Print this pageTime Equivalent Fluvial-Deltaic and Coastal Lithosomes of the Late Holocene Transgression on the East Texas Continental Shelf
RODRIGUEZ, ANTONIO B., JOHN B. ANDERSON, and JENNIFER N. SNOW
An ongoing detailed lithofacies analysis of transgressive sands on the east Texas shelf is aimed at understanding the factors that control along-strike differences in sand body character. From Sabine River to Matagorda Island, 3000 km of seismic data and 300 sediment cores were collected to address this problem. In the eastern study area the sand bodies located below the ravinement surface are mainly coastal lithosomes situated within the Trinity/Sabine incised fluvial valley. Their preservation is attributed in large part to high subsidence rates (0.62 cm/y over the valley, 0.01 cm/y in the interfluve) within the valley caused by dewatering and sediment compaction. They are strongly strike-aligned, disconnected and comprised of three discrete facies: 1) an interbedded sand and clay facies, 2) a muddy sand facies, and 3) a shelly sand facies. In the central study area there are no sand bodies within the transgressive systems tract. Thin Holocene marine muds lie directly on Pleistocene deposits. The western study area is characterized by fluvial channels beneath the ravinement surface capped by Holocene marine muds. Individual channels are filled with large scale cross-stratified sand. The channels are extensive on the mid-shelf and in places coalesce to form fluvial-deltaic sheet sands that are a minimum of 500 km{2} in area and are disoriented.
Remarkably little sand is preserved on the shelf above the transgressive ravinement surface in any of the three areas. The only exceptions are storm re-worked sand capping the banks. There are no other storm beds in the area. Even the distributary channels and deltas formed at the mouths of valleys occupied during the late Holocene-Recent have been reworked by shoreface ravinement.