A NEW STRATIGRAPHIC FRAMEWORK FOR CRETACEOUS COASTAL PLAIN SEDIMENTS WITHIN THE CAPE FEAR RIVER BASIN, NORTH CAROLINA

In the 1990’s, a detailed USGS study of 30 continuously cored holes in the South Carolina Coastal Plain provided the basis for a comprehensive comparison of Cretaceous formations using pollen and calcareous nannofossil zonations. These bio- and lithostratigraphic relationships were further refined by correlation across the NC/SC state boundary to five cored holes in the North Carolina Coastal Plain. Presently, this stratigraphic framework is being used to classify exposures along the Cape Fear River from Fayetteville to Wilmington, NC, and to correlate those exposures with stratigraphic units in two core holes near Elizabethtown (BL-244) and Kure Beach (NH-C-1-2001), NC.

Detailed lithologic and biostratigraphic examination of 32 outcrops along the Cape Fear River and the two core holes has shown that the majority of the (unconformity-bounded) stratigraphic units identified in South Carolina are present in outcrops on the river and(or) in the two core holes. In summary, the unit historically identified as the Cape Fear Formation contains at least three unconformable depositional subunits, the unit historically identified as the Black Creek Formation (Group) contains at least ten unconformable depositional sequences, and the unit historically identified as the Peedee Formation contains at least three unconformable depositional sequences. These sequences, which most likely represent changing sedimentation patterns in response to sea level rise and fall, are lithologically and biostratigraphically distinct, and their bounding unconformities can be traced from corehole to outcrop. Although the lithofacies change in a downdip direction, these “sequences” remain unconformity-bounded stratigraphic units characterized by diagnostic biozones. In addition, the continuity of these formations suggests that no major faults or folds vertically offset these layers along the line of section.