Structure of Continental Slope, Northern Gulf of Mexico: 3. Regional Stratigraphy and Structure

The continental slope in the northern Gulf of Mexico contains four structurally distinct provinces: northwest slope, central slope, Mississippi slope, and lower slope. Structural provinces are recognized through variations in structural styles which are related to the shape of diapirs and normal faults. On the central slope, diapirs are large, regular, and closely spaced or interconnecting. In the lower slope, diapirs are large, irregular, and interconnect at shallow depths. On the northwestern slope, diapirs are more widely spaced and a continuous (240 km) down-to-basin fault system develops at the shelf-slope edge. The Mississippi slope is structurally similar to the northwest slope. Differences in structural style may result from variations in initial thickness of the salt layer and loading rates as related to depositional rates and thickness of adjacent sediments. The central slope is an area where initial salt deposits were probably thick and sediment loading rates were high (3.6 km of Quaternary sediments alone at the shelf-slope boundary). Salt was initially thick, but sediments are thinner and loading rates were less in the lower slope. On the northwestern slope and Mississippi slope, salt was initially thinner and sediment loading rates were moderate to low. Relative initial salt thickness can only be estimated on the basis of present salt volume in diapirs. Salt domes and growth faults of the continental slope are similar to those that were ancestors to the domes and faults of the present coastal plain and shelf. Study of present slope features provides a better understanding of the evolution of diapirs from immature abyssal plain, continental rise, and slope features to the more mature features of the present coastal plain and shelf.