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.

The Gulf of Mexico covers an area of >1,500,000 sq km, has a maximum depth of about 3,700 m, and includes many of the geomorphic features of large oceans. The continental shelf, slope, rise, and abyssal plain comprise the major physiographic provinces of the gulf and contain a variety of subprovinces distinguished by topographic character and geomorphic history. The gulf shelf is a relatively smooth, gently sloping surface marked locally by low-relief features formed by sea-level fluctuation during the Pleistocene, reef growth, near-surface movement of diapiric salt and mud, and faulting. Shelf width varies from about 280 km off the Florida and Yucatan Peninsulas to <10 km at the Mississippi Delta. The continental slope consists of a considerable variety of physiographic subprovinces and individual features that encircle the deep gulf floor. The distinctive subprovinces of the gulf slope have evolved in response to reef building and constructional sedimentation on the Florida and Yucatan carbonate platforms; erosion, nondeposition, slumping, and faulting in the Straits of Florida and Yucatan Channel; salt diapirism and differential sedimentation in the region off Texas and Louisiana; the large accumulation of mainly Pleistocene sediment on a former continental slope seaward of the Mississippi Delta; tectonic uplift and diapirism in the Golfo de Campeche; and shale mobilization off eastern Mexico. In contrast to the greatly varied, irregular topography of the continental slope, the deep seafloor of the gulf (composed of continental rise and abyssal plain provinces) is an almost featureless plain smoothed by turbidite and pelagic sedimentation and marked locally by low-relief knolls, sedimentary aprons, and small-leveed channels.

The structure and topography of the continental slope in the northcentral and northwestern Gulf of Mexico are shaped principally by diapirs. The cores of most of these diapirs consist of salt that was originally deposited during Louann time (Middle and Late Jurassic). Most of these salt bodies are mantled by Tertiary shale and some diapirs may consist entirely of shale. Younger Tertiary and Quaternary sediments overlie most of these features. Submarine fans in this geologic setting are different from those explained by the generally accepted submarine-fan model because the canyons are extremely long and the fans are small. Much of the sediment that enters a canyon never reaches the submarine fan. Available bathymetric and subbottom-profile data suggest that only a small number of submarine canyon systems exist on this continental margin. Because diapiric activity is strongly influenced by differential sediment loading, these canyons are modified continuously.

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