LATE CRETACEOUS FACIES ARCHITECTURE AND SEQUENCE DEVELOPMENT IN THE SOUTH CAROLINA COASTAL PLAIN, USA

Cenomanian to Santonian facies assemblages were examined in nine cores taken from the South Carolina coastal plain and related to stratigraphic sequence development on a regional scale. Five major facies assemblages are identified: floodplain, braided stream, meandering stream, estuarine, and inner shelf. Changes in the vertical stacking pattern of these facies suggest that antecedent topography influenced the development of four stratigraphic sequences, which were identified from North Carolina and correlated to the area of interest. The Cenomanian Clubhouse II sequence is incomplete in most cores, but where present is characterized as a transgressive systems tract (TST) represented by meandering streams overlain by estuarine facies. Above the TST, estuarine facies of the early highstand systems tract (HST) grade into meandering stream and floodplain facies of the late HST. A sharp, vertical, basinward shift of facies marks the base of the Ft. Fisher sequence, which most likely corresponds to the Turonian to Coniacian Ft. Fisher I sequence in NC. At its base, the Ft. Fisher is characterized by a thick package of braided stream sediments in the south-central part of the study area, interpreted to have been deposited during a sea-level lowstand. Sediments representative of the lowstand systems tract are absent in other cores. The Ft. Fisher TST is characterized by meandering stream and floodplain facies in all cores except for the most down-dip location, where estuarine facies dominate. Thinner floodplain and thicker, progradational, meandering stream facies are present at the top of the Ft. Fisher sequence, suggesting the presence of a HST. A transgressive surface merged with a sequence boundary forms the base of the Coniacian to Santonian Pleasant Creek I sequence. Facies in the Pleasant Creek I TST range from up-dip floodplain and meandering stream to down-dip estuarine and inner shelf. The TST is overlain by finer-grained, aggradational early HST sediments that coarsen upward into a progradational late HST. Pleasant Creek I sediments are separated from the Santonian Pleasant Creek II sequence by a transgressive surface merged with a sequence boundary. Typically, inner shelf facies characterize the thin TST and HST of Pleasant Creek II in all but the most up-dip cores, where estuarine facies are present.