PRELIMINARY SEQUENCE STRATIGRAPHIC ANALYSIS OF TRANSITIONAL NON-MARINE - MARINE SEDIMENTS, CLUBHOUSE CROSSROADS CORE, SOUTH CAROLINA, USA

Preliminary results from sequence stratigraphic analysis of sediments taken from the Clubhouse Crossroads #1 core (Dorchester County, SC) reveal patterns that appear to match with Late Cretaceous sea-level estimates constructed for North Carolina, New Jersey and Europe. Samples were examined for calcium carbonate content and grain size distribution of the sand fraction in order to establish a sequence stratigraphic framework for the subsurface Upper Cretaceous of the South Carolina coastal plain. Of the 230 m of section studied, over 146 m is composed of non-calcareous, terrigenous materials deposited during an initial fall and then overall rise in base level from the Turonian(?) to the Coniacian. At the base of the section, oxidized and rooted muds with pervasive knobby texture and slickensides indicate paleosol development and suggest formation during forced regression. The muds are thought to have been deposited during times of reduced accommodation caused by falling sea level and represent well-developed floodplain soils with high rates of reworking. Overlying the sequence-bounding paleosol is a 61 m complex of internally cyclic, stacked, fluvially deposited sediments dominated by immature, coarse feldspathic sands and gravels. These stacked fluvial deposits are interpreted to represent the amalgamated channel fills formed during lowstand normal regression that gradually filled the incised valley formed during the preceding forced regression. Sediments near the bottom of the fluvial complex appear to have been deposited by higher energy braided stream systems, while sediments near the top of the complex are finer grained and interbedded with muddy overbank deposits, suggestive of deposition by lower energy meandering streams. Preservation of muddy overbank deposits and thinner, finer grained sands suggests a rise in base level and backstepping of sediments. A transition from non-marine to restricted marine sedimentation is marked by a marine ravinement surface comprised of poorly sorted, organic rich sand with a relatively high carbonate content and is overlain by tidally influenced, lignitic and carbonaceous flaser to lenticularly bedded, burrowed and bioturbated sands and muds of the transgressive systems tract.