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

ABSTRACT: Leveed Slope Channels and Shelf-Margin Deltas of the Late Pliocene to Middle Pleistocene Mobile River, NE Gulf of Mexico: Comparison with Sequence-Stratigraphic Models

Detailed mapping of Pleistocene stratigraphy in the DeSoto Slope regionusing exploration 2-D and 3-D seismic data and site-specific high-resolution data demonstrates relationships between shelf-margin deltas (SMD) of the ancestral Mobile River and continental-slope turbidite systems, in an area of high seismic continuity, excellent data quality, and relative minor structural complications. Post-Globoquadrina altispira, pre-Pseudoemiliana lacunosa slope deposits form a wedge which thins basinward from the shelf margin. Within this wedge are several SMD's shingled along strike, and subparallel, dip-oriented, leveed slope channels, each emanating from a canyon incised into its corresponding SMD. Levees attain maximum thickness (up to 500 ft) in the middle slope, reflecting a grade adjust ent by the channel relative to the concave profile of the pre-existing slope. At the base of slope (40 miles downdip from the shelf edge) the channels are truncated by erosion associated with the Mississippi deep-water province.

Together, each SMD, corresponding leveed channel, and laterally equivalent, thin hemipelagic drape constitute a regionally mappable seismostratigraphic unit. However, the erosional surfaces separating SMD's from their geographically associated, superjacent channel-levee systems (cf. Type 1 sequence boundaries) are not regionally mappable. A typical deltaic depocenter contains oblique clinoforms (with toplap at the upper unit-bounding surface), changing along strike to sigmoid clinoforms (with baselap on the lower unit-bounding surface). Offsetting and amalgamation of fourth-order deltaic depocenters creates a false impression (on individual dip sections) of third-order cyclicity.

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