WINKER, CHARLES D., Shell Development Company, Houston, TX

ABSTRACT: Pleistocene "Lowstand" Deposits of the Mississippi, Mobile, and Trinity Rivers: Models for Turbidite Sedimentation in the Gulf of Mexico

Selected Pleistocene "lowstand" depositional systems associated with three Gulf Coast rivers illustrate considerable variability among turbidite systems and their relationships to shelf-margin deltaic depocenters (SMD). Early/middle Pleistocene lowstand systems of the Mobile are characterized by leveed slope channels, each fed by a canyon incised into a corresponding SMD. In contrast, the latest Pleistocene ("Wisconsinan") Trinity system lacks a mappable feeder canyon at the shelf margin. The progradational SMD and salt-ponded intraslope fan system are linked by an upper-slope chaotic zone; the fan and delta are essentially coeval, within limits of seismostratigraphic resolution.

Lowstand depositional systems of the late Pleistocene Mississippi are much larger and more complex. The approximately Wisconsinan-age lowstand system includes (1) a large SMD extending from South Pass area to South Timbalier area; (2) ponded (low-relief) slope turbidites essentially coeval with the SMD; and (3) three canyons incised into the SMD and slope, which fed fanlobes of the Mississippi Fan (units 14-17 of Weimer, 1989). An older (pre-Wisconsinan, post-Pseudoemiliana lacunosa) lowstand system comprises (1) a large SMD in NW Garden Banks area; (2) ponded (high-relief) slope fans and chaotic zones indistinguishable in age from the SMD; and (3) canyons incised into the SMD and slope, which fed the Bryant and Alaminos fans south of the Sigsbee Escarpment.

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