--> Abstract: Facies Analysis of the Brazos River Wave-Dominated Delta, by M. Hamilton and J. B. Anderson; #90987 (1993).

Datapages, Inc.Print this page

HAMILTON, MICHAEL, and JOHN B. ANDERSON, Rice University, Department of Geology Geophysics, Houston, TX

ABSTRACT: Facies Analysis of the Brazos River Wave-Dominated Delta

Numerous ancient wave-dominated deltas have been documented for the Western United States and Gulf Coast. Emphasis upon these systems in the modern record, however, is lacking. An extensive grid of vibracores, grab samples, drop cores and 3.5 kHz seismic data in and around the pre- and post-1929 depositional site of the Brazos delta are being used to examine the facies architecture of this wave-dominated delta.

Preliminary analysis of vibracores reveals a classic coarsening upward sequence. Prodelta deposits are composed of a characteristic red clay. The most seaward portions of the prodelta contain alternating beds of fluvial and marine clays, interpreted as seasonal pulses in discharge. Thickness of the prodelta ranges from 4 meters offshore of the present mouth to 1.5 meters adjacent to the western flank of the pre-1929 delta. Delta front deposits consist mainly of interfingered silt and clay and are sometimes contorted by soft sediment deformation. Occasional thicker clay beds are preserved flood deposits. The delta front is thicker and more extensive than the prodelta, ranging 3-5 meters in the modern lobe. Interfingered laminae of clay and silt decrease upward into a clean, fine sand w th ripples and cross beds. These sands represent bar deposits, and they are repetitive in the sequence as old bars were abandoned and new bars created. Coarse sands and lag deposits (storm beds) are present in minor concentrations within the bar. Bar crest deposits are approximately 1.5 meters thick. Relatively thinner packages of back-bar deposits are finer grained, representing a shallow, protected environment, and contain extensively rippled beds. Shoreface sands overlie the sequence.

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