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The Autogenic Origin and Sequence Stratigraphic Setting of the Eocene Cocoa Sand Member of the Yazoo Formation in the Mobil-Mississippi Cores, Wayne County, Mississippi

Grigsby, Jeffry D.*1; Fluegeman, Richard H.2; Brissette, Nic 3
(1) Geological Sciences, Ball State University, Muncie, IN.
(2) Geological Sciences, Ball State University, Muncie, IN.
(3) Gunn Oil Company, Wichita Falls, TX.

The Eocene Cocoa Sand Member of the Yazoo Formation of Mississippi is a subrounded to subangular, moderately to well sorted, poorly cemented quartz arenite with a composition of Q96 F0 L4. Embayed and subhedral quartz grains are common. Lithic fragments are largely found at the base of the Cocoa Sand Member at the contact with the underlying North Twistwood Creek Member of the Yazoo Formation. These lithic fragments consist of sedimentary rock fragments and are interpreted as rip-up clasts from the underlying quartz-rich mudstone.

Previous work has interpreted the Cocoa Sand Member as a shelf margin sand deposited as part of a lowstand systems tract. The presence of rip-up clasts at the base of the Cocoa sand member supports the presence of a transgressive surface at the contact with the North Twistwood Creek. In addition, there is evidence that the upper contact of the Cocoa Sand with the Pachuta Marl is a sharp contact, representing an upper erosion surface.

We interpret the Cocoa Sand Member of the Yazoo Formation to be an autogenic sand sheet deposited as part of a transgressive systems tract. During transgression, the North Twistwood Creek Member was cannibalized, sediment reworked, and re-deposited with rising sea level.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California