TRANSGRESSIVE SYSTEMS TRACT
The most recent transgression, between oxygen isotope stages 2 and 1 (18,000 yr BP to present), resulted in widely variable shelf deposits. Sea level during this period rose from the shelf edge (approximately 120 m) to its present level. Over 20,000 km of high resolution seismic reflection data, hundreds of platform boring descriptions, and sediment cores were used to document the different transgressive deposits on the northern Gulf of Mexico shelf, from west Florida to south Texas.
Analysis of seismic data, sediment core descriptions, and paleogeographic maps indicate that no single stratigraphic model correctly predicts transgressive sedimentary facies. The high sediment supply Rio Grande and Western Louisiana deltas continued to prograde during the initial transgression despite increased accommodation. However, deltas with lower sediment supplies responded almost immediately to the transgression and began backstepping across the shelf and filling their valleys. In interdeltaic areas, transgressive muds were deposited, the thickness of which varies widely across the shelf. Scattered sand banks, representing partially reworked paleoshoreline deposits, exist along the Trinity-Sabine incised valley. Other transgressive deposits include sand ridges, fluvial-braid systems, and reefs.
Along-strike differences in transgressive deposits are readily seen throughout the area. Sediment supply and composition (bedload versus suspended load), as well as relict shelf topography appear to be the main factors controlling the distribution and characteristics of potential reservoirs in the northern Gulf of Mexico.
Paleogeographic map of transgressive depositional environments in the Gulf of Mexico