Variations in Slope Deposition, Plio-Pleistocene, Northern Gulf of Mexico

PULHAM, ANDREW, BP America, Houston, TX

Key controls on styles of northern Gulf of Mexico slope deposition in the past 8 Ma have been the shifting depocenter of the Mississippi Delta, amplitude and periodicity of eustatic sea-level changes, and the interaction of mobile, shallow-buried salt with changes in rates of sediment supply.

During the Pliocene sea-level falls were rarely great enough to fully expose shelfal settings. In addition, the principal depocenter of the Mississippi Delta moved across the Gulf of Mexico in a series of relatively large and instantaneous steps. These conditions promoted the repeated development of shelf margin deltas within each depocenter and the supply of sediment to the slope and deep-water via numerous, relatively small point sources. The development and evolution of numerous and to a certain degree semi-independent, intra-slope, salt-withdrawl basins containing their own turbidite complexes characterizes slope deposition during this time.

In contrast, the Pleistocene sea-level falls were closer spaced in time and typically greater relative amplitude. Shelfal environments were commonly fully exposed encouraging the connection of the Mississippi fluvial system directly into the top of the slope. These conditions together with greater sediment yield lead to the repeated development of major canyon systems and supply of sediment to the slope and deep-water via single large point sources. This created significant by-pass routes through the salt-floored slope, tied the depositional history of many intra-slope basins into the evolution of the canyons and allowed the development of major deep-water fan complexes in the central and eastern Gulf of Mexico.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)