Characteristics of Diapirs on the Outer Continental Shelf-Upper Continental Slope Boundary, Northwest Gulf of Mexico

ABSTRACT An 18,000 square kilometer segment of the shelf-slope boundary off southwest Louisiana was studied using high-resolution seismic profiles. Mapping of the distribution of diapirs, faults, synclinal and anticlinal axes, and the configuration of the subseafloor surface of diapiric material revealed significant patterns. On the outer continental shelf, diapirs are characteristically either buried or exposed and severely eroded. Erosional surfaces on upper-slope diapirs can be used to estimate subsidence rates. The complex bathymetric contours on the upper slope are the result of diapiric activity and show characteristic fault patterns and relationships to pierced sediments that can be attributed to gravity-induced movement of salt downslope triggered by the weight of overlying sediment prisms. Salt is present at shallow depths on the upper slope and is usually capped by a sheath of seismically chaotic, fine-grained sediments. Diapirism and the loading of sediments in depositional basins are interdependent processes actively reshaping the shelf-slope boundary through marginal accretion.