PRELIMINARY SEQUENCE STRATIGRAPHY OF UPPER CRETACEOUS SEDIMENTS IN THE SOUTHEASTERN NORTH CAROLINA COASTAL PLAIN

Eleven stratigraphic sequences, identified using facies analysis, process sedimentology, biostratigraphy, and strontium-isotope stratigraphy, are recognized from five cores (Kure Beach, Elizabethtown, Dixon, Smith, and Hope Plantation) located in the NC Coastal Plain. The sequences are middle Cenomanian through late Maastrichtian in age and record sea-level changes and possible tectonic activity.

Middle to upper Cenomanian marine sediments constitute two sequences (designated as Clubhouse Crossroads I and Clubhouse Crossroads II) and represent two of the highest sea levels documented during the early Late Cretaceous in NC. The lower Coniacian Fort Fisher Sequence, a thin (19.5 m) package of marine sediments interpreted as a highstand systems tract (HST), is present only in the downdip Kure Beach core. It is the only lower Coniacian unit known in North Carolina south of Cape Hatteras.

The marine transgressive systems tract (TST) and early HST of the upper Coniacian to Santonian Pleasant Creek I Sequence is identified in four cores from NC. These marine sediments are overlain in the updip cores by a relatively thick non-marine package representing a possible prograding shoreline of the late HST. A gradual rise in sea level is suggested by the return to more marine conditions in downdip cores during deposition of the upper Santonian Pleasant Creek II Sequence. In the updip Hope Plantation core, only nonmarine sediments are present. The transition of fluvial to marine sediments is not fully understood and requires additional analysis.

By the early Campanian, marginal (updip) to fully marine (downdip) conditions, represented by the Tarheel I Sequence, existed at all core sites. Relatively minor fluctuations in sea level throughout the Campanian resulted in the erosion of sediment in the updip cores. As a result, the Tarheel II, Donoho Creek I, and Donoho Creek II Sequences are missing from the Hope Plantation core, and the Donoho Creek II Sequence is missing from the Smith and Elizabethtown cores.

Normal regression during the Maastrichtian is represented by thick offlapping HST sediments of the lower to upper Maastrichtian Peedee I and Peedee II Sequences in the downdip Kure Beach and Dixon cores, and by a thin TST (6.7 m) unit in the updip Smith core. The upper Maastrichtian Peedee II Sequence is missing from all updip cores.