DEPOSITIONAL SEQUENCE STRATIGRAPHY OF CENOMANIAN TO SANTONIAN SEDIMENTS, CAPE FEAR ARCH, NORTH CAROLINA COASTAL PLAIN

Sequence stratigraphic analysis of Late Cretaceous age depositional sequences provide an improved understanding of the effects of changing sea level on coastal regions of North Carolina.

For this study, sediments from two cores from the Coastal Plain of North Carolina, the Kure Beach core (New Hanover County) and the Elizabethtown core (Bladen County), were analyzed to identify Cenomanian through Santonian depositional sequences, and to correlate them to regional patterns of coastal onlap. Sequences were identified using visual descriptions of the lithology, grain-size analysis, and patterns of geophysical well-log response. Sequence ages were determined through biostratigraphic and ⁸⁷Sr/⁸⁶Sr isotopic analyses. Integration of these data was essential to developing a sequence stratigraphic framework for the North Carolina Coastal Plain that can be correlated to other sites on the eastern seaboard.

A total of five depositional sequences were identified in this Cenomanian to Santonian interval from the two cores. The oldest sequence, Clubhouse II, is Cenomanian in age and represents deposition in a subtropical environment proximal to shore and includes the transgressive systems tract (TST) that grades into a highstand systems tract (HST). The overlying Fort Fisher I sequence is Turonian and represents decelerating base level rise and progradation of the shoreline; it contains a HST. The Clubhouse II and the Fort Fisher I sequences are only present in the Kure Beach core; in the Elizabethtown core basement was encountered but the Clubhouse II and the Fort Fisher I sequences were missing. The Fort Fisher I sequence is overlain by the Fort Fisher II sequence, which is Turonian to Coniacian in age. It has a thin basal TST in the Kure Beach core and a thicker, highstand derived package in both the Kure Beach and Elizabethtown cores. By the late Coniacian to Santonian, a rise in regional sea level resulted in fully marine conditions at both of these sites. The overlying Pleasant Creek I and Pleasant Creek II sequences are thick, and represent two distinct periods of sea level rise and fall in an outer to middle neritic environment. Both the Pleasant Creek I and Pleasant Creek II sequences contain a TST and HST. The Pleasant Creek II in the Elizabethtown core is the only sequence to have a Shelf Margin Systems Tract (SMST) preserved.