The Response of Low to Moderate Sediment Supply Incised Valley Systems to Episodic Sea-Level Rises

THOMAS, M. A., J. B. ANDERSON, and F. P. SIRINGAN, Rice University, Houston, TX

Low to moderate sediment supply incised valley systems (e.g., the Trinity, Sabine, and Lavaca rivers) are characterized by mud-dominated estuarine fill and by sedimentation that is limited to the valley cut during low sea level. In contrast, within the high sediment supply Brazos valley system substantial sedimentation has occurred between the lowstand valleys for at least the last 7000 years.

Within the Trinity/Sabine incised valley system, sand prone facies include fluvial and tidal inlet deposits. Fluvial deposits are relatively uniform in thickness and distribution, while tidal inlets form discontinuous and pod-like deposits. The valley-fill stratigraphy consists of transgressive parasequences, whose bounding flooding surfaces can be mapped with core and high resolution seismic data. Each parasequence is represented by paired upper bay marsh/bayhead delta and tidal inlet/flood tidal delta facies. Coeval shoreline facies are reworked during the sea-level rise that terminates a particular parasequence. Over 200 sediment cores from the study area are used to define the shapes of these sand bodies, and to establish their origin based on grain sizes, sedimentary structures, nd faunal assemblages.

The stratigraphy interpreted from these low to moderate sediment supply incised valley systems imply sea level rose episodically during the last transgression. Rapid sea-level rises are responsible for development of isolated shelf sand deposits and may correlate to stream piracy events in the nearby Brazos system.

Ongoing investigations concentrate on the distal portions of the incised valleys where they become the feeders to shelf margin deposits within the lowstand systems tract.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)