stratified. The Snapp kaolin is characteristically South Carolina (Figure 2), the entire Snapp hackly with irregular fracture and is generally Formation consists of kaolin and the lower part hard and tough when dry. Slickensided joints of the Snapp is gradational over approximately are common. Less silty intervals of the kaolin two feet into a gray, hard, siliceous clay and are soapy or waxy to the touch. As previously claystone 19 the kaolin is irregularly mottled &th~th some creek valleys in southern Aiken County, the highly pigmented, thread-like veins. overlying Snapp Formation may also crop out. Pigmentation of the Snapp kaolin ranges In all cores of eastern Georgia and through several shades of red, reddish brown, adjacent Allendale County, South Carolina, the purple, gray, orange, and rarely olive. Neutral Snapp Formation appears to grade downward hues range from light gray to white. into the undifferentiated Black Mingo The kaolin of the Snapp Formation Formation. Although some of the Snapp-Black generally grades downward into the sand, but Mingo contacts appear to be disconformable, locally, the contact is very sharp, having the having basal coarse sands containing pebbles, we appearance of a diastem. The transitional think these disconformable contacts are due to lithology contains common to abundant, and channel scour from a prograding, fluvial fine- to coarse-grained mica and interstitial environment. A few of the cores have good kaolin. The sand size ranges from fine- to very recovery across the contact and display gradation fine grained and well-sorted to medium- to and conformity over 1 to 2 feet. The coarse-grained and moderately sorted. Some stratigraphic interpretations of these gradational intervals are distinctly stratifiedstrased whereas others contacts are considered to be more reliable are massive-bedded and structureless. because sharp "disconformities" may occur at the The lower sand of the Snapp Formation base of channels in any formation of coastal is very finely to coarsely micaceous. Kaolin is marine to fluvial origin. mostly interstitial but there are rare and In contrast, the upper contact of the scattered beds of thin, carbonaceous clay with Snapp is strongly disconformable, exhibiting plant impressions. Quartz pebbles are found at irregular, surfaces. Burrows and joints in the the base of the formation in some cores and, less uppermost Snapp Formation are filled with commonly, are scattered throughout the sand sediment from the overlying Congaree section. Dark minerals, fine-grained pyrite, and Formation. The ''bleached'','%leachedn, commonly pyritic sulphur-bloom on the core surfaces are sporadic. zone in the upper several feet of the formation Sand size and sand sorting ranges from is conspicuous. very fine and well-sorted to very coarse grained The Snapp Formation ranges in and poorly sorted. The sand is massively bedded thickness from 27 feet (8.2 m) updip to 93.5 feet and structureless, but thinly bedded kaolinitic (28.5 m) downdip (Figure 8). Thickness remains sand also occurs in scattered sections. The sand constant along strike into South Carolina. The is generally firm, but it is rarely soft and kaolin bed ranges in thickness from about 11 incoherent. UnliieUnlike the kaolin, the sand is not feet (3.5 m) to 30 feet (9.0 m). pigmented but is very light gray to white. Structure contour lines of the upper surface of the Snapp Formation show the Stratigraphic Relationships characteristic regional southeast dip (Figure 9). In the vicinity of the Pen Branch fault, the The Snapp Formation underlies all of structure contours are somewhat subdued, with eastern Burke County, Georgia and is present in a small negative anomaly «(<10 feet (3 m))m» on the subsurface in the vicinity of Wrens, the northern (downthrown) block and a more Jefferson County, Georgia. Its full aerial extent prominent area of positive relief on the southern in eastern Georgia and western South Carolina (upthrown) block. is not yet known due to insufficient subsurface The environment of deposition of the data. It does not, however, exist as far west as Snapp Formation is interpreted to have been the kaolin mining district in the central Georgia fluvial, of braided stream origin. It could be Coastal Plain, nor is it known to exist in outcrop interpreted, with the available evidence, that the in the kaolin mining district in Aiken County, Snapp Formation represents the final South Carolina. However, because the Black withdrawal of the Midwayan sea, and the Mingo is thought to be exposed in some deep progradation of fluvial coastal plain environments. 20 Savannah River Site N miles 5 o 5 Contour interval 20 feet Core site • Figure 8. Snapp Formation isopach (thickness distribution) map. Thicknesses are in feet. Modified from Summerour and others (1994). Savannah River Site N miles 5 o 5 Contour interval 20 feet Core site. Figure 9. Structure contour map of the top of the Snapp Formation. Elevations are in feet relative to mean sea level. Age Coastal Plain were significantly different from that of the southern Atlantic Coastal Plain. In South Carolina, Fallaw and Price (1995) considered the Snapp Formation to be Undifferentiated Late Paleocene in age: "Fossils are mrerare in the Black Mingo Formation Snapp. There are not many age determinations, but judgingjudging from a few palynological Definition assemblages, and well-dated strata above and below, the unit is probably zone NP9, middle The undifferentiated Black Mingo Sabinian, perhaps correlating with the upper Formation in eastern Burke County, as defined part of the Williamsburg Formation (Van in this report, is a variably carbonaceous and Nieuwenhuise and Colquhoun, 1982; Colquhoun, lignitic, fine- to medium-grained, moderately to et aI,al, 1983) of eastern South Carolina. It well-sorted sand with scattered beds or lenses of appears to correlate with the TuscahomaTuscahorna Sand gray to black, thinly stratified to laminated clay. and perhaps the upper parts of the Nanafalia It is easily identified in cores and well-cuttings and Baker Hill (Gibson, 1982) formations of the because it is sandwiched between white to Gulf Coastal Plain (middle Sabiniarr;Sabinian; upper mottled kaolinitic sands (overlying Snapp Thanetian or Selandian)."Selandian). " Formation) and white to mottled sandy kaolins Based in part on the broadly gradational (underlying Steel Creek Formation).Formation).. The sands lower contact with the underlying Midwayan of the undifferentiated Black Mingo compose the Black Mingo Formation at some sites, and in locally restricted Millers Pond aquifer (Figure 3) part on a late Midwayan, Upper Paleocene (Falls and Baum, 1995). (Selandian) (Naheola-equivalent) age of the In its type area in the central Coastal uppermost Black Mingo (Edwards, personal Plain of South Carolina, the Black Mingo has communication, 1995), the most likely age for been elevated to group status (Van the Snapp Formation in the Savannah River Nieuwenhuise and Colquhoun, 1982) with a area is late Midwayan, early Late Paleocene, lower Rhems Formation (divided into two Selandian. There is no evidence for an early members) and an upper Williamsburg Sabinian, Thanetian age for the Snapp Formation (also divided into two members). Formation in Georgia, nor have any deposits of The lower Black Mingo Rhems Formation Sabinian age been identified in Burke County. consists mainly of sandy clay, and the upper In the eastern Gulf Coastal Plain, the Black Mingo Williamsburg Formation is most severe fall in sea level during the predominantly a siliceous claystone. The lower Paleocene occurred near the end of the Early Black Mingo is Midwayan in age, and the upper Paleocene, Midwayan (pre-Nanafalia) Stage. Black Mingo is early Sabinian in age. Because This regression and low stand of the sea the lower Black Mingo is mainly a clay and the resulted in the deposition of the basal Gravel upper Black Mingo is a claystone, and because Creek Member of the Nanafalia Formation in there is no Sabinian Black Mingo in Burke Alabama (LaMoreaux and Toulmin, 1959), and County, Georgia, the precise stratigraphic development of karstkarat topography on the top of relationships between the Black Mingo in its the Clayton Formation in the Chattahoochee type area and the Burke County Black Mingo is River area (Toulmin and LaMoreaux, 1963; not clear. However, the unit in Burke County Marsalis and Friddell, 1975; Reinhardt and is lithologically closely related to the Black Gibson, 1981). The two apparently severe low Mingo and, therefore, is included in that stands oftheof the sea, the post-Midway-pre-Nanafalia lithostratigraphic unit as undifferentiated Black event of the eastern Gulf Coastal Plain and the Mingo. post-Snapp event in the Savannah River area, In the past, the undifferentiated Black are considered here to be contemporaneous. If Mingo in Burke County has been called Ellenton they were not, the tectonics of the eastern Gulf Formation. For a discussion on the historical 23 review and relationship of the Black Mingo and the undifferentiated Black Mingo is clearly Ellenton Formations, see Appendix 2. divisible into an upper and lower part. The upper part is a conspicuously glauconitic sand Type Locallty and the lower part is a resistant, hack1y,hackly, dark gray clay. TR92-3 is designated as a reference The type locality of the Black Mingo, as locality for the Black Mingo Formation in central assigned by Sloan 0908,(1908, p. 4/52),452), is at Perkins eastern Burke County because it is characteristic Bluft'Bluff on the Black River near the confluence of of the formation in northern Burke County and the Black River with Black Mingo Creek. Sloan because the core recovery in the formation was (908)(1908) recognized both a lower and upper Black good (-77%). The Black Mingo in this core is Mingo and the Black %goMingo exposed at Perkins overlain with an apparent diastemdiadem by the Snapp Bluft'Bluff is lower Black Mingo. However, it is not Formation. Core TR92-6 is designated as a clear from the text whether Sloan (908)(1908) reference locality because it is characteristic of intended Perkins BluffBluft'to to be the type locality for the undifferentiated Black Mingo Formation in the entire Black Mingo phase or whether he northern Burke County, consisting of intended Perkins BluffBluft' to be the type locality approximatelyapprcdmately 87% sand beds and 13% clay only for the lower Black Mingo. He did not beds. Core recovery through the assign a type locality to the upper Black %go.Mingo. undifferentiated Black Mingo%go was good in the We conclude, therefore, on the basis of default core (-73%).(- 73%). The undifferentiated Black Mingo and original designation, that the type locality of Formation in core TR92-6 overlies the Steel the Black Mingo Formation must be at Perkins Creek Formation with a clear disconformity and Bluft'Bluff on the Black River. is overlain paraconformably by the Congaree The section of Black Mingo exposed at Formation. The USGS GirardGicore was chosen Perkins Bluft'Bluff is therefore, the type section, or as a hyposhatotypehypostratotype because the Black Mingo unit-stratotype (holostratotype) of the Black Formation in this core has a lower and upper Mingo Formation (Group). Perkins Bluft'Bluff on the part and resembles the lithologic descriptions of Black River is in Georgetown County, South the Rhems, Williamsburg, and Lang Syne Carolina, 10 miles northeast of Harpers and lithologies in the type area in South Carolina. about three miles west of Rope Ferry (Sloan, Core VG-6 is designated as a reference locality 1908, p. 452, 360). because it is lithologically characteristic of the For the Savannah River area, we formation in southern Burke County, and propose that the core from the monitoring well because there is a distinction between an upper P-18, taken less than 10 feet from the site of the and lower part. However, the distinction is less well 52-C,524, the type locality of the Ellenton obvious than in the Girard core. Bechtel core Formation of Siple (1967) be considered a VSC4VSC-4 is chosen because it is lithologically reference localityldty and reference section characteristic of the formation in western Oectostratotype)(ledostratotype) for the undifferentiated Black Allendale County, South Carolina, and because Mingo Formation. The surface elevation of the the Black Mingo is overlain gradationally by the core P-18 is 354 feet above sea level and the Williamsburg Formation, a stratigraphic elevation of the top of the Ellenton is at 250260 feet juxtaposition that does not exist in Burke in the core (104 feet above sea level). County. The Black Mingo Formation also is Useful reference sections characteristically sandier in South Carolina near (hypostratotypes) of the undifferentiated Black the Barnwell-Allendale County line than across Mingo Formation in Burke County, Georgia are the Savannah River in Burke County. listed in Table 6. The core sites (Figure 2) are described in Appendix 1 and the coordinates are Lithology listed in Table 1. The GGS McBean core was chosen as a In Burke County, Georgia, sand is the hypostratotype because it is the only core in dominant lithic component of the undiffer•undiffer- northern (northern-most) Burke County where entiated Black Mingo%go Formation but clay is 24 TaMeTable 6 Undifferentiated Black Mingo Formation reference sections. Core SIteStte GGS SiteSbElevationElovalion Top of formation- feet Bottom of formatlon- Hema FigureFlgure 2 core above belowbekw rurfacesurface teafeet below surface Table 1 number MeanM.an Sea!%a Levelbvel (feet)(fw 1 SRSSAS P.18P-18' njan/a 354 250 njan/a TFl92-3 GGS-3781 195 290 370 TR92-6 GGS-3794 240 274 324 11 GGS McBean I GGS-3757 ( 297 272 I 299 I I I USGS Girard nja 250 482 542 VSG-4 nja 156.5 3n.5 494 VG-6 nja 217 522 588 I 'n/an-~otn/a -Not applicable or not available 1. Not in area covered by flgureAgure 2 map. ubiquitous. Clay occurs both interstitially and pebbly, poorly sorted sand, at the base of the in thin and, rarely, thick beds. The gray to Black Mingo in some cores in northern Burke black clays in the upper part of the formation County, is similar to the Sawdust Landing probably are dominantly smectitic but kaolin Formation of SRaSRS of Fallaw and Price (1992, occurs in updip,updip, lower beds of the formation. A 1995). Sorting ranges from very well-sorted to thin bed of claystone (0.1 foot thick), virtually very poorly sorted. In some cores, (e.g., VG-3), identical to the Williamsburg Formation, in the grain-size is relatively coarse (medium•(medium- Barnwell and Allendale Counties, S.C., is grained) and the sorting is relatively poor present in the middle of the unwerentiatedundifferentiated (moderately to moderately poorly sorted). Black Mingo in core VG-4. Carbonaceous Sand is mostly incoherent to barely material, including lignite flecks, fragments and coherent and soft. However, the degree of scattered thin beds of lignite are characteristic of induration or consolidation of the sand ranges the Black Mingo Formation in Burke County, from incoherent, soft and disturbed to very and are present in all cores that penetrate the coherent, tough, and slightly indurated but formation. Other lithic components include fine friable. Hard, pyrite or silica-cemented (common) to coarse mica (rare), dark minerals, sandstone is rare. Sand color ranges from white scattered glauconite, scattered pyrite and rare to light-gray, shades of brown, and olive gray to pyrite-cemented sandstone, both acicular and olive black. cauliflower-like gypsum-bloom on core surfaces, Clay beds are variably silty and finely to some sulphur-bloom on core surfaces, rare and coarsely micaceous, micaceouq variably carbonaceous and local phosphatic vertebrate debris and a trace of lignitic, with rare and scattered thin beds of pelletal phosphate in southernmost Burke lignite, rare carbonaceous leaf prints on bedding County, rare interstitial silica(?) in sandstones, planes or partings, and carbon films on bedding traces of feldspar, thin limestone beds, and planes. Common to abundant sulphur- and calcareous macro- and microfossiliferous beds in gypsum-bloom occurs on the surfaces of the southernmost Burke County. cores. Sand content of the clay is variable. The BlackBlack. Mingo sand in Burke County is clay and fine sand layers are of varying most commonly medium- to fine-grained and thicknesses, ranging from thinly interbedded fine moderately to well-sorted, but may range from sand and clay, to interlaminated very fine sand very fine to coarse-grained, with local and clay, to laminated silty clay. Bedding is occurrences of pea-gravel. Coarse to granular; generally thin to laminated, fissile and papery, 25 but there are some beds of clay that are massive (Figure 10). This variability in thickness is and structureless. Clay beds in southernmost particularly notable in northern Burke County. Burke County are calcareous and macro- and The average thickness of the Black Mingo in microfossiliferous. northern Burke County is approximately 48 feet Carbonaceous clay colors range from (15 m). black to dark gray, and shades of brown and In southern Burke County the range of olive gray. Noncarbonaceous clays range in thickness of the Black Mingo is from 52 feet (16 color from shades of gray (rarely very light m) to 24+ feet (7.3+ m). Average thickness of gray). the Black Mingo in southern Burke County is Bedding in the Black Mingo ranges from about 38 feet (about 12 m). Thickness of the massive and structureless to crudely bedded, Black Mingo Formation in southern Burke faintly bioturbated, and thinly bedded County is uncertain, however, because there are (interlaminated in the clay intervals). There is intervals with no core recovery between the some undulatory bedding and weakly inclined Black Mingo and Snapp Formation in all cores. bedding. The direction of dip on the top of the In two Bechtel cores in Barnwell and Black Mingo Formation in Burke County is Allendale Counties, South Carolina, a short generally to the southeast (Figure 11). However, distance across the Savannah River, the Black the angle of dip is variable. Dip angles range Mingo divides into an upper Black Mingo, from 15 feet per mile to 26 feet per mile. There Williamsburg claystone (or mudstone) lithology is a dip reversal in the vicinity of the Pen and a lower sandy part that resembles the Branch fault. Burke County Black Mingo, but is neither In Burke County the Black Mingo carbonaceous nor lignitic. The two parts of the Formation appears to consist of interfingering or formation are gradational. In the VSC-3 in interlensed coastal marine and inner neritic, Barnwell County, the entire Black Mingo marine, siliciclastic deposits. This interpretation stratigraphic interval is 43 feet (13 m) thick, is based on the presence of dinoflagellates which whereas in the VSC-4, the interval is 67 feet (20 live only in a marine environment. m) thick, due in large part to the thicker Dinoflagellates are found throughout the claystone section in the unit. formation across Burke County. Other evidence for marine deposition includes scattered Stratigraphic Relationships glauconite in the formation throughout Burke County, and a shark tooth in the upper Eastward, at SRBSRS in South Carolina, the glauconitic sand in the GGS McBean core near stratigraphic equivalent of the undifferentiated McBean Creek in northern Burke County. On Black Mingo Formation of this report is the the other hand, a sample from 402-405 feet in Ellenton Formation of Siple (1967),(19671, the Rhems the core VG-3 contains the freshwater alga Formation of Colquhoun and others (1983) and Pediustrum,Pediastrum, indicating a freshwater influenceiduence McClelland (1987), and the Sawdust Landing even in southern Burke County (Edwards, 26 Savannah River Site miles 5 o 5 Contour interval 20 feet Core site • Figure 10. Undifferentiated Black Mingo Formation isopach (thickness distribution) map. Thicknesses are in feet. Savannah River Site N miles 5 o 5 Contour interval 20 feet Core site • Figure 11. Structure contour map of the top of the undifferentiated Black Mingo Formation. Elevations are in feet relative to mean sea level. Savannah River Site Contour interval 20 feet Core site. Figure 12. Undifferentiated Black Mingo/Snapp Formations isopach (thickness distribution) map. Thicknesses are in feet. Z representsrepresents the regressive, falling sea level of the Glaphyrocysta reticulosa of Firth Selandian, Upper Paleocene. (1993) Hystn'chokolpomaHystrichokolpoma cinctum? Age HystrichosphaeridiwnHystrichosphaeridium tubifemtubiferum Impagidiniwn?Impagidinium? sp. The undifferentiated Black Mingo weunecystalRjeunecysta sp. FormationFormation.inin southern Burke County, Georgia is Palaeocystodinium (fat) early to late Midwayan in age based on Phelodinium magnificum s.s. planktonic foraminifera, dinoflagellate Spiniferites spp. assemblages and pollen floras (Edwards, Tectadodinium rugulatum? Globorotalia pseudobulloides is early Late small peridiniaceansperidindaceans Paleocene, and GloborotaliaGloborotaliaperclamperclara is especially characteristic of the Early Paleocene, all of Edwards concluded that "the''the dinocysts Midwayan age, in Georgia. The benthic are most probably of the latter part of Early foraminifer,foraminifer, EouvigerinaEouuigerina exccwata,excwata, has been Paleocene age, but ranges are not well reportedreported only from Early Paleocene, Midwayan established and many of the formsforms are unnamed deposits inin the Coastal Plain. This assemblage -- so don't be surprisedsurpri8ed if it tunsturns out to be early isis characteristic of, and restricted to, the Clayton in the Late Paleocene. The environment isis and lowerlower Porters Creek Formations of Alabama marine, but probably not very farfar offshore."offshore." and western Georgia.Georgia Further, in VG-3, Edwards identified thethe Edwards(personal commundcation, communication, 1994) following dinoflagellate flora from a sample at identifiedidentitied the following dinocysts from a sample 459 feet in the Black Mingo Formation: at 281 feet inin core TR92-6 from Burke County, Alterbidiniwn?Alterbidinium? atT.aff. A?pentaradiatum Georgia: Caligodinium amiculum Andalusiella sp. aff.atT. A polymorpha of Palaeoperidinium pymphorumpyrophorum Edwards (1980) Spinidinium densispinatum Gordosphaeridium fibrospinosum Spinidinium pulchmpulchrum Glaphyrocysta ordinata small, pale peridinioidsperidindoids lRjeunecystaweunecysta spp. Operculodinium spp. According to Edwards (personal Palaeocystodinium golzowense communication, 1994),19941, "The age [of the above Phelodinium sp. of Edwards (1989) flomlfloral is Early Paleocene. The distinctive, but Spiniferites spp. unnamed species, Alterbidinium? aft:aft. A? small peridiniaceans gentamdiatumpentaradiatum is known fromfrom the Brightseat Formation in McuylandMaryland and the McBryde According to Edwards, "The dinocysts Limestone Member of the Clayton Formation inin are most probably of the early part of Late Alabama"Alabama." Paleocene age, but again ranges are not well Edwards identitiedidentified the following established and many forms are unnamed. The dinoflagellate flora from the Black Mingo environment isis marine, but probably not very far Formation at 423 feet in the core VG-3: offshore." Areoligera sp. Edwards identified the following Cordosphaeridium inodes dinocysts from a sample at 302 feet in the core Danea califonica?californica? TR92-6: Fibradinium annetorpense Alterbidinium? n. sp., near Kallosphaeridium sp. A pentaradiatapentamdiata Operculodinium centrocarpum Areoligera-Cyclonephelium group Palaeocystodinium golzowense Cordosphaeridium fibrospinoswn fibrospinosum Phelodinium magnificum-group Damassadinium califomicumcalifornicum Spinidinium cf. S. densispinatum Diphyes colligerum Spiniferites sp. 30 She concluded that "The age is River, the Congaree and Lisbon Formations are Paleocene, somewhere in the early or 'mid''mid'pcrrt.part. " known only as subsurface units. Except for one Based on the above microfossil exposure on lower McBean Creek in Burke identificationsidentifications and comments, the Black Mingo County, the Still Branch Sand is entirely a Formation inin eastern Burke County is early to subsurface unit in Georgia. "middle" Paleocene, entirely Midwayan in age The Congaree Formation is included inin (Figure(Figure 4). This corresponds to Early and the Claiborne Group in this report because of itsits earliest Late Paleocene, Danian and Selandian lithology and stratigraphic position. It has age. Most of the formation is Selandian in age. consistently been called TallahattaTallahatta. Formation inin the Chattahoochee River area since 1947 Claiborne Group (MacNeil, 1947a,1947% 194713;1947b; Toulmin and LaMoreaux, 1963; Marsalis and Friddell, 1975; Definition Reinhardt and Gibson, 1981; Huddlestun, et al, 1988) and, therefore, is an integral part of thethe The name Claiborne was first applied by concept of the Claiborne Group in Georgia. Conrad (1848a, 1848b)184823) to deposits that contain The Still Branch Sand is included in thethe a shelly fauna of similar composition to that of Claiborne Group because of its general lithologic thethe abundantly fossiliferous deposits exposed at similarity to Claiborne Group deposits (i.e., itit isis Claiborne Bluff on the Alabama River in Monroe a fossiliferous, variably argillaceous, calcareous County, Alabama. Smith (1907, p. 17) raised sand). Undifferentiated Still Branch Sand thethe name Claiborne to group rank and included grades updip into the Bennock Millpond Sand thethe Tallahatta buhrstone, Lisbon Formation, and Member. The Bennock Millpond Sand isis Gosport Greensand in the Claiborne Group. margixdymarginally a part of the Claiborne Group. Some The name Claiborne Group was extended into of the Bennock Millpond lithofacies (e.g. shell Georgia by Veatch and Stephenson (1911, p. beds) are lithologically much like the Lisbon 235-296)235-2961 and subsequent usage of the name in Formation in southwestern Alabama. However, Georgia has been varied (Brantley, 1916; Cooke the stratified, fine-grained, well-sorted sand of and Shearer, 1918; MacNeil, 1944a, 1944b, 1947; the Bennock Millpond is lithologically very Herrick, 1961;1961; Marsalis and Friddell, 1975). similar to the PewPerry Sand of the Fort Valley In this report, the Claiborne Group in Group (Huddlestun 31 Lithology foSsiliferous.fo8siliferous. In addition, the Wilcox Group sediments appear to be more abundantly and The lithology of the Claiborne Group as coarsely micaceous. The lithology of the a whole is dominated by quartz sand, clay and, Claiborne Group differsMers from that of the to a lesser degree, calcite and biogenic debris. overlying Ocala Group (where the two groups Locally, or in some beds or stratigraphic are in contact) in being more sandy, argillaceous, subdivisions, any of the primary three lithic glauconitic, less calcareous, and finer textured. components may be minor or, rarely, absent. In eastern Georgia, it differs from the overlying Subordinate lithic components include chert Barnwell Group in being more calcareous with "buhrstone" (or cristobolitic claystone), less separation of sand, calcite, and clay "marl". glauconite, greensand, phosphate (both in the In general, the depositional environment forms of vertebrate bone debris and black to of the Claiborne Group was open marine, inner brown, pelletal apatite), mica, pyrite, lignitic and to middle neritic, relatively fine-grained, carbonaceous material, zeolites, and shells and siliciclastic-dominated, continental shelf. Coastal other bioclastic debris. marine deposits, outer shelf deposits, and carbonate bank deposits are not present in the Stratigraphic RelationshipsRelationehips Claiborne Group. The Claiborne Group in Georgia extends Age across the state from the Chattahoochee River to the Savannah River and into western South The Claiborne Group is mostly Middle Carolina. In Georgia east of the Ocmulgee Eocene, Lutetian and Bartonian in age in River, the Congaree Formation appears to pinch Georgia. The oldest formation of the group in out in the shallow subsurface. The stratigraphic Georgia, the Congaree Formation, is interpreted relationship of the Congaree Formation with the to be contained in planktonic foraminiferal Zone Fort Valley Group and Oconee Group are P 10 or P 11 (JIantkenina(Hantkenina aragonensisamgonensis Zone or unknown. The northern limit of the lower Globigerinatheka subconglobata Zone). Gibson Lisbon Formation (Cubitostrea lisbonensis Zone) and Bybell (1983) reported Early Eocene ages for is in the subsurface from central or easternamtern the lower part of the Tallahatta in Mississippi, Alabama to the western edge of the Savannah Alabama, and Georgia. However, the senior River where the formation crops out near author has identifiedidenti6ied no Early Eocene planktonic McBean Creek. Stratigraphic relationships foraminifera indicating the presence of between the lower Lisbon-equivalent Still planktonic foraminiferal zones P7, P8, or P9 in Branch Sand, and the Fort Valley and Oconee Georgia or Alabama. In western South Carolina, Groups are unknown. The location of the the upper Lower Eocene (Edwards, personal northern limit of the upper Lisbon Formation in communication, 1993) Fourmile Creek eastern Georgia is probably defined by a Formation of Fallaw and Price (1992,(1992,1995)1995) is of coastward facies change into the kaolin-bearing Congaree Formation lithology and considered "Jeffersonville" member of the Huber Formation here to be lithostratigraphically a part of that (Oconee Group) of Huddlestun and Hetrick formation. Although we cannot confirm a late (1991). This stratigraphic relationship appears Early Eocene age for the Congaree and to hold as far east as the Savannah River area Tallahatta Formations, based on the in Georgia. In Burke County, Georgia, the identifications of Edwards (personal Claiborne Group disconformably overlies the communication, 1995) we can assign a late Early Snapp Formation and is overlain by the Eocene age for the lower part of the Claiborne Barnwell Group. Group in Georgia. The age range of the The lithology of the Claiborne Group Claiborne Group in Georgia, therefore, is late differsMers from that of the underlying Wilcox Group Early Eocene through the Middle Eocene. This in western Georgia in being typically less will be discussed more fully in the section on the argillaceous and more calcareous and age of the Congaree Formation. The youngest 32 confirmable Claiborne Group in Georgia, the early reports, it would not be litho•litho- upper part of the Lisbon Formation (CubitostTea(Cubitostrea stratigraphically proper to extend the name sellaefonnissellaeformis Zone) is interpreted to be in the Congaree to shallow subsurface sand sections in planktonic foraminiferal zone P 13 (Orbulinoides(Ohulimides SRS in South Carolina or in Georgia. However, beckmcznnibeckmanni Zone). Unless the Clinchfield Sand we believe the discrepancy between the reported is temporally equivalent to the Gosport outcropping Congaree shale and clay lithology in (Huddlestun and Hetrick, 1986), no post-Lisbon, its type area, and that in the shallow subsurface, Claibornian sediments are currently recognized is a result of relative ease of erosion and mass in Georgia. In that case, it is possible that the wasting of the soft sand lithofacies in outcrop. upper Claibornian Gosport Sand of the eastern This leaves a relatively high proportion of the Gulf Coast stratigraphically correlates with the argillaceousargill.aceous lithofacies exposed. As a result, we Clinchfield Formation of Barnwell Group, which propose to formally expand (redefine) the name is lower Jacksonian. According to established Congaree to include the shallow subsurface sand usage (Huddlestun and Hetrick, 1986), the sections in South Carolina and across Georgia Clinchfield may be Late Eocene in age but westward to the Chattahoochee River. Claibornian in stage. In the northern, updip part of Burke County, the Congaree Formation is more Congaree Formation lithologically variable than it is in southern Burke County and consists of sand and clay. In Definition southern Burke County, the Congaree Formation is homogeneous and consists of sand. As applied here, the Congaree Formation The Congaree sand extends across the in South Carolina and Georgia consists of an subsurface of Georgia to the Chattahoochee updip, variably siliceous clay, and clay and sand River area. lithofacies, and a downdip, shallow subsurface, In the past the lower Claibornian section massive-bedded, fine- to medium-grained, in Georgia and in the vicinity of the moderately to well-sorted, soft and barely Chattahoochee River has been called Tallahatta coherent sand lithofacies.Zithofacies. The Congaree Formation (MacNeil, 1944a.,1944% 1944b; Herrick, Formation of this report differs from the 1961; Toulmin and LaMoreaux, 1963; Owen, Congaree Formation of SRS in South Carolina 1963; MansalisMarsalis and Friddell, 1975; Reinhardt and (Fallaw and Price, 1992, 1995) in that the Gibson, 1981; McFadden, et aI,al, 1986). In its Fourmile Branch Formation of Fallaw and Price type area, the Tallahatta Formation is a (1992,1995), lithostratigraphically is included in lightweight, siliceous claystone (buhrstone), and the Congaree Formation, in Burke County. A quartz sand, if present, is a minor lithic further discussion of the Congaree component. The Tallahatta is very resistant to nomenclatural history is included in Appendix 3. erosion and, therefore, forms a cuesta where the Based on literature from the formation is presentpresent. Typical Tallahatta outcropping, type area of the Congaree Formation lithology is present only as lenses in Formation (Sloan, 1907, 1908; Cooke, 1936; an updip, predominantly argillaceous sand Cooke and MacNeil 1952),19521, the type Congaree formation east of southwestern Alabama and in consists primarily of shale and clay with the type area of the Congaree. The Tallahatta subordinate amounts of quartz sand occurring Formation exists neither in the lower either in beds or interstitially. According to Claibornian stratigraphic position in the Paul Nystrom (personal communication, 1995) of Chattahoochee River area, nor in the shallow the South Carolina Geological Survey, however, subsurface of Georgia east of the Chattahoochee. there is more sand in the Congaree Formation The lower Claibornian of the Chattahoochee in its type area than has been reported in the River area contains exposures that cannot be literature. distinguished from the Congaree Formation in If the type Congaree were consistently a its type area. Therefore, we recommend the clay and shale in its type area, as indicated in adoption of the name Congaree for the lower 33 Claibornian westward across the state of Georgia exposuresBxposures in the area covered on the 1:24,000 to the Chattahoochee River. Columbia NE Ah.-Ga.Ala.-Ga. quadrangle map, and four The Congaree Formation is placed in the cores from sites in southwestern and central Claiborne Group in this report because Georgia. The three exposures in the Columbia exposures of the formation in east central 1:24,000 quadrangle are hypostratotypes and are AlabamaAlabama-and-and the Chattahoochee River area have located: 1.) in Factory Creek, at and always been considered an integral part of the downstream from the County Road 140 bridge Claiborne Group. over the creek, two miles (3.2 km) from the northern-most measured section of the Type'Qpe Locality Tallahatta Formation of Toulmin and LaMoreaux (1963). This is stop 8, second day of Sloan (1907, 1908) did not designate a the Georgia Geological Society field trip type locality for the Congaree Formation and, (Marsalis and Friddell, 1975); 2.) exposures of therefore, there is no type locality by original the formation along Red Branch, a small designation for the formation. However, Cooke tributary of the Chattahoochee River, three (1936, p. 59) assigned the amphitheater at the miles (4.8 km) north of Factory Creek; and 3.) head of First Creek as the principal reference the exposure of the Congaree on Odum Creek, locality Oectostratotype)Qectostratotype) for the formation. The less than 0.25 mile (0.4 km) from the public exposure of the Congaree in the amphitheater is boat ramp at the confluence of Odum Creek the principal reference section Oectostratotype)aectostratotype) with the Chattahoochee River (near Mile 56 on for the Congaree Formation. The principal the Chattahoochee River). The Congaree reference locality is in Lexington County, 0.8 exposed at the waterfall on Odum Creek mile (1.28 km) west of Gaston in the updip exposure contains a calcareous and fossiliferous central Coastal Plain of South Carolina. bed, with the oyster Cubitostrea perplicata and In eastern Burke County, five cores are may represent Bed 28 of Toulmin and designated as Congaree Formation reference LaMoreaux (1963). localities in Georgia (Table 7). The core site The other core sites (hypostratotypes), localities are described in Appendix 1, and the not located in Burke County (Table 8), are listed coordinates are listed in Table 1. to illustrate lithofacies variations of the Core TR92-1 has good recovery of the Congaree Formation across central and formation (66%) and is representative of the southwestern Georgia. updip, mixed sand and clay lithofacies of the In the USGS Albany core (GGS-3187), Congaree in northern Burke County. Core the Congaree Formation occurs in the interval TR92-2 contains a representation of the from 401 feet to 539 feet. It is representative of bioturbated and burrowed lithofacies. The the massive-bedded, poorly coherent to TR92-4 core contains siliceous clay as the incoherent, sand lithofacies. The upper part of dominant lithic component. This lithofacies is the Congaree, from 401 feet to 478 feet, is similar to the typical outcropping Congaree in characteristically devoid of calcite (except for the type area in central South Carolina. Core widely scattered thin sandy limestone beds), and TR92-5 contains some of the ranges of lithology consists of variably coherent to incoherent, seen in the Congaree in northern Burke County. massive-bedded, sparsely and sporadically Core VG-6 is characteristic of the downdip, glauconitic, variably and slightly argillaceous massive-bedded, barely coherent, fine-grained, sand with scattered clay laminae and variable well-sorted sand lithofacies in Burke County and bioturbation. From 478 feet to the top of the of the shallow subsurface in Georgia westward Bashi Member of the Hatchetigbee Formation at to the Chattahoochee River area. The core approximately 539 feet, the Congaree Formation recovery of the Congaree Formation (93%) in consists of glaglauconitic,uconitic, calcareous, core VG-6 is unusually good for the formation. microfossiliferous, argillaceous, fine sand. The Other useful reference sections of the Congaree Formation is overlain with apparent Congaree Formation in Georgia include three gradation by the lower Lisbon Formation 34 Table 7 Congaree Formation reference sections Inin eastern Burke County. I, 11 CoreCOWSiteSI* ( GGS core number I SiteShe ElevaUonUntion a-above 1 Top of formation-formaUon- I Bottom of see FigureFlgure 2 Mean Sea Level feet below surface formation-formaUon- feet Table 1 (feet)(-1 below surface TR92-1 GG8-3674 235 245 270 TR92-2 GG8-3762 285 308 330 TR92-4 GG8-3782 192 182.5 213 TR92-5 GG8-3792 235 272 290 VG-6 n/anla 217 328 428 .."n/a9-Notnla -Not applicable (Cubitostrea lisbonensis Zone?) and is underlain communication, 1995) indicate an early Middle with apparent gradation (paraconformity?) by Eocene age for the Congaree Formation. the Bashi Member of the Hatchetigbee Formation. Lithology In the GGS Sumter 9A core from eastern Sumter County, the Congaree Formation In northern Burke County, the lithology is characteristically a poorly coherent, tine-fine- to of the Congaree Formation is variable, with medium-grained sand that is difficult to recover more beds of clay ("cristobolitic" claystone in the in coring operations (-28 % recovery). The core TR92-4), interstitial clay, some scattered sand is characteristically noncalcareous, massive-massive• clay clasts(?), and bioturbation. This lithofacies bedded and structureless with rare scattered is similar to the Congaree Formation in its type beds of laminated clay. area. In the southern part of the county the The GGS Laurens County core contains sand is almost barren of interstitial clay and is the only Congaree Formation that has been lithologically the same as that in the subsurface identified in the Ocmulgee River area. The sand in central and western Georgia. In general, in lithology is typical soft, incoherent (14% Burke County, there is more clay and silica in recovery), he-tine- to medium-grained and well-well• updip (nearshore) Congaree Formation, and sorted, with scattered, thin carbonaceous or relatively clean sand with minor clay and silica lignitic beds. There is a bed (9 feet thick) of in downdip (seaward) sections. hard, silty kaolin at the top of the formation. Subordinate lithic components of the Dinoflagellate identifications by Edwards Congaree Formation in Burke County include (personal communication, 1995) indicate a late mica, sporadic occurrences and low Early Eocene to early Middle Eocene age for the concentrations of pelletal phosphate (sandy formation in this core. The GGS PulaskiPula& 5 core phosphate pebbles occur rarely at the base of the contains the only section of Congaree Formation formation), scattered thin beds of siliceous that has been identified from the vicinity of the sandstone, variable occurrences of dark minerals, Oconee River in the central Georgia Coastal variable but minor amounts of lignitic Plain. The sand lithology is typical for the fragments, lignitic~gnitic flecks, and carbonaceous formation (tine-(fine- to coarse-grained and well-well• streaks (mostly(mo&ly in updip, northern Burke sorted). However, there are beds «(< 8 feet [2 County), rare to common acicular gypsum-bloom m]ml thick) of argillaceous, carbonaceous sand on cores (as opposed to "cauliflower""cauliflawei"-shaped-shaped scattered throughout the formation as thin beds gypsum-bloom), some sulphur bloom?, and to laminae of clay and carbonaceous clay. There minor pyrite. A thin bed of fossiliferous, is also a 10 foot thick, massive-bedded, greenish glauconitic, very calcareous sandstone to very gray kaolin at the top of the formation. sandy limestone occurs at the base of the Dinoflagellates identified by Edwards (personal(persod formation in southernmostsouthernmost. Burke County (core 35 Table 8 Congaree Formation reference sections In Georgia west of Burke County. CoreComSite.cn,SIte He GGS USGS quadrangleqWldrqle E1evlltlonElwaUon Top of Bottom of AppendlxAppendix 1 cor.0010 map/ feelfeetabveabove formation-feelformallon-feet fonnatlon-feetformation-feel number Latltude-NLatttudaN meanmwn ... below rurhcesurface below rurfacesurface /Longltudaw/Longftude-W levelled (.rt)(Mt.) USGS GGS-3187 Albany East 195195 401 539 Albany 31°31' 31' 05"05' 84°84O 06' 44'44" GGS GGS-3366GGS3366 Drayton 270 114 188188 Sumter 9A 32°32O 04' 03"w 83°83°ws59' 23" GGS GG8-3511GGS-3511 West Lake 355 228 380 PulaskiPulaskl 5 32°22'50"32O 22' !W 83°83O 29' 17"17- USGS GGS-3523 Dudley 285 312.5 421 Laurens 1 32°30'59"32O 30' 59- 83°83O 02' 43'43" VG-B).VG-8). Glauconite, limestone, calcite, and shells bioturbated intervals. There is minor are especially characteristic of the formation in "cristobolitic" claystone and silica-cemented the more downdip outcrop in southwestern sandstone in Burke County. The claystone is Georgia whereas traces of pelletal phosphate are siliceous, indurated, and shaley with very fine more conspicuous in central and eastern sand to silt and mica on bedding planes. The Georgia. claystone displays imgularirregular to conchoidal The Congaree typically is massive-massive• fracture. bedded and devoid of primary sedimentary The colors of Congaree clays range from structures. However, some intervals at some shades of olive grays, yellowish grays, greenish sites contain vaguely and crudely bedded to grays, brownish grays to light grays. conspicuously bedded sands and some thinly Near the Chattahoochee River and in layered to laminated lignitic clay beds. northern Burke County, the outcropping, updip Bioturbation is common in some cores from Congaree is lithologically more variable than in northern Burke County; the sand and clay the shallow subsurface across Georgia. This components are marbled in those cores. Only a lithofacies is also more reminiscent of the few, thin, clearly stratified sand intervals have Congaree in its type area. We interpret this been observed in the Congaree. pattern of lithology distributions as being The color of the Congaree sands includes consistent with the more varied coastal marine shades of brown, orange, greenish grays, olive to shallow, inner neritic lithofacies versus the grays, olive black to brownish bla*black, and light much less varied lithofacies of offshore grays. depositional environments. Smectitic clay beds from cores in the Because of the presence of partially Congaree are commonly gypsiferous, indurated, resistant, siliceous sand or thin beds noncalcareous, fissile and papery, waxy, and may of siliceous sandstone or claystone in the be slightly sandy to silty. They are finely western Georgia outcrop, waterfalls and rapids micaceous with some dark minerals found along are common along small tributary creeks of the partings. There are some interbeds or Chattahoochee River. Typical Congaree in interlaminae of fine to very fine grained sand. southwestern Georgia is commonly glauconitic Interstitial clay commonly occurs in the with scattered beds that are highly glauconitic 36 (Toulmin and LaMoreaux, 1963). Phosphate is slightly argillaceous. Some scattered thin clay not apparent on casual inspection of the beds are commonly carbonaceous or lignitic to outcropping formation, but Herrick (1961) some degree. Lignitic material is most reported "phosphate" in this formation from conspicuous in the updip areas and diminishes cuttings from most wells between the downdip. In the Pulaski County and Laurens Chattahoochee and Flint Rivers, and from sands County cores, a bed of hard, chunky and blocky we interpret to be Congaree Formation east of fractured, Middle Eocene-type kaolin occurs at the Flint River. Silica-replaced shells are locally the top of the Congaree Formation. present and blocks or pods of fossiliferous chert or chert-cemented sandstone are locally Stratigraphic Relationships conspicuous (Marsalis and Friddell, 1975), indicating that the formation was originally In the central Coastal Plain of Georgia, calcareous in the outcrop area. from northern Burke County, southwestward In the downdip outcrop area in through central Laurens County, through southwestern Georgia, the Congaree Formation Pulaski County, through Lee County and into is less variable than in the updip outcrop area Randolph County, the Congaree appears to and consists of thick, massive-bedded, pinch out northward (updip) in the subsurface. noncalcareous to calcareous sand. Locally, Further westward, the Congaree grades laterally scattered beds of calcareous sandstone or sandy into the Tallahatta Formation in central and limestone are present. Similarly in this area, western Alabama. the formation is more fossiliferousfossilifem with locally In northern Burke County, Georgia, the abundant Cubitostrea perplicata. Congaree Formation disconformably overlies the There are no known lithologically Snapp Formation and is gradationally (or varied, near shore lithofacies of the Congaree paraconformably) overlain by the Bennock between the drainage basins of the Millpond Sand Member of the Still Branch Chattahoochee and Savannah Rivers. The Sand. In southern Burke County, it is overlain characteristic, widespread sand lithofacies of the conformably or paraconformably by the Still Congaree occurs in the shallow subsurface and Branch Sand. extends westward across Georgia from the In western Georgia, the Congaree Savannah River area to the Chattahoochee River Formation disconformably, or paraconformably, area. Congaree sands are typically soft, barely overlies the Bashi Member of the Hatchetigbee coherent to incoherent, massively bedded and Formation, and is overlain by the Lisbon structureless. Sand size ranges from fine- to Formation. Elsewhere in the state, the coarse-grained with rare occurrences of very Congaree disconformably overliesthe Tuscahoma coarse sand, granules and pea gravel. Normally Formation and undifferentiated Wilcox or the sand is fine- to medium grained and well-well• Midway Groups. It is disconformably overlain sorted. Sand sorting is variable and ranges from by the Lisbon Formation (Cubitostrea well- to poorly sorted. Most commonly the sand sellaeformis Zone) in outcrop in western and is fine- to medium-grained and well- to central Georgia but appearsappem to be conformable moderately well sorted. Some coarser quartz with the Cubitostrea lisbonensis Zone of the sand grains are conspicuously rounded. lower Lisbon Formation in the subsurface of Core recovery in the sand is Georgia. characteristically poor. The Congaree Formation Throughout the subcrop area in Georgia, is very permeable and constitutes the "Claiborne" the Congaree Formation thickens rapidly part of the Clayton-Claiborne aquifer in downdip, increasing from 0 to over 100 feet southwestern Georgia and the Gordon aquifer in thick within a few miles. In the Savannah River eastern Burke County. In this predominantly area, however, the rate of seaward thickening is thick sand lithofacies, the Congaree is much less, approximately 2.3 feet per mile. The noncalcareous, nonglauconitic, nonphosphatic thickest known section of the Congaree (see Herrick, 1961),1981), nonsiliceous and vevery j Formation is 192 feet (59 m) near Albany, 37 Georgia, inin thethe USGS Albany core. The known papery clay. The Congaree is invariably average thicknessthickness of the Congaree Formation in noncalcareous and nonmacro-fossiliferous.nonmacro-fossiliferous. central and southwestern Georgia is 124 feet. In In southern Burke County, thethe overlying eastern Burke County, the thickness of the Still Branch Sand is invariably calcareous, Congaree Formation ranges from 0 feet in the microfossiliferous (calcitic microfossils), and north toto 62 feet (10 m) in the south (Figure 13). yellowish in color (due to calcareous particles). The average thickness of the Congaree in The Congaree consists of gray, noncalcareousnoncalcareous eastern Burke County is 38 feet (12 m). sand. The two formations are lithologicallylithologically However, in the study area in northern Burke similar except for the invariable presence of County, the Congaree Formation ranges in calcite in the Still Branch Sand. thicknessthickness from 0 feet in the GGS McBean core Based on the presence of dinoflagellates, toto 42 feetfeet in core TR92-3. The average the environment of deposition of thethe Congaree thicknessthickness of the formation is 21 feet (6.4 m). In Formation, in outcrop and in thethe shallow thethe vicinity of the projected location of the Pen subsurface, is inner neritic continental shelf. Branch fault,fault, the Congaree Formation thins to Farther downdip (in more offshore sections), thethe lessless thanthan 20 feet (Figure 13). Congaree was deposited in more open marine From northern Burke County to the conditions, based on the presence of glauconite, Screven County line, average dip on the top of phosphate, and diverse assemblages of thethe Congaree Formation is approximately 12 feet planktonic foraminifera and dinoflagellates. per mile toto the southeast (Figure 14). From the Normally, in updip and downdip vicinity of McBean Creek to the vicinity of the lithofacies relationships, the updip, shoreward Pen Branch fault, average dip is approximately deposits consist of coarser siliciclastics, and thethe 1414 feetfeet per mile. Southeast of the Pen Branch grain-size of the siliciclastics decrease inin a fault,fault, therethere isis a dip reversal (Figure 14), which downdip, seaward direction. One would expect, isis followedfollowed by a return to a dip of 14 feet per then, to find nearshore sands, offshore clays, and mile toto thethe county line. far-offshore limestones. In the case of thethe TheCongaree Formation is distinguished Congaree, the deposits are relatively fine updip,updip, fromfrom thethe underlying Snapp Formation by the and coarsen downdip. There are twotwo possible presence of gray sand and thinly bedded to interpretations of this depositional pattern. laminatedlaminated clay in contrast to the top of the The first interpretation is that thethe updip, Snapp Formation which consists of ''bleached'',"bleached", fine-grained Congaree may have been deposited pyritic, very light gray to white kaolin. in a coastal marine, back-barrier environment. Deeper in the Snapp Formation, the In Burke County, the Pen Branch fault appears kaolin isis mottled with various shade of red, to mark the area of lithofacies change from reddish brown, orange, and gray. The argillaceous, siliceous, and carbonaceous underlying sand is characteristically white, Congaree in the north, to medium toto coarse, kaolinitic, variably micaceous, poorly sorted and relatively clean sand to the south. A barrier medium- to coarse-grained. island may have developed along the crest of thethe In northern Burke County, the Congaree upthrown, south side of the fault although no isis distinguished from the overlying Bennock barrier island-type deposits have been identifiedidentified Millpond Sand Member of the Still Branch Sand along the projected trend of the fault. A second inin thatthat thethe Bennock Millpond consists of fine- to interpretation is that the Congaree deposits inin very finefine grained sand, the sand commonly is Burke County were deposited at different times. thinlythinly to very thinly bedded (some intervals are The oldest Congaree in northern Burke County massive-bedded and structureless), and variably is youngest Early Eocene, but most of thethe calcareous and fossiliferous with conspicuous dinoflagellate floras iden-edidentified by Edwards are aragonitic mollusk shells. The underlying older Middle Eocene or near the Middle/EarlyMiddlejEarly Congaree consists of interbedded, fine-grained Eocene boundary. This contrasts with thethe sandsand and siliceous clay with some sections sandy, downdip Congaree in southern Burke consisting mostly of variably siliceous, laminated, County where there are many youngest Early 38 Savannah River Site co co Contour interval 20 feet Core site • Figure 13. Congaree Formation isopach (thickness distribution) map. Thicknesses are in feet. Modified from Summerour and others (1994). Savannah River Site o miles 5 o 5 Contour intervalinterval 20 feet Core site • Figure 14. Structure contour map of the top of the Congaree Formation. Elevations are in feet relative to mean sea level. Eocene tlorasfloras and fewer Middle Eocene floras.tloras. Zone of the Lisbon Formation include the The depositional patterns could be interpreted to following:following indicate that the Congaree is a diachronous Morozovella aragonensis deposit. Most sedimentation firStfirst took place in Globigerina frontosa a more open marine environment in southern G. higginsi Burke County, and later, after broaching the G. inaequispira subtle topographic high on the Pen Branch fault, Acarinina spinuloinflata most sedimentation took place during the A. broedermannibroedermnni earliest Middle Eocene when carbonaceous, A. pentacamerata siliceous clays with interbedded fine sand was deposited in a protected coastal environment. The association of Globorotalia cerroazulensis pomeroli and forms close to Age Globigerina eocaena with Globigerina higginsi, Acarinina broedermanni, Morozovella In Georgia (and Alabama) the only aragonensis, and Pseudohastigerina wilcoxensis planktonic foraminifera from the Congaree (Stainforth et. al., 1975) indicates that the Formation (and Tallahatta Formation) are of Tallahatta Formation, the basal part of the early Middle Eocene age. This defines the Lisbon Formation (C. lisbonensis Zone), and the typical Congaree (and Tallahatta) as being of Congaree Formation of western Georgia are in early Middle Eocene, Lutetian, conventional the Hantkenina aragonensis Zone (P10(PI0 of early Claibornian age. Planktonic foraminiferal Berggren, 1971, 1972; Haq, et al, 1987). suites that determine the age of the Congaree ''Anodontia''?"Anodontia"? augustana is a useful and correlation of the Congaree Formation with macroguidefossil for the Congaree Formation in the Tallahatta Formation include the following its type area. "Anodontia"? augustana is also suite that the senior author has identified from found in the Congaree Formation in the the Tallahatta and Congaree Formations in sites Chattahoochee River area and in the upper part from Alabama and western and central Georgia of the Tallahatta Formation in Alabama (subsurface): (Toulmin, 1977). Morosovella aragonensis Bybell and Gibson (1982) have assigned M. spinulosa the lower part of the Tallahatta Formation of Globorotalia cerroazulensis pomeroli Alabama and the Congaree Formation of G. bolivariana western Georgia to the late Early Eocene on the Globigerina frontosa basis of calcareous nannofossils. The lower paitpalt G. linaperta of the Congaree and Tallahatta Formations are G. inaequispira normally noncalcareous and, therefore, do not G. cf.6.eocaena contain foraminifera. However, the lower part G. higginsi of the Congaree section in the USGS Albany Acarinina spinuloinflata core near Albany, Dougherty County, Georgia, is A. broedermanni (in part Globorotalia calcareous and contains planktonic foraminifera, crassata densa of Bandy, 1949) that do not differ in any way from that of the A. pentacamerata "(in'(in part upper part of the Congaree Formation in the Globigerinoides pseudodubia of Bandy, core (except for being less well preserved). 1949) We have seen no planktonic foraminifera Pseudohastigerina wilcoxensis from either the Tallahatta Formation or Congaree Formation that can be assigned an The planktonic foraminifera restricted to Early Eocene age. Those planktonic the Tallahatta Formation of Alabama (C. foraminifera that would be diagnostically late perplicata Zone), the Congaree Formation of Early Eocene include the following:following Georgia and the basal Cubitostrea lisbonensis Acarinina soldadoensis soldadoensis A soldadoensis angulosa 41 MomwvellaMorozovella fonnosaformosa fonnosaformosa than the TallakattaTallahafta Formation at Little.Little Stave M. caucasicacauccrsica Creek and younger than Gibson and Bybell's NP M.M.palmerae palmeme 12 Tallakatta.Talhhatta ... and ...should correlatecwmlate to NP 13 or NP 1414. ... Another scamscarce dinofloradinoflorn (289-(289 On the other hand, Edwards (personal 2942% feetfi?et in the corecwm VG-4) is indicative of the communiCation,communication, 1993) hashaa identified post-post• later part of Early Eocene time.time."" Hatchetigbee, Early Eocene dinoflagellate floras The dinoflagellatedinoflagehte flora from the core from the Congaree Formation in Burke County, hashaa an age thatthat: "is noticeably younger than the Georgia. She (personal communication, 1994) type Fishburne and the flomflora closely resembles identified the following dinoflagellate flora taken that of the upper part of the NcuycuyenwyNanjemoy from core samples of the Congaree Formation in FonnationFormation in Virginia and Mcuyland"Maryland." Burke County, Georgia: The stratigraphically higher Achilleodinium biformoidesbifonnoides dinoflagellate flora from 274-279 feet in the core Adnatosphaeridium sp. VG-4 consists of the following dinoflagellates:dinoflagellates.. AreoligemAreoligera coronatacomnata Areosphaeridium mutum/G.arcuatum/G. intricataintntncata AreoligemAreoligera spp. CordosphaeridiumConiosphaeridium fibmspinosumfibrospinosum Charlesdowniea tenuivirgula Cordosphaeridium gmcilegraeile Cordosphaeridium fibmspinosumfibrospinosum CribroperidiniumCribmperidinium giuseppei Cordosphaeridium gmcilegraeile Glaphyrocysta divmMcatadivaricata Cordosphaeridium inodes Glaphyrocysta?Glaphymysta? vicina CribroperidiniumCribmperidinium giuseppei HystntnchokolpomaHystrichokolpoma sp. Diphyes colligerumcolligerwn OperculodiniumOpemulodinium centrocarpum??centroccupum?? Eocladopyxis? n. sp. Pentadinium favatum (primitive) FibmcystaFibrocysta radiatamdiata SystematophoraSystematophom placcrcanthaplacacantha GlaphyrocystaGlaphymcysta intricata Wetzeliella lunaris Glaphyrocysta?Glaphymcysta? vicina GlaphyrocystaGlaphymcysta sp. For this sample, Edwards concluded that: "The HafniasphaemHa{niasphaera goodmanii species HafniasvhaemHafniasphaera noodmaniigoodmanii pmumablypresumably HafniasphaemHa{niasphaera septata gives rise to Pentadinium favatumfavatu"'- H. HomobybliumHomotryblium tenuispinosum goodmanii is known mmfrom Early Eocene material Hystrichokolpoma cinctum in Virginia and McuylandMaryland in sediments that have Hystrichokolpoma spp. been correlated to nannofossil wnezone NP 13. 14eunecystaLejeunecysta sp. Pentadinium favatum is known mmfrom the upper Lingulodinium machaerophorummachaemphorwn part of the Tallahatta Formation and the lower MumtodiniumMuratodinium jimbriatumfimbriatum part of the Lisbon FonnationFormation in AlabamaAlabama. OperculodiniumOpemulodinium centrocarpum Primitive fonns, such as found here,hem, suggest Pentadinium favatum correlation with the upperupperpartpart of the Tallahatta.Tallahatta Pentadinium favatum (primitive forms) I think the latest information on the Tallahatta Phthanoperidinium echinatum Formation is that it includes wneszones NP 12-14. Polysphaeridium subtile So the age of this sample is likely to be NP 14•14 - Polysphaeridium whqyizoharyi which conveniently straddles the Early-Middle SarnlandiaSamlandia sp. Eocene boundary.boundcuy. " Spiniferites spp. According to Snipes and others (1993) TurbiosphaeraTurbiosphaem galatea most of the Congaree in the Savannah River TurbiosphaeraTurbiosphaem d. T. galatea Site in South Carolina is Early Eocene in age. Wetzeliella lunaris According to Gohn and others (1983),(19831, the Wetzeliella spp. Congaree Formation: ""... contains fossil assemblages indicating an Early Eocene age, at According to Edwards, some least firfor most of the unit. The lower part of the dinoflagellate floras look: "... to be slightly older CongareeCongame is moderatelymodemtely to well-sorted, fine to 42 coarse quartz sand with clays a few feet thick in (itself a small tributaIytributary of the Savannah River) the middle and atQt the top in places. Glauconite,Glauwnite, east of Girard in southern Burke County, muscovite, and iron sulfide aream common Georgia.Georgia The type locality of the formation is accessones.accessorb. The lower part of the Congaree,Congame, as core VG-6 taken by Bechtel Corporation for the term is U8edwed in this paper, correlates Southern Company. The core site is at the biostratigraphically with the Fishburne intersection of River Road and an unimproved Formdon,Formation, a downdip carbonate".donate'! county road approximately 1.3 miles (2.1 kIn)km) Assuming that the age assignment and southeast of the River Road bridge over Sweet correlation between the Congaree and Tallahatta Water Creek. The site of core VG-6 is on the Formations is correct, the time intervals and USGS 1:24,000 quadrangle map Millett,MiUett, S.C.-Ga. lack of significant lithology differences (or sharp The type section or unit-stratotypeunit-atratotype (holo•(holo- contacts) within the formations indicate that stratotype), of the formation is the interval 328 during the long period of Tallahatta and feet to 388 feet in the core. The Still Branch Congaree deposition, eustatic changes in sea Sand is disconformably overlain by the Blue level and depositional environments on the Bluff Member of the Lisbon Formation at 328 continental shelf of Georgia remained unusually feet, and is paraconformably underlain by the stable. Congaree Formation at 388 feet. Three other core sites, VG-5 and TR92•TR92- Still Branch Sand 5, from Burke County, and the GGS Colquitt County 11, are designated reference localities Definition (parastratotypes) for the Still Branch Sand in Georgia (Table 9, Appendix 1). Core VG-5VG-6 is The Still Branch Sand is a subsurface chosen as a reference section because its basal formation proposed here for a calcareous sand in bed is lithologically distinctive and a planktonic Burke County. In the past, the Still Branch foraminiferal fauna that correlates with the Sand has been called the "unnamed basal sand lower part of the Lisbon Formation of Alabama of the Lisbon Formation" and "unnamed sands was identified at 227 feet in the core. Core and limestone of the Lisbon Formation"Formationn TR92-5 is designated a parastratotype because (Bechtel, 1982), and "unnamed member of the the typical calcareous sand of the Still Branch Lisbon Formation"Formationn (Gorday, 1985). We know of can be seen to intertongue with the updip, no references to the Still Branch Sand in the nearshore to coastal marine, Bennock MillpondMiUpond past, although it is likely that part of the surface Sand Member. Core Colquitt County 11, near and subsurface Santee Limestone of Fallaw and Doerun in northwestern Colquitt County, on the Price (1992, 1995) and D. Colquhoun and his western flank.flank of the Gulf Trough, is designated students may be the Still Branch Sand of this a reference locality and parastratotype because report. the general lithology of the formation is within There is one named member of the Still the range of typical Still Branch and because it Branch Sand in Burke County, the Bennock also represents a more downdip (offshore) MillpondMiUpond Sand (new name). The member will lithofacies of the formation. It is disconformably be described in the next section. The Still overlain by a limestone lithofacies of the Blue Branch Sand is considered to be a formation of BluffBlufF Member of the Lisbon Formation and the Claiborne Group because it is dominantly a conformably or paraconformably underlain by a calcareous, sporadically macrofossiliferousmamfderous sand very glauconitic to greensand lithofacies of the similar to the lower Lisbon in southwestern Congaree Formation. Alabama. Lithology Type Locality The Still Branch Sand is dominantly a The name Still Branch is taken from calcareouscalcareow sand but there commonly is a bed of Still Branch, a tributaIytributary of SweetwaterSwwtwater Creek moldic, sandy limestone or moldic, calcareous 43 sandstonesandstone at the top of the formation. wncalcareousnoncalcareous sand of the BenndBennock. Millpond Subordinate lithic components include minor Sand Member. interstitialinterstitial clay, rare thin beds of clay with MoatMost fossilefossils consist of molds and casts of acicular gypsum-bloom, (some beds appear to mollusks but chalky calcitic molliiskmollUsk shells, small contain no clay minerals), glauconite, rare and macrofossil debris, smaller foraminifera, scattered.scattered. carbonaceous material, scattered scattered bryozoan debris, dinoflagellates and phosphate pellets and phosphatized limestone palynomorphs also occur in the lower part of thethe pebbles near the top of the formation, a trace of Still Branch Sand below the upper limestone-limestone• dark minerals?, traces of pyrite in a few cores sandstone bed. Some bumsburrows from thethe and a trace of interstitial silicaailica and silicified shell overlying Blue BluffBlu1f can be found near thethe toptop fragmentsfragrnenta at the base of the formation in some of the formation. cores. Some chalky calcitic fossils and common Still Branch color is mostly yellawish-yellowish• toto abundant molluscan molds are present in the gray, with other minor shades of gray. Clay upper limestonelimestone or sandstone. colors range from olivegrayolive-gray to light olive gray. Limestone or sandstone at the top of the Still Branch Sand is typically moldic and Stratigraphic Relationships coquinoid. The degree of cementation is variable. The limestone is generally indurated The Still Branch Sand grades updip and thethe sandstone may be hard, dense and well•well- (shoreward) into the coastal marine Bennock induratedindurated or soft and friable. Limestone or Millpond Sand Member. Its downdip limitlimit and sandstonesandstone also occur in scattered, thin beds or western limit are not known at thisthis time,time, nodules throughoutthroughout the formation in downdip although it does occur as far west as areas. The limestone bed is also rubbly in northwestern Colquitt County, Georgia. Because places with bioclastic texture and much of the similarity of the limestones within thethe secondarysecondary porosity. Still Branch with the Santee Limestone, and Sand distribution is irregular or patchy also because of comparable stratigraphic inin thethe limestonelimestone which may be the result of position, it is possible that the Still Branch Sand bioturbation. The sand is fine- to medium•medium- may grade laterally eastward in South Carolina grained and moderately to well-sorted. Sand•Sand- into the lower part of the Santee Limestone. sizesize and sorting may be variable within any The Still Branch Sand overlies thethe given section. In the upper limestone-sandstone Congaree Formation either conformably or bed, the quartz sand component may be paraconformably in Burke County. It isis mediurn-medium- to coarse-grained and moderately disconformably overlain by the Blue BluffBlu1f poorly sorted. Quartz sand size and shell Member of the Lisbon Formation. The contact abundance decreases downward through the Still between the two formations is very pronounced, Branch. The sand is generally poorly as the top of the Still Branch commonly has thethe consolidated to incoherent. Core recovery is appearance of a hard ground. In eastern Burke typicallytypically lowlow in sand sections of the formation County, the thickness of the Still Branch Sand and is especially low in the lower or basal sand. ranges from 24 feet (8 m) to approximately 80 The sand is generally massive bedded feet (26 m) (Figure 15). and devoid of sedimentary or biogenic The average dip of the Still Branch Sand structures.structures. Sand bedding, where evident, is is approximately 8 to 10 feet per mile, with a typicallytypically vague and the stratification crude. slight dip reversal near Hancock Landing and a There are rare thin clay beds and some return to the typical dip southeast of Plant horizontal orientation of shells. The rare and Vogtle (Figure 16). scatteredscattered clay beds within the Still Branch have The Still Branch Sand is distinguished either fine, hackly fracture or are fissile.Me. In the from the underlying Congaree Formation inin intermediateintermediate lithofacies (in core TR92-5) being invariably calcareous, micro-fossiliferous calcareous sand of the undifferentiated Still (calcitic microfossils), and yellowish in color (due Branch Sand appears to grade downwarddownd into to calcareous particles). The Congaree consists 44 Table 9 StiliStlll Branch Sand reference sections. Core sa- GGS sa- Top of Bottom of ... Flgure2 core number ElevatIon formatlon- formation- Table 1 Appendix 1 Move ...... Sea feet below feet below l.AMlI (fMt) aurfllce aurfllce VG-5 n/a 94 187 236 TR92-5 GG8-3792 235 2ZT 272 Colquitt County 11 GG8-3545 350 791 1113 "n/a"·Not applicable of gray, noncalcareous sand. The two depth of 278 feet in core VG-8 in southern formations are lithologically similar except for Burke County: the invariable presence of calcite in the Still Acarinina spinuloinflata (in part = G. Branch. bullbrookibulhrooki of some authors) The Still Branch is distinguished from A pentammemtapentacamerata the overlying Blue Bluff Member of the Lisbon A crassatacmssata densa (sensu Bandy, 1949) Formation in that the Blue Bluff is a very Globigerina eocaena calcareous clay to very argillaceous limestone, G. primitiva typically massive-bedded in appearance but, on G. mntosafrontosa close inspection, is seen to be thinly bedded to G. d.cf. senni laminated. The top of the underlying Still Globorotalia cr.cf. G. renzi Branch Sand is an indurated coarsely GlobigerapsisGlobigempsis sp. fossiliferous, moldic, sandy limestone to very Truncorotaloides rohri calcareous sandstone. PseudohustigerinaPseudohastigerina micra The environment of deposition of the The overlapping ranges of typical Still Branch Sand is interpreted to have been Pseudohastigerina micra,micm, with Acarinina offshore,oflshore, inner continental shelf. Because the pentacamemta,pentacamerata, typical Globigerina frvntosafrontosa and upper part of the formation Oimestone•(limestone- typical Acarinina spinuloinflata is characteristic sandstone) extends the farthest updip where the of the Middle Eocene Globorotalia lehneri Zone Still Branch gradationally overlies the Bennock or planktonic foraminiferal Zone P12. This zone Millpond Sand Member, the Still Branch Sand is between the Congaree Formation (Tallahatta•(Tallahatta- appears to represent a transgressive half-cycle. equivalent) and the upper Lisbon Formation However, the foraminifera increase in diversity (Cook Mountain-equivalent) (probably P13).PI3). In downward in the section and coarse sand in the terms of calcareous nannofdnannofossil zones, the Still limestoneLimestone or sandstone at the top of the Branch should be within upper-most NP 15 to formation nwmay indicate a regressive half-cycle. lower-most NP 16. It is probably within the CubitostreaCubitostma lisbonensis Zone of !he+he eastern Gulf Age of Mexico Coastal Plain but no fragments of CubitostreaCubitostma were noted in any of the cores. The age of the Still Branch Sand is Lucy Edwards of the USGS has Middle Eocene, Claibornian, and appearsappm to be identified the following dinoflagellate flora from correlative with the lower or middle part of the the Still Branch Sand in the core VG-3: Lisbon Formation of Alabama (Cubitostrea(Cubitosm Achilleodinium bifomidesbiformoides lisbonensis Zone to the lower part of the Cribroperidinium giuseppei CubitostreaCubitostma selbformissellaefonnis Zone). The senior Diphyes d.cf. D. ficusoides author has identified the following planktonic Eocladopyxis n. sp. foraminifera from the Still Branch Sand at a HetemulaccrcystaHeteraulacacysta pustulata 45 Savannah River Site miles 5 o 5 Contour interval 20 feet Core site • Figure 15. Still Branch Sand isopach (thickness distribution) map. Thicknesses are in feet. Savannah River Site N miles 5 o 5 Contour interval 20 feet Core site • Figure 16. Structure contour map of the top of the Still Branch Sand. Elevations are in feet relative to mean sea level. HysHystrichokolpoma tricho kolpoma rigaudiae Millpond (Beds 2 and 3) during exploratory Lingulodinium machaerophorum drilling and they considered it to be McBean Membranophoridium sp. Formation. We know of no other references to Muratodinium fimbriatum the Bennock Millpond Sand Member. Pentadinium favatum The Bennock Millpond Sand Member is SarnlandiaSamlandia chlamydophora (var. 1) a lithologically variable unit and is composed Spiniferites spp. broadly of three distinctive sand lithofacies: 1.) SystematophomSystematophora placacantha a fossiliferous,fossilifemus, calcareous, fine sand; 2.) a Thalassiphora pelagica massive-bedded to thinly bedded, noncalcareous, Wetzeliella articulata (var. 1) fine to very fine grained sand that resembles.resembles,thethe PerryPeny Sand (Hetrick.,(Hetrick, 1990; Huddlestun and Edwards (personal communication, 1995) Hetrick.,Hetrick, 1991; Huddlestun, 1992) and 3.) a considers the above floratlora to be "of Middle Eocene noncalcareous, bioturbated sand. Most Age...... Based on the overallovemll floral similarity commonly, the fossiliferousfossilifemus sand gradationally ... most likely correlative with the lowest Lisbon overlies the massive-bedded to thinly bedded at Little Stave CreekCreek'!If. sand. Bennock Millpond Sand Member TypebeSection (new name) The name Bennock Millpond is taken Definition from a pond or small lake that was formed by the damming of McBean Creek where it enters The Bennock Millpond Sand is a new the Savannah River flood plain. The type member proposed here for a lithologically locality of the Bennock Millpond Sand Member variable sand member of the Still Branch Sand is along McBean Creek, at the base of the in northern Burke County. The Bennock northwestern part of "Sloan's scarp" (a term Millpond Sand Member grades downdip into used by Cooke, 1936), the western valley wall of undifferentiated Still Branch Sand in southern the Savannah River. The type section or unit-unit• Burke County. The Bennock Millpond Sand stratotype (holostratotype) of the member is that Member underlies the McBean Limestone and section (now mostly covered) exposed near the Blue Bluff Members of the Lisbon Formation. base of the valley wall. The type locality is It is mostly a subsurface unit but it crops out in located in the southeastern corner of the USGS a small area along lower McBean Creek, 1:24,000 Mechanic Hill Ga.-S.C. and the overlooking the Savannah River flood plain near southwestern corner of the USGS 1:24,000 the base of "Sloan's scarp" in Burke County. Jackson S.C.-GaS.C.-Ga. quadrangle maps. Due to The "McBean" shell bed, from which an erosion and vegetation cover, little can be seen extensive collection was made by Sloan (1908) of the member at the type locality. As a result, and reported on by Veatch and Stephenson the five cores, GGS-McBean, TR92-1, TR92-2, (1911) and Cooke and Shearer (1918), is TR92-4, and TR92-6, are designated as reference apparently from the Bennock Millpond Sand localities (parastratotypes)(parashatotypes) for the Bennock Member of the Still Branch Sand and not from Millpondhfillpond Sand (Table 10). the overlying McBean Limestone Member of the Lisbon Formation as was previously thought. Lithology There are few other references in the literature to the BennockBennock. Millpond Sand Member. These Quartz sand is the dominant lithic include the shell bed, called the McBean component of the Bennock Millpond Sand Formation by Veatch and Stephenson (1911),(19111, Member. Subordinate lithic components Cooke and Shearer (1918) Cooke (1936, 1943), includeclay that occurs interstitially, as rare clay Cooke and MacNeil (1952). LeGrand and clasts, and scattered lamjnaelaminae and thin beds «(< 1 Furcron (1956,(1966, p. 33) penetrated the BennockBennoclr foot thick). The thin clay beds are finely 48 Table 10 Bennock Millpond S8ndSand Member reference sections. Core&re SiteSib GGS SIteSb Top of Bottom of ...aaa mracore ElevatIonEbvdon member-nnmber- member- Figureflgum 2 number aboveaboveM8anSmMean Sea feet below feet below TableTabla 1 le¥eILsvd surtaee8uHace surfacerurtace GGS McBean GG8-3757GGS-3757 2!17297 186186 222 TR92-1TW-1 GG5-3674GGS3874 235 21211 1 245.5 TR92-2 GG8-3762GGS-3762 285 277 308 TR92-4 GG8-3782 192 145 182.5 TR92-6 GG8-3794 240 182 251 micaceous, noncalcareous and are thinly layered The fossil shells (mollusks) of this to laminated and fissile. AUAll other lithic member are distinct from the other fossil shells components are relatively minor and include in other formations in Burke County. The calcite; aragonite; variable amounts of fine•fine- Bennock Millpond Sand Member contains the grained mica (mica is coarser grained in the only well-preserved aragonitic shell fauna updipupdip area); glauconite; carbonaceous material; (Veatch and Stephenson, 1911; Cooke and lignitic flecks and rare lignite fragments (rare Shearer, 1918) that the senior author has found thin beds of lignite are present in the updip from the early Tertiary in eastern Georgia. area); pelletal phosphate,phosphate; traces of bone debris Although the McBean does contain a· a -fewfew and rare phosphatic clasts (in basal beds). scattered lenses that contain some aragonitic Acicular stellate gypsum-bloom; acicular shell fragments, mollusk shells of the Bennock gypsum-bloom; cauliflower-like gypsum-bloom Millpond Sand Member (both aragonitic and and rare sulphur-bloom occur on the surface of calcitic) are commonly thin shelled, delicate, the desiccated cores. The Bennock Millpond relatively small in size, and are commonly Sand Member is largely noncalcareous but in fragmented. Preservation of the shells is the upper part there are local or scattered beds variable and range from very well preserved to of calcareous, macro-fossiliferous(both aragonitic chalky and soft. The color of the well-preserved and calcitic fossils) fine sand. shells is tan to cream whereas the chalky shells The sand is mainly fine to very fine and are light gray to white. In general, the well-well• well-sorted to very well sorted. In the lower preserved aragonitic shells resemble, in size, part of the Bennock Millpond Sand Member, color and preservation, those of the Lisbon grain sizes and textures are more variable, Formation of western Alabama. ranging from fine to medium-fine, moderately Sand colors range through varying sorted sand to medium to coarse, well to poorly shades of olive-gray to yellowish-gray, shades of sorted sand. Granules and pebbles occur near brown, orange, gray, brownish-black to olive the base of member in the updip area. black where carbonaceous, and varying shades Bedding in the member varies from gray. massive-bedded and structureless, to very The colors of the clay beds range crudely and vaguely stratified, to massive-bedded through shades of olive-gray to olive-black to and bioturbated. Many sand intervals are brownish-black to yellowish brown. almost homogenized by bioturbation. Burrows are present but rare in core samples. Some of Stratigraphic Relationships the massive-bedded and structureless sands are incoherent. The Bennock Millpond Sand Member is known to be present in eastern Georgia from 49 northern Burke County, Georgia, in the east, appearance of paraconformity or disconformity is westward to the vicinity of Wrens in Jefferson certainly not obvious. This may be due to County. In Burke County, its updip limit reworking and mixing of the top of the Bennock appears to be the vicinity of McBean Creek MillpondMiUpond Sand Member by infaunal organisms where it is truncated by erosion. The downdip during the initial deposition of the Blue Bluff. limit in Burke County is in the vicinity of the Mixing of Blue Bluff and Still Branch sediments Pen Branch fault of Snipes and others (1992; was not possible farther south because the top of 1993) near Hancock Landing where the Bennock the Still Branch was indurated prior to Millpond Sand Member intertongues with and deposition of the Blue Bluff. grades laterally into undifferentiated Still Branch The Bennock Millpond Sand Member Sand (Figure 5). overlies the Congaree Formation with uncertain The only clear patterns in the contact relationships. There are only two cores distribution of the three lithofacies mentioned in (TR92-1 and TR92-4) that have close to 100% the section on lithology is that, where the shelly recovery across the contact. In TR92-1 the basal sand lithofacies is present, it occurs near the top bed of the Bennock Millpond Sand Member is a of the Bennock Millpond section and overlies the phosphatic, rather coarse, poorly sorted sand Perry-like sand. that abruptly overlies a thinly bedded to The Perry-like sand lithofacies in the laminated gray clay of the 'Congaree.bongaree. In TR92-4, Bennock Millpond Sand Member resemble the contact appears to be a bed change with a lenses of Perry sand lithology (Huddlestun, thin bed «(< 6 inches) of powdery chert at the 1992) in the upper Middle Eocene Tinker Creek top of the Congaree. These contacts appear to Formation of Fallaw and Price (1992, 1995). be a disconformity and paraconformity However, all evidence we are aware of indicates respectively. In all other cores that contain this that the Tinker Creek Formation is a nearshore, contact, recovery was not good and the contacts coastal marine facies of the Lisbon Formation. are apparently conformable. It is noted here The Bennock Millpond Sand Member, on the that the Bennock Millpond/CongareeMillpondjCongaree contact other hand, is a nearshore, coastal marine facies and the Still Branch/CongareeBranchjCongaree contact in Burke of the older, downdip Still Branch Sand of County, Georgia, and the Lisbon/Tallahatt.LisbonjTallahatta Georgia. contact in Alabama commonly appear to be The McBean and Blue Bluff Members of gradational. Additionally, the planktonic the Lisbon Formation overlie the Bennock foraminiferal faunas from the basal Lisbon Millpond Sand Member with a gradational Formation and the uppermost Tallahatta contact over an interval of one to two feet. This Formation in Alabama are in the same is surprising, because, farther downdip, the same planktonic foraminiferal zone P10.PlO. Similarly the contact between the Blue Bluff and the Still planktonic foraminiferal faunas from either side Branch is very distinctly disconformable. In of the equivalent contact between Tallahatta•Tallahatta- addition, the Bennock Millpond Sand Member equivalent and lower Lisbon-equivalent and Still Branch Sand both contain lower Lisbon formations at 1113 feet in core GGS Colquitt to upper Tallahatta dinoflagellate floras County 11, come from the same planktonic (Edwards, personal communication, 1995), foraminiferal zone P10.PI0. In general, it appears indicating an Early to middle Middle Eocene that this particular formational contact in age. The senior author has identified a small Georgia is subtle and may be locally lower (but not lowest) Lisbon planktonic disconformable but generally appears to be foraminiferal suite from core VG-8. The conformable and gradational (paraconformable). planktonic foraminiferal fauna is diagnostically The Bennock Millpond Sand Member Middle Eocene and is younger than the grades laterally downdip into the Still Branch Congaree Formation and older than the Blue Sand in Burke County, Georgia. Based on Bluff. There appears, then, to be a hiatus stratigraphic position and physical correlation, between the McBean-Blue Bluff and the the Bennock Millpond may grade laterally underlying Bennock Millpond although the 50 eastward and northeastward in South Carolina upward in the section. The sandy limestone-limestone• intointo thethe Warley Hill Formation. calcareous sandstone of the Still Branch appears The Bennock Millpond Sand Member is to be correlative with the shell beds in the upper distinguished from the overlying McBean part of the Bennock Millpond Sand Member. Member of thethe Lisbon Formation in that the Thickness of the Bennock Millpond latterlatter consists of an impure, variably fine Member ranges from 0 feet in the USGS Millers grained, sandy limestonelimestone that contains scattered Pond core (Figure 2), to 69 feet (21 m) in core calcitic fossils or molds and casts of aragonitic TR92-6. Average thickness in northern Burke fossilsfossils inin thethe limestone.limestone. Shell beds or scattered County is close to 30 feet (9 m). aragonitic shell fragments within the calcareous The depositional environment of thethe sandsand are typicaltypical of the Bennock Millpond. Bennock Millpond Sand Member appears toto Where thethe Bennock Millpond sands are have been in the inter!lngeringinterfingering area between thethe noncalcareous, the sands are thinly bedded to coastal marine and the inner neritic continental laminatedlaminated or massive-bedded with scattered shelf (Still Branch Sand), and most likelylikely ligniticlignitic and carbonaceous material. represents the shoreface environment of thethe The Bennock Millpond Sand Member is middle Claibornian. The Perry-like sand distinguished from the underlying Congaree lithofacies is a significant lithic component of thethe Formation inin being variably calcareous and Bennock Millpond Sand Member. In the Fort macrofossiliferous, and in containing a Valley area to the southwest, Huddlestun and significantsignificant amount of prominently and thinly Hetrick (1991) ascribed the depositional bedded, fine- toto very fine grained sand whereas environment of the Perry Sand to the shoreface thethe Congaree consists mainly of interbedded, based on geographic and facies position. The noncalcareous, fine-grained, well-sorted sand shallow to middle continental shelf Lisbon with thinlythinly bedded to laminated clay beds and Formation lies immediately to the south of0:( thethe silicifiedsilicified clay. Locally, the thinly bedded clay Perry Sand, and the coastal marine Mossy Creek may constitute the major lithic component of the Sand lies to the north. The outcrop band of thethe Congaree whereas clay is not known to be a Perry Sand is only a few miles across, similar toto significantsignificant component of the Bennock Millpond the outcrop-subcrop band of the Bennock Sand Member. Millpond in northern Burke County. The Bennock Millpond Sand Member is It appears that the Bennock Millpond distinguished from the downdip-equivalentdawndip-equivalent Still Sand Member represents a transgressive half Branch Sand inin that the Still Branch is mostly cycle. This interpretation is based on thethe massive-bedded and structureless, consistently assumption that shell beds occur seaward of thethe calcareous and macrofossiliferous to some degree shoreface and represent more open marine (calcitic(calcitic fossils),fossils), and contains a bed of moldic, conditions. This is compatible with thethe Still sandysandy limestone or, more rarely, moldic, Branch Sand grading downsection into thethe calcareous sandstone at the top of the formation. Bennock Millpond Sand Member where thethe twotwo The Bennock Millpond is a fine- to very fine units intertongue (i.e., in TR92-4 and TR92-5). grained sand that is variably calcareous with Similarly, the Still Branch Sand also appears toto noncalcareous sand being predominant. It is represent a transgressive half qcle~1de because thethe variably thin-beddedthin-bedded to laminated and massive•massive- formation fines and becomes more calcareous bedded and structureless. The Bennock and fossiliferous upward. Millpond Sand Member consists of three different lithofacieslithofacies whereas the Still Branch is Age consistently a calcareous, fine-medium to medium-coarse grained sand with either Edwards identified the following massive-bedded, moldic, sandy limestone or very dinoflagellates from GGS core samples of thethe calcareous sandstone at the top of the formation. Bennock Millpond Sand Member from northern The Still Branch Sand is least calcareous at its Burke County, Georgia: base and becomes progressively more calcareous Achilleodinium biformoides 51 Adnatosphaeridium? sp. According toto Edwards, thethe upper part of Cordosphaeridium, wilegracile thethe Bennock Millpond Member contains a ... Cordosphaeridium multispinosum "dinoflom"dinoflora (that) is definitely what I1 would call Cordosphaeridium fibrospinosumfibrospinosum 'Tallahatta or lower Lisbon equivalent' and "Dinoptelygium"Dinopterygium cladoides sensu looks mommore likelike the lowerlower Lisbon. I1 think thethe Morgenroth latest correlations place this in NP 14 or NP 16,15, Diphyes colligemmcolligerum earbearly Middle Eocene. The sample wntainscontains Emmetrocysta n. sp...... Middle EomneEocene dinocysts, dominated by Fibrocysta sp. WetzeliellaWetzeliella. Glaphyrocysta cf.d. G. demmexuberans The environment is likely to be mommore Glaph~cysta?Glaphyrocysta? cf.d. G. vicina nearshore than the samples below." Hystntnchoko&omaHystri.chokolpoma rigaurdiae For the middle part of the member, her LejeunecystaUdeunecysta sp. comments on the flora are as follows: 'The"The Lentinia sp. dinoflora looks to be the same age as the Lingulodinium machaerophommmachaerophorum Tallahatta Formation at Little Stave Cmek.Creek. 1I Microdinium sp. think it fallsfalls within NP 14, early Middle Muratodinium fimbriatumfimbriatum Eocene.Eocene." " Nematosphaeropsis spp. For the lower part of the member: "The Operculodinium centrocarpum dinoflomdinoflora looks to be the same age or slightly Operculodinium sp. older than the TallahnttaTallahatta Formation at Little Pentadinium favatum Stave CmekCreek and younger than Gibson and Pentadinium favatum (including Bybell's NP 12 Tallahatta. Thus this sample advanced forms) should cornlatecorrelate to NP 13 or NP 14. That Pentadinium favatumfavatum (including makes it latest Early Eocene or earliest Middle primitive forms) Eocene...... 1I didn't see any specimens of Pentadinium gonifemmgoniferum Wetzeliella sp.sp." " Pentadinium laticinctum laticinctumlaticinctu!m Based on dinoflagellates, the age of the (1 fragment) small peridiniacean Bennock Millpond Sand Member appears to Phthanoperidinium comatum range from earliest Early Eocene (older Phthanoperidinium echinatum Tallahatta-Congaree) to the middle Middle Polysphaeridium subtile Eocene (Cubitostrea lisbonensis Zone of Lisbon Polysphaeridium subtile or Formation). EocladopywisEocladopyxis n. sp. The senior author has found no Polysphaeridium zoharyiwharyi planktonic foraminifera in the Bennock Millpond Samlandia chlamydophorachlamydophom var. 1 Sand Member. However, a list of planktonic Samlandia reticulatamticulata foraminifera from the stratigraphically Samlandia reticuliferamticulifem equivalent Still Branch Sand was given in the Spiniferites spp. previous section. The age of the Still Branch SystematophoraSystematophom placcrcanthaplacacantha should be applicable to the age of the Bennock Tectatodinium pellitum Millpond Sand Member. ThalassiphoraThalassiphom pelagica At this time, we conclude that the best ThalassiphoraThalassiphom pelagag?capelagica n. var. approximation to the age of the Bennock TurbiosphaeraTufiiosphaem magnifica Millpond Sand Member is early Middle Eocene, Wetzeliella articulata approximately correlative to the lower Lisbon Wetzeliella articulata s.l.8.1. (Cubitostrea lisbonensis Zone) of Alabama and Wetzeliella articulata var. 1 Mississippi. Wetzeliella lunaris Wetzeliella/Gochtodinium sp.8p. 52 Lisbon Formation The Lisbon Formation of this report differs from past usage of the name Lisbon or Definition McBean in Georgia. The Lisbon Formation in Burke County of this report includes only those The Claiborne beds and Claiborne siliciclasticsilidclastic dominated, Claiborne Group deposits Formation of Smith, Johnson, and Langdon that overlie the Still Branch Sand and that are (1894, p. 122-137) were elevated to group rank overlain by the Barnwell Group. Usage of the by Smith (1907, p. 17). The middle part of the name Lisbon by Herrick (1961) and usage in earlier Claiborne Formation was named the this report is similar, except that Herrick (1961) Lisbon Formation for calcareous, fossiliferous,fossilirerous, included within the Lisbon Formation sands, clayey sands and sandy clay exposed at Lisbon clays and limestones that contained what he BluBBluff on the Alabama River in Clarke County, considered to be a Lisbon or Cook Mountain Alabama (Smith, 1907, p. 18). Veatch and foraminiferal fauna. Stephenson (1911, p. 235-237)235237) recognized Lithology of the typical Lisbon Claiborne Group deposits in Georgia but did not Formation in Alabama and Georgia is too apply any of the Claiborne Group formations of similar to warrant formational distinction Alabama (Le,(i.e, Tallahatta,TaUahatta, Lisbon and Gosport) to between the two states. In addition, application the Georgia deposits. of the name McBean to the Lisbon component of MacNeil (1947a,(1947% 1947b)194%) introduced the the Claiborne Group in Georgia is inappropriate name Lisbon Formation in Georgia and included because the distinctive lithology of the McBean all Claiborne Group deposits in it that overlie in its type area in Georgia is a soft, impure the Tallahatta Formation and underlie what he limestone distinct from the typical Lisbon believed to be Gosport Sand in the western part Formation. of the state. Subsequent to MacNeil (1947a,(1947% The Lisbon Formation is subdivided into 1947b)194%),, all investigators of TertiaryTertiaIY deposits in two formal members and an undifferentiated western and central Georgia have recognized sand (or undifferentiated Lisbon) in this report. only the Lisbon Formation for the upper part of The McBean Limestone Member (restricted) is the Claiborne Group (Herrick, 1961; Herrick reduced in rank, and the Blue Bluff Member and Vorhis, 1963; Toulmin and LaMoreaux, (new member) is formally described. The 1963; Owen, 1963; Wait, 1963; Marsalis and McBean Limestone Member consists dominantly Friddell, 1975; Huddlestun, 1981; Huddlestun, et of sandy limestone whereas the Blue Bluff al, 1988). Member consists dominantly of finely and Herrick (1961) and Herrick and Vorhis variably sandy and silty, very calcareous clay or (1963) were the first to extend the name Lisbon argillaceous and silty "marl" limestone. Beds or Formation across the entire state for Claiborne lenses of very calcareous sand to finely sandy Group deposits (Le.,i.., of Cook Mountain limestone are volumetrically minor. The equivalency) overlying the Tallahatta Formation. undifferentiated sand consists of calcareous, Subsequent investigators (H(Huddlestun,uddlestun, et al, argillaceous, fine- to medium-grained sand with 1974; Huddlestun 1981; Huddlestun, 1982; some finely sandy, calcareous clay beds or Bechtel, 1982; Gorday, 1985) also recognized the lenses. Undifferentiated Lisbon sand is found Lisbon Formation in the Savannah River area. only in the updip and nearshore area, and it As used in this report, the Lisbon occurs spatially between the areas of typically Formation of Georgia lithostratigraphically is the developed McBean and Blue Bluff. same as the upper Lisbon Formation of Alabama (Cubitostrea(CubitostreQ sellaeformis Zone-Cook Mountain TypemeLocality equivalent). Deposits correlative with the lower part of the Lisbon (C. lisbonensis Zone), crop The type locality of the Lisbon out only along lower McBean Creek in Burke Formation is Lisbon Bluff on the Alabama River County, Georgia, and are mostly confined to the in Clarke County, Alabama. The section of subsurface in Georgia. 53 Lisbon Formation exposed is the type section or very calcareous and may be more properly unit-stratotype (holostratotype). considered to be an impure argillaceous limestone. Lithology Bedding in typical Lisbon Formation is thick and massive with scattered thin beds that In Georgia, and especially in the may form either ledges or reentrants. Savannah River area, the Lisbon Formation is Sediments within the beds generally are characteristically a calcareous, finely sandy to partially to completely homogenized by silty clay or "marl". The three lithic components, burrowing organisms so that, other than clay, sand, and calcite, are present in most beds scattered burrows or traces of bioturbation, the or lithostratigraphic units. However, specificspec5c sediment is devoid of primary sedimentary or beds may consist mostly or completely of one or biogenic structures. Bedding contacts in this two of the major lithic components. Commonly lithofacies are gradational and rarely sharp. the formation is more sandy updip or Where the beds are not homogenized or shoreward, and more argillaceous and calcareous bioturbated, the Lisbon Formation is downdip where it is a very argillaceous characterized by thin bedding and lamination, limestone to calcareous "marl". Subordinate with intricate and prominent bioturbation lithic components include mica, chert, lignitic structures. and carbonaceous material, shells and other Degree of consolidation in the Lisbon bioclastic debris, glauconite, pelletal phosphate, Formation ranges from unconsolidated and scattered vertebrate debris, pyrite, zeolite, incoherent to indurated and recrystallized. Most feldspar, and dark minerals such as epidote, commonly, however, the sediments are compact zircon, staurolite, garnet, tourmaline and and resistant but unconsolidated. Sediments of hornblende. the argillaceous sand lithofacies are generally Smectite is the dominant clay mineral in unconsolidated, but the degree of consolidation the Lisbon Formation whereas kaolinite and increases seaward with increasing clay and illite are minor components of the clay mineral calcite content. Generally, only the very assemblage. Clay occurs both in discrete beds calcareous beds or limestone beds are indurated. and interstitially in the sand, silt, or calcitic Consistent with this pattern, the nearshore "marl","marl". Clay is the dominant lithic component of McBean Member in Burke County is variably the Blue Bluff Member of the lisbon.Lisbon. indurated. The quartz sand component of the The sandy, undifferentiated Lisbon is Lisbon Formation in Georgia is generally fine- to lithologically distinct from McBean and Blue very fine grained. However, specificspec5c beds, Bluff.BlufF. In core TR92-4, the lower 26 feet of the especially in the upupdip,dip, nearshore area may Lisbon consists of unconsolidated sand that is contain medium- to coarse-grained sand. Calcite very calcareous, argillaceous, glauconitic and occurs in variable proportions, absent only near phosphatic (pelletal) with fine bioclastic debris. the top of the formation in updipupdip areas, or in The sand is, in part, massive-bedded and areas where the lithofacies changes into structureless, but also contains some crudely stratigraphic equivalent, coastal marine and bedded or bioturbated intervals. The sand is fluvial deposits (Perry Sand and Jeffersonville mostly fine and well-sorted, and the sediment is member of the Huber Formation of Huddlestun granular in texture. The basal bed is an and Hetrick, 1991). indurated, structureless sandy limestone. Calcite is most commonly present The color of the lower part of the interstitially in clay in the form of minute undifferentiated Lisbon in core TR92-4 is mostly bioclastic debris and particles. The downdip, yellowish-gray with minor dark yellowish gray offshore transition from silty, calcareous clay but is grayish-orange where oxidized. The "marl" to silty, argillaceous limestone takes place limestone at the base of the member is both by gradation and interfingering. yellowish-gray.yellowish-gray. . Consequently, the downdip, subsurface Lisbon is 54 The upper part of the Lisbon Formation Stratigraphic Relationships inin core TR92-2 isis a sand but differs lithologically fromfrom thethe sand in the TR92-4. This lithology Generally, the Lisbon Formation probably represents and interfingering between thickens in a seaward or downdip direction. It sandysandy McBean and undifferentiated sand. The thins updip in Georgia by gradation into thethe upper 22.5 feet of the Lisbon Formation in the Perry Sand (Huddlestun and Hetrick, 1991) inin core consists predominantly of unconsolidated, western Georgia and, in eastern Georgia, by glauconitic, calcareous sand with a trace of mica gradation into the Perry Sand or thethe and delicate, aragonitic shell fragments, and very Jeffersonville member of the Huber Formation sandysandy limestone. It is massive-bedded and (Huddlestun and Hetrick, 1991). The Tinker structureless,structureless, but with some indication of Creek Formation of Fallaw and Price (1992, stratificationstratijication by horizontal orientation of shell 1995) is thought to be a coastal marine fragmentsfragments and medium to thick beds or lenses of equivalent of the Lisbon Formation in thethe calcareous sandstone. This sandy interval in the northern part of the SRS and in southern Aiken upper part of the Lisbon Formation appears to County, South Carolina. resultresult fromfrom a seaward decrease in calcite content In Burke County, Georgia, known of thethe Lisbon and a simultaneous increase in thicknesses of the Lisbon range from a quartz sand content. minimum of 39 feet (12 m) in core TR92-6 toto 84 The colors of the calcareous, sandstone feet (26 m) in core VG-1VG-l (Figure 17). Thickness beds, lenseslenses or nodules in the Lisbon Formation of the Lisbon Formation is most variable in inin thethe core TR92-2 are pale yellowish orange northern Burke County where it ranges from 39 and are gray to lightlight gray in the unconsolidated feet (12 m) to 83 feet (25 m) in core TR92-2. In sand.sand. In core TR92-2, the undifferentiated southern Burke County, thickness of the Lisbon Lisbon grades downward into the Blue Bluff Formation is quite uniform, ranging from 71 feet Member by diminishing sand content and (22 m) in core VG-7 to 84 feet (26 m) in core increasingincreasing clay content. VG-1.VG-l. Average thickness of the Lisbon Similarly, in core TR92-1, the upper 23 Formation in eastern Burke County isis feetfeet (7.0(7.0 m) of the Lisbon Formation also approximately 71 feet (22 m). consists of a very sandy phase. Sand in the The average dip on the top of the Lisbon Lisbon isis fine-grained and well-sorted, massive•massive- Formation in eastern Burke County isis bedded and structureless except for the presence approximately 10 feet per mile (Figure 18) with of somesome thinthin lutiticlutitic limestone beds. It is slightly a minor dip reversal southeast of the Pen argillaceous, and calcareous with some calcite Branch fault, with a return to a shallow, nodules and thin ((<< 1 foot thick) lutitic variable southeast dip, to the Screven County limestonelimestone beds. The fine sand is slightly line. glauconitic with fine-grained pyrite in the lower The Lisbon Formation (Cubitostrea part. Both clay and calcite are minor sellaeformis Zone) contains a diverse fauna of components of the lithology and there was poor tropical planktonic foraminifera and a diverse core recovery due to the incoherence of the fine•fine- flora of dinoflagellates. Planktonic foraminifera grained, well-sorted sand. The contact between inhabit only open marine watsiwatf.i· masses with thethe undifferentiated sand and Blue Bluff normal salinity. Their presence in continental Member results from an abrupt decrease in the shelf waters far from the continental margin of sandsand content and a simultaneous increase in clay eastern North America suggests that there must content. Supporting the gradational character of have been strong offshore currents on the shelf, thethe twotwo lithologies,lithologies, the basal bed of the Blue and possibly some upwelling off the continental Bluff isis more argillaceous than overlying beds, shelf, to bring planktonic foraminifera into and thethe upper-most bed of the Blue Bluff is nearshore waters. This is also compatible with sandiersandier thanthan underlying beds. the reports of scattered pelletal phosphate (which is derived from cold, deep, oceanic water) in the Lisbon Formation in Georgia (Herrick, 55 1961). The diverse planktonic foraminiferal foraminifera1 These groups of fossils establish faunas in the Lisbon Formation in Burke biostratigraphic correlation of the Lisbon County, occur in scattered stratigraphic intervals Formation of Georgia with the upper Lisbon throughout the sections, such as the exposure at Formation of Alabama (Toulmin, 1977; Harris, the type locality of the McBean Limestone 1919; Palmer, 1937; Herrick and Vorhis, 1963). Member. However, many samples have small Although the nominate taxon of the populations and low diversity. Orbulinoides beckmanni Zone has not been In Burke County, benthic foraminifera reported from Middle Eocene Coastal Plain from the Lisbon Formation are characterized by sediments, the abundance of Truncorotaloides low diversity and high faunal dominance (a rohri and the local occurrence of T. topilensis in fauna dominatf"ddominated by a few species). This is the Lisbon Formation indicates an age close to consistent with an inner neritic, marine that of P13PI3 of Blow (1969) and the Orbulinoides environment. beckmanni Zone of Bolli (1957) and Stainforth and others (1975). Age Blue Bluff Member Characteristic macrofossils of the (new name) outcropping Lisbon Formation in Georgia include: Definition Cubitostrea sellaeformis Pteropsella lapidosa The name Blue Bluff Member of the Barbatia rhomhoidellarhomboidella Lisbon Formation has been used informally in the Savannah River area in Burke County Benthic foraminifera include: (Huddlestun, 1981; Bechtel, 1982; Gorday, 1985; Cibicides westi Laws, et al, 1992; Fallaw and Price, 1992, 1995) Eponides m.exicanusmexicanus for several years. The Blue Bluff Member is Asterigerina lisbonensis formally named and described here for the characteristically thinly bedded, bioturbated, Larger foraminifera reported by Herrick fine-grained, very calcareous clay ("marl") to very (1961) and Herrick and Vorhis (1963) include: argillaceous limestone ("marl") lithofacies of the Asterocyclina monticellensis Lisbon Formation. It occurs across the state Lepidocyclina untilleaantillea from the Chattahoochee River area in western Georgia to the Savannah River area in eastern We have identifiedidentifled the following Georgia and western South Carolina. It is planktonic foraminifera from the Lisbon largely a subsurface unit and represents an Formation in Georgia: offshore, transitional phase between the Truncorotaloides cf. topilensis nearshore, sandy undifferentiated Lisbon T. rohri Formation (and McBean Limestone Member in Globorotalia spinulosa Burke County), and an offshore, subsurface, Acarinina cf. spinuloinflata (in part = unnamed Lisbon-equivalent limestone in G. bullbrooki of some authors) Georgia. A crassata densa (sensu Bandy, 1949) In the past, deposits here called Blue A. sp. Bluff have been included in the McBean Globigerina eocaena Formation (Veatch and Stephenson, 1911, p. G. cf. senni 249; Cooke, 1936; Cooke and MacNeil, 1952; G. sp. Siple, 1967) and the Lisbon Formation generally Globorotalia cf. renzi (Herrick, 1961; Herrick and Vorhis, 1963; Globigerinatheka sp. Bechtel, 1982). GlobigerapsisGlobigeqsis sp. Pseudohastigerina micmmicra 56 Savannah River Site N miles 5 o 5 Contour interval 20 feet Core site. Figure 17. Lisbon Formation isopach (thickness distribution) map. Thicknesses are in feet. Savannah River Site N miles 5 o 5 Contour interval 20 feet Core site • Figure 18. Structure contour map of the top of the Lisbon Formation. Elevations are in feet relative to mean sea level. Modified from ~..mmArnur ::mn nthAr!:: f1QQ4 \ Type Locality are the only good example of the member in thethe Oconee River and Ocmulgee River areas The name Blue Bluff is taken from Blue respectively. Bluff on thethe Savannah River in Burke County, The reference locality at Coheelee Creek Georgia. The exposure at Blue Bluff is here is in a state park, approximately 0.4 miles east designated the type localityldty of the Blue Bluff of the confluence of the creek with thethe Member of the Lisbon Formation (for described Chattahoochee River, 2 miles (3.2 km) northeast sections, see Veatch and Stephenson, 1911, p. of Columbia, Alabama, and 1.6 miles (2.6 km) 249-250, and Brantly, 1916, p. 54). Blue Bluff is northwest of the community of Hilton, Early approximately 2 miles (3.2 km) downriver from County, Georgia. All the deposits exposed along Hancock Landing, and is now in the southern Coheelee Creek in the state park compose thethe part of thethe property of Georgia Power Company parastratotype of the member. Plant Vogtle. The type section, or unit•unit- stratotype (holostratotype) is the entire section Lithology exposed at Blue Bluff. Neither the lower nor upper boundaries .are exposed at the type The Blue Bluff Member of the Lisbon locality.locality. Exposures of the member at Blue Bluff Formation is best described as a "marl", and north of Blue Bluff in the river bluffs at consisting dominantly of clay and calcite with Plant Vogtle are the only known outcrops of the minor, but irregularly distributed fine-grained member inin the Savannah River area (though it quartz sand. The Blue Bluff Member typicallytypically was intermittentlyintermittently exposed during construction is a thinly bedded to laminated or bioturbated, of thethe power plant at Plant Vogtle and is the silty to finely sandy, very calcareous clay ("marl") foundationfoundation on which the Plant is constructed). to very argillaceous limestone ("marl"). In the Chattahoochee River area, the Although clay and calcite are the Blue Bluff Member is exposed at Coheelee Creek dominant lithic components of the Blue Bluff inin Early County, Georgia (Marsalis and Friddell, Member, it is dif6cultdifficult to determine which 1975,1975, stop 9, p. 68-70). component is dominant. Some beds consist Four core sites (Table 11),ll), and one primarily of clay whereas others consist of fine-fine• outcrop are designated here as reference grained, argillaceous limestone. In addition, localitieslocalities and reference sections (para•(para- there are scattered but volumetrically minor stratotypes) of the Blue Bluff Member. In the lenses of sand in the Blue Bluff, especially at or Tritium Project study area, TR92-3 and core near the top of the member. Brantley (1916, p. VG-6 are designated as reference localities. 54) presented one chemical analysis for a sample Outside the study area, USGS Laurens County from Blue Bluff. The percent of carbonate inin core, GGS Pulaski 3, and the exposure of the the sample was 56.1%, indicating that clay and Blue Bluff Member at Coheelee Creek in Early calcite are present in nearly equal proportions. County, Georgia are designated as reference Most likely, calcite is the dominant component localities.localities. downdip, whereas clay is dominant updip. Core TR92-3 is chosen as a Fallaw and Price (1992) reported (by way of parastratotype because it is characteristic of the personal communication with Pa-APa~ Thayer) thatthat member near its lithofacies transition into the much of the Blue Bluff has more thanthan 75% McBean Limestone Member. Core VG-6 is calcium carbonate from SRS cores. chosen as a parastratotype of the Blue Bluff Smectite is the dominant clay mineral, Member because it is lithologically characteristic kaolinite and illite are minor constituents of thethe member in southern Burke County. The (Bechtel, 1982). Calcite principally is interstitial Blue Bluff lithologylithology is well-developed and the in the form of bryozoan fragments, foraminifera, core recovery was good. The Laurens County ostracods, unidentified skeletal fragments. core and thethe Pulaski 3 are chosen as a reference Undefinable microscopic calcite particles and sections for the Blue Bluff Member because the limestone form thin beds, stratified lines of member isis typically developed in the cores and 59 Table 11 Blue Bluff Member reference sections. Core SiteSb GGS SiteSbElevationElevallon Top of member- BattomBottom of see FigureFlgure 2 core above Mean Sea feet below member-feet below Table 1 number Level (feet) surface surface TR92-3 GG8-3781 195 95.5 159.5 VG-6 nfa 217 255 328 GGS Laurens GGS-3523 285 247.5 312.5 CountyCountv Pulaski 3 GG8-3111GGS-3111 300 210 315 ..nfan/aU-Not ..-Not applicable calcite nodules, and irregularly distributed calcite Stratigraphic Relationships nodules. Other subordinate lithic components The Blue Bluff Member of the Lisbon includeinclude mica (which is commonly conspicuous), Formation extends across southern Georgia from finelyfinely disseminated pyrite, lignitic flecks and the Chattahoochee River into the southern part fragments,fragments, heavy minerals including epidote, of SRS in western South Carolina (Fallaw and zircon, garnet (Bechtel, 1982); opaque minerals, Price, 1992, 1995). In eastern Burke County, glauconite, pelletal phosphate, zeolite, sodium Georgia, the updip limit of the Blue Bluff and potassium feldspar (Na-feldspar and K•K- Member is near Hancock Landing, north of feldspar),feldspar), chert, and minor calcitic, aragonitic, Plant Vogtle, where it intertongues with and phosphatic biogenic debris. undifferentiated Lisbon sand. There are also Clay-rich layers are a darker olive gray scattered lenses of Blue Bluff lithology within color thanthan thethe sand or calcite-rich layers, which the McBean Limestone Member. The downdip are lighterlighter shades of olive gray. Bedding in the limit of the Blue Bluff Member in the Savannah Blue Bluff Member, therefore, is commonly River area is in Screven County, where thethe highlighted by color differences in the sediment upper part of the unit consists of an unnamed, ratherrather thanthan by definition by parting along fine-grained, dense limestone. Presumably thethe bedding planes. As a result, the Blue Bluff limestone thickens at the expense of thethe commonly appears to be massive-bedded in underlying, siliciclastic Blue Bluff Member. outcrop and in cores, but, upon close inspection, West of the Savannah River area, its downdip thethe bedding can be clearly discerned. Bedding limit is uncertain but the southern-most limit inin thethe Blue Bluff Member ranges from thin to could be the northern flank of the Gulf Trough. laminar,laminar, and bedding orientation varies from flat However, it seems unlikely that typical Blue toto undulatory and, rarely, to gently inclined. Bluff Member lithology extends that far south. Bioturbation ranges from minor rupturing of Conventionally the Blue Bluff Member stratificationstratification to complete homogenization. has been correlated with the Santee Limestone The Blue Bluff Member is generally of South Carolina (Fallaw and Van Price, 1992, tough,tough, cohesive, and dense. Although 1995). This correlation, however, is not certain nonindurated (except for calcite nodules and in our estimation. We know of no evidence thatthat thinthin limestonelimestone beds or lenses), the typical the Blue Bluff grades laterally into the Santee sedimentsediment disaggregates with some difficulty in Limestone or know of no area where the Santee microfossil preparation. and Blue Bluff are present in the same geographic area or stratigraphic position. The Blue Bluff certainly does not appear toto grade southeastward or downdip in Georgia intointo 60 Santee lithology. Rather, it grades downdip into GloborotaliaGlobomtalia spinulosa an unnamed, dense, fine-grained limestone in Acarinina d.cf. spinuloinflata (in part = G. Screven County. bullbmokibullbrooki of some authors) In Burke County, the Blue Bluff A crassata densa (sensu Bandy, 1949) Member disconformably overlies the Still Branch A. sp. Sand, except in core TR92-6 (two miles updip Globigerina eocaena from the Pen Branch fault), where it overlies the G. d.cf. senni BennockBennock. Millpond Sand Member (of the Still G. sp. Branch Sand). Normally the Blue Bluff Member GloborotaliaGlobomtalia cf.d. renzi disconformably underlies the Utley Limestone Globigerinatheka sp. Member of the ClinchfieldClincbfield Formation, but Globigerapsis sp. locally, where the Utley is absent, the Blue BluffBlutr Pseudohastigerina micramicm disconformably is overlain by the Dry Branch Formation. Cibicides westi is a characteristic benthic There is 33 feet (10 m) of Blue Bluff foraminifer of the Blue Bluff Member. Herrick Member at the type section at Blue BlutrBluff on the (1961, p. 173) reported Asterocyclina Savannah River. Neither the upper nor the monticellensis from deposits referred to the Blue lower contacts of the member are present in BluffBlutr Member of this report in well GGS-248 in outcrop at the type locality. In the subsurface of Dougherty County, Georgia. Burke County, the thickness of the Blue Bluff DinoflagellatesDinotlagellates identified by Edwards of Member ranges from 64 feet (20 m) in TR92-3, the USGS include the following: to 84.5 feet (26 m) in core VG-1VG-l taken near the Adnatosphaeridium multispinopsum community of Girard in Burke County. Aeriosphaeridium pectiniforme Based on benthic foraminiferalforaminifera1 faunas Cordosphaeridium cantharellum that are characterized by high faunal dominance "Corrudinium sp. 1" of Edwards (1984) and low diversity, the environment of deposition CribroperidiniumCribmperidinium giuseppei of the Blue Bluff Member is interpreted to be Glaphyrocysta?Glaphymcysta? vicina open marine, inner continental shelf. The Heteraulacacysta porosa scattered, relatively diverse assemblages of Hystrichokolpoma rigaudiae planktonic foraminifera, and the diverse tloraflora of HystrichosphaeropsisHysmchosphaeropsis sp. dinotlagellatesdinoflagellates indicate that the member must 14eunecystaweunecysta sp. have had open access to outer neritic and deep Leninia sp. ocean water masses. Lingulodinium machaerophorum Operculodinium sp. Age Pentadinium goniferum (including granulate forms) The Blue Bluff Member of the Lisbon PentadiniumPentadiniumgoniferum/membranaceum goniferum/membranaceum Formation is Middle Eocene, Bartonian, Pentadinium/ImpagidiniumPentadinium/lmpagidinium Claibornian in age and is Cook Mountain-Mountain• Samlandia chlamydophora var. 1 equivalent. It occurs in the upper part of the Spiniferites spp. Cubitostrea sellaeformis Zone although only Systematophora placantha juvenile specimens of Cubitostrea are present at Tectatodinium pellitum Blue Bluff and in the past excavation at Plant Thalassiphora pelagica Vogtle. Pteropsella lapidosa, a pelecypod fossil known only from the Cook Mountain and Edwards concluded that the above equivalents (Toulmin, 1977) is present at Blue "dinotlora"dinoflora is typical of the 'upper Lisbon to Bluff. Characteristic planktonic foraminifera Gosport equivalent.' late Middle Eocene, include: correlative to NP 16 or NP 17." Welzeliella was TruncorotaloidesTruncomtaloides d.cf. topilensis not found in the sample, indicating the T. rohri environment was offshore, continental shelf. 61 McBean Limestone Member There is currently little to be seen of thethe (restricted) McBean LimeatoneLimestone Member at the type locality, however, most of the McBean Limestone Definition Member section is exposed at Shell Bluff on thethe Savannah River. Because Veatch and The McBean Formation of past usage Stephenson (1911,0911, p. 243-247) extensively (Appendix(Appendix 4) isis reduced in rank to member discussed the McBean section at Shell Bluff, itit statusstatus inin thisthis report. Its geographic extent is stands as a reference locality (parastratotype) for limited,limited, occurring only in northern Burke and the McBean LimeatoneLimestone Member. Shell Bluff isis southernsouthern Richmond Counties (Hetrick, 1992). located at Shell Bluff Landing on the Savannah The McBean, :'nia the strict sense of this report, is River at the end of Ga. Hwy. 80 in Burke not known to exist anywhere else in Georgia. County, Georgia. The name McBean is retained because the unit The site of the GGS McBean core isis lithologicallylithologically distinctive. (Figure 2, Table 1) is here designated a The McBean Limestone Member of the reference locality for the McBean Limestone Lisbon Formation consists largely of soft to hard Member. This site is 1.2 miles (1.9 km) limestonelimestone thatthat isis variably calcarenitic, slightly southeast of the exposure of the limestone in thethe and variably macro-fossiliferous, finely sandy easternmost gully of the type locality. The throughout,throughout, and variably argillaceous.argiUaceous. The section from 112 feet to approximately 186 feet limestonelimestone isis generally thick-bedded, crudely and is a reference section (hypostratotype) for thethe massive-bedded, and devoid of sedimentary or McBean Limestone Member. The upper biogenic structures. boundary stratotype is at 112 feet where thethe McBean Limestone Member is disconformably Type Locality overlain by the Utley Limestone Member of thethe Clinchfield Formation. The lower boundary The name McBean was taken from the stratotype is at 186 feet where the McBean community of McBean and from McBean Creek. paraconformably overlies the Bennock Millpond Veatch and Stephenson (1911) did not expressly Sand. designate a specific type locality. Their principle concept of thethe formation is, however, inherent in Lithology theirtheir listlist of measured sections (p. 242) and includesincludes thethe ravines or gullies in the southern In outcrop and in nearby cores, thethe valley wall of McBean Creek in Burke County, lithology of typical McBean is dominantly a Georgia. The section of the McBean now finely sandy limestone. In the GGS McBean exposed inin the ravines and gullies, core, the McBean LimeatoneLimestone Member primarily approximately 0.4 to 0.5 miles (0.64 to 0.8 km) consists of limeatonelimestone that is variably calcarenitic, southeastsoutheast toto east of the McBean railroad finely sandy throughout, and variably crossing, along the south side of Ga. Hwy. 56 argillaceous. Minor lithic components include spur,spur, isis thethe principal reference section variable but minor amounts of fine mica; (neostratotype)(neostratotype) of the McBean Limestone variable and minor fine lignitic and Member. Sloan (1908, p. 269-271) however, carbonaceous debris in beds, laminae, and presented the most thorough measured section parting surfaces; variable and minor amounts of thisthis locality,locality, and the McBean Limestone and fine-grained glauconite (most beds are Member includesincludes beds (f)(0 and (g) of Sloan's nonglauconitic); some dark minerals; common section.section. Other measured sections of the McBean gypsum bloom on desiccated core surfaces; fine-fine• typetype localitylocality are to be found in Veatch and grained and trace amounts of fine-grained pyrite; Stephenson (1911, p. 2420), Cooke (1943, p. 56), some "marl", wad and MnO,Mn02 dendrites; pelletal LeGrand and Furcron (1956, p. 33), and Herrick phosphate and very fine vertebrate bone debris; and Counts (1968,. p. 54-57). minute spicules and spicule molds; and scattered, thin, hard limestone beds or lenses. 62 In the McBean core, the limestone is The McBean Limestone Member is best generally thick-thick.- and massively bedded, crudely developed near McBean Creek from several stratified, and devoid of sedimentary or biogenic miles above the community of McBean to Shell structures. Some thin beds or intervals with Bluff. In this area, there are beds or lenses of horizontally oriented, fossil molds and casts can Blue Bluff lithology within the McBean, be found. There is some interlayering of soft, although there is no Blue Bluff lithology in the sandy limestone with thin layers of hard, McBean at Shell Bluff. indurated, fine-grained, dense, argillaceous limestone. Stratigraphic Relationships The limestone tends to be hard to mildly indurated, friable and brittle. In the GGS The areal extent of the McBean McBean core, all of the McBean Limestone Limestone Member of the Lisbon Formation is Member is consolidated to some degree. small. Its northern limit in Richmond County is However, at the type locality of the McBean and not currently known but it probably grades in the USGS Millers Pond core, the member laterally a mile or two north of McBean Creek consists of unconsolidated finely sandy into Oconee Group sediments. The Barnwell calcarenite. From 121 feet to 138 feet in the Group disconformably overlies Oconee Group GGS McBean core, the limestone lithology is deposits a few miles north of McBean Creek in similar to the Blue Bluff Member in that it is southeastern Richmond County. The McBean more argillaceousargiIlaceous than the rest of the McBean outcrop extends about 15 miles (24 km) up section, more thin- to medium-bedded and McBean Creek from Shell Bluff, and a shorter shaley, and has minor bioturbation. It differs distance up Boggy Gut Creek (Hetrick, 1992). from typical Blue Bluff lithology in that the bed The McBean Limestone Member grades seaward is conspicuously sandy and indurated. into the undifferentiated sand in the vicinity 'of.of Typical McBean is slightly and variably the Pen Branch fault near Hancock Landing. macrofossiliferous; some beds are barren of In northern Burke County, the McBean macrofossils but most beds are sparsely Limestone Member of the Lisbon Formation fossiliferous. In some beds fossils occur in small overlies the Bennock Millpond Sand with concentrations. Most of the macrofossils consist apparent conformity and gradation. In turn the of molds and casts of aragonitic fossils, rare and McBean is overlain disconformably by the Utley chalky aragonitic shells and shell fragments in Limestone Member of the Clinchfield Formation various stages of decomposition, and scattered or the Dry Branch Formation. The McBean calcitic fossils (oysters, scallops and barnacles). Limestone Member of the Lisbon Formation Cubitostrea sellaeformissellaefonnis and rare CrassostreaCmssostrea grades laterally downdip into the Blue Bluff gigantissima (in place) are scattered in the Member of the Lisbon Formition.Fornuition. limestone. The range of known thickness of the The color of unweathered or unoxidized McBean Limestone Member in northern Burke McBean Limestone Member (dry core) ranges County is from 74 feet (16 m) to 23 feet (7 m) from light olive gray through yellowish-gray to (Table 12). Average total thickness of the very light gray. McBean Limestone Member in northern Burke We have not yet identified any discrete County is 52 feet (16 m). beds of sand or clay in the McBean Limestone An open marine origin for the McBean Member. The quartz sand component is Limestone Member is attested to by the interstitial and usually fine- to very fine grained presence of planktonic foraminifera and and well-sorted, but some beds contain medium-medium• Cubitostrea sellaeformis, both of which are and coarse-grained, well-rounded, moderately restricted to open marine water-mass conditions. well to poorly sorted sand. Typically, the On the other hand, the regional distribution of texture of the McBean Limestone Member is the McBean is small and the lithology is equigranular, calcarenitic, and finely bioclastic. dominated by calcite, a product of biological activity. Based on the above observations, it 63 Table 12 Thickness variations for the McBean Limestone Member in northern Burke County. 11 I I 11 I! Core sitestte I GGS core number ThlcknesaThickness In feet !I GGS McBean GG8-3757GGS-3757 74 11 I - I - ~ - 11 11 USGS Millers Pond 1 p GG8-3758GGS-3758 1 78.5 11 TR92-1 GG8-3674 23 TR92-2 GG8-3762 23 TR92-4 GG8-3782 62 would appear that the McBean was deposited in 1995). The basal formation of thethe Barnwell an area that was partially cut off from a source Group consists only of the Utley Limestone of siliciclastics,siliciclastics, most conspicuously by the near Member of the ClincMeldClinchfield Formation. The Dry absence of clay. There is no indication of any Branch Formation overlies the Utley Limestone sortsort of barrier to the open ocean because the Member either paraconformably or gradationally. McBean, Blue Bluff, and undifferentiated Lisbon In Burke County, the only mappable interfingerinterfinger and interlense between the vicinities subdivisions of the Dry Branch Formation are of Shell Bluff and Hancock Landing. the Irwinton Sand Member, which dominates the Dry Branch section in northern Burke Age County, and the Griffins Landing Member, which dominates the section in southern Burke The age of the McBean Limestone County. The Twiggs Clay, a member of thethe Dry Member is Middle Eocene, Bartonian, upper Branch Formation in central Georgia, isis Claibornian, and Cook Mountain-equivalent. represented only by beds or lenses of Twiggs F'ossils~ossilsfrom the McBean useful in correlation clay lithology scattered throughout thethe Dry purposes include:include: Branch Formation in Burke County. These clay Truncorotaloides rohri beds are least common in the upper part of thethe T. cf. topilensis formation, and are most common in thethe lowerlower Globorotalia spinulosa part of the formation, especially in thethe basal part. Other than that, there does not appear toto among thethe planktonic foraminifera, and: be any systematic pattern to the distribution of the Twiggs-type clay beds between northern and Cibicides westi southern Burke County. The Tobacco Road Sand covers most of the upland intertluveintertluve among thethe benthic foraminifera. surfaces in northern Burke County (Figure 191,19), but farther south and west, the upland surface BamwellBarnwell Group is covered by the Altamaha Formation which disconformably overlies the Tobacco Road Sand Definition in that area. The Barnwell Group consists of a series Lithology of Upper Eocene near shore to coastal marine, sandysandy deposits in the Fall Line hills area of The lithology of the Barnwell Group isis central toto eastern Georgia and western South dominated by quartz sand. Minerals or Carolina. In Burke County, Georgia, the lithologies that are normally subordinate may Barnwell Group is subdivided (Figure 3) into the dominate the lithology of particular beds or followingfollowing formations and members (Huddlestun lenses in the group. These include dayclay (both and Hetrick, 1978, 1986; Fallaw and Price, 1992, smectite and kaolinite), limestone, greensand, 64 oumternmry ~IIUVIU~ 1m Miocene Altamaha Formation Upper Eocene Tobacco Road Sand § Upper Eocene Dry Branch or ClinchfieldCllnchfield Formation GTLE ' • Middle Eocene Lisbon Formation miles o0123452 3 4 5 Figure 19. Geologic map showing the extent of the Upper Eocene Barnwell Group in eastern Burke County. From Summerour and others (1994). lignite,lignite, opal-cristobalite, chert, sandstone, and older Middle Eocene deposits exposed inin thethe gravel. Shells, mica, hydrated iron oxides, and lower parts of stream valleys and along bluffs of wad (hydrated(hydrated Mn0MnO,)2) may be locally the Savannah River. conspicuous. Other accessory lithic components The Barnwell Group grades downdip of thethe Barnwell include aragonitic shells, pyrite, into the Ocala Group in Screven County. There flecksflecks of carbonaceous matter, siliceous are no other stratigraphic equivalents inin microfossils (diatoms and sponge spicules), and GeorgiaGeorgia. In Burke County the Barnwell Group generally small marine vertebrate phosphatic either occurs at the tops of the sections, as inin bone debris such as fish teeth, scales and bones. the study area, or is overlain disconformably by The quartz sand of the Barnwell Group the Miocene Altamaha Formation farther west ranges fromfrom vel)veq fine to very coarse grained and and south. The Barnwell Group disconformably locallylocally contains lenses of gravel and mixtures of overlies the Middle Eocene McBean Limestone sandsand and pebbles. Sorting ranges from very well Member of the Lisbon Formation inin northern toto very poorly sorted. In general, very fine to Burke County and the Blue Bluff Member of thethe medium-grained sands are well-sorted and lack Lisbon Formation in central and southern Burke any appreciable clay component. These sands County. In upland, interfluve areas in Burke (and(and carbonates of the Utley Limestone County, thickness of the Barnwell Group ranges Member) are highly permeable and constitute from 112 feet in GGS McBean core toto as much thethe unconfined Upper Three Runs aquifer as 252 feet in core VG-2. Because of thethe erosion (Summerour,(Summerour, et aI,al, 1994) in Burke County. of the upper portions of the Barnwell Group, With increasing grain size, sorting commonly isopach and structure contour maps of thethe deteriorates, producing very poorly sorted Barnwell Group formations are of questionable sedimentssediments such as pebbly, coarse-grained sand value and are not included in this report. with a fine-grained or clayey matrix. However, Environment of deposition of thethe somesome beds or lenses of well-sorted, coarse to Barnwell Group ranges from littoral toto shallow very coarse sand are locally common. marine, inner neritic, continental shelf. Based - Typical Barnwell lithologies have on the presence, and local abundance of prominent bedding that ranges from horizontal CrassostreaCrassostma gigantissirnugigantissima in addition toto thethe (thick-bedded,(thick-bedded, thin-bedded, and laminated), absence of planktonic foraminifera inin all but undulatory, and cross-bedded. Some deposits southernmost Burke County, the salinity of thethe may display little bedding, probably due to water-masses probably was slightly brackish. bioturbation and complete mixing of the sediments.sediments. These include the Griffins Landing Age Member of the Dry Branch Formation, parts of thethe Tobacco Road Sand, and parts of the Utley The Barnwell Group is Jacksonian, Late Limestone Member. Eocene (Priabonian) in age (see discussion, Huddlestun and Hetrick, 1986, p. 9-12). Stratigraphic Relationships Clinchfield Formation The Barnwell Group covers most of the Utley Limestone Member upland surface of eastern Burke County. East and south of the study area in northern and Definition eastern Burke County, the Barnwell Group is overlain by the Miocene Altamaha Formation. The Utley Limestone Member of thethe The hard, brick-red to reddish brown residuum Clinchfield Formation was named by of thethe Tobacco Road Sand is most commonly Huddlestun and Hetrick (1986) for a encountered on the upland surface, but in•in- fossiliferous, sandy limestone at the base of thethe stream valleys, loose to almost incoherent sands Barnwell Group throughout eastern Burke of thethe Dry Branch Formation cause steep valley County. The Utley Limestone was differentiated sides.sides. Only in northernmost Burke County are from the Clinchfield Formation because beds or 66 lenses of Utley Limestone lithology occur within where the limestone is sandy, fractures are the ClinchfieldClinaeld Formation in central Georgia. irregular. Similarly, beds or lenses of Clinchfield sand The 'UtleyUtley is variably and finely to lithology occur within the Utley Limestone in coarsely moldic, with varying degrees of Burke County. secondary porosity and bioclastic texture. Some limestone beds are very finehegrained but not Type Locality lutitic. The limestone exhibits varying degrees of consolidation. Most commonly the Utley is The name Utley was taken from Utleys indurated, hard, dense and recrystallized, but Cave at the upper end of Mallards pond in some beds are only partially indurated and very eastern Burke County. The type locality is at friable. The Utley Limestone Member is Utleys Cave, approximately 0.8 mile (1.3 km) variably fossiliferousfossilifemus and is subcoquinoid in southwest of Hancock Landing and on the some beds. Unaltered calcitic shells are locally property of Georgia Power Company Plant abundant, but the original aragonitic shells Vogtle. The section exposed at Utleys Cave is generally have been leached, leaving molds and the type section, or unit-stratotype for the impressions. There are also some concentrations member (Huddlestun and Hetrick, 1986). of the oyster CrassostreaCmssostrea gigantissima near the base of the member, similar to concentrations in Lithology the Riggins Mill Member (Huddlestun and Hetrick, 1986). Faunal diversity is fairly high. The Utley LimestoneLimedone Member of the Most of the fossils consist of molds and casts of Clinchfield Formation typically is a moldic, mollusks but include unaltered bryozoa, fossiliferous,fossilifemus, variably glauconitic, variably sandy barnacles, crab claws and echinoids. Also, the limestone. Some beds consist of calcareous Utley Limestone is the eastern-most knownknow sandstonesanddone or, more rarely, unconsolidatedunconsolidatad occurrence of the PerimhuaPeriarchus lyelli bed, and the calcareous sand. The sand is generally fine•he- fragments of the sand dollars are locally grained and well-sorted, but there are minor common. occurrences of coarse-grained, well- to The color of the limestone is most moderately sorted sand. Other subordinate commonly very pale orange but other colors lithic components include small, dark grains include variable shades of yellowish-gray, olive•olive- (heavy minerals?); minor amounts of clay gray and light-grays. minerals; some unconsolidated calcarenite becLs,beds; a trace of pelletal phosphate in southern Burke Stratigraphic Relationships County; scattered shell fragments and other calcitic fossil debris; and rare foraminifera.foraminifera In In Georgia, the Utley Limestone is southern Burke County the lower part of the currently known only from the Savannah River formation consists of a calcareous, glauconitic area in Burke and Screven Counties, Georgia sand with some 'calcareous,calcareous greensand. The (Huddlestun and Hetrick, 1986). However, beds associated limestone has a salt and pepper or lenses of Utley-like limestone are present in appearance because of the light colored the Riggins Mill Member of the Clinchfield calcarenite and dark glauconite. Clayey, Formation in the central Georgia Coastal Plain. calcareous "marl" is rare in the Utley. Fallaw and Price (1992) have identifiedidentifled the The Utley Limestone Member is Utley Limestone in the southeastern part of SRS typically massive- and thick-bedded but there is in Barnwell County, South Carolina, but report some crude stratification.stratitication. Most shell molds its absence updip in the middle part of SRS. appear to be randomly oriented, but there is a In eastern Burke County, the Utley slight tendency toward horizontal alignment in Limestone is locally absent due either to solution some thin intervals. Some thin bedding occurs or nondeposition on topographic highs during in the sandier parts of the limestone. Except the Jacksonian transgression. Where the Utley Limestone is present, it disconformably overlies 67 the McBean Member and undifferentiated of the Barnwell Formation of Shearer, 1917; or Lisbon Formation in northern Burke County, as undivided Barnwell Formation of Veatch and and disdisconformablyconformably overlies the Blue Bluff Stephenson, 1911). As defined by Huddlestun Member in central and southern Burke County. and Hetrick (1979, 1986),19861, the Dry Branch The Utley in turn is overlain with apparent Formation consists of three formal members, conformity by the Dry Branch Formation, but each one of which constitutes the entire Dry the contact is generally sharp. Branch section in the areas where they are In northern Burke County, Utley typically developed. These are the Twiggs Clay Limestone ranges in thickness from 0 feet Member, IIWintonIrwinton Sand Member and Griffins (where absent) to 13 feet (4 m) at the type Landing Member. Where these particular locality. Its average thickness in northern Burke lithofacies are not well-developed, the Dry County (basedCbased on 8 sites) is approximately 7 feet Branch Formation may be composed of any two (2 m). The Utley limestone is systematically or three of the member lithofacies. In Burke thicker in southern Burke County where it County, all three lithofacies are present, but only ranges from 10 feet (3 m) in core VG-4 to 34 the IIWintonIrwinton Sand and Griffins Landing can be feet (10 m) in core VG-8. Fallaw and Price considered as members. A Twiggs-type clay (1992, 1995) reported 30 feet (9 m) in the occurs as thin beds or lenses within IrwintonIIWinton southeastern part of SRS. Sand Member and Griffins Landing Member. Age TypemeLocality There is some controversy over the age The name Dry Branch is taken from the of the Clinchfield Formation and, therefore, also community of Dry Branch, located on U.S. Hwy. of the Utley Limestone Member. 80 on the Bibb-Twiggs County line. The type Paleontologically, it could be late Claibornian in locality of the Dry Branch Formation is in age and correlative with the Gosport Sand of Twiggs County, along an abandoned kaolin haul sopthwesternsouthwestern Alabama. Like the Gosport, the road at the entrance to an abandoned kaolin Clinchfield Formation is variable in thickness mine, 0.6 miles (1 km) from the junction of the over short distances in kaolin mines in central haul road and U.S. Hwy. 80 at the highway Georgia due, apparently, to filling of topographic bridge over the Seaboard Coast Line Railroad, lows on the top of the Oconee Group 2.3 miles (3.7 km) south of Dry Branch. The (Huddlestun and Hetrick, 1986) during the section of Barnwell exposed beneath the Tobacco Barnwell transgression. In most places, the Road Sand is the type section, unit-stratotype upper contact of the Clinchfield with the (holostratotype) of the Dry Branch Formation overlying Tivola Limestone (or Dry Branch (Huddlestun and Hetrick, 1986). The section of Formation) appears to be conformable, Dry Branch exposed in the pit consists of the gradational and horizontal in most kaolin mines IIWintonIrwinton Sand Member with beds or lenses of in central Georgia (in contrast to a basal Twiggs-type clay. irregular contact). Lithology Dry Branch Formation The Dry Branch Formation locally Definition consists of three distinct but interfingering lithofacies: 1.) a marine smectitic clay lithofacies The Dry Branch Formation was named (Twiggs Clay); 2.) a prominently stratified sand by Huddlestun and Hetrick (1979, 1986) for a and sand-clay lithofacies (lIWinton(Irwinton Sand); and 3.) body of deposits that had been previously called a crudely bedded, thick-bedded and massive, members of the Barnwell Formation (IrwintonUIWinton calcareous, fossiliferous, argillaceous sand Sand Member of the Barnwell Formation of lithofacies (Griffins Landing Member). In many LaMoreaux, 1946a, 1946b; Twiggs Clay Member areas of Georgia, however, a fine distinction 68 between thethe lithofacies,lithofacies, due to complex Because the Dry Branch Formation isis interfingeringinterfingering and intergradation,intergradation, is not possible. deeply dissected in Burke County, its apparent InIn thosethose areas, for mapping purposes and thickness is quite variable, being absent where purposes of discussion, it is best to distinguish stream erosion has completely removed thethe only thethe formationformation and to recognize the facies formation. However, the variation in original subdivisionssubdivisions as informalinformal lithofacies, lithosomes thickness of the Dry Branch Formation can be or lithostromes.lithostromes. determined where the overlying Tobacco Road Sand is still present. Only three cores inin Stratigraphic Relationships eastern Burke County were taken at sufficiently high elevations for the Tobacco Road toto be InIn northern Burke County, the Irwinton identified. These three cores are GGS McBean, SandSand constitutes most of the Dry Branch TR92-2, and VG-6 (Figure 2, Table 1). The Dry Formation and, in Richmond County Branch is 67 feet (20 m) in the GGS McBean immediatelyimmediately toto the north, the Irwinton core near McBean Creek, 101 feet (30.8 m) inin constitutes'constitutes all of the Dry Branch. In the TR92-2 core in central Burke County near northernmost Burke County, the GriffinsGfins Hancock Landing, and 163 feet (49.7 m) in thethe Landing Member occurs at the base of the VG-6 core east of Girard in southern Burke formationformation and thickensthickens irregularly southward at County. These three thicknesses suggest thatthat thethe expense of the overlying Irwinton Sand. In the Dry Branch Formation thickens at thethe rate southernsouthern Burke County, the Dry Branch of approximately 4 feetlmilefeet/mile (1.2 m/km)mjkm) toto thethe Formation consists mostly of the GriffinsGfins southeast. Landing Member with Irwinton Sand occurring The depositional environment of thethe Dry only at thethe toptop of the formation. Farther south Branch Formation was shallow to very shallow inin northern Screven County, the GriffinsGfins water, inner neritic, marine. The abundance of Landing Member constitutes all of the Dry sand, undulatory bedding and cross bedding, and Branch Formation. the presence of Crassostrea gigantissima The Dry Branch Formation overlies, suggests a near-shore environment near an with apparent conformity, the Utley Limestone influx of fresh water as opposed to normal, Member of thethe Clinchfield Sand. Within the open-ocean water. The presence of Twiggs clay Dry Branch Formation in central and southern and GriffinsGfins Landing interfingering strongly Burke County, the GriffinsGfinsLanding appears to suggests a near-shore facies mosaic that includes grade both upward and laterally into the bays and lagoons, beaches, tidal inlets, and IrwintonIrwinton Sand suggesting that, for a brief time, oyster reefs. Water depth during deposition of both members were being deposited the Irwinton Sand must have been very shallow contemporaneously. During the later phase of subtidal whereas that of the Griffins Landing deposition of the Dry Branch Formation, the was only slightly deeper, such that open-ocean, IrwintonIrwinton Sand was deposited across the entire planktonic foraminifera could survive inin eastern part of Burke County. In addition, the southern Burke County. However, the presence contact between Griffins Landing Member and of Crassostrea gigantissima bioherms suggest IrwintonIrwinton Sand Member is obscured by deep that the sea water was also sligh'dyslighily brackish at weathering of thethe Irwinton sand and the upper times. part of thethe Griffins Landing. However, in most cores, therethere isis a clear distinction between Age weathered Irwinton Sand and weathered Griffins Landing. Bedding characteristics of the two The Dry Branch Formation is Late members are different and leaching of the Eocene, early Jacksonian in age (Huddlestun calcareous Griffins Landing commonly results in and Hetrick, 1986). precipitation of wad on bedding surfaces, joints, or fractures.fractures. 69 Twiggs Clay Lithofacies Type Locality Lithology The type locality of the GriffinsGrBns Landing Member of the Dry Branch is at GriffinsGrithns Clay beds within the Dry Branch Landing on the Savannah River, 1.4 miles (2.3 Formation essentially have the same lithology as km) north of the junction of GriffinsGrifhs Landing the eastern facies of the Twiggs Clay Member of Road and River Road, and 5.2 air-miles (8.4 km) the Dry Branch Formation (Huddlestun and north of Girard in Burke County. The section Hetrick, 1986),19861, characterized by a paucity of exposed at GriffinsGrBns Landing is the type section, calcite and glauconite and the presence of opal•opal- or unit-stratotype of the GriffinsGrBns Landing cristobalite. Ifo140 opal-cristobalite has been Member. Neither lower nor upper boundaries reported from the Twiggs-type clay beds in are exposed at the landing but Price (personal Burke County, however. communication, 1993) identified the top of the In general, the Twiggs-type clay is a Utley Limestone several hundred feet south of yellowish gray to light olive gray, dense, silty the landing. clay with hack1y,hackly, blocky, shaley, subconchoidal to conchoidal fracture. Where the clay is almost Lithology pure and unaltered by weathering, it commonly displays a combination of blocky and conchoidal In general, the GriffinsGrBns Landing Member fracture. Where it is weathered, its fracture is is a fairly well sorted, massive to vaguely and pronouncedly hack1y.hackly. rudely bedded, calcareous sand. In the updip areas of Burke County, thin limestone beds, clay Stratigraphic Relationships beds or lenses, local oyster 70 Member west of Burke County in Georgia (see Irwinton Sand Member Huddlestun and Hetrick, 1986). The GriffinsGSnsLanding Member is in the Definition lowerlower part of the Dry Branch Formation where itit grades laterally and vertically into the The Irwinton Sand was named by IrwintonIrwinton Sand (Huddlestun and Hetrick, 1986). LaMoreaux (194%(1946a, 1946b)194613) for a soft, commonly The Griffins Landing is absent farther north in loose and incoherent, fine to medium, stratified, Richmond County where the Irwinton Sand noncalcareous sand that contains thin beds, Member directly overlies either the Albion lenses, laminae, or clasts of Twiggs-type clay (see Member of thethe Clinchfield Formation or the Huddlestun and Hetrick, 1986). underlying Oconee Group. Farther south in Screven County, Georgia, the Griffins Landing Type Locality Member composes the entire Dry Branch Formation. The name Irwinton is derived from thethe The GriffinsGSnsLanding Member thickens town of Irwinton in Wilkinson County, Georgia. southeastwardsoutheastward inin Burke County. In northern The type locality of the Irwinton Sand is in Burke County, itsits thickness is variable, ranging gullies, now overgrown, on the west side of U.S. fromfrom 0 feetfeet where it is locally absent due to non•non- Hwy. 441 (Ga. Hwy. 29), 0.3 mile (0.5 km) deposition, toto as much 96.5 feet in the core south of the courthouse in Irwinton. The typetype TR92-5. Average thickness of the GriffinsGSns section, unit-stratotype (holostratotype), of thethe Landing Member in northern Burke County is Irwinton Sand is the section of sand overlying 34 feetfeet (11 (11 m). Where the GriffinsGSns Landing the Twiggs Clay in the gullies at Irwinton. Member isis absent, either the Irwinton Sand When LaMoreaux (194%(1946a, 194613)1946b) described thethe directly overlies the McBean Member of the type section, there was 44 feet (13 m)'mr of Lisbon Formation or undifferentiated Dry Irwinton Sand overlying 20+20+ feet (6.1 + m) of Branch Formation directly overlies the Utley Twiggs Clay and underlying about 12 feet (3.7 Limestone. In southern Burke County, where m) of weathered clay that LaMoreaux (1946a, thethe GriffinsGfins Landing Member is consistently 1946b)194613) described as colluvium but Huddlestun present, thickness ranges from 36 feet (12 m) in and Hetrick (1986, p. 40) considered to be a core VG-3 toto 123 feet (40 m) in core VG-2. deeply weathered bed or lens of Twiggs-clay Average thicknessthickness of the GriffinsGfins Landing lithofacies. Member inin southern Burke County is approximately 74 feet (23 m). Lithology The environment of deposition of the Griffins Landing Member was shallow, inner The Irwinton Sand typically consists of continental shelf. The common occurrence of fine- to medium- grained, well-sorted, almost CrassostreaCrassostrea suggests that the salinity of the sea pure quartz sand that shows well-developed water may have been slightly brackish or small-scale, horizontally bedded, undulatory variable. bedded, and cross-bedded sand. Accessory lithic components include mainly smectitic clay and Age minor amounts of illite and kaolinite. Some weathered beds of clay in the Irwinton are The age of the GriffinsGfinsLanding Member composed entirely of kaolin, apparently altered of thethe Dry Branch Formation is Late Eocene, from smectite. All Irwinton clay beds (smectite) early Jacksonian (Huddlestun and Hetrick we know of are of Twiggs Clay-type lithology. (1986).(1986). Other accessary minerals in the Irwinton Sand include chert, locally conspicuous dark minerals, and very minor mica. Sand in the Irwinton is fine- to medium-medium• grained and well-sorted. Coarser beds are more 71 poorly sorted. Typically, the Irwinton Sand is Age soft and unconsolidated, in some places even incoherent. Therefore, the Irwinton is a "slope•"slope- The age of the Irwinton Sand Member of former". There are some poorly sorted sand the Dry Branch Formation is Late Eocene, early beds within the Irwinton, especially in the far Jacksonian (Huddlestun and Hetrick, 1986). updip areas. Some sections are dominated by medium to coarse, rarely pebbly, moderately Tobacco Road Sand well to poorly sorted sand. Most exposures of the Irwinton Sand Definition contain some beds, lenses, and laminae of disrupted clay clasts of Twiggs-type smectiticsmeditic The Tobacco Road Sand was named by clay. In general, all the clay beds in the Huddlestun and Hetrick (1978) for upper Irwinton probably are lenses, but the thicker Jacksonian deposits that previously had been clay beds are more areally extensive than the called the upper sand member of the Barnwell thin beds, and the clay laminae are especially Formation by LaMoreaux (1946a,(19464 1946b). discontinuous. The clay beds and lenses within the Irwinton Sand produce locally perched water Type Locality tables. The name Tobacco Road was taken from Stratigraphic Relationships the Tobacco Road highway in southern Richmond County. The type locality of the The Irwinton Sand Member of the Dry Tobacco Road Sand is located on the east side of Branch is present throughout Burke County. It Morgan Road, 0.3 miles (0.6 km) north of the is thickest in the northern part of the county, intersection of Morgan Road and Tobacco Road, especially in the study area where its thickness Richmond County, Georgia. The type section, or can be as much as 80 feet (24 m). In some unit-stratotype (holostratotype) of the Tobacco exposures, the Irwinton/Tobacco Road contact Road Sand is that section of the formation appears to be slightly gradational. In other exposed at the type locality (Huddlestun and exposures, it appears that the basal flat pebble Hetrick, 1978, 1979, 1986). bed of the Tobacco Road disconformably overlies the Irwinton Sand. Lithology The Irwinton Sand gradationally overlies the Griffins Landing Member. In addition, the Tobacco Road is predominantly a sand, lower part of the Irwinton appears to grade all other lithic components (clay minerals, chert, laterally into the upper part of the Griffins calcite, limestone, mica, glauconite, dark Landing. The vertical gradation between the minerals and wad) are only locally significant. Irwinton and Griffins Landing is rarely seen in The most characteristic lithology of the Tobacco outcrop and, because of deep weathering and Road Sand is a burrowed and bioturbated, poor core recovery across the Irwinton-Griffins massive-bedded, moderately poorly sorted, Landing boundary, it is rarely seen in cores. medium- to coarse-grained, pebbly, weathered Where there is poor recovery in cores, we sand. This particular lithofacies of the formation arbitrarily place the Irwinton-Griffins Landing is more prevalent in the downdip areas of the contact near the lowest occurrence of prominent outcrop belt such as Burke County. Although bedding, and.and the highest occurrence of wad most exposures show little or no bedding, vague, (hydrated Mn0MnO,),2), chert, or calcium carbonate. rude bedding and disrupted thin bedding are The Irwinton is most easily identifiedidentilied where the probably the norm for the formation as a whole. sand is conspicuously and thinly stratifiedstratilied and For example, at Stop 3 of the 1992 Carolina noncal~a~eous.noncaleateous. Geological field trip (Fallaw and Price, 1992), most of the 35 feet (11 m) of Tobacco Road Sand section consists of crudely bedded, very broadly 72 cross-bedded toto horizontally bedded sand with mollusks with Periarchus quinquefarius, flat massive-bedded,massive-bedded,variablyvariably sorted, medium-grained pebbles, and the local occurrence of prominent sandsand inin thethe lowerlower part. The characteristic undulatory bedding and cross bedding, thethe burrowed and bioturbated sand occurs only in environment of deposition of the Tobacco Road thethe upper 6 feetfeet (2 m) of the formation. In most is inferred to be coastal marine, beach, toto back-back• places, however, crude bedding can be observed barrier (Huddlestun and Hetrick, 1978, 1986). only on close inspection. A zone of flat pebbles occurs at the base Age of thethe Tobacco Road Sand in many places in central and eastern Georgia. Although The Tobacco Road Sand is Latest discontinuous, thisthis bed is very useful for locating Eocene, late Jacksonian in age (Huddlestun and thethe base of thethe Tobacco Road and the top of the Hetrick, 1978, 1986). underlying Dry Branch Formation (Huddlestun and Hetrick, 1978,1978,1986). 1986). The flat pebble bed is REFERENCES CITED common inin northern Burke County but becomes lessless common southward as average siliciclastic Aadland, R. K.; Thayer, P, A.;A; and Smits, A.A D., grain-size decreases. Where the flat pebble bed 1992 Hydrostratigraphy of the Savannah River isis absent, chert, or coarse, granular sand is Site region, South Carolina and Georgia, b-in• commonly present at the base of the formation, Fallaw, W., and Price, V., (eds.), Geological especially where the formation is unusually fine investigations of the central Savannah River grained and consists mainly of fine- to medium•medium- area, South Carolina and Georgia; South grained, well-sorted sand. Carolina Geological Society (SCGS) Field Trip Guidebook 1992, p. CGS-92-B-X-1-6. Stratigraphic Relationships American Commission on Stratigraphic The Tobacco Road Sand occurs at the Nomenclature, 1961 Code of Stratigraphic toptop of upland, intertluveinterfluve sections in the study Nomenclature; American Assoc. Petroleum area. The upper part of the formation generally Geologists (AAPG) Bulletin, vol. 45, no. 5, p. isis deeply weathered and highly pigmented (most 645-665. commonly moderate reddish brown), although in somesome exposed sections or cores the pigmentation American Commission on Stratigraphic isis more variegated. Deep weathering of the Nomenclature, 1970 Code of Stratigraphic Tobacco Road Sand has caused it to become Nomenclature (2nd printing); AAPG, Tulsa, case-hardened and resistant to both chemical Okla, 22 p. and physical weathering. Thus, it is a ledge•ledge- formingforming unit, and commonly is eroded by Bandy, 0.O. L., 1949 Eocene and Oligocene undercutting of the soft sands of the Dry Branch foraminifera from Little Stave Creek, Clarke Formation. County, Alabama; Bulletin American The Irwinton Sand Member of the Dry Paleontology, vol. 32, no. 131, p. 210. Branch Formation underlies the Tobacco Road Sand paraconformably or with abrupt contact. Bechtel Corporation, 1982 Studies of thethe InIn thethe study area in northern Burke County, the postulated Millett fault; Bechtel Corporation, Tobacco Road Sand occurs at the top of the San Francisco, vol. 1 stratigraphicstratigraphic section. Elsewhere in Burke County, thethe Miocene Altamaha Formation Berggren, W. A.,A, 1972 A Cenozoic time-scale-time-scale• overlies thethe Tobacco Road disconformably. some implications for regional geology and Based on the local abundance of the paleobiology; Lethaia, vol. 5, p. 195-215. ghost shrimpshrimp burrow OphiomorphaOphiomrpha nodosa, the presence of the sand dollar Periarchus Blow, W. 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Georgia; USGS Professional Paper 120, p. 41-81. Bybell, L.M., and Gibson, T.G., 1982 The Cumbest, R. J.; Price, V.; and Anderson, E. E., Eocene Tallahatta Formation of Alabama and 1992 Gravity and magnetic modeling of the Georgia: its lithostratigraphy, biostratigraphy, Dunbarton Triassic basin, South Carolina; and bearing on the age of the Claibornian Stage; Southeastern Geology, vol. 33, #1, p. 37-51. U. S. Geological Survey (USGS) Professional Paper 1615, 20 p. Fallaw, W. C., and Price, V., 1992 Outline of stratigraphy at the Savannah River Site, in-in• Clark, W. Z., Jr. and Zisa, A. C., 1976 Fallaw, W. C., and Price, V. (eds.), Geological Physiographic map of Georgia; GGS, scale investigations of the Central Savannah River 1:2,000,000, 1 sheet. area, South Carolina and Georgia; Carolina Geological Society Field Trip Guide Book 1992, Clarke, J. S.; Falls, W. F.; Edwards, L. E.; p. CGS-92-B-II-1.CGS-92-B-11-1. Frederiksen,Fi-ederiksen, N. 0.; Bybell, L. M.; Gibson, T. 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W.; and Howell, P. near the Savannah River, Georgia and South D., 1983 Surface and subsurface stratigraphy, Carolina; USGS Open-File Report 82-156, 73 p. structure and aquifers of the South Carolina Coastal Plain; University of South Carolina Fenneman, N. M., 1938 Physiography of report to South Carolina Department of Health eastern United States; McGraw-Hill Publishers, and Environmental Control, 79 p. New York, pp. 38-46. Cooke, C. W., 1925 b-in- Laforge,LaForge, et al (eds.), Gibson, T. G., and Bybell, L. M., 1981 Facies Physical Geography of Georgia; GGS Bulletin 42, changes in the Hatchetigbee Formation in p.p.39-40. 39-40. Alabama-Georgia and the Wilcox-Claiborne 74 Group unconfomity;unconformity; Transactions Gulf Coast Hetrick, J. H., 1990 Geologic atlas of the Fort Assoc. Geologic Societies, vol. 31, p. 301-306. Valley area; GGS Geologic Atlas 7, 2 pl.pI. Gohn, G. S.; Hazel, J. E.; Bybell, L. M.; and Hetrick, J. H., 1992 A geologic atlas of the Edwards, L. 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D., 1919 Pelecypoda of the St. Guidebook 1982, p. 21-33. Maurice and the Claiborne stages: Bulletin American Paleontology, vol. 6, no. 31, 260 p. Huddlestun, P. F., 1992 Upper Claibornian coastal marine sands of eastern Georgia and the Harris. W. R, B., and Zullo, V. A.,A, 1990 Sequence Savannah River area, in- Fallaw, W. C, and stratigraphy of Paleocene and Eocene deposits in Price, V. (eds.), Geological investigations of the the Savannah River region, in- Zullo, V. A.,A, central Savannah River area, South Carolina Harris, W. R,B., and Price, V. (eds.), Savannah and Georgia: Carolina Geological Society Field River region: Transition between the Gulf and Trip Guidebook 1992, p. CGS-92-B-Xll-I-6.CGS-92-B-XU-1-6. Atlantic Coastal Plains; Proceedings of the Second Bald Head Island conference on Coastal Huddlestun, P. F., and Hetrick, J.H., 1978 Plains geology; University of North Carolina at Stratigraphy of the Tobacco Road Sand - a new Wilmington and U. S. DOE, p. 122-130. formation: $-in- Platt, P.A,P.A., (ed.), Short Contributions to the geology of Georgia; GGS Henry, V. J., 1994 Summary of results of a Bulletin 93, p. 56-77. seismic survey of the Savannah River adjacent to the Savannah River Plant Site, Burke County, Huddlestun, P. F. and Hetrick, J. H., 1979 The Georgia; unpublished report to GGS, 20 p. stratigraphy of the Barnwell Group of Georgia; Georgia Geological Society, 14th Field trip Herrick, S. M., 1961 Well logs of the Coastal guidebook, Georgia Geologic Survey, Atlanta, 89 Plain of Georgia: GGS Bulletin 70, 462 p. Pp. - Herrick, S. M., and Counts, H. R,B., 1968 Late Huddlestun, P. F. and Hetrick, J. H., 1986 Tertiary stratigraphy of eastern Georgia: Upper Eocene stratigraphy of central and Georgia Geological Society, 3rd Field trip eastern Georgia; GGS Bulletin 95, 78 p. guidebook, 88 p. Huddletun, P. F. and Hetrick, J. H., 1991 The Herrick, S. M., and Vorhis, R. C., 1963 stratigraphic framework of the Fort Valley Subsurface geology of the Georgia Coastal Plain: Plateau and the central Georgia kaolin district,district; GGS Information Circular 25, 78 p. Guidebook for the 26th Ann. Field Trip, Georgia Geological Society, vol. 11, no. 1, 119 p. 75 Huddlestun, P. F.; Braunstein, J.; and Biel, R., Age, environment, or both?; Geological Society of 19881988 Correlation of stratigraphic units in North America (GSA) Abstracts with Programs, vol. America-Gulf Coast region correlation chart, 20, p. 277. AAPG, Tulsa, Oklahoma. Lucas-Clark, J., 1992 Problems in Cretaceous Huddlestun, P. F.; Marsalis, W. E.; and and Paleogene dinoflagellate and pollen Pickering, S. M., Jr., 1974 Tertiary stratigraphy stratigraphy--Savannah River Plant area, &J-in• of thethe central Georgia Coastal Plain, Georgia Zullo, V. A.,A, Harris, W. B., and Price, V. (eds.), Geological Society Guidebook 12, pt. 2, 35 p. Savannah River region: Transition between thethe Gulf and Atlantic Coastal Plains; Proceedings of Hurst, V. J.; Crawford, T. J.; and Sandy, J., the second Bald Head Island Conference on 19661966 Mineral resources of the Central Coastal Plains Geology; University of North Savannah River Area; University of Georgia, et Carolina at Wilmington and U. S. DOE, p. 81-81• al, 2 Volumes, 231 p. 82. InternationalInternational Subcommission on Stratigraphic MacNeil, F. S., 1944a The Coastal Plain of Classification, 1976 International stratigraphic Georgia, h-in- Southwestern Georgia field trip;trip; guide; Hedberg, H. D. (ed.), John Wiley and Southeastern Geological Society, 2nd field triptrip Sons, New York, 200 p. guidebook, p. 3-5. LaMoreaux, P. E., 1946a Geology of the Coastal MacNeil, F. S., 1944b The Tertiary formations, Plain of east-central Georgia; GGS Bulletin 50, -in- Southwestern Georgia field trip;trip; 26 p. Southeastern Geological Society, 2nd field triptrip guidebook, p. 35-37. LaMoreaux, P. E., 1946b Geology and ground•ground- water resources of the Coastal Plain of east•east- MacNeil, F. S., 1947a Correlation chart for thethe central Georgia; GGS Bulletin 52, 173 p. outcropping Tertiary formations of thethe eastern Gulf region; USGS Oil and Gas Inv.,lnv., Prelim. LaMoreaux, P. E., and Toulmin, L. D., 1959 Chart 29. Geology and ground-water resources of WilcoxWicox County, Alabama; Alabama Geologic Survey, MacNeil, F. S., 1947b Geologic map of thethe County Rept. 4, 280 p. Tertiary and Quaternary formations of Georgia; USGS Oil and Gas Preliminary Map 72. Laws, R. A;A.; Harris, W. B.; and Zullo, V. A, 19921992 Nannofossil biostratigraphy and sequence Marine, 1.I. W. and Siple, G. E., 1974 Buried stratigraphystratigraphy of Middle to Upper Eocene strata in Triassic basin in the central Savannah River thethe southwestern Savannah River Site and area, South Carolina and Georgia; GSA Bulletin, adjacent areas of Georgia, h-in- Fallaw, W., and VO~.vol. 85, p. 311-320. Price,Piice, V. (eds.), Geological investigations of the central Savannah River area, South Carolina Marsalis, W. E., and Friddell, M. S., 1975 A and Georgia: Carolina Geological Society, Field guide to selected Upper Cretaceous and Lower Trip Guidebook 1992, p. CGS-92-B-VII-I-4.CGS-92-B-W-1-4. Tertiary outcrops in the lower Chattahoochee River valley of Georgia; Georgia Geological LeGrand, H. E. and Furcron, AS.,A. S., 1956 Society guidebook 15, 79 p. Geology and ground-water resources of central•central- east Georgia; GGS Bulletin 64, 164 p. McClelland, S. A, 1987 Surface and subsurface stratigraphy of Cretaceous and younger strata Lucas-Clark, J., 1988 Significance of the along the Savannah River from southern distribution of dinoflagellate assemblages in the Richmond County through Burke County, typetype Ellenton Formation, Savannah River Plant: 76 Georgia; unpublished Master's thesis, University Cephalopoda of the southeastern United States: of South Carolina, 123 p. Bull. Am. Paleontology, vol. 7, no. 32, 730 p. McFadden, S.S.; Hetrick, J.H.; Kellam, M.F.; Pickering, S. M., 1970 Stratigraphy, Rodenback, S.A.; and Huddlestun, P.F., 1986 paleontology, and economic geology of portions Geologic data of the Gulf Trough area, Georgia; of Perry and Cochran quadrangles, Georgia; GGS Information Circular 56, 345 p. GGS Bulletin 81, 67 p. Muthig, M. G. and Colquhoun, D. J., 1988 Price, V.; Fallaw, W. C.; and Thayer, P. A.,A, 1992 Formal recognition of two members within the Lower Eocene strata at the Savannah River Site, Rhems Formation in Calhoun County, South South Carolina; in-h-Zullo, V. A.;A; Harris, W. B.; Carolina; South Carolina Geology, vol. 32, #1 # and Price, V. (eds.), Savannah River Region: 2, p. 11-19. Transition Between the Gulf and Atlantic Coastal Plains; Proceedings of the Second Bald Muthig, M. G., Colquhoun, D. J., and St. C. Head Island Conference on Coastal Plains Kendall, C., 1990 Sequence stratigraphystmtigraphy of the Geology, University of North Carolina and U. S. Black Mingo Group (Lower Tertiary) in South DOE, p. 52-53. Carolina, in- Zullo, V. A,A., Harris, W. B., and Price, V. (eds.), Savannah River region: Prowell, D. C., Edwards, L. E., and Frederiksen, Transition between the Gulf and Atlantic N. 0.,O., 1985a The Ellenton Formation in South Coastal Plains; Proceedings of the second Bald Carolina-a revised age designation from Head Island conference on Coastal Plains Cretaceous to Paleocene; USGS Bulletin 1605-A, geology; University of North Carolina at p. A63-A69. Wilmington and U. S. DOE, p. 118-121. Prowell, D. C.; Christopher, R. A.;A; Edwards. E.; North American Commission on Stratigraphic Bybell, L. M.; and Gill, H. E., 1985b198523 Geologic Nomenclature, 1983 North American section of the updipupdip Coastal Plain from central Stratigraphic Code; AAPG Bulletin, vol. 67, no. Georgia to western South Carolina; USGS 5, p. 841-875. Miscellaneous Field Studies Map, MFMF-1737,-1737, 10 Pp. . Nystrom, P G.; Willoughby, R. H.; and Kite, L. E.; 1982 in- Nystrom, P. G., and Willoughby,Wioughby, R. Reinhardt, J., and Gibson, T. G., 1981 Upper H., (eds.), Geological investigations related to the Cretaceous and Lower Tertiary geology of the stratigraphy in the kaolin mining district, Aiken Chattahoochee River valley, western Georgia and County, South Carolina; Carolina Geological eastern Alabama: Georgia Geological Society Society Field Trip, 1982, p. 121, 158-161. 16th Annual Field trip, 88 p. Oman, C. H., 1965 Micropaleontology of the Rock-Color Chart Committee, 1963 Rock-color Lisbon Formation of Alabama; unpublished chart; Geological Society of America, New York. Ph.D. dissertation, Florida State University, 101 p., 10 plates. Schroder, C. H., 1982 Trace fossils of the Oconee Group and basal Barnwell Group of Owen, V., Jr., 1963 Geology and ground-water East-Central Georgia; GGS Bulletin 88, 125 p. resources of Lee and Sumter Counties, southwest Georgia; USGS Water-Supply Paper Shearer, H. K, 1917 A report on the bauxite 1666,671666, 67 p. and fuller's earth of the Coastal Plain of Georgia; GGS Bulletin 31, 340 p. Palmer, K V. W., 1937 The ClaibornianClaibomian Scaphopoda, Gastropoda, and dibranchiate Siple, G. E., 1967 Geology and ground water of the Savannah River Plant and vicinity, South 77 CarolinajCarolina; USGS Water-Supply Paper 1841, 113 Summerour, J. H.jH.; Shapiro, E. AjA.; Huddlestun, Pp. . P. F.jF.; and Hall, M. A,A,, 1996 An investigation of tritium in the Gordon and other aquifers in Sloan, E., 1908 Catalogue of the mineral Burke County, Georgia-Phase III1 (in(inpmpamtion).preparation). localities of South CarolinajCarolina; South Carolina Geological Survey Bull. 2, 505506 p. Toulmin, L. D., 1977 Stratigraphic distribution of Paleocene and Eocene fossils in the eastern Smith, E. A,A., 1907 The underground water Gulf Coast regionjregion; GSA Monograph 13, I, 602 p. resources of AlabamajAlabama; Alabama Geological Survey Monograph 6. Toulmin, L. D. and LaMoreaux, P. E., 1963 Stratigraphy along the Chattahoochee River, Smith, E. A.; Johnson, L. C.; and Langdon, D. connecting link between Atlantic and Gulf W., Jr., 1894 Report on the geology of the Coastal Plainsj Plains; AAPG Bulletin vol. 47, p. 385•385- Coastal Plain of Alabama; Alabama Geological 404. Survey Special Report 6. Van Nieuwenhuise, D. S., and Colquhoun, D. J., Snipes, D. S.; Fallaw, W. C.; and Price, V., 1992 1982a Contact relationships of the Black Mingo Structural geology of the Savannah River Site in and Pee Dee Formations - the Cretaceous•Cretaceous- the Coastal Plain of South Carolina, h-in- Zullo, V. Tertiary boundary in South Carolina, U.S.A:U.S.A.: A;A.; Harris, W. B.; and Price, V. (eds.), Savannah South Carolina Geology, vol. 26, no. 1, p. 1-14. River region: Transition between the Gulf and Atlantic Coastal Plains; Proceedings of the Van Nieuwenhuise, D. S., 1982b19822, The Paleocene•Paleocene- second Bald Head Island Conference on Coastal Lower Eocene Black Mingo Group of the east Plains GeologyjGeology; University of North Carolina at central Coastal Plain of South Carolina: South Wilmington and U. S. DOE, p. 33-36. Carolina Geology, vol. 26, no. 2, p. 47-67. Snipes, D. S.; Fallaw, W. C.; Price, V., Jr.; and Veatch, 0.,O., and Stephenson, L. W., 1911 Cumbest, R. J., 1993 The Pen Branch fault: Preliminary report on the geology of the Coastal documentation of Late Cretaceous-Tertiary Plain of GeorgiajGeorgia; GGS Bulletin 26, 466 p. faulting in the Coastal Plain South Carolina; Southeastern Geology, vol. 33, no. 4, p. 195-218.195218. Stainforth, S. M.; Lamb, J. L.; Luterbacher, H.; Beard, J. H.; and Jeffords, R. M., 19751976 Cenozoic planktonic foraminiferal zonation and characteristics ofindexfonns:of index forms: Univ. Kans.Kms. Paleo. Contributions, Article 62, 425 p. Steele, K B., 19851986 Lithostratigraphic correlation of Cretaceous and younger strata of the Atlantic Coastal Plain Province within Aiken, Allendale and Barnwell Counties, South CarolinajCarolina; unpublished Master's thesis, UniversityUnivedty of South Carolina, 174 p. Summerour, J. H.; Shapiro, E. A; Lineback, J. A;A.; Huddlestun, P. F.jF.; and Hughes, AA. C., 1994 An investigation of tritium in the Gordon and others aquifers in Burke County, GeorgiajGeorgia; GGS Information Circular 95, 93 p. 78 APPENDIX 1 DESCRIPTIONSDESCWP1'IONS OF CORE SITE LOCATIONS GGS·3537GGS-3537 (Burke 6, McBean core) Location: In northern Burke County, on the north shoulder of Collins Road, 1.4 airline miles (2.2 km) southeast of the Ga. Hwy. 56 bridge over McBean Creek, 1.1 miles (1.8 km) east of the intersection of Ga. Hwy. 56 and Collins Road, and 1.2 miles (1.9 km) southeast of the only remaining exposed McBean Limestone at the type locality. The core site is in the McBean USGS 1:24,000 quadrangle map. GGS·3758GGS-3758 (Burke 6, USGS MillereMillers Pond) Location: M. A. Miller property, approximately 0.5 miles south-southwest of the intersection of River Road and Millers Pond Road and approximately 0.5 miles (0.8 km) north-northeast of Millers Pond, a dammed segment of BowBoggy Gut Creek (a.k.a.(a.k.a McKinney Branch) in northeastern Burke County, Georgia. The core site is in the McBean USGS 1:24,000 quadrangle map. GGS·3764668-3164 (Burke 7, TR92·1)TR92-1) Location: On Georgia Power Company property, on the shoulder of an unimproved road approximately 1 mile (1.6 km) south of Gobbie Grove Church and 1.75 miles (2.8 km) west-northwest of the intersection of Hancock Landing Road and River Road in eastern Burke County. The core site is in the Shell Bluff Landing USGS 1:24,000 quadrangle map. GGS·3762GGS-3762 (Burke 8, TR92·2)TR92-2) Location: In an abandoned trailer park on Hancock Landing Road, approximately 0.15 mile (0.1 km) east of the intersection of Hancock Landing Road and River Road, behind the abandoned Shell station and abandoned Southern Fried Chicken restaurant in eastern Burke County. The core site is in the Shell Bluff Landing USGS 1:24,000 quadrangle map. GGS·3781GGS-3781 (Burke 9, TR92·3)TR92-3) Location: On Georgia Power Company property, off Ebenezer Church Road, on the upland surface approximately 0.4 mile (0.6 km) south of Beaverdam Creek, approximately 2.4 miles (3.8 km) north of the intersection of Ebenezer Church Road and Ga. Hwy. 23. It is also approximately 2 miles (3 km) south-southwest of Plant Vogtle in Burke C",unty.Cdunty. The core site is in the Alexander USGS 1:24,000 quadrangle map. GGS·3782668-3782 (Burke 10, TR92-4)TR92·4) Location: On Robert Mobley property, immediately southeast of Allen Chapel Road near the northwestern valley wall on an unnamed Savannah River tributary, approximately 1 mile (1.6 km) east of the intersection of Allen Chapel Road and River Road, and 2.8 miles (4.5 km) southeast of the intersection of River Road (Ga. Hwy. spur 56) and Ga. Hwy. 80 (Shell Bluff Landing Road) in eastern Burke County. The core site is in the Shell Bluff Landing USGS 1:24,000 quadrangle map. 79 GG8-3792GGS-3792 (Burke 11, TR92·5)TR92-5) Location: In DeLaigle Mobile Home Park (A & A Trailer Park), on River Road, approximately 0.5 mile (0.8 km) west of Georgia Power Company Plant VogtleVogUe near the large horizontal water tank. The core site is in the Shell Bluff Landing USGS 1:24,000 quadrangle map. GGS·3794GGS-3794 (Burke 12, TR92·6)TR92-6) Location: ThomsonThomeon Oak.Oak Flooring Company property, near the edge of the blu£€bluff overlooking thethe Savannah River flood plain, approximately 1.8 miles (2.9 km) northwest of Hancock Landing on thethe Savannah River in Burke County, Georgia. The core site is in the Shell Bluff Landing USGS 1:!24,0001:24,000 quadrangle map. USGS Girard core Location: Adjacent to a fire lookout tower on GriffinsGrif6ns Landing Road, 0.75 mile (0.45 km) north of thethe intersectionintersection of GriffinsGfinsLanding Road and Ga. Hwy. 23 and approximately 1.8 miles (2.9 km) northnort;p of Girard inin southeastern Burke County. The core site is in the Girard USGS 1:24,000 quadrangle map. Bechtel core VG-lVG-1 Location: On the northeast shoulder of River Road, approximately 1.1 miles (1.76 km) northwest of thethe crossing of Sweetwater Creek. The core site is in the Girard USGS 1:24,000 quadrangle map. Bechtel core VG·2VG-2 Location: On the shoulder of River Road near the southeast cornercomer of the intersection of River Road and Brighams Landing Road. The core site is in the Girard USGS 1:24,000 quadrangle map inin southeasternsoutheastern Burke County, Georgia. Bechtel core VG·3VG-3 Location: On the northeastern shoulder of River Road, on the northern valley wall of Old Mill Branch valley, immediately northwest of the River Road crossing of this dry creek bed. The core site isis inin thethe Girard USGS 1:24,000l:24OOO quadrangle map, in southeastern Burke County, Georgia. Bechtel core VG·4VG-4 Location: On the northeastern shoulder of River Road, on the southeast valley wall of Little Beaverdam Creek. The core site is in the Girard USGS 1:24,0001:!24,000 quadrangle map, in southeastern Burke County, Georgia. Bechtel core VG-5VGS Location: Near the foot of the easterneastam valley side of Sw&waterSweetwater Creek and Still Branch, on thethe shoulder of River Road approximatelyappnximately 0.15 mile (0.26(026 km) east oftheofthe bridge over Sweetwater CreekCreek. The core site of the VG-5 is at the boundary of the USGS 1:24,000 quadrangle map8maps GiiGirard, Ga-S.CGa.-8.C and Millett, S.C.-Ga in southern Burke County, Georgia. 80 Bechtel core VG6VG-6 Location: On the shoulder of River Road at the intersection with an unimproved county road, approximately 1.4 miles (2.2 km)kIn) southeast of the River Road bridge over Sweetwater Creek.,Creek, and 3 miles (5(6 km)kIn) from the Burke/Screven Counties line in southern Burke County, Georgia. The core site is located in the Millett, S.C.-Ga., USGS 1:24,000 quadrangle map. Bechtel core VG-7 Location: On the shoulder of River Road near the northeast comercorner of the intersection of River Road and GriffinsG-ns Landing Road. The core site is in the Girard USGS 1:24,000 quadrangle map in southeastern Burke County, Georgia. Bechtel core VG-8VG·8 Location: On the northeast shoulder of River Road bridge, on the northwest site of the pond formed by the damming of Little Sweetwater Creek. Approximately .65 miles (l0.4(10.4 km) northwest of the intersection of River Road and Stony Bluff Road. The core site is located in the Millett, S.C.-Ga., USGS 1:24,000 quadrangle map. Georgia Power core B-246B·246 Location: On Georgia Power Company Plant Vogtle property, on an upland spur or lead, overlooking the southern end of Utleys Pond, slightly less than 0.1 mile (1.4 km) west of the end of Utleys Pond (also referred to as Mallards Pond). The core site is locatedldcated in the Shell Bluff Landing, USGS 1:24,000 quadrangle map. The core was inadvertently destroyed in the late 1970's while in storage at Georgia Power Plant Vogtle, but a log of the core is available at the Georgia Geologic Survey in Atlanta. CORE SITES OUTSIDE BURKE COUNTY Bechtel core VSC-3VSC·3 Location: On shoulder of dirt road, 0.5 mile (0.3 kIn)km) north-northeast of St. Marys Church; St. Marys Church is on the north side of S.C. Hwy. 125, 0.4 mile (0.25 km)kIn) west of the Barnwell-Allendale County in Barnwell County, South Carolina. The core site of the Bechtel VSC-3 is located in the Girard NE USGS 1:24,000 quadrangle map. Bechtel core VSC-4VSC·4 Location; On the northern valley wall of the Savannah River, less than 0.1 mile (0.16 km) north of S.C. Hwy. 125, less than 0.1 mile (0.16 kIn)km) west of Barnwell-AllendaleBarnwell-AUendale County line, 2.2 miles (3.5 km) northeast of Savannah River in AUendaleAllendale County, South Carolina. The core site of the Bechtel VSC-4 is located in the Millett S.C.-Ga., USGS 1:24,000 quadrangle map. 81 GGS·3187668-3187 (Dougherty 2, USGS Albany core) Location: Dougherty County, approximately 0.2 mile (0.3 km)kIn) east-northeast of the intersection of U.S. Hwy. 19 and a county road, approximately 0.8 mile (0.13 km)kIn) south of the intersection of U.S. Hwy. 19 and Holley Highway (Ga. Hwy. 257). The core site is on the Albany East USGS 1:24,000 quadrangle map. GGS-3366668-3366 (Sumter 9A) Location: Sumter County, approximately 0.75 mile (0.12 km)kIn) north of Ga. Hwy. 27 and approximately 0.5 mile (0.8 km)kIn) west of the Flint River, near the site of the old Danville Ferry. This site is located in the Drayton USGS 1:24,000 quadrangle map. GGS·3111 (Pulaski 3) Location: On the south shoulder of a paved county road, approximately 200 feet northeast of the Pulaski :lirefire tower, 0.35 mile (0.2 km)kIn) west of the intersection of the paved county road and U.S. Hwy. 129, 1.9 miles (1.1 km)kIn) south of the intersection of Broad Street GGS·3511668-3511 (Pulaski 5, PulaskiPulaeki County core, Arrowhead core) Location: On the top of a hill, approximately 1.7 miles (2.7 km)kIn) west of Ga. Hwy. 26 and 0.5 mile (0.8 km)kIn) southwest of the Bleckley-Pulaski Counties line in northern Pulaski County. The core site is in the southwestern corner of the West Lake USGS 1:24,000 quadrangle map. GGS-3545668-3545 (Colquitt 11, Doe Run core) Location: on Harrell farm property, on a valley side between an unimproved county road and a farm pond, 0.25 mile (0.15 km)kIn) east of junction of the county road and Ga. Hwy. 133, approximately 2.0 miles (1.2 km)kIn) southeast of the intersection of Ga. Hwy. 133 and Ga. Hwy. 270 in Doe Run, Colquitt County, Georgia (also see McFadden and others, 1986, p. 323). The core site is in the Doe Run USGS 1:24,000 quadrangle map. GGS·3523668-3523 (Laurens(Laurene 1, LaurensLaurene County core) Location: In an east-bound Interstate 16 rest area, 2.8 miles (4.5 km)kIn) east of the intersection of Interstate Hwy. 16 and Ga. Hwy. 338. The core site is in the southern part of the Dudley USGS 1:24,000 quadrangle map. 82 APPENDIX 2 HISTORICAL REVIEWREWEW OF BLACK MINGO AND ELLENTON FORMATIONS The undifferentiated Black Mingo Lower Black Mingo", "Black Mingo Shale", Formation of this report previously, in Burke "Upper and Lower Black Mingo formations", County, had been referred to the Ellenton "Upper Black Mingo", "Upper Black Mingo phase Formation of Siple (1967) (Bechtel, 1982; Harris or RhemaRhems Shale",Shalew,"Rhems Shale", "Upper Black and Zullo, 1990). Prowell and others (1985b)(198Sb) Mingo (Rhems and Williamsburg"). described a core section of the Ellenton "WilliamsburgPseudo-Buhrstone",WilliamsburgPseudo-Buhrstonen,'Williamsburg 'Williamsburg Formation from SRS (not at the site of the type Pseudo-Buhrw,Pseudo-Buhr", "Lang Syne beds", "Lang Syne?" locality) and determined that the Ellenton in its (Sloan,(Sl~an,1908, p. 449-452). type area consisted of a lower, Lower Paleocene The Upper Black Mingo formations are part (Midwayan) and an upper, Upper Paleocene observed in Williamsburg County near Rhems, part (lower Sabinian). Similarly, early ... (p. 461)451) ...shales and pseudo-buhratonepseudo-buhrstone with paleontologic observations (Sloan, 1908; Cooke,Cwke, Eocene fossils, ...interpreted as the probable 1936) of the Black Mingo Formation and recent equivalent of the Upper Black Mingo (p. 451-451• palynological studies of the Black Mingo 462)452) ....The Lower Black Mingo formations afford Formation and the Ellenton Formation of Siple the first expression of the great land subsidence (1967) (VanWan Nieuwenhuise and Colquhoun, which caused the shore line to retreat inland at 1982; Muthig and others, 1990) indicate that the beginning of the Eocene period. The type the Black Mingo and Ellenton are Early exposure is at Perkins Bluff on the Black River Paleocene to Late Paleocene in age (i.e., two near its confluence with the Black Mingo River. discrete biostratigraphic and chronostratigraphicchronoatratigraphic (p. 452)462) The Upper Black Mingo was units). This resulted in questioning or inaugurated by a renewal of sedimentation abandoning the name Ellenton and replacing the which afforded additional gray laminated shales name Ellenton with names of subdivisions of the inclosing a small variety of the Venericardia Black Mingo Formation (or Group). planicosta in the form of molds and casts;casts, best The Black Mingo has not been formally exhibited at Rhems Landing on the Black Mingo recognized in Georgia. The type area of the River (p. 452).462). At Lang Syne and Warley Hill formation is in the central Coastal Plain of the Congaree shales rest on fine grained, black, South Carolina where the name has been used slightly glauconitic, sand and partly indurated since 1908. It is to be noted that in the type gray sands, both of which contain tender casts of area of the Black Mingo Formation, the Black small shells. We shall refer to them as the Lang Mingo is an off-shore, fossiliferous, continental Syne beds. Stratigraphically they belong below shelf deposit deposit. In SRS and northern Burke the Congaree shales, and are tentatively treated County. the correlative deposits are inner as a part of the Black Mingo, pending further continental shelf with some coastal marine investigations. It is recognized that there is a lithofacies. As a results, there are some faunal advance from the Lower to the Upper differences in the gross lithologies of the Black Mingo formations, but in so much as the correlative deposits. later are so intimately associakdassocia~d over a large The historical development of the Black area, without stratigraphic break, it has been Mingo concept has been restricted to South decided that the distinction of Upper and Lower Carolina but, because the name has been will prove satisfactorysatkhctory for the general informally used in Georgia, and the Black Mingo discrimination of these beds. The Upper Black is crucial to understanding the Ellenton, the Mingo comprises: (a) The WilliamsburgWiamsburg Pseudo-Pseudo• historical usage of the name is of concern in Buhr consisting of yellow-red sands which Georgia as well. Sloan (1907, 1908) named the inclose a hard silicified ledge about two feet Black Mingo stratigraphic unit but his use of the thick, in which casts of Ostrea msisarrasis and the name was vague. He referred to it as: "Black Venericardia planicosta occur ... (p. 452) (b)01) Mingo Phasew,Phase", "Lower Black Mingo series",seriesw," RhemaRhems Shale. Light gray to black shale 83 interlaminated with thin seams of fine grained 385 feetf&t in well 52-C62-C in SRS. A reformatted sand and mica.mica...... (p. 453). It is clear that type description of the Ellenton Formation as Sloan (1908) recognized lower and upper given by Siple (1967, p. 29) is as follows: subdivisions of the Black.Black Mingo, but the Cretaa!olUlCmincwud ('i)(9 2&&m-EUentonSystem-Ellenton Fomation-Formotion- (310•(310- distinctions appear to be related more to 335 feet)-%feet)-25 foot thick clay, bluish-gray,bluish-gmy, paleontology (age) and stratigraphic position micaceous,micaceoua, lignitic sandy; muscovite common to than to lithology. However, Sloan (1908) abundant; altered pyrite or marcasitemamite fairlyfairly considered the type "exposure" of the lower common. Subangular to submundedsubrounded fine Black.Black Mingo to be at Perkins Bluff and the medium quartz grains. Trace of chlorite. Upper Black Mingo being best exhibited at Interval from 32533532~335 feet predominantly clay. Rhems Landing.Landin~. Both the sections exposed at (335345(33~345 feet)-10 foot thick sand, coarse, clayey, Rhems Landing and Perkins Bluff are now micaceousmicaceoua lignitic;lignitig subangular milky quartz; considered to be lower Black Mingo (Van dark gray clay; minor percentage shows Nieuwenhuise and Colquhoun, 1982b).198213). conchoidal fractures. Heavy minerals in raremre to Cooke (1936, p. 41) was the first to trace amounts-may be contamination. (345-365(345365 describe the formation in a more modern feet)-20feetJ-20 foot thick sand, same as above except for context. He paraphrased Sloan's use of the appearance of colorless acicular crystals of name Black Mingo as follows: "The name "Black gypsum (selenite) in the dark gray clay. Other Mingo shales", taken from Black Mingo Creek, a gypsifemusgypsiferous fonnsforms noted include satin spar. tributary of the Black River in Williamsburg and Some of the lignite replaced by pyrite or Georgetown Counties, S. C., was applied by marcasite;mamite; 55 percent of sand coarse to very Sloan in 1907 to laminated sandy shale exposed coarse. Laboratory determination ofofpermabilitypermeability along the Black River fromfrom Brewington Luke,Lake, in indicates 66 gpd (Meinzer's units). (365-370 Clarendon County, to the mouth of Black Mingo feet)-5 footfoot thick sand, white to gray, clayey and Creek, and up Black Mingo Creek to a point silty, micaceous and lignitic. Subangular finefine to between Rhems and the General Marion Bridge. coarse quartz. Driller logged interval as clay. In 1908, he extended the name to a more TuscaloosaTwrccrloosa Formation-(370-385Formotion-(370-385 ft.)-15 footfoot thick comprehensive unit, his Black Mingo ''phase'','Iphase", Sand, tan totoyellow,yellow, clayey, micaceous, kaolinitic; which included all the strata of lower Eocene age contains scattered red ferruginousferruginous sand nodules. east of the Santee River." Siple (1967, p. 28-29) described the Ellenton as Cooke (1936, p. 41) applied the name follows: The Ellenton Formation consists of a Black Mingo Formation to all Tertiary strata dark-gray to black sandy lignitic micaceous clay older than the "McBean" Formation, including interbedded with medium to coarse quartz sand. the Congaree Formation, and correlated it (Black Some of the quartz grains contain inclusions of Mingo) mainly with the Tuscahoma Formation pyrite, others are rutilated. Much of the free of the eastern Gulf Coastal Plain. However, pyrite appears to be decomposed. Authigenic Cooke and MacNeil (1952, p. 21-21) later gypsum crystals are commonly distributed correlated the Black Mingo with the lower throughout the fornation.formation. Wilcox, Nanafalia Formation of the eastern Gulf Generally,Genemlly, the upper part of the Coast. Their (Cooke, 1936; Cooke and MacNeil, formation contains a gray silty to sandy 1952) correlation was based on macrofossils from micaceousmiccrceous lignitic clay with which the gypsum is the more marine, type area of the Black Mingo commonly associated. In some wells the clay Formation. zone may be overlain by coarse quartz sand. The Siple (1967, p. 28-31) introduced the lower part of the Ellenton consists genemllygenerally of name Ellenton Formation for what he clayey quartz sand of medium to coarse texture, considered to be an Upper Cretaceous unit that which in some areas becomes very coarse and overlay the "Tuscaloosa""Tuscaloosatt Formation in the gravelly. The quartz grains are bluish gray. subsurface of the Savannah River Plant in Lignite and decomposed pyrite or marcasite western South Carolina. The type section of the @zgments,fragments, muscovite, and aggregates of Ellenton Formation is the interval 310 feet to kaolinite or other very sopsoft minerals are fairlyfairly 84 common. The Ellenton FormutionFonnation pmbablyprobably i8is Further, Van Nieuwenhuise and unconformable with the underlying Tuscaloosa Colquhoun (1982b) divided their Rhems FormutionFonnation and the overlying Tertiary sediments. Formation into a lower BmsBrowns Ferry Member The lower contact is characterizedchrrmcterized by a change in and an upper Perkins Bluff Member. The color of the clay and a change in the composition Browns Ferry (lower) and Perkins Bluff (upper) of the sand. The dark-graydark-gmy to black clay of the Members (Fig. v) of the Rhems were considered Ellenton i8is readily di8tinguishabledistinguishable fivmfrom the to grade laterally and vertically into each other. variegated clay of the Tuscaloosa.Tuscaloosa likewi8e,likewise, the Van Nieuwenhuise and Colquhoun (1982b) also quartzose sand of the Ellenton can genemllygenerally be divided the Williamsburg Formation into a lower diffeerentiateddifferentiated fivmfrom the arkosic sand of the Bridge Member and an upper Chicora Member. Tuscaloosa.Tuscaloosa The upper contact is also The Lower Bridge Member was also described as characterized by a change in the color of the clay grading vertically and laterally, in part, into the above and below the contact...... The type-locality overlying Chicora Member. well forfor the Ellenton FormutionFonnation is well 52-C According to Van Nieuwenhuise and which is 4 miles northeast of the town of Colquhoun (1982b, p. 54,): "The'The Rhems Shale of Ellenton and 7 3/4 miles southeast of Jackson, Sloan (1908) is a distinctive shale containing Aiken County, S. C....C. ... The Ellenton FormationFonnation almost no sand-sized particles and very few was penetrated in the type well at a depth of 31031 0 calcareous micmfossils.microfossils. ... The type Rhems of to 370 feet.feet...... (Siple, 1967). Sloan (1908)(1908) at RhRhems Landing is considered to The type section consisted of well-well• be the finer-grained end member of the total cuttings from 52-C but the cuttings are now lost. range of the fine-grainedfine-grained clastics comprising the In general in SRS and eastern Burke County, Browns Ferry Member." and "The lithology of the the basic criteria for identification of the type Black Mingo Shale of Sloan (1908) is Ellenton Formation were the consistent presence characteristic of a greater portion of the Browns of carbonaceous and lignitic material in the Ferry Member and also the overall Rhems formation, the prevalence of well-sorted, fine•fine- FormutionFonnation than any of the other composite grained sand, and the unit's prevailingly neutral lithologies. " tones of white to gray to black. Subsequent Van Nieuwenhuise and Colquhoun authors adopted the name Ellenton (Bechtel, (1982b) did not fully discuss the lithologies of 1982; Prowell and others, 19800;1985a; Prowell and the Black Mingo formations and their members. others, 1985b;198%; Harris and Zullo, 1990). Others They described the Browns Ferry Member, have not (Fallaw and Price, 1992, 1995). which evidently is the principal concept of their Van Nieuwenhuise and Colquhoun Rhems Formation, as an "arenaceous mud" , (1982b, p. 52) reintroduced the Rhems and clayey sand or, generally, as a silty clay. They Williamsburg of Sloan (1908) in the type area of (p. 54) described the Perkins Bluff Member of the Black Mingo: "The Black Mingo Shale, the Rhems Formation as an: ""...imbricated,...imbricated, Rhems, WilliamsburgWilliamsbuqg and Lang Syne subphases pelecypod-rich. argillaceous sand ...resistant, of formationsfonnations of Sloan (1908) comprise what is partially silicified Perkins Bluff Member formsforms a herein defined as the Black Mingo Group.Gmup. prominent ridge that extends along the Black Elevation of the Black Mingo to group status is River and overhangs the BrowncBrowne Ferry Member actually only recognitionerecognition of the range implied by sevemlseveral feetfeet near river level." and "The Perkins Sloan (1908) who considered the "Black Mingo Bluff Member lithology is considered somewhat Phase" as an aggregationaggrvgation of several formationsfonnations variable but throughout maintains a coarser•coarser- or "subphases"."subphasesf! However, redefinition of the grained texture than the Browns Ferry Member. composite formationsfonnations of the Black Mingo Group Parts of the Perkins Bluff member are almost is necessary in order to eliminate a great deal of "coquina,""coquinq" such as at its type locality, but grade confusion in the literatureliteraiure and to incorporate the to an argillaceous sand with numerous much more detailed stmtigraphicstratigraphic data now pelecypods either as fragments,fragments, internal molds, available.available."" or whole shells."shells. " (Van Nieuwenhuise and Colquhoun, 1982b).19823). 85 Van Nieuwenhuise and Colquhoun sedimentary Sequence8sequences with different lithologies (1982b,(198213, p. 57) described. described the Williamsburg deposited during separated cycles of deposition."deposition. " Formation, or upper Black Mingo, as: They recognizedrecognized. two formations in the ""...... arenaceous shales, "fullers"f&llers earth," and Ellenton stratigraphic position in the subsurface fossilifemus,fossiliferous, argillaceous sands of the UJwerLower of the Savannah River area south of Aiken, Bridge Member and the fossiliferous,fossiliferous, South Carolina and Augusta, Georgia: the argillaceous sands and molluscan-rich bioclastic Sawdust Landing Formation and the Lang Syne limestones of the Chicora Member. The UJwerLower Formation. The Sawdust Landing Formation Bridge and Chicora members tend to be was described by Fallaw and Price (1992, 1995) gradational fromfrom the very fine-grainedfine-grained clastics of from the northwestern part of SRS as ""...... gray,gmy, the UJwerLower Bridge:Bridge to the coarse-grained clastics poorly and moderately sorted, micaceous, silty and limestones of the Chicora." and the Lower and clayey quartz sands and pebbly sands with Bridge Member as: "'!..siliceous...siliceous mudstone and interbedded dark gray clays. In some wells in arenaceous shale ...... "" and "'!..fine-grained...fine-grained clastic the northwestern part of SRS, it consists of unit is predominantly clay-size with some silt yellow, orange, tan, moderately to poorly sorted, and occasional clean sand lenses... lenses ... Internal micaceous, quartz sands. It is locally molds of pelecypods oriented parallel to bedding feldspathic, and ironimn sulfides and lignite are planes can be found." Van Nieuwenhuise and common in the darker parts of the section. The Colquhoun, 1982b. clays are fissile in places and contain micaceous Finally, Van Nieuwenhuise and silt and fine sand laminae. There appear to be Colquhoun (1982b) described the Chicora two fining-upward,fining-upward, sand-to-clay sequences in the Member of the Williamsburg Formation as ""...... a downdip part of the Site." glauconitic, argillaceous, fossilifemusfossiliferous sand and The Sawdust Landing Formation, as it indurated molluscan-rich limestone... Within the has been lithologically described, does not occur indurated limestone beds large internal and in Georgia. However, some Sawdust Landing-Landing• external molds of Turritella are present along type sediments are present in the Black Mingo with large valves and fragments of Ostrea Formation in Burke County, indicating physical sinuosa Rogers and Rogers, ...... "" correlation with the Sawdust Landing of Price In South Carolina, the Ellenton and Fallaw (1992,(1992,1995).1995). Most Sawdust Landing Formation has been recently subdivided into two lithology is seen in northern Burke County in chronostratigraphic subdivisions, a lower the basal beds of the Black Mingo. In the Midwayan (Danian) Ellenton and an upper Millers Pond core (GGS- 3758) and in the GGS•GGS- Sabinian (Thanetian) Ellenton (Prowell and 3764, the lower part of the Black Mingo others, 19800).1985a). This subdivision has resulted in Formation consists of coarse, micaceous, poorly the establishment of a variety of new formations: sorted, coarse-grained, pebbly sand of Sawdust Rhems Formation (McClelland (1987), Sawdust Landing lithology as described by Fallaw and Landing Formation and Lang Syne Formation Price (1992, 1995). This updip lithofacies of the (Fallaw and Price, 1992, 1995); or combinations Lower Paleocene appears to be the downdip of the Ellenton Formation with other formations extremity of coastal marine/fluvial sediments in the Ellenton interval defined by Siple (1967): that are widespread in the subsurface of western Ellenton Formation and Rhems Formation South Carolina. (Colquhoun and others; 1983), P1PI and P2 Fallaw and Price (1992, 1995) described (Prowell and others, 1985a, 1985b), Ellenton the lithology of their Lang Syne Formation in Formation and Black Mingo Formation (?), SRS as follows: "At SRS the Lang Syne typically Ellenton Member of the Rhems Formation consists of dark gray and black, lignitic clays (Steele, 1985), Ellenton and WiamsburgWilliamsburg and poorly and moderately sorted, micaceous, Formations (Aadland and others, 1992). lignitic, muddy quartz sands and pebbly sands. Fallaw and Price (1992,(1992,1995)1995) abandoned ImnIron sulfides are common in the darkerdarkerpartsparts of the name Ellenton ''because"because the sediments named the section. Both sands and clays are by Siple 1967) consist of two different glauconitic in places, especially in the 86 southeastern part of the Site. The basal unit is and not Thanetian (Edwards, personal a greensand in some wells. The clays tend to be communication, 1995). fissile and contain micaceous silt and fine sand Finally, there appears to be a change in laminae. Cristobalite is common in some cores. tectonism in the vicinity of the Savannah River. Deposits composed of yellow, orange,omnge, tan, The Williamsburg claystone is relative thick in modemtelymoderately to poorly sorted, micaceous quartz the SRS Ellenton reference core P-18 and in the sands are common in the northwestern part of cores VSC-3 and VSC-4, but is not present a few SRS, with darker, poorly sorted, micaceous miles west in Georgia even though the facies becoming dominant to the southeast. In stratigraphic units overlying and underlying the some wells, clean, moderately to well-sorted claystone are present and unchanged on either sands occur near the top of the unit." side of the river. The Lang Syne Formation of the Fallaw and Price (1992, 1995) in SRS is lithologically Discussion more similar to the Black Mingo Formation section in eastern Burke County, than it is to The Ellenton Formation of Siple (1967) other subdivisions of the formation. However, consists of two distinct lithostratigraphic units in according to their description of the unit, their the Ellenton reference core P-18 from SRS in Lang Syne has more clay than the Black Mingo Aiken County, South Carolina; a lower of Burke County, and the sand in the SRS is carbonaceous and lignitic sand unit with coarser and more poorly sorted. The principal virtually the same lithology as the correlative distinguishing lithic character of the Lang Syne formation in Burke County, and an upper sandy of Sloan (1908) is glauconite, and the Lang Syne opaline claystone (or mudstone) unit of Fallaw and Price (1992, 1995) and the upper (Williamsburg) (a few inches of the claystone are part of the Burke County Black MhgoMingo does present in the middle part of the Black Mingo in contains scattered glauconite. But there is no the core VG-5 in Burke County). The lower consistent Lang Syne lithology in the upper part sand unit and the claystone unit are also present of the Black Mingo in Burke County. Therefore in the cores VSC-3 and VSC-4 from southern it is questionable whether the upper part of the Barnwell and northern Allendale Counties, undifferentiated Black Mingo Formation in . South Carolina, respectively. Siple (1967) did Burke county is the same as the Lang Syne beds not identify claystone chips in his type of Sloan (1908) from the type area of the Lang description of the Ellenton. Syne plantation 1.5 miles east of Fort MotteMoth in The lower carbonaceous sand unit is Orangeburg County, South Carolina (see Cooke, distinct from all named subdivisions of the Black 1936, for fuller discussion). Furthermore, the Mingo in that the unit is predominantly a age of the Lang Syne of Fallaw and Price (1992, carbonaceous, lignitic, well-sorted, fine-grained 1995) is considered to be Late Paleocene sand with some medium- to coarse-grained sand. (Thanetian or Selandian) (late Midwayan or Of the named subdivisions of the Black Mingo, early Sabinian): "The term ''Lang"Lung Syne" for the the Lang Syne Formation as described by Fallaw SRS deposits is used here rathermther than "Rhems';"Rhems'~ and Price (1993, 1995) is most similar to the because of greater lithologic similarity with the lower carbonaceous sand unit izii~ core P-18 and type Lange Syne. Our palynological data in Burke County. However, the Lang Syne as indicate that the LungLang Syne (upper "Elknton'7"Ellenton'~ described by Fallaw and Price (1992, 1995) strata at SRS and vicinity are Thanetian or should be present only in the stratigraphic Selandian rather&her than Dani~n;Danian; the Rhems has position of the Williamsburg? claystone rather been dated as Danian (VanNan Nieuwenhuise and than underlying the claystone as is the case in Colquhoun, 1982bJ."1982b)." the western SRS. We have seen no lithofacies Palynological dating of the upper part of intermediate to the Williamsburg? claystone and the Black MingoMhgo in Burke County indicates that Lang Syne in western South Carolina or in it is mostly Selandian, late Midwayan in age, Georgia. Therefore, the stratigraphic position assigned to the Lang Syne by Fallaw and Price 87 (1992,(1992, 1995)1995) is problematic. On the other hand, formation in question in Burke County is clearly thethe upper part of the undifferentiated Black not Sawdust Landing Formation as applied by Mingo Formation in Burke County is slightlyalightly Fallaw and Price (1992, 1995). It also is not more glauconitic than the lower part of the clearly Rhems lithology of the central South formation,formation, adding credence to the stratigraphic Carolina Coastal Plain. On the other hand, position of the Lange Syne assigned by Fallaw except for its being persistently carbonaceous, and Price (1992, 1995). Yet, the lower and the Burke County unit is broadly compatible upper parts of the Black Mingo Formation in with Black Mingo lithology. But, the unit is not Burke County are too similar to subdivide and, consistently divisible into lower and upper inin most cores, there is no distinctive bed change lithostratigraphic subdivisions as in the typetype thatthat could be cited as a upperupper/lower/lower Black area of the Black Mingo. According toto Edwards Mingo boundary. (personal communication, 1995), on thethe other According to the modern codes of hand, maintains that the Burke County Black stratigraphic nomenclature (American Mingo is generally biostratigraphically divisible Commission on Stratigraphic Nomenclature, into lower (Danian) and upper (Selandian) parts. 1961,1961, 1970;1970; North American Commission on SupportingtheSupportingthe biostratigraphy, there are Stratigraphic Nomenclature, 1983), and guides some scattered instances in Burke County where toto stratigraphic nomenclature (International the Black Mingo does have lower and upper Subcommission on Stratigraphic Classification, lithostmtigraphiclithostratigraphic subdivisions. Out of 15 cores 1976),19761, ifif a lithostratigraphic unit is subdivided logged in eastern Georgia, we have found 4 intointo two or more lithostratigraphic units, the inches of Williamsburg-type claystone thatthat isis original name of the unit cannot be restricted to present in the middle part of the Black Mingo at a subdivision of the unit. If the old name is to a depth of approximately 410 feet in Bechtel be retained, then the original lithostratigraphic core VG-5. Of the 15 cores, 11 clearly consist of unit must subdivided into members or the unit one lithostratigraphic unit. In all of thesethese be raised in rank to group. Because the sections sampled for dinoflagellate siliceoussiliceous claystone in the upper part of the biostratigraphy, most were early toto middle Ellenton Forma.tionFormation of Siple (1967) has always Midwayan in age with a few samples (from thethe been a critical lithic component of the Black USGS Girard core) near the top of the formation Mingo, we believe that the name of the siliceous being of late Midwayan age (Edwards, personal claystone, the Williamsburg Formation, be communication, 1995). Therefore we conclude retained in western SM.SRS. As a result, the name that most of the biostratigraphic evidence Ellenton cannot be retained unless the Ellenton indicates that the Black Mingo Formation inin isis raised to group rank, in which case the lower eastern Burke County is of early and latelate carbonaceous sand must be given a new Midwayan age (and is correlatable with thethe formationformation name. Or, the name Ellenton be Rhems in the type area of the Black Mingo). retained at formation rank, the lower In two cores in Burke County thethe Black carbonaceous sand be given a new name at Mingo does consist of a lower and upper part. member rank, and the Williamsburg dropped in In the core GGS-3757, taken near McBean Creek rankrank inin thethe Savannah River area to a member of in northern Burke County, the lower part of thethe thethe Ellenton Formation. The later solution is Black Mingo consists of a dark gray toto black viable according to Article 25 of the North laminated clay abruptly overlain by an upper American Stratigraphic Code (1983). glauconitic sand. In the USGS Girard core,core. thethe The course we choose to take in this Black Mingo also is divisible into lower and report is neither of the above because we upper parts and the lithostratigraphic divisions currently lack critical data from the SM.SRS. We are compatible with the Rhems and suggest thatthat the name Ellenton be considered a Williamsburg Formations as described inin eastern junior synonym of Black Mingo and the South Carolina by Van Nieuwenhuise and formationformation in question in Burke County be called Colquhoun (198223).(1982b). The lower part of thethe Black undifferentiated Black Mingo Formation. The Mingo consists mainly of finely sandy clay 88 whereas thethe upper part consists of glauconitic, middle Midwayan) was a mufacesurface of calmuacalcareous aandatone;sandstone; ghuconitic,glauconitic, calcare0~8calcareous nondeposition (sediment by-pass), or thatthat thethe sand; and, at thethe toptop of thethe section, a bed of dQ'silty toptop of thethe lawerlower Black Mingo was eroded. The laminated clay. The lowerlower part of thethe BlaclrBlack variable thicknessthickness of thethe formations suggests thethe Mingo was correlated with thethe Clayton later scenario. Formation of the eastern Gulf CoaatalCoastal Plain and the upper part is in calmuacalcareous nannofd nannofossil zone NP 65 (Ectwards,(Edwards, personal co~l~munication,communication, 1996).1995). The upper Midwayan Naheola Formation of the eastern Gulf Coastal Plain occurs in Zone NP 65 (Siesser, 1983). Therefore the glauconitic sand in the upper part of the Black Mingo in the Girard core would be in the upper Midwayan and the lawerlower part of the Upper Paleocene (lower Thanetian),Thane'tian), consistent with a Late Paleocene age as determined by manyD18D.y paleontologietspaleontologists for the upper Black Mingo. To summarize, our conclusion concerning the stratigraphic position and lithostratigraphy on the "Ellenton" in eastern Burke County is that the name Ellenton is a junior synonymsynonym. of the name Black Mingo in that lithologies and stratigraphic position of the stratigraphic unit in the Savannah River area are all compatible with the Black Mingo Group of South Carolina. In addition, the Paleocene (Midwayan and lowerlawer Sabinian) in the Savannah River area in Georgia cannot be assigned to the Clayton Formation, MatthewsMatthew8 Landing Member of the Clayton, Naheola Formation or Nan&Nanafalia Formation of western Georgia on the baaisbasis of lithology. We do not recognize the Black Mingo&go as a group in Burke County because moatmost of the cored sections consist of only one identifiable lithostratigraphic unit. There is evidence of an upper glauconitic stratigraphic interval in the Black Mingo in Burke County, but itsita occurrence appears to be local and shows no systematic pattern of occurrence. Neither the Rhems Formation nor the WilliamsburgWilliamaburg Formation are present in eastern Burke County, nor are any of the members of the RhemsRheme and Williamsburg Formations present inin Georgia.Georgia The absence of mappable, Thanetian, upper Black.Black Mingo inin eastern Georgia and itsib consistentoccurrence in South Carolina suggestssuglgeets that during the Late Paleocene, either the Georgia coastal area was tectonically~nicallystable and the top of the lower Black Mingo (early to 89 APPENDIX 3 HISTORICAL REVIEW OF CONGAREE FORMATION Sloan (1907, 1908) named the Congaree Formation but did not designate a type locality forfor thethe formation. However, Cooke (1936, p. 59) and Cooke and MacNeil (1952, p. 22) suggested a lectostratotypelectostratotype for the Congaree Formation. The following discussion of Cooke (1936) and Cooke and MacNeil (1952) concerns the type localitylocality problpmproblem for the Congaree Formation in South Carolina: "The type locality of the Congaree shale appears to be on Elmore WilliamsWilliams place at the head of First Creek.Creek, 0.8 miles west of Gaston. Sloan reports an 8-foot&foot ledgeledge offuller'sof fuller's earth containing numerous large casts of Venericardia "planicosta"'blanicosta" and shark teeth.teeth, overlain by fossiliferous quartzite, exposed on thethe south side of a large naturalnatuml amphitheater. The fuller's earth is provisionally assigned to the McBean Formation." (Cooke, 1936, p. 59-60)69-60) and "Sloan specified no single localitylocality as the type of his Congaree "shale", "sands","sands",or "buhrstone"."buhrstone'! The name is evidently takentaken from thethe Congaree River, and it has been suggested (Cooke, 1936, p. 59) that Sloan's localitylocality 505 on the Elmore Williams place at the head of First Creek, a tributary of the Congaree River, be regarded as typical. This locality is difficultdimcult toto find witlwutwithout a guide. However, ledgesledges of similar rock are exposed on the road south of Bull Swamp Creek 2~2+ miles west•west- northwest of Swansea and·and also at a waterfall north of the east-west county road about 2~2+ miles west by north of Swansea."Swansea" (Cooke and MacNeil,Mdeil, 1952, p. 22). Considering that Cooke (1936) and Cooke and MacNeil (1952) were correct in assigning thethe exposure in the amphitheater at thethe head of First Creek at Elmore Williams place, thenthen that would be the principal reference localitylocality for the formation but not by original designation. The principal reference section (lectostratotype)Oedostratotype) is the section of Congaree Formation exposed in the amphitheater. The principal reference locality according to CookeCmke (1936)(1936) isis in Lexington County, 0.8 mile west of Gaston in the updip central Coastal Plain of South Carolina. 90 APPENDIX 4 HISTORICAL REVIEWREMEW OF THE MCBEAN FORMATION Sloan,Sl-, 1908, p. 269-278,269-273, 459, 460) firstM (1970) continued the usage of the name McBean referredreferred to thethe limestonelimestone exposed along McBean rather than Lisbon for upper Claibornian marine Creek and at Shell Bluff as Santee Limestone. deposits in central Georgia. Herrick (1961) andaIid Veatch and Stephenson (1911) subsequently Herrick and Vorhis (1963), however, extended abandoned the name Santee, without the name Lisbon Formation to the Savannah explanation, for the limestone exposuresexpmurea at Shell River, and Huddlestun, Marsalis, and Pickering Bluff and McBean Creek in Burke County, (1974) questioned the lithostratigraphic validity Georgia. They referred these exposures to their of the McBean Formation in central and eastern newly proposed McBean Formation. Georgia.Georgia Huddlestun (1982) discussed thethe Veatch and Stephenson (1911, p. 237•237- history of the marine Claibornian and 284) named the McBean Formation for Jacksonian terminology in eastern Georgia and Claibornian deposits in Georgia that they western South Carolina. believed were equivalent to the Tallahatta, Confusion regarding the propriety of thethe Lisbon, and possibly lower part of the Gosport name McBean as opposed to the name Lisbon in Sand of Alabama. The reason they gave for Georgia resulted from the original ambiguity of proposing a new formation rather than adopting both the type lithostratigmphiclithostratigraphic concept of thethe a previously named formation was that: McBean Formation, and the stratigraphy of thethe ''Although'IAlthough inin a generalgeneml way the correlatives of type locality of the unit. The only sections cited thesethese formations {Tallahatta,[Tallahatta, Lisbon, and by Veatch and Stephenson (19ll)(the(1911)(the Gosport] may be recognizedmgnized in Georgia, the descriptions of the McBean were taken from extension of thethe use of these terms to this State notes by T. W. Vaughan) from the type area of isis inappropriate,inappropriate, since the Claiborne group is not the McBean Formation were in ravines and naturallynatumEly divisible into the same units as in gullies approximately: ... one-quarter of a mile Alabama."Alabama " VeatchVeatch and Stephenson 1911,1911, p. 236 south of McBean Station (Veatch and It isis not clear whether they believed that Stephenson, 1911,1911, p. 242). thethe Alabama formations could not be The only "ravines and gullies" that are lithologicallylithologicallydiscriminated dimiminated (divisible) in Georgia, still exposed in that area occur between 0.4 and or whether the lithostratigraphic sequence was 0.5 mile (0.66(0.65 and 0.8 Ism)kIn) southeast to east of not thethe same and, therefore, the application of the railroad crossing at McBean. The distance thethe Alabama names was inappropriate. given by Veatch and Stephenson (p. 242) as one-one• However, Veatch and Stephenson (1911) did quarter mile south of the station would place thethe apply thethe name McBean Formation generally to "gullies""gulliesI'inin McBean Creek, and the southern siliciclastic,siliciclastic, marine deposits they believed to be valley wall due south of McBean contains no of Claibornian age across the entire state of gullies. However, the precise location of thethe Georgia. "gullies" of Veatch and Stephenson (p. 242) isis Although Shearer (1917) and Cooke and uncertain but appear to be the ravines in thethe Shearer (1918) restricted the McBean to its type eastern valley wall of McBean Creek area inin eastern Georgia, Cooke (1986)(1936) approximately 0.60.5 miles (0.8 km)kIn) southeast toto SUbsequentlysubsequently expanded the definition of the unit east of the railroad crossing in the community of again toto conform to that of Veatch and McBean. Stephenson (1911). Later authors, however, At this time, most of these ravines recognizedrecognized only the lisbonLisbon and TaIlahattaTallahatta expose only bland Barnwell residuum with rare Formations inin western Georgia (MacNeil, 19478,19474 "nodules", cobbles or boulders of chert. Only thethe 1947b;1947b; Herrick, 1961; Toulmin and LaMoreaux, eastern-most ravine still exposes approximately 1963;1963; Herrick and Vorhis, 1963; Owen, 1963;1963, 3 feet (1 m) of McBean (according to thethe original Marsalis and Friddell, 1975; Huddlestun, 1981; lithologic descriptions of Veatch and Stephenson, Huddlestun and others, 1988). Only Pickering 1911). Based on the lithologic descriptions of 91 Sloan (1908, p. 270),2701, Veatch and Stephenson (p. the Dry Branch Formation. Finally, The 242) and on my own experience in the type area northward projection oftheofthe Dry Branch/McBeanBranchjMcBean of thethe McBean, the only lithology that can be contact from the McBean core (GGS-3537) clearly attributed to the Claibornian McBean at should be at approximately 20 to 30 feet above thethe typetype localitylocality is an impure, unconsolidated, the floor of the McBean swamp, consistent with mostly massive-bedded, fairly even-textured,even-textwed, the altitude of the McBean-Barnwell residuum calcarenitic, finely bioclastic,bioclarrtic, finely sandy at the McBean type locality. limestonelimestone to very calcareous, calcareniticcalamnitic sand As an indication of the lithologic (calcareous(calcareous marl and soft, chalky limestone of distinctiveness of the McBean, Brantley (1916, p. Veatch and Stephenson, 1911). 44-55) presented seven chemical analyses of The overlying greenish or drab clays and samples from the McBean Formation along greenish yellow sands included in the McBean McBean Creek and in the vicinity of Shell BldBluff Formation by Veatch and Stephenson (p. 242),2-42), on the Savannah River. The percent calcium and which are not presently exposed in the carbonate in these seven samples ranged from ravines, are more consistent with the lithology of approximately 70% to 8796,87%, compatible with thethe thethe Dry Branch Formation than with any other impure limestone lithology of the presently lithologylithology known in the McBean. The Dry exposed McBean at the type locality and at Shell Branch Formation is exposed at the same Bld.Bluff. elevation as the type McBean, 0.2 mile (0.3 mile According to Veatch and Stephenson south of thethe junction of Ga. Hwy. 5666 and Ga. (1911, p. 239) Earle Sloan made a large spur 56) from the McBean type locality. At the collection of fossils: I!.."... at Sloan's Scarp on typetype localitylocality of the McBean, approximately 30 McBean Creek, between McBean Station and feetfeet (9(9 m) of soft, yellow to white sand, included Savannah River. " inin thethe Barnwell Formation by Veatch and Vaughan identified the fauna and Stephenson (p. 242, section 1, bed 4) and presented a faunal list in Veatch and LeGrand and FureronFurcron 1956),1966), and in the McBean Stephenson (1911, p. 238240)239-240) and correlated itit Formation by Cooke (1943, p. 56),661, was assigned with the Lisbon Formation of Alabama, thethe St. toto thethe Irwinton Sand by Herrick and Counts Maurice Formation in Louisiana, and the Cook (1968,(1968, p. 54). Huddlestun (1982) included this Mountain of Texas (see Veatch and Stephenson, sand section inin the Irwinton Member of the Dry 1911, p. 240, for the extensive list of fossils Branch Formation on lithologic grounds;grounds, soft between McBean station and Savannah River). white sand is not known to occur in the McBean The shell bed is signiscantsignificant for the concept of thethe Limestone Member in its type area, but does McBean Formation of Veatch and Stephenson occur inin the Dry Branch Formation. Bed (e) of (1911) and Cooke and Shearer (1918) as well as Sloan (1908,(1908, p. 270) was reported to rest "on many subsequent authors. irregularirregular surface of (f)",(Ow, which is the McBean Veatch and Stephenson (1911) gave no Limestone Member as we understand it. The explanation or precise location for "Sloan's "irregular surface" of Sloan (p. 270) may scarp", and it would presumably be thethe "scarp" represent the disconformitydisconforrnity between the McBean mentioned by Sloan (1908) 269-2101269-270) as and thethe Dry Branch or a solution horizon at the occurring: "0.3'U.3 miles south of McBean station ... toptop of thethe McBean. Unfortunately, this contact on the south side of McBean Creek...':Creek... '~ and isis no longerlonger exposed in outcrop in the type area.area exhibiting "'!..a...a seriesserie8 of deeply incised gulliesgullie8 InIn thethe nearby McBean core (GGS-3757),(GGS-37671, which expose the lower portion of the...the... unweathered McBean limestone extends to the section...,"... ," i.e.,Le., the "gullies"mentioned by Veatch toptop of the Claibornian section where it underlies and Stephenson (1911, p. 242). Therefore, based calcareous sands and limestone of the Utley on the evidence presented by Sloan (1908) and Limestone Member of the Clinchfield Formation. Veatch and Stephenson (1911), it would appear Because of physical resemblance, sands and clays that the fossil collection reported by Veatch and immediatelyimmediately overlying the soft limestone of the Stephenson (1911, p. 239-240) came fiomfrom thethe McBean at the type locality are here included in near vicinity of the type locality of thethe McBean, 92 i.e., the soft limestonelimeatone or "marl""marln in the lower lithologically the same as the section exposed at part of the describedddbedsections. Hawever,However, neither Shell Bluff and in the McBean and Millers Pond Sloan (1908) nor Veatch and Stephenson (1911)(1911) cores. Therefore, it appears likely that the fossil mentioned the preaencepresence of richly fossiliferousfoeailiferous shell assemblage attributed to the McBean did shelly deposits in their measured sections of the not come from the McBean Limestone Member type locality. In addition, calcitic fossilsfoesils from the as we now know it, but from the underlying soft limestone in the McBean Member at the Bennock Millpond Sand Member that is type locality and at Shell Bluff are rare, and correlative with the lower part of the Lisbon aragonitic shells are absentabsent. Formation in Alabama. This interpretation is The molluscan assemblage reported by consistent with the presence of both aragonitic Veatch and Stephenson (1911, p. 239-240) is a mollusk shells and fine, well-sorted sand that is diverse, aragonitic, shelly fauna, and has the characteristic of the sands in the fossil shells in same delicate shells and preservation as that in the collections of the U. S. National Museum, the collections of the U.S. National Museum that and with the very well sorted, fine-grained sand the senior author examined in 1976. The in the lower part of the bluff (Sloan's(Soan's scarp). sediment still adhering to these fossils is not a Currently, the Bennock Millpond Sand Member limestone or finely sandy calcarenite but an is largely covered by leaf drift along the face of olive-gray, argillaceous,argiUaceous, very fineline sand. the bluff but very fine, well-sorted sand with Therefore, based on the literature, there is doubt common dark minerals can be seen in small as to the precise location of the shell bed at braided rivulet8rivulets from springs and seeps in the "Sloan's scarp", and to the precise lower part of the bluff. Very fine, well-sorted lithostratigraphiclithoatraligmphic context of the shell bed. sand with dark minerals is characteristic of the The location given by Veatch and Bennock Millpond Sand Member, not the Stephenson (1911, p. 239) "between McBean McBean LimeatoneLimestone Member. In addition, the station and Savannah River" suggests that the structural contour map on the top of the source bed of the fossil shells could be exposures Bennock Millpond Sand Member (Fig. 15) along the right bank of McBean Creek below indicates that the top of the formation should be Bennock Millpond at the foot of a steep bluff roughly 20 feet (6 m) above the base of the ("Sloan's scarp"?),scarp?), where McBean Creek passes valley wall (Sloan's scarp) or the floor of the into the Savannah River flood plain. This Savannah River swamp. This matches the interpretation is supported by a comment of elevations of the seeps and springsspring in the bluff Cooke (1936, p. 56) that: "The''The best collection and the elevation of the McBean Limestone thus far obtained was made by Sloan near the Member in the upper part of the bluff. Finally, mouth of McBean Creek in Georgia.Georgia."rr based on drilling, LeGrand and Furcron (1956, Based on that comment, the fossil p. 33) included an incoherent sand, below assemblage reported by Veatch and Stephenson ground level at the type locality of the McBean (1911) did not come from the type locality of the LimestoneLimeatone Member, in the McBean formation. McBean as it must be understood today (the The incoherent sand is compatible with the southern valley wall of McBean Creek from 0.3 Bennock Millpond Sand Member and not with to 0.5 mile [0.5 to 0.8 km]kml southeast of the McBean Limestone Member. community of McBean). Rather, the shells Because the only distinctive Claibornian appear to have been collected from the lower lithology present at the type locality of the part of the steep western valley wall of the McBean is the soft, "marly", massive-bedded Savannah River (Sloan's scarp), less than 2 limestone, then clearly the principle miles (3 km) from the confluence of McBean lithostratigraphic concept of the McBean must Creek and the Savannah River. be that of a sandy limestone. This is at variance The Bennock Millpond Sand Member with the correlative upper Claibornian deposits crops out in the lower part of this bluff and the south of the vicinity of Hancock Landing in McBean Limestone Member crops out in the Burke County and the rest of Georgia where upper part of the bluff. The McBean isie upper Claiborne Group deposits consist of 93 calcareous clay, or very argillaceous limestone ("marl"). Because of the historic confusion in use of the name McBean, and because Sloan (1908) originally referred the limestones along McBean Creek and Shell Bluff to the Santee, Fallaw and Price preferred the name Santee Limestone to that of McBean Limestone in the type area of the McBean. BasedBmed on lithology, we conclude that there is no Santee Limestone in Georgia, unless it is the sandy limestone at the top of the Still Branch Sand in southern Burke County. We conclude that; 1.) the name McBean be should be changed in lithostratigraphic rank to McBean Limestone Member of the Lisbon Formation. The characteristiccharadenstic lithology of the McBean is a sandy limestone; 2.) In this context, the McBean is restricted to the vicinity of McBean Creek, Shell Bluff and the area north of the projected extension of the Pen Branch fault in Burke County; 3.) The name McBean Limestone should not be extended away from the area of its typical development; 4.) the limestone lithology of the McBean is different from the predominantly moldic and indurated Santee Limestone; 5.) the precise bio-bio• stratigraphic correlation of the McBean to the type Santee has not been rigorouslyrigorou$ly established; 6.) there is an updip, calcareous, argillaceous, probably nearshore sand referred to in this report as Bennock Millpond Sand Member;Member, and 7.), it has never been demonstrated that the McBean fossil fauna collected by Sloan is from the McBean Limestone Member of the Lisbon Formation. It hasbas only been assumed to be from the McBean. 94