SCALES OF CYCLICITY AND STRATIGRAPHIC CORRELATION OF UPPER CRETACEOUS STRATA IN THE NORTHEASTERN GULF OF MEXICO AREA

Third-order depositional cycles or sequences and Milankovitch-scale cycles were integrated with nannoplankton and foraminiferal biostratigraphy to assist with correlation of Upper Cretaceous strata in the northeastern Gulf of Mexico area. Three depositional sequences were identified for the Upper Cretaceous strata from seismic and well log data in the offshore Alabama and Mississippi area by defining four major sequence boundaries. These sequence boundaries were found to correlate with four major unconformities recognized in previous outcrop and subsurface studies. Two maximum flooding surfaces were identified in the lower two sequences. Upper Cretaceous strata were correlated from the outcrop areas in western and central Alabama, and north and northeastern Mississippi to areas near the mid-Cretaceous shelf break, offshore Alabama and Mississippi. Stratal correlation was constrained by the maximum flooding surfaces and sequence boundaries. Facies changes in a dip-oriented direction in these strata were determined by constructing a cross section based on well log data. Decimeter- to meter-scale chalk-marl cycles were attributed to the Earth's orbital perturbation cycles. Cycle counting on the eccentricity and long eccentricity scales, integrated with nannoplankton biostratigraphy, provided an orbital cyclostratigraphy-based chronology. A high-resolution record of temporal changes in sedimentation rate was established for the Upper Cretaceous Mooreville Chalk. Two sediment starvation surfaces were identified in the Mooreville Chalk. The lower starvation surface was found to correspond to the maximum flooding surface recognized as a downlap surface from seismic data; and the upper starvation surface was found to correspond to the maximum bathymetric surface recognized as a faunal abundance reflection point observed from outcrop data. The established integrated stratigraphic framework was used to interpret fluctuations in sea level during the Late Cretaceous and depositional environments of the Upper Cretaceous strata in the northeastern Gulf of Mexico area.