AN OVERVIEW OF THE STRUCTURAL EVOLUTION OF THE GULF COAST REGION OF TEXAS AND LOUISIANA

The Gulf Coast Plain (GCP) of Texas and Louisiana is a Jurassic rifted margin covered by a thick sedimentary sequence. Over the northern Gulf of Mexico ocean-to-continent transition (OCT), a broad and thick sedimentary succession has built upward and seaward which creates uncertainty about the nature and location of the transition from craton to extended continental crust to oceanic crust in this region. Our lack of understanding about the deep structure of the GCP is particularly striking since the sedimentary package there is likely the most intensely geologically investigated regions in the USA. Key constraints in attempts to understand the deeper structures are deep seismic refraction and broad-band seismic investigations that indicate the upper crust beneath the GCP is thin (10-15 km). Thus, the crustal-scale structure has been interpreted to be attenuated continental crust caused by rifting in either the early Mesozoic or the early Paleozoic or both. In addition, the integration of a regional seismic refraction profile along the Texas-Louisiana border integrated with gravity and offshore refraction profiles indicates the presence of an upper mantle low velocity anomaly that is consistent with a depleted mantle or a rift pillow.

Since structures due to Paleozoic and Mesozoic tectonic events are a key understand the evolution of the GCP, we have undertaken an integrated analysis of geological and geophysical data aimed at understanding the tectonic evolution of the region. Our analysis is focused on understanding two proposed models of the crustal structure from the craton, as exposed in the Llano uplift, across the buried Ouachita system that covers the rifted Eocambrian margin, across the coastal plain where thin crystalline crust has been documented, to the Gulf of Mexico. Both models are based gravity data, drilling results, and available deep seismic data modeling results. One model is also constrained by magnetic data as linear magnetic high follows the coast of Texas and is offset from the parallel gravity high that lies approximately 50 km offshore. This model suggests that the continental margin in this area may be a volcanic margin.