The Morphology and Evolution of Basins on the Continental Slope, Northwest Gulf of Mexico

BRYANT, WILLIAM R., and GREGORY R. SIMMONS, Texas A&M University, College Station, TX, and PAUL GRIMM, National Oceanic and Atmospheric Administration, Washington, DC

Newly constructed bathymetric charts and recent multibeam surveys by the National Oceanic and Atmospheric Administration of the continental slope of the northwestern Gulf of Mexico reveal the presence of over 90 intraslope basins with relief in excess of 150 m. The evolution and the general configuration of the basins are a function of halokinesis of allochthonous salt. Intraslope-interlobal and intraslope-supralobal basins occupy the upper and lower continental slope respectively. The intraslope-interlobal basins of the upper continental slope are elongate in shape with a north to south and northwest to southeast orientation. These basins are located in areas where salt is deeply rooted. The intraslope-supralobal basins of the lower slope have a more circular geometry and are located in the Sigsbee salt nappe; the Sigsbeen Escarpment is the southern boundary of the nappe.

Detailed bathymetry proves to be extremely valuable in displaying characteristics of salt structural styles based on multichannel seismic interpretation. In general, bathymetric highs correspond to shallow salt structures buried less than one second (two-way traveltime) below the sea floor. Bathymetric lows correspond to thicker sediment-filled intraslope basins.

The upper continental slope consists of very large domes and ridges separated by trough and valley-like basins. The salt structures responsible for the large domes and ridges include deeply rooted

domes and massifs and laterally spreading salt tongues. Each style has fairly distinctive bathymetric characteristics. Deeply rooted massifs and adjacent interdomal basins are particularly well represented in the Garden Banks and northern Keathley Canyon areas. The ridges are commonly elongated in a northwest-southeast direction, a prominent trend across the northern Gulf of Mexico which appears to correspond with a deep crustal fabric. The upper surfaces of the ridges are generally uneven or domed at various points along the ridges. The adjacent interdomal basins tend to have a fairly rounded cross section shape. The sediment fill within the basins dips away along the ridge flanks, reflecting both doming within the ridges and salt withdrawal from below.

AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)