Intraslope Basin Deposits and Potential Relation to the Continental Shelf, Northern Gulf of Mexico

ABSTRACT The continental slope in the north central Gulf of Mexico has a very hummocky topography in which the highs are underlain by diapirs. The topographic depressions, or intraslope basins, can be divided into blocked-canyon basins, interdomal basins, and collapse basins. Only the blocked-canyon basins may have a direct relationship to the continental shelf. An acoustical sequence is typical for blocked-canyon intraslope basins. The sequence starts with a semitransparent or a chaotic seismic facies, overlain by a zone with discontinuous, slightly irregular, parallel reflectors, and topped by continuous, distinct, parallel reflectors. Inferred lithologies and processes (bottom to top) are: sandy, silty, and clayey; and density currents and slumps, low density turbidity currents, and pelagic-hemipelagic deposition. Transport and deposition can be related to relative changes in sea level; the lower zone being deposited during a falling sea level and perhaps during the initial rise, the middle zone during a rise in sea level, and the upper zone during high sea level stands. When sediments, emplaced on the outer shelf and upper slope, are put in motion as a result of slope failure, they can move downslope for long distances through channel-like depressions. Different sediment thicknesses in the channel and on the diapiric highs will cause differential loading which results in diapiric activity. As a consequence, damming of a channel can result and an intraslope basin is formed. Once a channel blockage is sufficiently high, it will block bottom-hugging currents from further downslope movement. Combining seismic characterization, borings, well logs, stratigraphic analyses, and palimspastic reconstruction of the diapiric activity, may make it possible to determine which stratigraphic zones contain sands and silts. Application of the Mississippi Fan depositional model may help in determining the distribution of sediment types.