Evolution of stocks and massifs from burial of salt sheets on the continental slope, northern Gulf of Mexico
Data from conventional two- and three-dimensional seismic surveys and wells were used to analyze the morphology of salt structures and to determine the history of salt emplacement in a 1,500 mi² (3,850 km²) region of the continental slope, northeast Green Canyon Area. Salt structures within the region include stocks, massifs, an allochthonous sheet, and remnant-salt structures. Also within this region is a largely salt-free area (at least to a depth of 20,000 to 25,000 ft--6,100 to 7,600 m) that coincides with a U-shaped submarine trough. A large graben between a east-northeast-trending zone of growth faults near the shelf margin and a parallel trend of counterregional growth faults located 30 to 40 mi (48 to 64 km) basinward, contains the submarine trough, stocks, and massifs. The graben is inferred to have formed from extension and subsidence as burial of the landward portion of a thick salt sheet produced massifs and stocks by downbuilding. Large-displacement counterregional growth faults form the northern, landward margin of a large salt sheet that extends to the Sigsbee Escarpment. Differential loading separates salt stocks and massifs from the trailing margin of a salt sheet. The former presence of salt below the submarine trough is inferred on the basis of remnant-salt structures and a turtle-structure anticline lying on a discontinuity. Where salt is absent, this discontinuity is a salt weld representing suturing of sediments formerly separated by a salt sheet. The age of sediments below the weld indicates sheet extrusion occurred in the late Miocene to early Pliocene (4.6 to 5.3 Ma). The age of sediments above the weld is late Pliocene (2.8 to 3.5 Ma). Sheet burial began in the late Pliocene in the area of the submarine trough to early Pleistocene in the area of the massifs.