--> Abstract: The Effects of Basin Morphology and Salt Dynamics on the Gulf of Mexico Shelf Margin and Slope Systems, by G. M. Apps and C. A. Yeilding; #90987 (1993).

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APPS, GILLIAN M. and CINDY A. YEILDING, BP Exploration, Houston, TX, USA.

ABSTRACT: The Effects of Basin Morphology and Salt Dynamics on the Gulf of Mexico Shelf Margin and Slope Systems

Slope gradients and the activity of salt at the site of sediment input are the fundamental controls on the Tertiary depositional systems. These controls vary laterally, giving rise to distinct slope architecture. They determine the response of the systems to sea level changes and account for variations in stratigraphic signature of eustacy.

The Lower Miocene, offshore South Texas, built on a pre-existing, low angle clastic wedge, with limited amounts of salt. Major growth faults (up to 250 miles long) stabilized a shelf margin ramp and probably limited the amount of sand supplied to the slope.

The upper Miocene, offshore eastern Louisiana, encountered the steep topography of the Cretaceous shelf edge. A thick package of basin sediments progressively onlapped the slope and was completely detached from thin shelf sediments. They were overlain by basin sediments attached to a prograding shelf margin. The evolution from bypass to progradation occurred once the steep relief was subdued by clastic sediment.

The lower Pleistocene system, offshore central Louisiana, built onto a low-angle clastic margin, underlain by 3-4 km of salt. The salt created accommodation space, which focussed the deltaic input and the slope sediment fairways for a significant length of time. The natural instabilty of the strongly progradational system was enhanced by the salt withdrawal, resulting in gravity slides wasting up to 50 km of the shelf margin. The failures themselves generated large mass flows and left steep scars which further focussed sediment onto the slope.

With time, the deltaic systems became less focussed as the salt canopies at the shelf margin were gradually displaced, giving the river systems freedom to switch.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.