--> Abstract: Facies in a Shelf-Edge Delta--An Example from the Subsurface of the Gulf of Mexico, Middle Pliocene, Mississippi Canyon, Block 109, by M. Mayall, C. Yielding, J. Oldroyd, A. Pulham, and S. Sakurai; #91004 (1991)

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Facies in a Shelf-Edge Delta--An Example from the Subsurface of the Gulf of Mexico, Middle Pliocene, Mississippi Canyon, Block 109

MAYALL, MIKE, CINDY YIELDING, JOHN OLDROYD, and ANDY PULHAM, BP Exploration, Houston, TX, and SHINICHI SAKURAI, ARCO Research Lab, Plano, TX

Two vertically stacked shelf-edge delta systems occur in the middle Pliocene of Mississippi Canyon Block 109. A series of facies have been identified in cores including a-, b-, and c-division turbidites, low-angle laminated and rippled wave deposits, slumps, laminated silts and muds, and muds.

The upper of the two deltas is represented on seismic data as a series of prograding clinoforms approximately 400 ft thick. Electric logs indicate these are composed of a lower mud-dominated interval and an upper delta slope dominated by slumps with locally restricted turbidite sands and coarsening/cleaning-upward mouthbar deposits comprised of ripple-laminated and parallel laminated sands interbedded with muds and silts. The lower delta shows similar vertical sequences, but also contains a seismic facies that may represent either a major shelf-edge failure or a later channel feature incised across the entire delta. Apart from this possible channel, neither delta shows evidence of emergent delta top facies.

In the cored intervals of the deltas, turbidite sands immediately overlay muddy slumps in the upper delta slope suggesting that retrogressive failing of developing slump structures tapped back into sandy mouthbar setting causing turbidity currents to develop.

Possible characteristic facies associations and features of shelf-edge deltas may include extensive upper delta slope deformations, locally ponded, slump-induced turbidites in the upper slope, a complex association of depositional processes, relatively thin preserved mouthbar deposits, and absence of delta top/plain facies.

 

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