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OUTLINE OF STRATIGRAPHY AT THE SAVANNAH RIVER SITE
Baum, 1982; Dockery and Nystrom, 1991; Harris and Zullo,
1991) in central eastern South Carolina.
Environment
The environment of deposition was probably mostly
inner to middle neritic.
“Blue Bluff” unit
Lithology and stratigraphic terminology Calcareous
strata occur for many miles along the Savannah River valley
in the same stratigraphic position as the Santee Limestone
but with sufficient areal extent, thickness, and distinctiveness
in lithology to warrant recognition as a separate unit. Huddlestun
and Hetrick (1986, p. 4) informally used “Blue Bluff
member of the Lisbon Formation”. The unit is a cliff-former
and is exposed at several bluffs one the Georgia side of the
Savannah opposite SRS (see Veatch and Stephenson, 1911,
p. 249-250). The “Blue Bluff” is gray and pale green, clayey,
laminated calcilutite, calcarenite, and calcareous silts and
clays, with shell layers, indurated nodules, thin indurated
limestone lenses, calcareous muds, and quartz sand laminae
in places. Brantley (1916, p. 54) reported an analysis from
the exposure at Blue Bluff with a carbonate content of 56%.
Much of the sediment form SRS cores has more than 75%
(Paul Thayer, personal communication). Thin, phosphatic
crust in SRS well P 21TA suggests that the basal contact is
unconformable. On geophysical logs, the “Blue Bluff” is
characterized by having high gamma ray counts and low
resistivities compared to sediments above and below.
“Blue Bluff” sediments are widespread in the southern
part of the Savannah River Site. They interfinger and are gradational
with the cream-colored Santee facies, and, in general,
tend to be more common in the lower part of the
calcareous section than the lighter-colored carbonates. The
“Blue Bluff” lithology appears to extend as thin beds as far
northwest as McBean, Georgia, judging from the subsurface
descriptions of McLelland (1987); it extends to the southeast
at least as far as the deep wells near Barnwell and Allendale,
South Carolina. The “Blue Bluff” is about 90 ft thick at the
southeastern boundary of SRS.
The “Blue Bluff” has been assigned to the “McBean
Formation” or Santee Limestone by most workers in the
area. Colquhoun and others (1983), Steele (1985), McClelland
(1987), and Logan and Euler (1989) used the terms
“Santee” downdip and “McBean” updip for carbonates
within the study area. The “Blue Bluff” may be part of the
E4 unit of Prowell and others (1985a); most is unit E5.
Paleontology, age, and correlation
The benthic foraminiferal species Cibicides westi
appears to be a marker for the Santee and “Blue Bluff” in
this area (Huddlestun and Hetrick, 1986, p. 15). Cubitostrea
sellaeformis and Pteropsella lapidosa, characteristic of the
upper Lisbon, occur in the “Blue Bluff” with numerous other
molluscan taxa. Calcareous nannoplankton, palynomorphs,
and other taxa indicate an approximate zone NP 16 age
assignment (late Lutetian, middle Claibornian).
Environment
Sediments and fossils in the “Blue Bluff” suggest a
lower energy environment than that of the Santee.
Tinker Creek Formation—A New Formation
Lithology and stratigraphic terminology
The Tinker Creek consists of quartz sands, silts, and
clays which, in general, occur updip form the Santee. The
type section is described in the appendix from core from well
MWD-5A in northwestern Barnwell County, South Carolina.
In general, the sands of Tinker Creek are finer than the sands
above and below, contain more heavy minerals, and are more
likely to contain glauconite, although glauconite is often
found in the Warley Hill. Yellow, tan, and white sands are
common, and pale green sands occur in the center of SRS.
Clay beds and laminae are underlying and overlying units.
The clays of the Tinker Creek tend to be illite/smectite rather
than kaolinitic as in other parts of the section (Dennehy and
others, 1989). Tan clays are more prominent in the overlying
Dry Branch Formation while green clays are common in the
Tinker Creek. Silica cemented zones occur in many places.
Burrows of the Ophiomorpha type are abundant in some outcrops
of the Tinker Creek. Most burrows are less than 1 inch
in diameter and have thin walls of white clay. Although very
fine and fine sands are typical of some of the Tinker Creek,
medium and coarse sands are common in SRS wells, especially
updip. The fine sand facies can also be found many
miles updip. An exposure of very fine, well-sorted, burrowed
sand on Good Hope Farms Road in Aiken County, about 0.9
mi west of Silver Bluff Road (South Carolina Highway 302),
appears to be the Tinker Creek. A similar exposure is in a
borrow pit-landfill on the north side of Herndon Dairy Road,
about 1.3 mi west of Silver Bluff Road. The fine, wellsorted,
burrowed sand here is topped by massive clay. These
sediments were assigned to the “Huber Formation” by
Nystrom and others (1982, p. 121).
The clay between 187 and 190 ft in the type section is
part of the “green clay interval” (Dennehy and others, 1989;
Snipes and others, 1992), a series of clay beds and clayey
sands ranging for the upper part of the Congaree Formation
through the lower part of the Tinker Creek. A fossiliferous
section of the Tinker Creek “green clay” several feet thick is
exposed in a road cut on the east side of Upper Three Runs
were SRS road 2-1 crosses the creek. Molluscan molds,
including Pteropsella lapidosa, occur here. Outcrops of green
caly, green clayey sand, and the fine, well-sorted, burrowed
sand facies occur in northwesterly-flowing tributaries to
Upper Three Runs at SRS. In a few cored wells near the center
of SRS, part of Tinker Creek consists of light tan to buff,
low density silt.
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