STRUCTURAL AND STRATIGRAPHIC EVOLUTION OF THREE MESOZOIC, RIFTED-PASSIVE MARGINS: GUINEA PLATEAU, DEMERARA RISE, AND SOUTHEASTERN GULF OF MEXICO

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2020-08

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Abstract

The deep-water, southeastern Gulf of Mexico covers an area of 112,000 km² from the West Florida Shelf to the Yucatan Platform, and the Guinea Plateau-Demerara Rise conjugate margins cover areas of 180,000 km² and 170,000 km², respectively, along northwestern Africa and northeastern South America. This dissertation uses regional seismic reflection datasets tied to wells to better understand their Mesozoic to recent, tectonic, structural, and stratigraphic histories along with their hydrocarbon prospectivity. In Chapter 2, structural restorations were used to calculate the upper crustal extension of rifted continental crust adjacent to the tip of an extinct, late Jurassic, oceanic spreading ridge in the southeastern Gulf of Mexico. 2D forward gravity models show variations in crustal thickness across the rifted southeastern Gulf of Mexico and analysis of thinning factors shows decreasing crustal thickness from south to north towards the propagating ridge tip. Discrepancies between the upper crustal extension and overall crustal thinning can be explained by depth-dependent extension. In Chapter 3, 2D gravity modeling was used to constrain and compare the crustal structure of the Guinea Plateau-Demerara Rise volcanic conjugate margins. My models take into account the volcanic origin of seaward-dipping reflectors identified for the first time from my dataset on the Guinea Plateau. Gravity modeling also shows that the Guinea Plateau is underlain by rifted continental crust and that high-density underplated rocks underlie a large area of the western Demerara Rise. In Chapter 4, six tectonostratigraphic sequences were mapped across the Guinea Plateau using a regional seismic grid tied to well data. Structural and isopach maps reveal the locations of deeply-buried Triassic rifts, migration of rift-related sag basins though time, and the interplay between Central Atlantic-related rifts and Equatorial Atlantic-related shearing effects of those older Central Atlantic rifts. Paleogeographic maps show the progression from a carbonate dominated margin in the Jurassic-Early Cretaceous to a clastic dominated margin from the Mid-Cretaceous-present. Thermal maturity modeling of industry wells and pseudo wells indicates over-mature Jurassic source rocks, mature Albian source rocks, and variably mature Cenomanian-Turonian source rocks.

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Passive margin, gravity modeling, paleogeography, upper crustal extension, Gulf of Mexico, Guinea Plateau, CAMP, seismic stratigraphy

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