Seismic and Sequence Stratigraphy of Upper Cretaceous Strata, Offshore Alabama and Mississippi Area

Kaiyu Liu
The Department of Geological Sciences, the University of Alabama, Tuscaloosa, AL

Upper Cretaceous (Cenomanian to Maastrichtian) strata in the offshore Alabama and Mississippi area consist of a thick section of siliciclastic and carbonate sediments of about 1000 meters. These sediments were deposited on a broad shelf where eustasy had significant impacts on sedimentation patterns. An integrated seismic and sequence stratigraphic approach improves the understanding of Late Cretaceous paleoenvironments, sea level fluctuations and depositional patterns.

202 lines of high quality, two dimensional, multi-channel seismic reflection data, approximately 3,500 kilometers in total length, were studied in order to decipher the geometry and architecture of Upper Cretaceous strata in the study area. The stratal patterns as interpreted from seismic reflector configurations are distinct for different positions on the continental shelf. Four major sequence boundaries and two maximum flooding surfaces were interpreted from these seismic configurations and traced across the shelf. The four sequence boundaries correspond to major regional unconformities as recognized from outcrop and core studies. These include a mid-Cenomanian unconformity, a Turonian-Coniacian unconformity, a Campanian-Maastrichtian unconformity, and a Maastrichtian-Paleocene unconformity and two maximum flooding surfaces that correspond to the Marine Tuscaloosa Shale and middle Mooreville Chalk intervals.

Well log data were integrated with the seismic data through the use of synthetic seismograms and check shot surveys. This established an integrated seismic and sequence stratigraphic framework. Facies architecture from the middle shelf to outer shelf areas was interpreted from seismic facies analysis and well log correlations.

AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004