A 2,700-km high-resolution seismic-reflection data set, acquired in recent years, has helped resolve some old problems concerning the age of Quaternary formations along the east Texas coast, and has resulted in mapping of the Trinity/Sabine incised valley. The seismic data were used in conjunction with oil company platform borings and recently acquired sediment cores to examine the stratigraphy of the incised-valley fill and to map the distribution of sand bodies on the shelf.

The Trinity/Sabine valley has experienced at least two episodes of incision and infilling. The earliest incision occurred during δ¹⁸0 substage 5d and the latest reincision occurred during δ¹⁸0 stage 2. The late Wisconsinan-Holocene transgressive deposits that now fill the valley include the following facies (from bottom to top): fluvial; upper estuary/bayhead delta; middle estuary; lower estuary/tidal inlet/tidal delta; and offshore marine deposits. Backstepping parasequences, indicating an episodic rise in sea level, characterize the valley fill.

Sandbody formation and preservation on the shelf also has been influenced strongly by the episodic nature of the late Wisconsinan-Holocene sea-level rise. Sabine Bank, the largest of the sand bodies and the only one studied in detail, is a reworked coastal lithosome that rests on the ravinement surface. Inner-shelf muds contain few discrete storm beds. Relatively thick (<75 cm) amalgamated storm deposits are restricted to sand banks and the incised valley.

The modern Sabine Lake and Galveston Bay estuaries formed initially by flooding of the Sabine and Trinity valleys approximately 8 ka. The subsequent flooding event, which inundated the broad, shallow meander portions of the valleys, occurred approximately 4 ka and appears to have been rapid.

Extant coastal systems of the study area incorporate a wide range of environments, including barriers, strandplains, chenier plains, and tidal inlets. The systems formed predominantly during the stillstand of the past 3,500 years. Galveston Island and Bolivar Peninsula were derived from offshore sand sources. Progradation of the coastal barriers ceased with the exhaustion of the sand supply.