ABSTRACT: Late Quaternary Shelf-Margin Sequences and Systems Tracts, Offshore Louisiana

LIN, FENG-CHIH, ANTHONY R. GILBY, and JOHN R. SUTER, Exxon Production Research Company, Houston, TX

The boundaries, geometries, and stacking patterns of depositional sequences and systems tracts were analyzed using high-resolution seismic data in a shelf-margin setting to the east of the present-day Mississippi Delta. Many of the shelf-margin deposits constitute progradationally stacked deltas. Five unconformity-bounded depositional sequences can be resolved. Systems tracts within each sequence, separated by transgressive and maximum flooding (downlap) surfaces, are recognized on the basis of stacking patterns. At the base of each sequence lies an aggradational lowstand wedge systems tract, which onlaps the shelf margin of the underlying sequence except where these sediments extend onto the shelf in incised valleys. The transgressive systems tract is generally thin and extends from lope to shelf.

Eustatic fluctuations are a primary control on the origin and development of these deposits. Oxygen isotope stages are recognized in nearby cores and can be correlated with the seismically determined sequences and systems tracts. The transgressive systems tracts appear to correlate with odd-number, high-sea-level stages and are associated with shoreline transgression and a rising sea level. In contrast, the lowstand systems tracts correspond to even-number, low-sea-level stages. The lowstand systems tract of the youngest sequence is stage 2 in age, and the overlying transgressive systems tract corresponds to stage 1. This in turn is overlain by the current Mississippi Delta complex, which is the start of a highstand systems tract.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)