The Eocene Cocoa Sand Member of Yazoo Formation is fine grained, moderately to well sorted, poorly cemented, quartz arenite. Surface exposures are poor, but it has been mapped from west Choctaw County, Alabama to eastern Jasper County, Mississippi. In the subsurface, the Cocoa Sand Member is identified by obvious protrusion both in Spontaneous and Resistivity Logs. Northeast to southwest cross-sections (perpendicular to the paleo-shoreline) and northwest to southeast cross-sections (parallel to the paleo-shoreline) were developed, along with isopach maps, to determine the sequence stratigraphic setting and a depositional model of the Cocoa Sand Member. Previous work has interpreted the Cocoa Sand Member as a shelf margin sand deposited as part of a lowstand systems tract or as a transgressive sand. Grain size analysis indicates that the sand coarsens upward and there is evidence in core that the upper contact of the Cocoa sand with the Pachuta Marl is sharp, representing an upper erosion surface. 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. Based on the sand thickness distribution as identified in the Cocoa Sand isopach map and cross sections, two sand ridges have been recognized extending nearly parallel to the paleoshoreline across the Mississippi and Alabama. A three stage model is presented suggesting the formation of these ridges during transgression with the source of the sand being from the eroded and reworked underlying North Twistwood Creek Member. / Department of Geological Sciences
| Identifer | oai:union.ndltd.org:BSU/oai:cardinalscholar.bsu.edu:123456789/197814 |
| Date | 14 December 2013 |
| Creators | Zhang, Xiaodong |
| Contributors | Grigsby, Jeffry D. |
| Source Sets | Ball State University |
| Detected Language | English |
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