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ABSTRACT: Depositional, Tectonic, and Eustatic Controls on Hydrocarbon Distribution in Devergent Margin Basins--Gulf of Mexico Case History

Robert A. Morton, William E. Galloway

The origin and distribution of hydrocarbon reservoirs on divergent margins, like that of depositional sequences, reflects an interplay among sediment supply and depositional process, eustatic sea level change, and tectonic history. Cenozoic sequences of the northwestern Gulf Coast basin contain prolific hydrocarbon fairways defined by each of these end-member processes. The Oligocene Frio sequence records moderate rates of sediment supply, locally rapid load or salt-induced subsidence, and infrequent, relatively low-amplitude eustatic change. Accommodation space was created by growth-fault extension or salt evacuation along with progradation into the deep-water Gulf. Shore-zone deposits are sand rich because limited eustatic shore line shift promoted effective reworking a d storage of coastal facies. Progradational depocenters were characterized by large, wave-dominated shelf-edge deltas; sands were stored in close proximity to the delta fronts. Prolonged intervals of aggradation and retrogradation preserved thick interdeltaic facies sequences deposited by barrier/lagoon systems. More than 18 billion BOE of produced Frio hydrocarbons accumulated primarily in structurally and depositionally defined plays. In contrast, Pliocene-Pleistocene sequences are the products of frequent, high-amplitude eustatic cycles, rapid rates of subsidence, and locally high rates of sedimentation. Accommodation space was created by salt evacuation and relative rises in sea level. Shore-zone deposits are heterolithic because rapid subsidence and frequent eustatic cycles prevente extensive reworking. Progradational depocenters were characterized by small, mud-rich, river-dominated shelf-edge deltas. Rapid lowering of sea level promoted deposition of highly elongate, sand-rich submarine fans extending more than 120 km from the paleoshelf margin. Structurally defined Pliocene-Pleistocene plays contain nearly 1.5 billion BOE.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990