Sedimentary facies and evolution of Late Pleistocene to recent coastal lithosomes on the east Texas shelf
Rodriguez, Antonio Beyra
Anderson, John B.
Doctor of Philosophy
Examination of Late Pleistocene to recent coastal lithosomes on the east Texas continental shelf can help refine current models aimed at understanding how coastal environments respond to a variety of forcing mechanisms including changes in subsidence rate, sediment supply (climate), and eustasy. High-resolution seismic data, sediment cores, paleontologic data, and radiocarbon ages were examined from bay complexes (fluvial, bay-head delta, middle bay, tidal delta, and barrier shoreline environments), offshore banks, incised valleys, and the Brazos Delta. Within the study area, preservation of these deposits on the shelf has been variable. Coastal lithosomes had a high preservation potential in the eastern portion of the study area (around the Trinity/Sabine incised valley) and a low preservation potential in the western portion of the study area (offshore of Follets Island and the Brazos Delta). Sabine, Heald, Shepard, and Thomas banks, located above and adjacent to the Trinity and Sabine incised fluvial valleys, represent submerged barrier shorelines. The shoreline submergence events have been correlated with flooding surfaces located within the Trinity incised valley. Maps of the paleoenvironments bound by these flooding surfaces indicate that each paleoshoreline submergence event is associated with estuarine environments being shifted tens of kilometers landward. Rising sea level during the Holocene was the forcing mechanism behind these events. Freeport Rocks Bathymetric High, a bank located further to the west, also represents a submerged barrier shoreline. However, this feature was not emplaced during the Holocene transgression; rather, it was deposited during the middle Wisconsin (oxygen isotope stage 3) sea-level highstand. The shoreline associated with the bank was mapped regionally at -15 m +/- 2 m. This suggests sea level was around 15--30 m shallower than what oxygen isotope and coral records indicate for stage 3. A detailed sedimentary and geomorphologic study was undertaken on the Brazos Delta, Texas to better define the facies architecture and controlling processes on wave-dominated delta evolution. The Brazos Delta is primarily composed of fine-grained sediments; prodelta clay composes more than half of the sediment volume. The facies architecture is not representative of the classic strandplain model for wave-dominated deltas due to the strong influence of floods on deltaic evolution.
Geology; Physical oceanography; Paleoecology