Sample analysis and geophysical profiles across the continental slope and shelf of the northern Gulf of Mexico indicate that, as a result of a comparatively rapid rise in sea level, the Holocene transgressive facies is not as well developed as that of the Pleistocene. This rise in sea level, combined with the decrease in the rate of precipitation in the Pleistocene and Holocene, caused a diminution of sediment supply to the western margin. The Mississippi River system maintained an adequate sediment flux and a prograding delta to the edge of the shelf. As a result, the mass wasting potential was lessened on the western slope but maintained in the central region. The present sedimentation rates measured by ²¹⁰Pb-dating vary from 1 cm/year on the upper slope near the delta to 1 mm/year on the western slope off the Rio Grande.

The mineral composition of the fine sediment varied very little if at all during the transgression. The sandsize fraction, however, changed from a dominantly detrital to a biogenic-organic composition. Organic material in the sediment increased and is dominantly of marine origin. The level of the oxygen minimum was elevated to near the shelf and slope break.

Although thinner, the Holocene transgressive unit is similar stratigraphically to units lower in the section and to units that envelope hydrocarbon-producing horizons in the Gulf Coast. In addition, the fine, organic-rich sediment rapidly deposited in an area of low oxygen may become petroleum source beds. The abundance of marine organic materials in this unit favors generation of petroleum over gas.

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