--> Abstract: Failed Shelf-Margin Embayments: An Alternate Depositional System to Transfer Sand from the Shelf into Deep Water, by R. A. Morton; #90987 (1993).

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MORTON, ROBERT A., Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

ABSTRACT: Failed Shelf-Margin Embayments: An Alternate Depositional System to Transfer Sand from the Shelf into Deep Water

Like submarine canyons, shelf-margin embayments can focus the downslope transport and deposition of sand in submarine fans. The embayments, which are excavated by massive slope failures, resemble submarine canyons on seismic profiles, but they are different in their size, morphology, origin, and hydrocarbon exploration potential. Diagnostic seismic patterns of ancient slides and filled embayments are basinward-thickening wedges of landward-dipping and chaotic reflections overlain by sub-horizontal and clinoform reflections.

In the Gulf Coast Basin, several interdeltaic embayments record similar sequences of events including (1) basinwide flooding of the continental platform. (2) deposition of low-strength muds (condensed section) that contain the slide detachment surface, (3) catastrophic failure of the shelf margin and basinward transport of slump blocks and gravity flows, (4) continued excavation by retrogressive failure of the continental shelf as well as scouring by turbidity currents, (5) backfilling of the embayment, and (6) reconstruction of the shelf margin.

The slide deposits are resedimented shelf-margin deposits, whereas the overlying embayment fill consists of gravity flow and submarine channel-levee deposits as well as deltaic deposits. Reservoir-quality sandstones commonly occur above the slide deposits in the embayment fill and in channel deposits associated with submarine fans. On passive margins, embayment-forming slides are primarily products of eustatic fluctuations and sediment mobilization. The embayments were probably excavated during periods of lowered sea level and filled during the subsequent sea-level rise and highstand.

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