ANDERSON, JOHN B., KEN C. ABDULAH, S. SARZALEJO, FERNANDO P. SIRINGAN, and MARK THOMAS, Rice University, Department of Geology and Geophysics, Houston, TX 77251

ABSTRACT: Distribution of Sandy Facies within Late Quaternary Systems Tracts of the East Texas Continental Shelf and Upper Slope

Nearly 8,000 km of high resolution seismic reflection data and several hundred sediment cores and platform borings, some with gamma-log data, comprise the data set used to examine the late Quaternary sequence stratigraphy of the east Texas continental shelf and upper slope. A primary objective of this study is to examine the distribution of sand bodies within various systems tracts for at least one full glacial/interglacial cycle.

Reincision of the Trinity/Sabine fluvial valleys resulted in significant sediment bypassing of the inner shelf and accumulation of sandy facies within the updip portion of a large shelf margin delta complex; most of the delta complex is comprised of mud. Volumetric estimates of sand eroded from the Trinity/Sabine valley during the last lowstand indicate

significant bypassing of the shelf. The Brazos River has experienced greater avulsion than the other rivers of the area and much of the sand delivered to its valleys was sequestered on the shelf. The Colorado shelf margin delta has a sandy distributary mouth bar and connects with a sandy slope fan.

Transgressive valley fill deposits of the Trinity and Sabine valleys are dominated by estuarine muds, while the Brazos and Colorado valleys are dominated by fluvial sands. During transgression, shoreface ravinement of the Trinity/Sabine valleys produced mostly muddy interfluve deposits, with the exception of scattered sand banks that are reworked coastal lithosomes. In contrast, shoreface ravinement of the sandy Brazos and Colorado river valleys resulted in the formation of large transgressive sand bodies. During high stands, the Brazos and Colorado rivers constructed fluvial dominated deltas. There are no conspicuous fluvial-dominated deltas associated with the Trinity/Sabine rivers.

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