USING CORE AND GEOPHYSICAL WELL LOGS TO REFINE CRETACEOUS SUBSURFACE STRATIGRAPHY IN THE SOUTH CAROLINA COASTAL PLAIN

Subsurface strata in the South Carolina coastal plain consists of Cretaceous-Recent terrestrial and marine deposits and serve as a critical source of groundwater for growing population centers. Previous efforts have divided these strata into first-order allostratigraphic formations; however, finer-scale changes in lithologies and depositional environments are present within the formations, but remain undocumented. We examined core and geophysical well logs in central South Carolina in order to better characterize the stratigraphy of upper Cretaceous clastic units in the region. The Campanian-age Cane Acre Formation is part of the Black Creek Group and consists of approximately 60 meters of sandstone, siltstone and claystone. The lower 45 meters contain multiple fining-upward successions that are interpreted as fluvial deposits. The upper 15 meters of the Cane Acre Formation consist of a heterolithic succession of sandstone and kaolinite-rich mudstone that record a regional marine incursion. The overlying Coachman Formation was deposited in fluvial environments and rests atop an erosive surface, which in some locations contains a basal lag of phosphatic pebbles. In sequence stratigraphic terms, we interpret the upper portion of the Cane Acre Formation as a transgressive systems tract, the unconformity as a sequence boundary, and the overlying Coachman Formation as part of a subsequent lowstand systems tract. This work demonstrates the complexity within recognized stratigraphic units in the South Carolina subsurface. These smaller-scale heterogeneities are important for understanding past depositional histories and relative sea-level changes as well as for improving next-generation groundwater models.