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Cenomanian (Cretaceous) Deepwater Reservoirs of the Deep Gulf of Mexico Basin: Source to Sink Conundrums


For many years, Cenomanian-age (Upper Cretaceous) sandstones have been economically attractive reservoirs in onshore parts of the greater Gulf of Mexico, with prolific hydrocarbon production in East Texas (Woodbine) and Louisiana (Tuscaloosa) fields. However, recent drilling has attempted to extend the play into shelf and deep-water areas of the Gulf, raising major questions about the source to sink pathways and responsible depositional processes. Interpretation of depth-imaged seismic data, paleogeographic reconstructions, scaling relationships, and new ideas on deep-water depositional processes can shed some light on these conundrums. Paleogeographic maps demonstrate that the Woodbine system, derived from the Ouachita terrain, had limited sedimentary influence beyond its local basin axis in East Texas and was not a significant source of the thick (>1000 ft) Cenomanian reservoirs penetrated in the deep Gulf basin. By contrast, the Tuscaloosa depositional system, sourced from the Appalachian highlands, maintained a large integrated drainage system and is the best candidate for a pathway into the deepwater domain. Transport pathways follow NE-SW tectonic trends of the eastern Gulf. However, restored Cenomanian fan length compared to reconstructed Tuscaloosa alluvial river dimensions greatly exceeds predictions from empirical relationships observed in modern systems. This suggests that a major tectonic event such as uplift of the Mississippi embayment (due to plate migration over an active hotspot) created an oversupply of terrigenous clastics that overwhelmed normal source to sink Tuscaloosa distributive systems and generated long-lived, sustained point inputs to the basin. Examination of wells and depth-imaged seismic data from Alaminos Canyon, Keathley Canyon, and South Marsh Island areas of the Gulf confirm the high net to gross and sand-rich nature of the progradational delta-fed slope aprons and linked abyssal plain submarine fans. The high argillaceous content of some zones suggests that low yield strength debris flows and linked transitional flows were as common as high-density turbidity flows. Evolving consensus on the substantial transport distance of debris flows, as demonstrated with published physical experiments, fits with these observations from Cenomanian-age sandstones of the Gulf of Mexico.