SUPPLEMENT TO THE PRELIMINARY STRATIGRAPHIC DATABASE FOR SUBSURFACE SEDIMENTS OF DORCHESTER COUNTY, SOUTH CAROLINA

By Lucy E. Edwards, Gregory S. Gohn, Laurel M. Bybell, Peter G. Chirico, Raymond A. Christopher, Norman O. Frederiksen, David C. Prowell, Jean M. Self-Trail, and Robert E. Weems

U.S. Geological Survey Open-File Report 00-049-B
2000
Prepared in cooperation with the South Carolina Department of Natural Resources

TABLE OF CONTENTS

INTRODUCTION

This report is a prototype product that provides subsurface geologic information in a variety of digital formats for a small segment of the South Carolina Coastal Plain. The preliminary stratigraphic database found in Chapter A is designed to present and store subsurface geologic and paleontologic data in a GIS environment for selected Dorchester County, South Carolina drill holes. The information presented in graphic and tabular form in the database also is presented in a non-GIS, widely distributed format, an Adobe Acrobat (.pdf) file, in Chapter C. This chapter (Chapter B) provides a variety of supplementary and background information for the stratigraphic database. The largest section in this chapter reviews the physical stratigraphy and biostratigraphy of the sedimentary units found in Dorchester County. Chapter D informally presents recent results of a palynostratigraphic examination of Maastrichtian (Upper Cretaceous) sediments in Dorchester County and adjacent areas.

CONTRIBUTORS

Principal responsibilities for the information provided in this report are as follows:

Acknowledgments. -- We wish to acknowledge the South Carolina Deparment of Natural Resources for their long-standing support of our studies in the South Carolina Coastal Plain. In particular, we thank Karen Waters and Joseph Gellici of the Department of Natural Resources for their contributions to our program. Drill-site and laboratory descriptions of the USGS-Clubhouse Crossroads No. 1 core by Brenda B. Houser (USGS) and Charles C. Smith (formerly USGS) were used extensively in the study of that section.

DRILL HOLE NOTES

The drill holes studied for this report consist of three continuously cored test holes, two partially cored test holes, and one uncored water well. The three continuously cored holes, and their numerical designations are USGS-Clubhouse Crossroads No.1 (DOR-37), USGS-Pregnall No.1 (DOR-208), and USGS-St. George No. 1 (DOR-211). The two partially cored holes are USGS-Stallsville No. 1 (DOR-st1) and USGS-Stallsville No.2 (DOR-st2). The water well is the Summerville Water Plant well (DOR-52).

The St. George and Pregnall core sites are located near each other in the northern part of Dorchester County, southeast of the town of St. George. The Clubhouse Crossroads site is in the southwestern corner of the county along Cane Acre Road. The remaining three core sites are closely spaced in the southeastern part of the County near the Ashley River and Cooke Crossroads southwest of Summerville.

An attribute table that lists basic information about the drill holes is included in the drill-hole database in Chapter A of this report. This table is reproduced at the following link:

Drill-hole database attribute table --

SUBSURFACE STRATIGRAPHY

Dorchester County is underlain by Coastal Plain sediments of Late Cretaceous, Tertiary, and Quaternary age. Total thicknesses of this sedimentary section vary from near 2,000 ft in northern Dorchester County to about 2,500 ft in the southern part of the county. Dominant lithologies include fluvial-deltaic and marine sands and clays in the Cretaceous and Paleocene sections, and marine limestones and marls in the Eocene and Oligocene sections. Thin Neogene and Quaternary deposits constitute the surficial section in the study area. Only the upper Upper Cretaceous and lower Tertiary (Paleocene through Oligocene) parts of the section are considered in detail in the four chapters of this report.

View stratigraphic chart for Dorchester County --

View table showing distribution of stratigraphic units in studied drill holes --

In this section, the stratigraphic nomenclature, lithologies, ages, biostratigraphy, and occurrences of upper Upper Cretaceous and younger stratigraphic units are briefly described. Graphic displays of stratigraphic and paleontologic data for the studied Dorchester County cores are presented in Chapter A and Chapter C.

Donoho Creek Formation (Black Creek Group)

Campanian

Stratigraphy. -- The Donoho Creek Formation of the Black Creek Group was formally named by Sohl and Owens (1991) for beds extending from the upper part of the bluff at Donoho Creek Landing to Black Rock Landing along the Cape Fear River, Bladen Co., N.C. This unit was subsequently extended into Dorchester County, S.C. by Gohn (1992). In Dorchester County, the Donoho Creek Formation is consistently present in the subsurface where it is underlain disconformably by the Bladen Formation of the Black Creek Group and overlain disconformably by the coarse-grained, phosphatic basal bed of the Peedee Formation. The lower part of the Donoho Creek and the units below the Donoho Creek are not covered in this report.

Lithology. -- The upper Donoho Creek Formation is a homogeneous section of calcareous, muddy quartz sand (olive gray, 5Y 4/1); the sand fraction is typically very fine to fine but locally may include up to 15 percent medium sand. The 197-ft-thick section in the Clubhouse Crossroads core (DOR-037) was designated as a principal reference section for the Donoho Creek Formation (Gohn, 1992). There, the lower 10 ft consists of medium-gray, fine to medium, poorly sorted, bioturbated, megafossiliferous, clayey sand with large mollusk fragments, some phosphate, mica, and glauconite and is clearly representative of a lag deposit. The remainder of the Donoho Creek consists of a relatively uniform sequence of calcareous clayey silts and fine sands and calcareous silty clays varying from light olive gray to medium gray and containing mica. The entire unit contains some pyrite, glauconite, and phosphatic fecal pellets. Macrofossils and microfossils are present but sparse. Widely spaced zones of calcite-cemented nodules and zones of secondary irregular calcite cementation are present.

Paleontology. -- The Donoho Creek is dated as late Campanian on the basis of calcareous nannofossils (Self-Trail and Gohn, 1996; Self-Trail and Bybell, 1997; Self-Trail, 1999). The part of the Donoho Creek discussed here is assigned to calcareous nannofossil Zone CC 22 of Perch-Nielsen (1985) and includes sediments above the lowest occurrence of Quadrum trifidum and below the highest occurrence of Reinhardtites anthophorus. Ostracodes from the St. George core at 889 and 816 ft are assigned to the Haplocytheridea sarectaensis assemblage. This assemblage is approximately equivalent in age to calcareous nannofossil Subzone CC 22c.

Calcareous nannofossil Zone CC 22 is divided into two subzones (CC 22 a/b and CC 22c) based on the lowest occurrence of Reinhardtites levis. Both subzones were recognized in the St. George (DOR-211) and Clubhouse Crossroads (DOR-037) cores. Because sediments of Subzone CC 22a/b from the St. George core contain Lithastrinus grilli, they are likely to be slightly older than sediments of Subzone CC 22a/b from the Clubhouse Crossroads core.

Foraminifers, pollen, dinoflagellates, and mollusks from the Donoho Creek have been discussed by Gohn (1992), although the early Maastrichtian age he reported is now considered to be late Campanian. The lowest occurrence of the mollusk Exogyra costata marks the base of the Donoho Creek Formation. Dinoflagellates from the Donoho Creek Formation from the St. George core (DOR-211) were discussed by Habib and Miller (1989). The flora and fauna of the Donoho Creek Formation from a core in neighboring Charleston County, S.C. are discussed by Edwards and others (1999).

The sediments of the Donoho Creek represent a middle neritic marine environment.

Occurrence in studied cores --

 

Peedee Formation

Maastrichtian

Stratigraphy. -- Originally called the Peedee bed (Ruffin, 1853) and later the Peedee sand (Stephenson, 1912), the Peedee Formation was named by Stephenson (1923). The type locality is at Burches Ferry, on the west side of the Peedee River, Florence Co., S.C. Its stratigraphy in Dorchester County was described by Gohn (1992).

The Peedee is consistently present in the subsurface of Dorchester County. Its basal contact with the Donoho Creek Formation is unconformable and marked by a lag deposit. In the Clubhouse Crossroads core (DOR-037), it is overlain unconformably by the Tertiary Rhems Formation. In two other cores (DOR-211 and DOR-052), recovery was poor at the top of the Peedee and above it. In these cores, the lowest fossiliferous material above the Peedee is Selandian (lower upper Paleocene) and we have assigned, or questionably assigned, these sediments to the Chicora Member of the Williamsburg Formaiton.

Lithology. -- The basal part of the Peedee Formation is a lag deposit consisting of phosphate pebbles in a muddy matrix with phosphate and quartz sand. The Peedee Formation above its base consists predominantly of calcareous silty clays (olive gray 5Y 4/1 to light olive gray 5Y 6/1) that contain trace amounts of mica and very fine quartz sand. Glauconite is present in trace amounts. Calcareous microfossils and mollusk fragments are common to locally abundant throughout. The uppermost Peedee in the St. George core (DOR-211) was poorly recovered; available core material consists of sparingly shelly, slightly muddy, fine to coarse quartz sand.

Paleontology. -- The Peedee Formation is dated as late Maastrichtian and is assigned to calcareous nannofossil Zones CC 25 and CC 26 of Perch-Nielsen (1985). Subzone CC 25b is recognized in the lowest Peedee sediments because they contain the lowest occurrence of Lithraphidites quadratus. This subzone is present throughout Dorchester County. Zone CC 26 is absent in the updip St. George core (DOR-211). This zone, recognized on the basis of the lowest occurrence of Ceratolithoides kamptneri, is represented by only 3 ft of sediment in the Clubhouse Crossroads core (DOR-037). Christopher (this volume, chapter D) introduces three pollen zones in the Peedee, two of which are recognized in cores from Dorchester County.

The fauna and flora of the Peedee Formation in South Carolina have been discussed by a number of authors (Habib and Miller, 1989; Gohn 1992; Wingard 1993; Edwards and others, 1999; and Self-Trail, 1999) and include calcareous nannofossils, dinoflagellates, foraminifers, ostracodes, and mollusks.

We infer an upward change from outer neritic deposition to middle neritic deposition from the characteristics of the ostracode assemblages and the lithologic trend.

Occurrence in studied cores --

 

Rhems Formation (Black Mingo Group)

Lower Paleocene

Stratigraphy. -- The Rhems was originally described by Sloan (1908) as the Rhems shale, a part of the Upper Black Mingo phase. The unit was abandoned by Cooke (1936) as simply part of the Black Mingo Formation. It was later reinstated as the Rhems Formation by Van Nieuwenhuise and Colquhoun (1982). These authors recognized two members: the Browns Ferry Member and the Perkins Bluff Member, whose type sections are in Georgetown County, S.C. They identified these members in the Clubhouse Crossroads core (DOR-037) in Dorchester County. Muthig and Colquhoun (1988) recognized two additional members of the Rhems Formation, the Sawdust Landing Member and the Lang Syne Member, updip in Calhoun County, S.C. We have not used the members of the Rhems Formation in this report.

In Dorchester County, the Rhems is present as a subsurface unit that unconformably overlies the Peedee Formation and is overlain by the Lower Bridge Member of the Williamsburg Formation. It was not present, or not recognizable as a distinct unit, in the St. George (DOR-211) and DOR –052 cores.

Lithology. -- The Rhems Formation consists of fine to coarse arenaceous shale and argillaceous sand, and pelecypod-poor to pelecypod-rich clayey sand (Van Nieuwenhuise and Colquhoun, 1982). In the Clubhouse Crossroads core (DOR-037), the Rhems Formation is a medium-gray-green silty clay above a basal unit of nodular, glauconitic, muddy sand. The unit is predominately a calcarous silty clay but locally a sandy clay. Calcium carbonate averages 10 to 20 percent. Bedding is typically disrupted or obliterated by burrows.

Paleontology. -- The Rhems Formation is dated as early Paleocene, and it represents calcareous nannofossil Zone NP 1 on the basis of the presence of Cruciplacolithus primus and Cruciplacolithus intermedius (lowest occurrences within Zone NP 1) and on the absence of Cruciplacolithus tenuis (lowest occurrence defineds the base of Zone NP 2). Nannofossil Zones NP 2 and NP 3 are not clearly identified in any samples from South Carolina. However, in the Clubhouse Crossroads core, there is some uncertainty concerning the age of the samples at 647 and 643 ft. These samples were examined twenty years ago and were reported to have a few specimens of Chiasmolithus consuetus, which first appears near the bottom of Zone NP 3. However, a more likely interpretation is that these specimens represent either contamination from above or they are poorly preserved angled specimens of Cruciplacolithus asymmetricus. And in fact, the sample at 643 ft does contain a significant amount of downhole contamination. Unfortunately, the slides for these two samples cannot be reexamined because they were prepared with a mounting medium that over the years dissolved away all the calcareous nannofossils.

The situation is further complicated by the fact that two cores from Berkeley County (Santee Coastal Reserve core and St. Stephen core) also contain a small number of specimens of Chiasmolithus consuetus and Cruciplacolithus tenuis (first appearance defines the base of Zone NP 2) in the upper part of the Rhems Formation (Edwards and others, 1999). Paleomagnetic data for these two cores indicate that sediments representing Zones NP 2 and NP 3 may be present. Until further data are available to resolve this, the age of the Rhems is definitely within Zone NP 1 and possibly within Zones NP 2 and NP 3. Early Paleocene pollen, dinoflagellate cysts, and foraminifers also are present in the Rhems Formation.

Occurrence in studied cores --

 

Williamsburg Formation (Black Mingo Group)

The Williamsburg Formation is named for exposures in Williamsburg County and Berkeley County, South Carolina. Sloan (1908) originally called this unit the Williamsburg pseudobuhr, a subdivision of his Black Mingo phase. This unit was abandoned by Cooke (1936) but was reinstated as the Williamsburg Formation of the Black Mingo Group by Van Nieuwenhuise and Colquhoun (1982).

Van Nieuwenhuise and Colquhoun (1982) proposed a composite stratotype consisting of outcrops at Lower Bridge (highway 377 bridge) on the Black River (Williamsburg County) that represent their Lower Bridge Member of the Williamsburg Formation and outcrops just downstream from Wilson's Landing on the Santee River (Berkeley County) that represent their Chicora Member of the Williamsburg. Van Nieuwenhuise and Colquhoun (1982) assigned a late Paleocene age to the Williamsburg Formation and indicated its distribution in drill holes in Georgetown, Williamsburg, Berkeley, and Dorchester Counties.

As described by Van Nieuwenhuise and Colquhoun (1982, p. 57), the older Lower Bridge Member of the Williamsburg Formation consists of arenaceous shales, fullers earth, and fossiliferous, argillaceous sands. The younger Chicora Member consists of fossiliferous, argillaceous sands and mollusk-rich, bioclastic limestones. We anticipate the elevation in rank of the members of the Williamsburg Formation.

Lower Bridge Member of the Williamsburg Formation

Lower and upper Paleocene

The Lower Bridge Member of the Williamsburg Formation was named by Van Nieuwenhuise and Colquhoun (1982) for siliceous mudstone and arenaceous shale outcropping along the Black River, Williamsburg County, S.C. They identified the Lower Bridge in the Clubhouse Crossroads core (DOR-037) from 630 to 550 ft. Because we are using log depth rather than core, this interval translates to 635 to 546 ft in the core. We chose to use log depth because the distinctive log signature at 546 is easily recognizable, whereas core loss succeeded by excess core recovery obscures core measurements in this critical part of the core. Further, we recognize an unconformity within the Lower Bridge Member in Dorchester County and recognize the possibility of an additional unconformity in nearby areas.

Lower Bridge Member, subunit A

Stratigraphy. -- The Lower Bridge Member, subunit A, was recovered in only two of the six Dorchester County cores. This subunit was discussed under the name "upper part of the Rhems Formation (Black Mingo Group) sensu Bybell and others (1998)" in Edwards and others (1999) in the Santee Coastal Reserve core, Charleston County, S.C. In this Charleston County core, the paleomagnetic signature suggests a latest early Paleocene age (Edwards and others, 1999). Subunit A is underlain unconformably by the Rhems Formation and overlain unconformably by subunit B-C of the Lower Bridge Member of the Williamsburg Formation.

Lithology. -- The Lower Bridge Member, subunit A, consists of very fine to fine quartz sand and interbedded sandy and silty clay. Near its base, phosphate (up to granule size) and glauconite are abundant. Mud is more abundant, and phosphate and glauconite less so, in the upper part of the subunit. Calcareous microfossils are moderately common throughout.

Paleontology. -- The Lower Bridge Member, subunit A, is placed in calcareous nannofossil Zone NP 4 on the basis of the presence of Ellipsolitus macellus (lowest occurrence defines the base of NP 4) and Toweius pertusus (lowest occurrence within NP 4). Individual specimens of Chiasmolithus bidens/solitus (believed to have its lowest occurrence within Zone NP 5) occur in samples from 621, 611, and 601 ft in the Clubhouse Crossroads core. The marker for Zone NP 5 (Fasciculithus tympaniformis) is rare in South Carolina and cannot be used as a zonal marker. There are three possible explanations: the three specimens represent downhole contamination, C. bidens actually first appears in the upper part of Zone NP 4, or Zone NP 5 is present in Lower Bridge A. The most likely answer is that there is downhole contamination.

According to the time scale of Berggren and others (1995), Zone NP 4 is both early and late Paleocene. Because the early Paleocene pollen species Pseudoplicapollis serenus (highest occurrence defines the top of the lower Paleocene P. serenus Zone) is not present in this unit in the Clubhouse Crossroads core, we consider the Lower Bridge Member, subunit A to be late Paleocene in age in this core. The type section in Williamsburg County includes early Paleocene pollen and dinoflagellates.

Occurrence in studied cores --

 

Lower Bridge Member, subunits B and C

Stratigraphy. -- The Lower Bridge Member, subunits B-C, was recovered in only two of the six Dorchester County cores. These subunits were considered to comprise the entire Lower Bridge Member of the Willliamsburg Formation by Bybell and others (1998) and Edwards and others (1999) in two cores in Charleston County, S.C. Subunits B-C are underlain unconformably by subunit A of the Lower Bridge Member of the Williamsburg Formation and overlain unconformably by the Chicora Member of the Williamsburg Formation.

Lithology. -- In Charleston County, S. C. , subunits B and C of the Lower Bridge Member consist of two unconformity-bounded packages. The lower one is a muddy, glauconitic, very fine to fine sand that has phosphate granules and pebbles at its base. This subunit is extensively bioturbated. Common, irregularly distributed calcite-cemented layers typically are about 0.5 ft thick, and two or three usually occur in a given 10-ft interval. The upper subunit consists of a homogeneous section of calcareous, silty and sandy clay that has a muddy, very fine to medium quartz-glauconite-phosphate sand forming a basal lag. Fabrics in these fine-grained deposits vary from laminated to partially bioturbated to completely bioturbated. In Dorchester County, a single subunit (B-C) is recognized; it consists of bioturbated, calcareous, sandy and silty clay above a basal glauconite-phosphate lag deposit.

Paleontology. -- The Lower Bridge Member, subunit B-C, of the Williamsburg Formation is dated as early late Paleocene. This subunit is placed in the lower part of calcareous nannofossil Zone NP 5 on the basis of the presence of Chiasmolithus bidens/solitus (lowest occurence near the base of Zone NP 5) and the absence of species that have lowest occurrences in the upper part of Zone NP 5 (Heliolithus cantabriae) or Zone NP 6 (Heliolithus kleinpellii).

Dinocysts in subunits B-C consist of moderately diverse assemblages that include Amphorosphaeridium multispinosum, Damassadinium californicum, Deflandrea delineata, Palaeoperidinium pyrophorum, and Phelodinium sp. of Edwards (1989). In the Clubhouse Crossroads core (DOR-037), as in two cores in Charleston County, D. delineata has its lowest occurrence and P. pyrophorum has its highest occurrence in this subunit of the Lower Bridge. This subunit is in the Caryapollenites prodromus pollen interval zone.

Occurrence in studied cores --

 

Chicora Member of the Williamsburg Formation (Black Mingo Group)

Upper Paleocene

Stratigraphy. -- The Chicora Member of the Williamsburg Formation was named by Van Nieuwenhuise and Colquhoun (1982) for outcrops along the south bank of the Santee River just downstream from Wilsons Landing, Chicora 7.5' quad., Berkeley County, S.C. We anticipate that this member will be raised to formation status in the future.

The Chicora Member of the Williamsburg Formation is underlain by the lower and upper Paleocene Lower Bridge Member of the Williamsburg Formation. The Chicora Member of the Williamsburg Formation is overlain by the middle Eocene Santee Limestone in northern Dorchester County. In southern Dorchester County, the Williamsburg Formation is overlain by the lower Eocene Fishburne Formation (Gohn and others, 1983).

Lithology. -- The Chicora Member of the Williamsburg Formation recovered at Pregnall consists of two contrasting lithologic units, a lower siliciclastic section of terrigenous sand, silt, and clay, and an upper carbonate section of moldic pelecypod limestone. Regionally, the Chicora is a heterogeneous unit consisting of shelly quartz sands, indurated, moldic limestone, and dark, calcareous sndy and silty clays.

Paleontology. -- The Chicora Member of the Williamsburg Formation is dated as late Paleocene and represents the upper part of calcareous nannofossil Zone NP 5 to Zone NP 9. In the Pregnall core (DOR-208), Zone NP 9 and questionably Zone NP 7/8 are present. In the Clubhouse Crossroads core (DOR-037), nannofossil Zones NP 5 (upper part) and NP 9 are present, although the interval between 531 and 454 ft, which contains no diangostic species, probably represents time between upper Zone NP 5 and NP 9. In the St. George core (DOR-211), Zones upper NP 5, NP 8, and NP 9 are present.

The pollen of the Chicora Member of the Williamsburg Formation is in the upper part of the Caryapollenites prodromus Interval Zone and the Carya Interval Zone.

Occurrence in studied cores --

 

Fishburne Formation (Black Mingo Group)

Lower Eocene

Stratigraphy. -- The Fishburne Formation was defined by Gohn and others (1983); its type section is the Clubhouse Crossroads core (DOR-037), Dorchester County, S.C. It unconformably overlies the Chicora Member of the Williamsburg Formation and underlies the Santee Formation. In the original publication, Gohn and others stated that the Fishburne underlies the Moultrie Member of the Santee Limestone. Here, we reinterpret this overlying unit as the Cross Member of the Santee Limestone. The Fishburne has been recognized only in the subsurface of the Coastal Plain southwest of the Charleston-Summerville area, S. C. Thickness at the type section is 24 ft.

Lithology. -- In its type section in Dorchester County, the Fishburne consists of nodular, glauconitic, clayey limestone. The limestone typically is greenish gray to pale olive and shows little evidence of stratification. This apparent lack of bedding is probably due to bioturbation.

Paleontology. -- The Fishburne Formation contains common to abundant sand-sized and larger mollusk framents, and abundant microfossils, principally ostracodes and benthic foraminifers. Calcareous nannofossils, plantonic foraminifers, ostracodes, dinoflagellate cysts and acritarchs, and pollen indicate an early Eocene age. Calcareous nannofossils from the Fishburne Formation in the Clubhouse Crossroads core (DOR-037) indicate Zone NP 11 on the basis of the presence of species that have their lowest occurrences in Zone NP 10 (Chiasmolithus eograndis) or near the Zone NP 9/10 boundary (Transversopontis pulcher), on the absence of species confined to NP 10 (Rhomboaster bramlettei and Rhomboaster contortus), and on the presence of species that occur no higher than zone NP 11 (Neochiastozygus concinnus and Zygodiscus herlyni). The ostracode assemblage suggests deposition in shallow water in a warm climate.

Occurrence in studied cores --

 

Moultrie Member of the Santee Limestone

Middle Eocene

Stratigraphy. -- Sloan (1908) named the Santee Limestone for the Santee River and established its type section at Eutaw Springs, Orangeburg County, S. C. The Santee Limestone is a subsurface unit in Dorchester County, S. C. Ward and others (1979) defined two members in the Santee, a lower Moultrie Member consisting primarily of macrofossiliferous limestone and an upper Cross Member consisting typically of finer grained, microfossiliferous limestone. Baum and others (1980) subsequently raised the Cross Member to formation status and restricted the name Santee Limestone to the interval assigned to the Moultrie Member by Ward and others (1979). Here, we follow the usage of Ward and others (1979).

The Moultrie Member of the Santee Limestone is present in only two of the cores studied in Dorchester County (Pregnall and St. George), where it is underlain unformably by the Chicora Member of the Williamsburg Formation. It is overlain unconformably by the Cross Member of the Santee Limestone.

Lithology. -- The Moultrie Member in Dorchester County consists primarily of bryozoan-pelecypod-peloid packstones and grainstones. Gastropods, serpulid worm tubes, and corals are present but distinctly less abundant. The peloids may be fecal pellets or rounded fossil fragments, or both. Very fine to medium-grained glauconite occurs in trace amounts throughout most of the Moultrie section, except where it is more abundant (with phosphate) at the basal contact. Quartz is virtually absent except at the base where it is likely reworked from the underlying Paleocene section. The Moultrie sediments are typically massive with few, if any, discernible sedimentary structures. The Moultrie limestones are very light colored; most are nearly white with a light yellowish cast that is much lighter than yellowish gray (5Y8/1).

On the gamma-ray log, the Moultrie Member of the Santee Limestone is bounded by two large spikes that represent glauconite-phosphate lag deposits at the base of the Santee and the base of the overlying Cross Member of the Santee Limestone. Between the spikes, appropriately low gamma-ray values represent the carbonate lithologies of the Moultrie. The gamma-ray values are slightly but uniformly higher below 226 ft than above in the Pregnall core (DOR-208). These log values may indicate a small amount of detrital clay in the lower part of the section.

Paleontology. -- Bryozoans and pelecypods are locally abundant in the Moultrie Member of the Santee Limestone. Benthic foraminifers are the most abundant microfaunal element, although ostracodes and planktonic foraminifers are present in small numbers. Calcareous nannofossils from the Moultrie Member are placed in the middle Eocene Zone NP 16 on the basis of the presence of Chiasmolithus bidens/solitus (highest occurrence defines the top of Zone NP 16), Cribrocentrum reticulatum (lowest occurrence in Zone NP 16), and large forms of Reticulofenestra umbilicus (lowest occurrence within Zone NP 16).

Palynological recovery from the Moultrie is poor. Dinocysts of mixed ages were reported from the Pregnall core. Fallaw and Price (1995) infer an inner to middle shelf depositional environment whereas Popenoe and Idris (1987) infer a middle to outer shelf environment further downdip.

Occurrence in studied cores --

 

Cross Member of the Santee Limestone

Middle and late Eocene

Stratigraphy. -- The Cross Member of the Santee Limestone was defined by Ward and others (1979). The unit was subsequently removed from the Santee and raised to formation rank by Baum and others (1980), but their usage is not followed here because it can result in confusion about what is or is not part of the Santee Limestone.

The Cross Member of the Santee Limestone is a widespread unit in Dorchester, Berkeley, Charleston, and southern Orangeburg Counties, S. C. It is underlain by the Fishburne Formation or the Moultrie Member of the Santee Limestone and overlain by the Harleyville Formation or the Harleyville-Parkers Ferry (undifferentiated) formations of the Cooper Group.

Lithology. -- The Cross Member of the Santee Limestone consists primarily of locally shelly, microfossiliferous limestone. The basal contact is a burrowed unconformity. In the Pregnall core, glauconite- and phosphate-filled burrows extend over a foot into the underlying Moultrie Member from the basal glauconite-phosphate bed of the Cross, and the upper surface of the Moultrie is partially coated with a phosphate crust.

The lower part of the Cross consists of foraminiferal-peloid packstones. Pelecypods, bryozoans, and serpulid worm tubes are present but are typically sparse in this lower part. Pelecypod-serpulid-foraminifer-peloid packstones dominate the middle of the Cross Member. The upper 20 feet of the Cross in the Pregnall core consists of foraminifer-peloid-pelecypod grainstones and packstones. Glauconite and quartz occur only in trace amounts in the Cross, except at the base.

Paleontology. -- The bivalve Crassatella alta is commonly found in the Cross Member of the Santee Limestone (Ward and others, 1979). The Cross is dated as both late middle Eocene and late Eocene, representing calcareous nannofossil Zones NP 16, NP 17, and NP 18. In the Clubhouse Crossroads (DOR-037) and DOR-St2 cores, the Cross is in Zone NP 16 on the basis of the presences of Chiasmolithus bidens/solitus (highest occurrence defines the top of Zone NP 16), Cribrocentrum reticulatum (lowest occurrence in Zone NP 16), and large forms of Reticulofenestra umbilicus (lowest occurrence within Zone NP 16) and Zone NP 17 on the basis of the absence of C. biden/solitus and the presence of Helicosphaera compacta (lowest occurrence near the top of Zone NP 16). In the Pregnall core (DOR-208), the Cross is in Zone NP 17 and NP 18 (lowest occurrence of Chiasmolithus oamaruensis, which defines the base of Zone NP 18, is at 123.3 ft). Only the lower part of the Cross was examined in the St. George core (DOR-211), and that is Zone NP 16. Dinocysts also indicate middle and late Eocene ages.

Occurrence in studied cores --

 

Harleyville Formation (Cooper Group)

Upper Eocene

Stratigraphy. -- The Harleyville Formation originally was defined as a member of the Cooper Formation by Ward and others (1979) with its type locality at the Giant Portland Cement Company quarry just north of Harleyville in Dorchester County, South Carolina. The Harleyville type section had previously been grouped with the Ashley Formation in an undivided section assigned to the Cooper Marl (Cooke and MacNeil, 1952). Weems and Lemon (1984) raised members of the Cooper Formation defined by Ward and others (1979) to formation status and raised the Cooper Formation to group status. The Harleyville is a widespread subsurface unit in Dorchester County. It is typically underlain by the Cross Member of the Santee Limestone and overlain by the Parkers Ferry Formation or the Ashley Formation of the Cooper Group (Ward and others, 1979).

Lithology. -- The Harleyville Formation typically consists of clayey, thoroughly bioturbated, fine-grained limestone and calcareous clay (Ward and others, 1979). Calcareous microfossils are common to abundant. The Harleyville typically has a basal glauconitic-phosphate lag deposit.

Paleontology. -- The Harleyville Formation is dated as late Eocene and is assigned to calcareous nannofossil Zone NP 18 and NP 19/20. The lowest occurrence of Chiasmolithus oamaruensis defines the base of Zone NP 18, and in the Pregnall core (DOR-208), the Harleyville is assigned to Zone NP 18. In the Clubhouse Crossroads core (DOR-037), the Harleyville is assigned to Zones NP 18 and 19/20 on the basis of the lowest occurrence of Ismolithus recurvus at 205 ft (lowest occurrence defines the base of Zone NP 19/20). Dinocysts indicate a late Eocene age. Vertebrate fossils, including Basilosaurus and Zygorhiza, have been reported from the Harleyville Formation at the type area in Dorchester County (Sanders, 1974).

Occurrence in studied cores --

Harleyville Formation:

Harleyville-Parkers Ferry (not differentiated):

 

Parkers Ferry Formation (Cooper Group)

Upper Eocene

Stratigraphy. -- Ward and others (1979) originally described the Parkers Ferry Member of the Cooper Formation from core and auger material in Dorchester and Charleston Counties, S.C. It was raised to formation status by Weems and Lemon (1984). The type section is the Clubhouse Crossroads core (DOR-037), in southern Dorchester County. The Parkers Ferry Formation is absent in the northern part of Dorchester County. The Parkers Ferry Formation is overlain by the Ashley Formation or the informally named "Drayton limestone beds." It is underlain by the Harleyville Formation.

Lithology. -- In its type section, the Clubhouse Crossroads core, the Parkers Ferry Formation consists of glauconitic, clayey, fine-grained limestone that contains abundant microfossils and locally common to abundant molluscan and bryozoan fragments (Ward and others, 1979). It typically has a basal glauconitic-phosphate lag bed.

Paleontology. -- The Parkers Ferry Formation throughout South Carolina is dated as late Eocene and is assigned to calcareous nannofossil Zone NP 19/20 and planktonic foraminiferal Zone P17 (Ward and others, 1979). This formation is no younger than Zone NP 19/20 because it contains Discoaster barbadiensis, D. saipanensis, and Cribrocentrum reticulatum (all have their highest occurrences at or just below the top of Zone NP 19/20). Dinoflagellates in the Parkes Ferry include Cordosphaeridium funiculatum and Charlesdowniea coleothrypta.

Occurrence in studied cores --

Parkers Ferry Formation:

Harleyville-Parkers Ferry (not differentiated):

 

Drayton limestone beds

Upper Eocene and (or) lower Oligocene

The Drayton limestone beds form an informal unit mapped by Weems and Lemon (1996) in Charleston and Dorchester Counties, S.C. The beds consist of calcarenite that may be composed of bryozoan fragments. At the base, phosphate pebbles and glauconitic sand may be present. Calcareous nannofossils indicate placement within Zone NP 21.

Occurrence in studied cores --

(not present in the studied cores)

 

Ashley Formation (Cooper Group)

Lower-upper Oligocene

Stratigraphy. -- Tuomey (1848) and Sloan (1908) applied the name Ashley to beds in marl pits along the Ashley River in Dorchester County, S. C. Subsequent authors generally included these beds in a loosely defined Cooper marl until Ward and others (1979) re-established the unit as the Ashley Member of the Cooper Formation. Weems and Lemon (1984) later raised the status of these units, resulting in the Ashley Formation of the Cooper Group. Hazel and others (1977) assigned a late Oligocene age to beds subsequently assigned to the Ashley Formation in the Clubhouse Crossroads core (DOR-037), Dorchester County. The Ashley Formation is a widespread shallow-subsurface unit in Dorchester County. It is typically underlain by the Harleyville or Parkers Ferry Formations of the Cooper Group or the Cross Member of the Santee Limestone and overlain by a wide variety of generally thin Neogene and Quaternary units.

Lithology. -- The Ashley Formation consists of a relatively homogeneous section of calcareous, phosphatic, microfossiliferous, silty and sandy clays. Parts of the section may be sufficiently calcareous to warrant their description as clayey, very fine microfossil calcarenites. The basal contact is a burrowed and unconformable. Very fine to fine-grained glauconite and phosphate sand are present in small amounts throughout the Ashley section, except in the basal 10 feet where the phosphate increases in grain size and abundance. Ashley sediments typically are massive or faintly texture-mottled, suggesting thorough bioturbation.

Paleontology. -- The Ashley Formation is dated as early-late Oligocene and is assigned to calcareous nannofossil Zones NP 24 and 25. Zone NP 24 includes sediments of both early and late Oligocene age (Berggren and others, 1995). In the Clubhouse Crossroads core (DOR-037), the Ashley is placed in Zone NP 24 on the basis of the presence of Helicosphaera recta (lowest occurrence in Zone NP 24. The ashley in the Pregnal core (DOR-208) is in Zone NP 24 and possibly Zone NP 25 (based on the absence of Sphenolithus distentus, which has its highest occurrence at the top of Zone NP 24). Dinocysts in the Ashley indicate a late Oligocene age and correlation with the Old Church Formation in Virginia. Pollen in Ashley samples is consistent with a late Oligocene age and indicates a tropical to warm-temperate terrestrial climate.

Occurrence in studied cores --

 

Chandler Bridge Formation

Upper Oligocene

Stratigraphy. -- The Chandler Bridge Formation was named by Sanders and others (1982). Its type section is at an excavation in southern Dorchester County, and the unit recently has been mapped in Dorchester County by Weems and others (1997). The basal contact of the Chandler Bridge with the underlying Ashley Formation is a burrowed, gently rolling unconformity. The Chandler Bridge is overlain unconformably by various Pleistocene units. The Chandler Bridge occurs only in isolated patches in the southern part of Dorchester County. It may be up to 10 feet thick but usually is much thinner. This formation was not mapped in the present study.

Lithology. -- The Chandler Bridge consists of fine-grained, quartz-phosphate sand and, locally at its base, silty, calcareous clay. The color ranges from greenish-gray (5GY 6/1), dark-greenish-gray (5GY 4/1), and greenish-black (5GY 2/1) to dark-yellowish-brown (10YR 4/2). The dominant clay mineral is illite/smectite with lesser amounts of illite and kaolinite.

Paleontology. -- The Chandler Bridge has yielded abundant remains of marine vertebrates. An age of middle Chattian (late Oligocene) can be inferred from the odontocete whale fauna collected from this unit (Sanders and others, 1982).

Occurrence in studied cores --

(not present in the studied cores)

 

Edisto Formation

Lower Miocene

Stratigraphy. -- The "Edisto marl" was named by Sloan (1908) for sandy, microfossiliferous limestones that occur unconformably above the Ashley or Chandler Bridge formations. The Edisto was formalized by Ward and others (1979), and its type section was placed in the Givhans Ferry bluff along the Edisto River in Dorchester County. There, the unit is only about 1 foot thick, but in the subsurface, it is known to range up to 16 feet in thickness. The Edisto Formation was not mapped in the present study.

Lithology. -- At the type section, the Edisto Formation consists of indurated, olive-gray (5Y 5/2) to greenish-gray (5GY 6/1), quartz and phosphate sandy, calcarenite (Ward and others, 1979).

Paleontology. -- The mollusk Ostrea haitiensis has been reported from the Edisto Formation (Ward and others, 1979). Edwards (1986) has discussed the dinocysts from this unit. The Edisto is early Miocene in age (Ward and others, 1979; Ward and Blackwelder, 1980; Edwards, 1986).

Occurrence in studied cores --

(not present in the studied cores)

 

Marks Head Formation

Lower Miocene

Stratigraphy. -- The "Marks Head marl" was named by Sloan (1908) for sparsely fossiliferous, phosphatic, clayey quartz sands that occur unconformably above the Ashley and Edisto formations. The Marks Head Formation was formalized by Huddlestun (1988) and its type section was placed in Marks Head Run, west of Porters Landing on the Georgia side of the Savannah River. In Dorchester County, the unit only occurs in the southern part, where it is less than 10 feet thick. It is overlain by various Pleistocene units. The Marks Head Formation was not mapped in the present study.

Lithology. -- In the Dorchester County region, the Marks Head Formation consists of clayey phosphatic quartz sand, dominantly fine-grained. The clay fraction includes abundant attapulgite. Color ranges from grayish-olive (10Y 4/2) and olive-gray (5Y 3/2) to moderate-olive-brown (5Y 4/4) (Weems and Lemon, 1996).

Paleontology. -- Locally, the Marks Head contains abundant marine vertebrate remains. Dinoflagellates have been recovered (Edwards, 1990) in the Dorchester County region, and foraminifers have been reported from farther south (Abbott and Huddlestun, 1980). These fossils indicated that the unit is of early Miocene (Burdigalian) age.

Occurrence in studied cores --

(not present in the studied cores)

 

Goose Creek Limestone

Lower Pliocene

Stratigraphy. -- The "Goose Creek phase" was named by Sloan (1908). It was formalized by Weems and others (1982) as the Goose Creek Limestone. In Dorchester County, this unit overlies the Ashley or Edisto formations unconformably and is overlain by the Penholoway Formation. Blackwelder and Ward (1979) referred the Pliocene beds in the Givhans Ferry bluff in Dorchester County to the Raysor Formation, but Weems and others (1982) demonstrated that lithologically those beds are identical to the Goose Creek and should be assigned to that unit. This bluff is the only known occurrence of the Goose Creek in Dorchester County. Its maximum thickness is about 10 ft. This Goose Creek Limestone was not mapped in the present study.

Lithology. -- The Goose Creek consists of sparsely to abundantly shelly, medium- to coarse-grained, quartzose and phosphatic calcarenite that ranges in color from pale-orange (10YR 8/2) to chalk-white. Dominant clay minerals are kaolinite and illite/smectite. The basal contact is typically marked by a lag deposit of rounded phosphate pebbles to cobbles.

Paleontology. -- The flora and fauna of the Goose Creek include calcareous nannofossils, ostracodes, mollusks, and marine vertebrates. Mollusks and vertebrates indicate a Pliocene age, and calcareous nannofossils indicate an age no younger than early Pliocene (NN 15 or older) (Weems and others, 1982).

Occurrence in studied cores --

(not present in the studied cores)

 

Unnamed unit

Pliocene

Stratigraphy. -- A unit of Pliocene age, underlying the Wicomico Formation in central Dorchester County and underlying the Waccamaw Formation in the Pregnall core, has not been certainly correlated with any named unit. It may well correlate with a unit that Sloan (1908) named the "Salkehatchie phase" for soft, glauconitic and phosphatic sands that occurred near the Salkehatchie River in southern South Carolina. Beds of similar lithology were described by Weems and others (1997) from Dorchester County and equated with the Raysor Formation of Cooke (1936), but it now seems unlikely that the "Salkehatchie phase" correlates with the Raysor. This lithology is very reminiscent of the Wabasso beds of Huddlestun (1988). This unit is up to 14 feet thick and lies unconformably on the Ashley Formation.

Lithology. -- The unnamed unit consists of fine- to medium-grained quartzose and phosphatic sand that ranges in color from medium-dark-gray (N4) to grayish-brown (5YR 3/2), dark-olive-green (5GY 2/2), or black (N1). The unit may be sparsely shelly. The basal contact commonly is marked by a thin layer of black, rounded phosphate pebbles 1-2 in. in diameter and clasts of Ashley sediment.

Paleontology. -- Nothing has been published on the paleontology of this unit, but it is known to contain abundant small bones and teeth of fish. Unpublished USGS reports indicate a Pliocene age.

Occurrence in studied cores --

 

Sunderland Formation

Upper Pliocene

Stratigraphy. -- Sunderland Formation was first used in South Carolina by Cooke (1936), and has been adopted for usage by Cooke and MacNeil (1952) and Doering (1958, 1960). The name applies to surficial deposits directly underlying land surfaces between 100 and 170 feet elevation. This unit occurs in Dorchester County only in areas lying west of Harleyville. Regional relations suggest that this unit is late Pliocene in age. It ranges from 0-30 ft in thickness. The Sunderland Formation was not mapped in the present study.

Lithology. -- Variable, including gravel and gravelly, poorly sorted, coarse-grained sands (fluvial facies), and clayey to silty sands, sandy to clayey silts, and sandy to silty clays (estuarine facies). Dominant clays are kaolinite, illite/smectite, illite, vermiculite, and gibbsite. The color is dark-gray (N3) to light-gray (N7) where fresh but often weathered to dark-yellowish-orange (10YR 6/6), moderate-reddish-brown (10R 4/6), or dark-reddish-brown (10R 3/4) mottled very-light-gray (N8). The basal contact usually marked by a coarse, gravelly lag bed of quartz and/or phosphate pebbles.

Paleontology. -- No fossils are known from the Sunderland in the Dorchester County area.

Occurrence in studied cores --

(not present in the studied cores)

 

Waccamaw Formation

Lower Pleistocene

Stratigraphy. -- The Waccamaw Formation was named by Dall (1892) and revised by subsequent authors (LeGrand and Brown, 1955; Blackwelder, 1979). Its age has been discussed by a number of workers (Swain, 1968; Blackwelder, 1979; Hazel, 1983; Gibson, 1983; Campbell, 1992). The unit underlies the Wicomico terrace of Colquhoun (1974). The aerial distribution of the unit has been indicated by Ward and others (1991). It represents a coastal complex of estuarine, lagoonal, barrier island, and shallow marine shelf deposits. Based on microfossils found in marine outliers of this unit in the Summerville quadrangle, the age of this unit is estimated to be 1.6 to 1.4 Ma. This is the age range that has been determined for the Waccamaw Formation, described from the Myrtle Beach region, so the deposits beneath the Wicomico terrace are assigned to that unit. The Waccamaw may be up to 30 feet thick and typically overlies the Ashley Formation.

Lithology. -- Variable, including gravel and gravelly, poorly sorted, coarse-grained sands (fluvial facies), fine- to coarse-grained, heavy-mineral-rich, crossbedded sands (barrier island facies), clayey to silty sands, sandy to clayey silts, and sandy to silty clays (estuarine facies), and fine- to medium-grained calcareous, shelly sands (marine shelf facies). Dominant clays are kaolinite, illite/smectite, illite, vermiculite, and gibbsite. The color is dark-gray (N3) to light-gray (N7) where fresh but often weathered to dark-yellowish-orange (10YR 6/6), moderate-reddish-brown (10R 4/6), or dark-reddish-brown (10R 3/4) mottled very-light-gray (N8). The basal contact usually is marked by a coarse, gravelly lag bed of quartz and/or phosphate pebbles.

Paleontology. -- The shallow marine shelf facies contains sparse calcareous nannofossils that suggest an early Pleistocene age.

Occurrence in studied cores --

 

Penholoway Formation

Lower Pleistocene

Stratigraphy. -- The Penholoway Formation, named by Cooke (1925) for Penholoway Creek in Wayne County, Ga., represents a coastal complex of estuarine, lagoonal, barrier island, and shallow marine shelf deposits. It underlies the Penholoway terrace of Colquhoun (1974). Based on microfossils found in marine facies of this unit in the Summerville quadrangle, the age of this unit is estimated to be between 970 and 730 ka. The Penholoway may overlie the Ashley, Chandler Bridge, Edisto, Marks Head or Goose Creek formations and may be up to 70 ft thick. The Penholoway Formation was not mapped in the present study.

Lithology. -- The lithology of the Penholoway is variable and includes fine- to medium-grained, heavy minerals-rich, crossbedded sands (barrier island facies), clayey to silty sands, sandy to clayey silts, and sandy to silty clays (estuarine facies), and fine- to medium-grained calcareous, shelly sands (marine shelf facies). Dominant clay minerals are kaolinite, illite/smectite, illite, and vermiculite in variable proportions. The color is medium-gray (N5), medium-bluish-gray (5B 5/1), or greenish-gray (5G 6/1) where fresh, but commonly weathered to dark-yellowish-orange (10YR 6/6), moderate-reddish-brown (10R 4/6), or dark-reddish-brown (10R 3/4) mottled light-gray (N7). The basal contact is usually marked by a coarse, gravelly lag bed of quartz and/or phosphate pebbles.

Paleontology. -- The basal beds of the Penholoway in the vicinity of Summerville have yielded sparse calcareous nannofossils, none of which suggest an age older than the upper part of the Quaternary Zone NN 19 (L.M. Bybell in Weems and others, 1997).

Occurrence in studied cores --

(not present in the studied cores)

 

Ladson Formation

Middle Pleistocene

Stratigraphy. -- The Ladson Formation, named by Malde (1959) for deposits near Ladson, S.C., underlies the upper Talbot terrace of Colquhoun (1974). It represents a coastal complex of estuarine, lagoonal, barrier island, and shallow marine shelf deposits. Based on normal magnetic polarities retained in backbarrier clays of this unit, and U/Th ages of corals in the next younger unit, the age of the Ladson must lie between 730 and 240 ka (Weems and others, 1997). It may be correlative with the Canepatch Formation of the Myrtle Beach area, which has yielded corals with a U/Th age of 450 ka (Cronin and others, 1981). The Ladson may be up to 40 ft in thickness and typically overlies the Ashley Formation, although occasionally it overlies the Marks Head, Edisto, or Chandler Bridge formations. The Ladson Formation was not mapped in the present study.

Lithology. -- The lithology of the Ladson Formation is variable and includes coarse-grained, poorly sorted, heavy minerals-rich, crossbedded sands (barrier island facies) and clayey to silty poorly sorted medium-grained sands, sandy to clayey silts, and sandy to silty clays (estuarine facies). Dominant clay minerals are kaolinite, illite/smectite, illite, and vermiculite in variable proportions. The color is medium-light-gray (N6), dark-yellowish-orange (10YR 6/6), moderate-reddish-brown (10R 4/6), or moderate red (5R 4/6). The basal contact usually is marked by a coarse, quartz gravel lag bed.

Paleontology. -- No stratigraphically useful microfossils have been found in this unit in the Dorchester County area. Terrestrial vertebrate remains have been found in the Summerville area.

Occurrence in studied cores --

(not present in the studied cores)

 

Ten Mile Hill beds

Middle Pleistocene

Stratigraphy. -- The Ten Mile Hill beds, informally applied by Weems and Lemon (1984) to a unit called "sands on Ten Mile Hill" by Sloan (1908), underlie the lower Talbot terrace of Colquhoun (1974). Regionally they represent a coastal complex of fluvial, estuarine, lagoonal, barrier- island, and shallow-marine shelf deposits, but in the Dorchester County area only fluvial and estuarine deposits are present. Based on U/Th ages of corals in this unit, the age of the Ten Mile Hill beds is around 240 to 200 ka (Cronin and others, 1981). The unit may be up to 40 ft in thickness and typically overlies the Ashley Formation but locally overlies the Chandler Bridge, Edisto, or Marks Head formations.

Lithology. -- The lithology of the Ten Mile Hill beds is variable and includes coarse-grained, poorly sorted, crossbedded sands (fluvial facies) and clayey, fine- to medium-grained quartz sands, sandy to clayey silts, and sandy to silty clays (estuarine facies). Dominant clay minerals are kaolinite, illite/smectite, and illite in variable proportions. The color is typically medium-light-gray (N6) or dark-yellowish-orange (10YR 6/6), but also sometimes medium-bluish-gray (5B 5/1), greenish-gray (5G 6/1), moderate-reddish-brown (10R 4/6), or moderate red (5R 4/6). The basal contact often is marked by a coarse, quartz gravel lag bed.

Paleontology. -- No stratigraphically useful microfossils have been found in this unit in the Dorchester County area. Terrestrial vertebrate remains have been found in the Summerville area.

Occurrence in studied cores --

 

Wando Formation

Upper Pleistocene

Stratigraphy. -- The Wando Formation, named by McCartan and others (1980) for outcrops near the Wando River, underlies the Pamlico and Princess Anne terraces of Colquhoun (1974). Regionally, it represents a coastal complex of fluvial, estuarine, lagoonal, barrier-island, and shallow- marine shelf deposits, but in the Dorchester County area only fluvial and estuarine deposits are present. Based on U/Th ages of corals in this unit, the age of the Wando Formation is around 130 to 70 ka (Cronin and others, 1981). The unit may be up to 30 ft in thickness. It typically overlies the Ashley Formation, but may overlie the Chandler Bridge, Edisto, or Marks Head formations.

Lithology. -- The lithology of the Wando Formation is variable and includes coarse-grained, poorly sorted, crossbedded sands (fluvial facies) and clayey, fine- to medium-grained quartz sands, sandy to clayey silts, and sandy to silty clays (estuarine facies). Dominant clay minerals are kaolinite, illite/smectite, and illite in variable proportions. Typically grayish-orange (10YR 7/4) and medium-light-gray (N6) in color, the Wando weathers to dark-yellowish-orange (10YR 6/6) and grayish-yellow (5Y 8/4). Its basal contact is often marked by a coarse, quartz gravel lag bed.

Paleontology. -- No stratigraphically useful microfossils have been found in this unit in the Dorchester County area. Numerous terrestrial vertebrate remains have been found in the Giant Cement Quarry near Harleyville (Bentley and others, 1994; Bentley and Knight, 1998).

Occurrence in studied cores --

PALEONTOLOGY NOTES

Calcareous Nannofossils

Laboratory Methods. -- For each sample, a small amount of sediment was extracted from the central portion of a core segment (freshly broken where possible). The samples were dried in a convection oven to remove residual water, and the resultant sediment was placed in vials for long-term storage in the calcareous nannofossil laboratory at the U.S. Geological Survey in Reston, Va. A small amount of sample was placed in a beaker, stirred, and settled through 2 cm of water. The first settling time was one minute to remove the coarse material; the second settling time was 10 minutes to remove finer material. Smear slides then were prepared from the remaining suspended material. Cover slips were attached to the slides using Norland Optical Adhesive (NOA-65), a clear adhesive that bonds glass to glass and cures when exposed to ultraviolet radiation. All samples were examined initially using a Zeiss Photomicroscope III. A few samples, which were determined to have the best preservation and the highest abundances of calcareous nannofossils, were later scanned using a JEOL 35 scanning electron microscope.

Table of Tertiary calcareous nannofossil datums --

Full taxonomic citations for Tertiary calcareous nannofossils used in this report --

Full taxonomic citations for Cretaceous calcareous nannofossils used in this report --

Palynomorphs

Laboratory Methods. -- Samples were treated with hydrochloric and hydrofluoric acids. Organic material was separated by using a series of soap washes and swirling. Material was stained with Bismark brown, sieved at 10 to 200 micrometers, and mounted for light microscope observation using glycerin jelly. All samples were examined for marine palynomorphs (dinocysts and acritarchs) and (or) nonmarine palynomorphs (pollen and spores). Some pollen samples were screened at >10 micrometers and <40 micrometers to concentrate the angiosperm pollen. Samples studied for dinocysts were sieved at >20 micrometers.

Full taxonomic citations for dinoflagellates used in this report --

Full taxonomic citations for pollen and spores used in this report --

Sample, Core, and Log Depths

In all but the Clubhouse Crossroads core (DOR-037), the cored or drilled depths and the log depths are, within our resolution, the same. For the Clubhouse Crossroads core, the top of the Kelly bushing, which served as the 0-point for the log depths, is approximately 5 ft above the ground level, which served as the 0-point for the core depths. Due to inherent imprecision in both logging and core-recovery, the 5-ft correction factor is only approximate. Paleontologic samples for this core are recorded in core depths, as recorded at the time of sampling. These recorded depths may be inaccurate, especially in intervals of substatial core loss. The positioning of paleontologic samples, however, should always reflect their correct relative order. In the few instances where the core-depth to log-depth correction would place a sample in the wrong lithostratigraphic unit, we have maintained the correction factor but noted the inconsistency in a footnote or remark.

DATABASE NOTES

The information provided in the stratigraphic database found in Chapter A has been collected in an ArcView project file (dorchest.apr). Although the user may prefer to assemble the data files in Chapter A to suite their particular purposes, the existing project file provides a good introduction to the potential uses and configuration of the Dorchester County database.

Three VIEWS, each containing several THEMES, are immediately presented when the project file is opened in ArcView. The BASE MAP view displays the county boundary, major roads, topography, and hydrography as well as the location of each of the six studied drill holes. The data theme that contains the drill-hole locations (cores_dor.shp) also provides detailed information about the holes themselves. This data table contains a unique identifier for each hole, a date for when the hole was drilled, the name of the agency who drilled it, depth information, the types of geophysical logging performed in each hole, and related information. The drill-hole data table may be viewed by activating (single click) the cores_dor.shp theme and then selecting the "identify tool" (letter "i" in a dark circle) on the button bar and clicking on the desired drill-hole on the map.

The second VIEW shown in the project is called FIELD LOGS. This view presents the same basemap layout seen in the BASE MAP view with the same point data showing the location of the core holes. In this view however, a hotlink option has been added to each hole. To activate the hotlink feature, the user must again select the core hole theme (cores_dor.shp) by highlighting it in the view menu. Second, the user must select the hotlink key (lightening bolt) from the button bar in the ArcView interface. The cursor will change to a lightening bolt to indicate that some features in the theme have a hotlink. Clicking on a selected drill-hole point on the map will bring up a separate VIEW containing a graphic FIELD LOG (.dxf files) for that hole. To view the FIELD LOG in more detail, choose the zoom button ("plus" sign) from the button bar in the ArcView interface and zoom into a particular section of the log. After a user has finished with a hot-linked graphic, they may dismiss the graphic by clicking on the Close Window box located at the top right hand corner of the appropriate graphic window.

The third VIEW in the Dorchester County project is called GEOSUMMARY LOGS. This view is accessed the same ay as the other views in the project. The GEOSUMMARY LOGS view looks similar and functions identically to the FIELD LOGS view with the same hotlink functions. The hot-linked graphic files for this view present summaries of lithologic and paleontologic information as well as geophysical logs for the selected drill holes.

In addition to the map-oriented VIEWS presented in the Dorchester County project file, several databases of fossil occurrences and biostratigraphic information are stored as (.dbf) files under the TABLES option in ArcView. This information may be displayed by clicking on TABLES in the dorchest.apr window displayed on the screen and then double-clicking on the desired table. These paleontology files have a column corresponding to the unique identifier of the drill holes presented in the VIEWS. A user of this system may want to link the TABLES with the corresponding drill holes to create new VIEWS. Instructions for that purpose may be found in the ArcView online help.

DISCLAIMERS

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic code.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Although all data and software released on this CD-ROM have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the functioning of the software.

TRADEMARKS

"Adobe" and "Acrobat" are trademarks of Adobe Systems Incorporated.

"ArcView" and "ARC/INFO" are registered trademarks, and "ArcExplorer" is a trademark, of Environmental Systems Research Institute.

"Windows" is a registered trademark of Microsoft Corporation.

All other trademarks are the property of their respective owners.

METADATA

Metadata for the information used in this report are contained in the text file, metadata.txt . This file is contained within the root directory of the CD.

REFERENCES

Abbott, W.H., and Huddlestun, P.F., 1980, The Miocene of South Carolina, in Frey, R.W., ed., Excursions in Southeastern Geology: American Geological Institute, Falls Church, Virginia, vol. 1, p. 208-210.

Baum, G.R., Collins, J.S., Jones, R.M., Madlinger, B.A., and Powell, R.J., 1980, Correlation of the Eocene strata of the Carolinas: South Carolina Geology, v. 24, no. 1, p. 19-27.

Bentley, C.C., and Knight, J.L., 1998, Turtles (Reptilia: Testudines) of the Ardis local fauna late Pleistocene (Rancholabrean) of South Carolina: Brimleyana, v. 25, p. 3-33.

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