SEDIMENTARY FACIES AND GENESIS OF
HOLOCENE SAND BANKS ON THE EAST TEXAS INNER
CONTINENTAL SHELF
ANTONIO B. RODRIGUEZ AND JOHN B. ANDERSON
Department of Geology and Geophysics, Rice University, Houston, TX 77005,
USA FERNANDO P. SIRINGAN
University of the Philippines, Quezon City, Philippines
MARCO TAVIANI
Istituto per la Geologia Marina, Via Zamboni 65, 40127 Bologna,
Italy

ABSTRACT: Sediment cores and high-resolution seismic and side scan sonar data were collected from four shelf banks on the east Texas inner continental shelf. Sabine, Heald, Shepard, and Thomas banks all have similar sediment facies, structure, and genesis. The banks are comprised of three facies (top to bottom): A) an interbedded shell hash and sand unit; B) a muddy-sand unit characterized by a seaward-prograding and chaotic seismic facies, and C) an interbedded sand and mud unit characterized by landward-dipping seismic reflectors. These three sediment facies represent amalgamated storm beds, lower-shoreface or ebb-tidal delta, and back-barrier/flood-tidal delta environments respectively. Facies B and C were deposited during a time of relatively slow sea level rise and were stranded on the shelf during a rapid sea level rise. Facies A is the result of storms and wind-driven currents reworking the paleoshoreline deposits on the shelf. The banks are drowned paleo-shorelines restricted to the area above and immediately adjacent to the Trinity and Sabine incised fluvial valleys. This association is explained by the greater thickness of sands within the valleys (larger sources of sands), greater accommodation space, and greater subsidence rate within the valleys (greater preservation potential).

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