Mesozoic plate reconstruction, salt tectonics, and hydrocarbon potential of the western Gulf of Mexico basin



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This dissertation integrates the basement-to-recent structure, salt tectonics, and hydrocarbon prospectivity of the deepwater area of the northwestern US Gulf of Mexico in the offshore area of Texas. All three chapters seek to answer the same question: why does this 30,000 km2 area of the northwestern shelf and slope of the GOM basin form a petroleum-poor “desert” surrounded by hydrocarbon-rich areas on both shelf-slope margins and in deepwater are sourced by world-class Jurassic source rocks? This dissertation presents three integrated studies of the plate tectonic history, salt tectonics, and hydrocarbon potential of the Gulf of Mexico basin with two of the studies focused on the northwestern part of the basin in the US maritime sector. The first chapter summarizes my background and how and this dissertation and how the study evolved. The second chapter reconstructs the Mesozoic opening of the Gulf of Mexico (GOM) basin using marine satellite gravity data, regional magnetic surveys, deep-penetration grids of 2D seismic reflection data, seismic refraction surveys, and heatflow measurements. These various datasets are used to improve the definition of the continent-ocean boundary (COB) of the GOM, especially in the extensive areas of the northern conjugate margin that are obscured by a thick, layer of Middle Jurassic salt. In this northern salt area, I use these integrated datasets to show that the Walker Ridge Salient is not a promontory of continental crust as proposed by previous workers but is instead underlain by remobilized salt that has moved over late Jurassic oceanic crust. Using this improved map of the COB from the US and Mexican conjugate margins of the GOM, I quantitatively reconstruct and restore the basin to its pre-rift state during the Late Triassic with minimal errors by realigning the smoothly-curved, northern and southern conjugate margins. I use magnetic and gravity data as a test for this fit and to show asymmetrical late Jurassic oceanic spreading with the wider limb to the north. I also propose a new mechanism for the 33° counterclockwise rotation of the Yucatan microplate-based on how the earliest continental rifts interacted with variably-oriented, pre-rift basement orogenic grains formed during the Appalachian orogeny. The third chapter describes salt tectonics in a 55,000 km2 Port Isabel area of the northwestern GOM using a dense grid of industry seismic data tied to wells. Mapping shows multiple salt-related detachments with an updip, low-angle normal fault, and two stacked, downdip, thrust detachments that parallel a lower salt body above the basement and the salt canopy ~6 km above the basement. Structural restorations show that salt bodies originated as an elongate, salt wall (named here the Rio Grande salt wall) that underwent its highest rate of basin ward collapse during the Oligocene and Miocene. Isopach mapping of seven horizons that range in age from late Jurassic to recent show the development of the 7-km-thick, 20,000 km2, Oligo-Miocene clastic basin that formed above the collapsing salt wall. This salt withdrawal basin is described here in detail for the first time and is named the “Texas salt withdrawal basin." The fourth chapter applies 1D and map-based basin modeling to the hydrocarbon-poor Port Isabel foldbelt that builds on the structural and stratigraphic study of the Texas salt withdrawal basin in the second chapter. My basin modeling shows that Tithonian, Upper Cretaceous, and Paleocene-Eocene source rocks are mature and began expelling hydrocarbons during the initiation of Oligocene subsidence and Middle Miocene Texas salt withdrawal basin. I proposed that some of these source rocks were structurally displaced during salt movement in the Oligocene and Miocene and this structural displacement of the source rocks may have contributed to the lack of hydrocarbons in the Port Isabel area.



Salt withdrawal basin, Salt wall, Olio-Miocene depocenters, Salt tectonics, Port Isabel Foldbelt