UPPER CRETACEOUS BIOSTRATIGRAPHY OF THE SCDNR TESTHOLE C-15, JASPER COUNTY, SOUTH CAROLINA, AND ITS CORRELATION WITH THE SUBSURFACE SECTION AT THE SAVANNAH RIVER SITE

CHRISTOPHER, R. A., christ7@mail.clemson.edu, Dept. Geological Sciences, Clemson University, 340 Brakett Hall; Clemson, SC and VAN PELT, R.S., robert.vanpelt@srs.gov, Environmental Restoration Technologies, Bechtel Savannah River Inc., Savannah River Site, Aiken, SC 29808

Sidewall cores from the Cretaceous section of the South Carolina Department of Natural Resources Testhole C-15 were examined for organic-walled microfossils in order to correlate the well with updip subsurface sections at the Savannah River Site (SRS).

Eight fossil zones were identified in the Upper Cretaceous section of the C-15 Testhole, which ranges in age from Cenomanian to Maastrichtian. Each of the six youngest zones reflect a single marine transgression, and the maximum landward extent of each transgression varies considerably; some transgressions extended further updip than the SRS, whereas others reached their maximum landward extent downdip of the SRS.

Within the Upper Cretaceous section of the C-15 Testhole, regional unconformities were identified at several horizons. Three of these unconformities have a significant impact on the litho- and hydrostratigraphy of the SRS; these unconformities occur at the Santonian-Campanian Stage boundary, at the Campanian-Maastrichtian Stage boundary, and within the lower part of the Maastrichtian. In C-15, unconformities were also identified between the Cenomanian and Coniacian Stages, and within the Santonian(?) section.

Based on the palynological investigation of the C-15 Testhole and its correlation with the subsurface section at the SRS, the following conclusions are drawn:

Lithostratigraphic nomenclature should be revised to reflect the observation that the "Middendorf" Formation as currently mapped at the SRS is chronostratigraphically equivalent to the downdip Caddin and lower Black Creek Formations of early Campanian age; stratigraphic equivalents of the downdip "Middendorf," which is Santonian in Age, are absent at the SRS, as are equivalents of the overlying Shepherd Grove Formation, also of Santonian Age.

At the SRS, movement along the Pen Branch Fault was episodic rather than continuous. During the Late Cretaceous, significantly greater movement occurred during the late early and earliest late Campanian than at other times. This period of accelerated fault movement coincides with the time of maximum Late Cretaceous marine transgression.

The hydrostratigraphic units defined as the McQueen Branch confining unit and the Crouch Branch aquifer both include significant regional unconformities as well as sediments that reflect deposition in highly varied environments. These observations suggest that attempts to characterize the hydrogeologic parameters and/or groundwater movement within these units will be minimally successful without consideration of the intra-unit lithostratigraphic relationships, ages, and depositional facies.