ABSTRACT: Slope Sedimentation above an Allochthonous Salt Substrate, Northwest Gulf of Mexico

SIMMONS, GREGORY R., and WILLIAM R. BRYANT, Texas A&M University, College Station, TX

Sedimentation across the Texas-Louisiana slope is intimately associated with a variety of salt structural styles. The lower slope is characterized by isolated supralobal basins subsiding into a nearly continuous substrate of allochthonous salt. Circular to elliptical depressions represent unfilled space evacuated by underlying salt.

The upper to middle slope is characterized by allochthonous salt fronts forming distinct, interlobal basin margins. Bathymetric relief of interlobal basins is due to uplift associated with the lateral intrusion of salt. Although a salt substrate is generally unresolved, the interlobal-basin fills include depositional geometries attributed to halokinesis (i.e., turtle-structure anticlines) overlying salt-evacuation surfaces.

Studies of slope to shelf margin development within the overall progradation of the Cenozoic clastic wedge commonly show development initially as isolated depocenters, presumably above an allochthonous salt substrate. Initial subsidence is apparently accomplished by differential loading from sediments that are buoyant with respect to the underlying salt. Density-depth relationships for typical marine sediments suggest that sand represents a major component of the supralobal-basin fills. Rapid subsidence and complete evacuation of salt is accomplished locally when sediments reach a critical thickness. The final stages of supralobal basin development involves onlapping fill of the depressions created by salt evacuation. Supralobal-basin flanks are further evacuated with continued burial the surrounding salt becomes increasingly isolated, and the supralobal-basin geometries are inverted into turtle-structure anticlines. With further burial the isolated salt domes and massifs develop extensive allochthonous overhangs spreading laterally over interlobal basins.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)