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Structural Architecture and Evolution of Eastern Mississippi Canyon, Northern Gulf of Mexico


The eastern half of Mississippi Canyon is an ideal locale for elucidating the entire post-Louann history of salt-related deformation due to the relative scarcity of shallow salt. Here, we use modern wide-azimuth, reverse-time migrated 3-D seismic data to define the styles and distribution of different salt structures and the evolution of both salt evacuation/diapirism and gravitational failure of the margin. Salt movement began during the Late Jurassic shortly after evaporite deposition, with no relationship to earlier, underlying rift tectonics. In the east, symmetrical depocenters formed between areas of thin overburden. Small-scale contractional structures are confined mostly to the areas of thicker sediment. They trend NE-SW and record early gravity gliding as the margin tilted to the southeast in this area due to differential thermal subsidence. To the west, Upper Jurassic strata are thin, due to either regional salt inflation or depositional downlap, and apparent shortening was minimal. Gravitational deformation was largely absent during the Cretaceous. Instead, small vertical diapirs and broad areas of inflation formed between depocenters with variable patterns: south-directed expulsion rollovers in the northwest; southwest-directed rollovers in the northeast; and symmetrical depocenters in the south. This presumably reflects convergent depositional slopes to the north and low slope and/or distal inflation to the south. Small bodies of allochthonous salt formed in the east during the Late Cretaceous to Paleogene, probably due to very slow sedimentation. Evacuation and diapirism continued during the early-mid Miocene, with a boundary between basinward-leaning diapirs and expulsion rollovers in the northwest and vertical diapirs and turtle structures in the south probably representing the paleo toe-of-slope. Evacuation largely ceased by the late Miocene. The Miocene was a time of renewed gravitational failure, dominated by gravity spreading toward the south-southeast in response to proximal sedimentary loading. Deformation, recorded by updip extension and downdip contraction linked by strike-slip systems, shifted to the east and increased in rate through the Miocene, again related to proximal depositional patterns. Salt diapirs began flaring in the early Miocene, spread laterally from proximal counterregional feeders during the middle Miocene, and then from distal vertical feeders during the Late Miocene.