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ABSTRACT: The Variety of Shelf Sand Bodies within the Transgressive Systems Tract as Illustrated by the High-Resolution Sequence Stratigraphy of Late Wisconsin/Holocene Deposits from the Continental Shelf of Texas

Louis R. Bartek, J. B. Anderson, M. A. Thomas, F. P. Siringan

An ongoing investigation of the high-resolution sequence stratigraphy of the Texas continental shelf indicates that a variety of shelf sand bodies formed during the late Wisconsinan-Holocene transgression. Episodic variations in eustasy and sediment supply have apparently caused the formation of backstepping parasequences (bayhead delta progradational units bounded by flooding surfaces) within the incised valley systems of the continental shelf. The Trinity/Sabine incised valley systems contain isolated sand bodies within the dip-aligned incised valleys whereas the Brazos/Colorado incised valley systems apparently contain broad sheetlike sand bodies. Sabine Bank is also associated with the Trinity/Sabine incised valley systems. The Sabine Bank is thought to be comprised o either reworked, overstepped shoreline sands or sand that was mined from the incised valley system and reworked into a strike-aligned sand body as the shoreface migrated across the shelf during the transgression.

Transgressed wave-dominated deltas are another important type of shelf sand body in the transgressive systems tract of the Texas continental shelf. Sediment texture maps and high-resolution seismic data suggest that strike-aligned sand bodies lying offshore of the modern Brazos delta are modified remnants of ancestral Brazos and Colorado river deltas. These delta deposits may have been isolated on the shelf during intervals when eustatic rise was more rapid. Seismic data indicate that the upper part of these deltaic deposits was reworked into strike-aligned shelf sand bodies whereas the lower portion was preserved in place.

The relative significance of storms in both sourcing and altering shelf sand bodies in this setting is still being addressed. Two hurricanes struck the study area during the past summer and post-storm surveys were conducted. These results indicate little or no significant sand transport onto the shelf during these low-magnitude storms and no measurable influence on Sabine Bank.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990