Basement controls on hydrocarbon systems, depositional pathways, and exploration plays beyond the Sigsbee escarpment in the central Gulf of Mexico

Stephens, B. P., Minerals Management Service, New Orleans, LA

Abstract

Improved understanding of the interaction between basement structure, salt tectonics, and depositional systems can be of great value in tract evaluation and resource assessment, particularly in subsalt areas or under-explored, emerging plays. One such area is the abyssal fan play of the ultra-deep water Gulf of Mexico. Here, an ordered basement fabric appears to have influenced the vertical juxtaposition of potential Mesozoic source rocks, Tertiary reservoirs, and vertical migration pathways.

Examination of Central Gulf of Mexico tectonic elements, structural features, salt systems, and field distributions reveals patterns of systematic right-lateral offsets along trends that approximate North-Atlantic fracture zones. Regional maps of Mesozoic and Tertiary horizons generated from a modern 2x2-mile 2-D seismic grid have been used to interpret transfer fault trends and delineate Mesozoic rift basins beneath the abyssal plain. These basins are seen to be right-stepping across a series of northwest-southeast trending transfer faults in southern Atwater Valley, Walker Ridge, and Lund. These basins may contain source rocks of Jurassic or Cretaceous age. Dramatically high-standing basement blocks beneath the abyssal plain may be Cretaceous volcanic edifices that exploited the transfer fault zones during a period of post-rift tectonism.

Transfer fault zones have served as sediment fairways through the salt canopy and foldbelt throughout the Tertiary. Point sources for Miocene deep water fans emanate from the Mississippi Fan Foldbelt where fold axes are offset along transfer fault zones. The Middle Miocene section contains an apron of fans just outboard of the Sigsbee Escarpment, but is condensed over most of southern Walker Ridge, Atwater Valley, and Lund. This probably reflects ponding of sediments shoreward of the Mississippi Fan Foldbelt during the middle Miocene. Seismic facies suggest that lower Miocene fans were deposited beyond the southern margin of Lund and Lund South, prior to development of the Mississippi Fan Foldbelt.

Across the northeastern half of the abyssal plain, within the corridor between the Cuba and Campeche fracture zones, regional dip is to the southwest. Across southwestern Lund and western Walker Ridge, to the west of the Campeche fracture zone, regional dip is to the northwest, as the section climbs toward the Yucatan Block. This basin configuration focused deposition toward southeastern Lund, where lower Miocene fans onlap the outer reaches of the Campeche rise.

Combination structural-stratigraphic traps in lower Miocene fans overlying uplifted basement or Cretaceous volcanic edifices can be sourced from adjacent rift basins by a series of regional joints and fractures. These elements comprise a new play that extends the lower Miocene frontier 150 miles south, to the limits of U.S. waters.