ABSTRACT: Structural Style Along the Salt-Front Walker Ridges OCS Area, Gulf of Mexico

Gregory R. Simmons, William R. Bryant, Joel S. Watkins

The northern Gulf of Mexico continues to be a frontier exploration province as the search for hydrocarbons moves progressively into deeper water. Shallow salt occurs extensively across the middle to lower slope, where structural complexity accentuates difficulties in seismic imaging. Early models portray all salt as deeply rooted whereas recent views rely on predominantly horizontal flow of salt. Observed characteristics along the base of slope through the Walker Ridge OCS area suggest a structural style consisting of a shallow allochthonous salt sheets sourced by deeply rooted stocks toward the updip margins. A typical bathymetric profile exhibits domal areas surrounding the stocks with collapse basins at the crest, relatively flat tops across the sheet, and gentle escar ments marking the basinward extent of each sheet. Basinal stratigraphic sections are deformed locally by adjacent stocks and overriding sheets. These basins contrast with stratigraphic sequences filling the relatively young, rapidly subsiding intraslope basins. Blocky to v-shaped valleys typify coalescence between adjacent salt sheets. Narrow overthrust zones occur where salt sheets override previously emplaced stocks and sheets. Similar characteristics across the middle to lower slope facilitate mapping the geometry and assessing the interaction between salt bodies. Accurate prediction of structural style and resultant geometry has important implications in the search for hydrocarbons and is one of the challenges faced in this deep-water frontier. Diapiric stocks and associated faulting are likely migration pathways, and allochthonous sheets may act as efficient seals to trap migrating hydrocarbons.

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