Structural architecture and evolution of eastern Mississippi Canyon, northern gulf of Mexico

Abstract

3-D, depth-migrated seismic data are used to evaluate the structural architecture and evolution of eastern Mississippi Canyon, northeastern Gulf of Mexico. The W-dipping base of the Louann salt is mostly unfaulted, such that basement faults did not influence Late Jurassic to Recent deformation. Instead, the suprasalt evolution was driven by a combination of lateral (gravity-driven) and vertical (differential loading) forces that varied in importance and direction over time. Salt movement was initiated in the Late Jurassic by SW-directed, convergent gravity gliding on an arcuate margin. This resulted in both contractional thrust faults and folds and dome-and-basin structures that set up the initial configuration of minibasins, salt plateaus, and early diapirs. The minibasins evolved as either turtle structures or expulsion-rollover structures, with the distribution of the two defining a convergent Mesozoic paleo-slope and age-equivalent basin floor. Gravity-driven deformation waned and differential loading gradually became more important during this time. The relative interplay between the two drivers reversed again during the Miocene due to a combination of progressive welding of the Louann salt and an eastward shift of Miocene deltaic shelf edges updip of the study area. The latter triggered SSE-directed gravity spreading, with most of the resultant extension and contraction located in more proximal and distal areas, respectively. The study area was mostly in the translational domain, which was bounded by a zone of sinistral strike-slip deformation downdip of the lateral edges of the deltaic depocenters. Miocene salt structures defined two provinces: a proximal domain characterized by counterregional feeders and basinward-flowing salt sheets; and a distal domain with vertical feeders and radially-spreading allochthonous salt. The boundary between the two marked the Miocene toe of slope. Lessons derived from the study area can be applied to help understand the more complex structures and evolution farther west in the northern Gulf of Mexico.