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Abstract

The Gyre basin is one of the many intraslope basins on the continental slope in the northwestern Gulf of Mexico. This depression, elongate NNW-SSE, is 33 km long and 11 km wide. It srim lies at depths between 900 and 1, 100m, the deepest center of the basin lies just below 1, 650 m. Themorphology of the surrounding slope, and of the sediments recovered in a nearby core hole,suggest that the basin was formed during the late Pleistocene by salt diapir blockage of a submarine canyon system.

High-resolution subbottom profiles depict the disrupted nature of the surficial sediments on the basin rim and slopes.Clear indications of slumping are visible on some of the profiles; and hyperbolic returns probably have masked numerous slump features on the basin flanks.

Gravity and piston cores from the Gyre basin area display large lateral variations in sediment texture. The basin floor and the lower southern slope contain much sand-sized clastic material, displaced shallow-water benthic foraminifers, rock fragments, and shallow-water mollusks that suggest bottom density-current transport. Topographic high sand most slope areas contain no sand sized clastic material. Rates of sediment accumulation are considerably lower and the percentage of carbonate higher in these sections than on the basin floor.

Distribution of clay and heavy minerals is fairly uniform throughout the area. Heavy minerals in the sandstones appear to reflect a mixing of Rio Grande and Mississippi sources. The montmorillonite to illite ratios are lower than those reported for Mississippi and Rio Grande clay-mineral provinces.

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