SULLIVAN, NEIL M., GREG L. WHITTLE, and CHRISTOPHER G. ST. C. KENDALL, Department of Geological Sciences, The University of South Carolina, Columbia, SC; ALLEN LOWRIE, Consultant, Picayne, MS; ROBERT L. CANNON, Department of Computer Sciences, The University of South Carolina, Columbia, SC; PHILIP MOORE, Department of Geological Sciences, The University of South Carolina, Columbia, SC; and DOUGLAS R. HELLMANN and KEITH SPAINHOUR, Department of Computer Sciences, The University of South Carolina, Columbia, SC

ABSTRACT: Variations Explained Between the Sequence Stratigraphy of East and West Offshore Louisiana Using a Sedimentary Simulation

Sedimentation, subsidence, and sea level oscillation are the three major interrelated quantifiable processes controlling the geologic evolution of a passive continental margin. A forward modeling of simulated sedimentary fill (SEDPAK) was used to analyze the rates of these three processes at different portions of the Louisiana shelfbreak, starting from specified initial conditions dictated by seismic interpretation. Iterative modeling allowed the effects of these processes to be calculated until the simulations matched the original data.

Geologic differences between eastern and western offshore Louisiana (Mississippi Canyon Lease Area versus Garden Banks/Green Canyon Lease Areas) can be seen in the seismic stratigraphy and paleo-physiography of the outer shelf/upper slope. In the Mississippi Canyon Area, the shelfbreak retreated 6 miles (11 km) from 10.0 to 8.2 Mybp, then advanced 55 miles (100 km) from 8.2 to 2.8 Mybp, followed by a retreat of 30 miles (54 km). In contrast, in the western Louisiana offshore the shelfbreak prograded 100 miles (185 km)during the last 6.7 Mybp. These stratigraphic differences were dated and the ecological determination of "shelfbreak" was defined by foraminiferal analyses of well cuttings. Variations between eastern and western offshore Louisiana modeled include: lithologies, rates of d position and subsidence, sealevel oscillations, tectonic motions, salt movements, and compaction effects. The simulations show that sediment supply and tectonic accomodation can control the position of the basin margin independent of sea level variation. This approach fosters the testing of reasonable solutions to a non-unique answer.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.