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CAROLINA GEOLOGICAL SOCIETY
Guidebook for 1992 Annual Meeting
Pages 59-62
NANNOFOSSIL BIOSTRATIGRAPHY AND SEQUENCE STRATIGRAPHY OF MIDDLE TO UPPER EOCENE
STRATA IN THE SOUTHWESTERN SAVANNAH RIVER SITE AND ADJACENT AREAS OF GEORGIA
Richard A. Laws, W. Burleigh Harris and Victor A. Zullo
Department of Earth Science
University of North Carolina at Wilmington
Wilmington, N.C. 28403
INTRODUCTION
Core VSC-4 (Figure 1, 2) contains a relatively complete
middle to upper Eocene stratigraphic section typical of the
southwestern Savannah River Site and adjacent areas of
Georgia. The core is at an elevation of 156.7 feet; and penetrates
a Cenozoic section of almost 500 feet; the Cretaceous
Tertiary boundary is placed at a depth of 494.6 feet. Paleogene
stratigraphic units recognized in the core include the
Paleocene Ellenton Formation, an upper Paleocene/lower
Eocene Un-named unit, the middle Eocene Congaree Formation,
Warley Hill () Formation and Blue Bluff Marl, and
the upper Eocene Utley Limestone Member of the Clinchfield
Formation, the Griffins Landing Member of the Dry
Branch Formation and undifferentiated Barnwell Group
sands. We will focus our attention on the middle to upper
Eocene section which extends from the surface to a depth of
325 feet at the base of the Congaree Formation (see Figure
2).
Figure 1. Location of cores and outcrops.
Lithostratigraphy
The Congaree Formation extends from 325 to 236 feet
depth and comprises clean, coarse, pebbly, Fe-stained quartz
sand with occasional kaolin lithoclasts at the base grading
upward into fine to medium clean quartz sand with occasional
thin gray to green clay beds. The contact with the
underlying intensely weathered kaolinite of the un-named
unit is sharp, is characterized by local concentrations of
reworked coarse sediments, and represents a regional unconformity.
From 236 to 218.6 feet depth interbedded calcareous
sand and sandy molluscan-mold grainstone may
correlate to the Warley Hill Formation. The contact with the
underlying Congaree is subtle and is marked by a change in
sand size and the addition of calcareous material. The Blue
Bluff Marl extends from 218.6 to 136 feet depth and consists
of impure micrite or argillaceous, silty to sandy micrite
becoming clayey at the top. The contact with the underlying
Warley Hill Formation is picked where sand suddenly
decreases in quantity and size; it represents a regional unconformity.
The Utley Limestone in 21 feet thick in the core and
comprises a sandy, molluscan-mold biosparudite. Thin interbeds
of calcareous quartz sand are present in the Utley. The
contact with the underlying Blue Bluff Marl is quite distinct
and represent a major regional unconformity that is mapped
over the area. The Griffins Landing Member extends from 45
to 115 feet depth and consists of sandy calcareous and kaolinitic
clays containing large Crassostrea. The contact with the
underlying Utley Limestone is sharp and represents a
regional unconformity. We assign the remainder of the core
from the top of the Griffins Landing at 45 feet to the surface
to undifferentiated Barnwell Group sands and clays (see Figure
2).
Biostratigraphy
Poorly to well preserved calcareous nannofossils occur
in the interval from 76 to 256 feet depth, (i.e. mid Congaree
Formation through mid Griffins Landing Member). Preservation
is best in the Blue Marl and Griffins Landing Member
which includes the Middle-Upper Eocene boundary. Table 1
presents a list of calcareous nannofossil species recorded
from the lithic units included in this study. That list was compiled
from examination of samples from cores VSC-3,
VSC4, VG-7, and VG-8. Figure 2 shows the occurrence of
selected age-diagnostic nannofossils in VSC-4. Range of
calcareous nannofossils for the purpose of correlation are
taken from Perch-Nielsen (1985). “NP” zones refer to the
zonation of Martini (1971) as described in Perch-Nielsen
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