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Jurassic Gravitational Shelf Spreading in the Western DeSoto Canyon Salt Basin, Mobile, Viosca Knoll and Destin Dome Areas, East-Central Gulf of Mexico


The western DeSoto Canyon Salt Basin contains a gigantic array of arcuate extensional faults that provide evidence for a major episode of gravitational shelf spreading during the Late Jurassic. The array extends along strike for ~210 km and downdip for > 80 km. Norphlet sandstone reservoirs are productive along the crests of salt rollers in the updip reaches of the fault array, and the downdip portion is underexplored. Fault length and displacement increase basinward, and heave locally exceeds 9 km. Regional faulting is dominant, and counterregional fault arrays are developed locally. Fault geometry grades from planar to listric as displacement increases, and the longest faults merge with horizontal salt welds in a major salt diapir province. Structural and stratigraphic analysis indicates that the faults become younger landward, with extension beginning at the start of Smackover Limestone deposition in the southwest part of the fault array and during mid Smackover deposition in the northeast part. Most faults terminate within the Cotton Valley Group, although some faults offset Early Cretaceous strata near the northern margin of the salt basin. The base of the suprasalt section is grounded on basement in downdip areas, whereas a significant quantity of salt remains updip, where tilted blocks of carbonate tend to form line welds separating salt rollers. Growth strata in tilt blocks, hanging-wall rollover folds, and in roller-cored anticlines are imaged clearly in seismic profiles, and the growth section contains a pronounced angular unconformity at the Smackover-Haynesville contact. Cotton Valley strata are welded to basement where rafted Smackover-Haynesville blocks are imaged. A giant, counterregional tilt block contains a Smackover-Haynesville section thicker than 3 km, and basinward of this structure, pre-Cotton Valley strata have been rafted at least 12 km, well beyond the Cretaceous reef trend. Balanced structural cross sections based on depth-converted seismic profiles indicate that layer-parallel strain at the base of the Smackover ranges from 38 to 52%. 3-D computer visualizations reveal the slump-like nature of the shelf spreading event. The unusually thin pre-growth section suggests that salt was already in motion as Jurassic carbonate deposition commenced, and evacuation of salt into the juvenile Gulf of Mexico ocean basin is interpreted as the principal mechanism of halokinesis.