Tectonostratigraphy, Structural Styles, and Hydrocarbon Prospectivity of the Rifted-Passive Margins of the Southern Gulf of Mexico and the Atlantic Margin of Morocco

This dissertation addresses the tectonic evolution, structural style, source rock maturity, and hydrocarbon prospectivity of rifted-passive margins of the Gulf of Mexico (GOM) and circum-Atlantic and western Indian Oceans. The datasets for both of these study areas include: 1) pre-stack depth migrated (PSDM) 2D seismic reflection and shipborne potential field data; 2) satellite free-air gravity and magnetic data; and 3) previous geologic cross-sections, offshore seismic reflection profiles, and on- and offshore wells from the oil industry and the International Ocean Drilling Project (IODP). Chapter 2 compiles information from my own study of the southern GOM with previously published information on the structural evolution and similarities of shale- and salt-detached, deepwater passive margin foldbelts (PMFBs) of the Gulf of Mexico, Atlantic Ocean, and western Indian Ocean. Comparison of the thirteen passive margin foldbelts from these margins shows that their shared structural characteristic of linked updip normal faults and downdip folds and thrust faults are driven by gravitational forces resulting from thermal subsidence, onshore cratonic uplift, tectonic oversteepening of the margin, and deltaic depositional loading. Symmetrical detachment folds typically dominate systems associated with salt detachment, whereas shale-detached PMFBs are characterized by imbricate thrusts and more asymmetrical fault-bend and fault-propagation folds. Chapter 3 focuses on the tectonic evolution of the Campeche salt basin in the southern Gulf of Mexico and integrates shipborne magnetic data with 28,612 km of pre-stack, depth-migrated, 2D seismic data to reconstruct the geometry of the top of the Paleozoic crystalline basement and the base of the Jurassic salt body. This mapping better defined the 400-km-long and 40-55-km-wide outer marginal trough, which formed adjacent to the late Jurassic oceanic crust of the central GOM and acts to channel the downslope flow of gravitationally-driven salt of the Campeche passive margin foldbelt. Restoration of seismic lines established the 20.5 km updip extension in the Comalcalco rift. In Chapter 4, I conducted thermal stress modeling along the Campeche salt basin to better understand the spatial variation of present-day maturation of the potential source rocks in the southern Gulf of Mexico and their expelled petroleum volume. The critical feature for the maturation of hydrocarbons is the elongate outer marginal trough described in detail in Chapter 3. My 1D and map-based modeling demonstrate that the more deeply buried, late Jurassic source rocks matured in the late Paleogene to early Neogene and are currently expelling oils into the water column as known from natural oil surface seeps emanating from the seafloor overlying the outer marginal trough. Seismic reflection data show large, salt-related traps are directly connected by faulted pathways to oil kitchens within deep minibasins. Chapter 5 uses the same mapping approach as Chapter 4 to describe an elongate, 80-150-km-wide marginal rift that overlies the zone of continental necking and parallels the modern coastline of Morocco. 1D and map-based thermal maturity modeling show that Jurassic source rocks of the marginal rift are mature for petroleum expulsion along a 400-km length of this rift. Late Cretaceous uplift and erosion of the margin documented in IODP wells are related to Africa-Eurasia convergence across northern Africa and provide an explanation for the observed immaturity of Cretaceous source rocks and the maturity of the underlying Jurassic source rocks.