MANCINI, ERNEST A. , Department of Geological Sciences, University of Alabama, Tuscaloosa, AL

Upper Eocene (Jacksonian) strata of the Eastern Gulf Coastal Plain have included the Yazoo Clay of the Jackson Group and its members (North Twistwood Creek Clay, Cocoa Sand, Pachuta Marl and Shubuta Clay Members). Lower Oligocene (Vicksburgian) strata have included the Red Bluff Clay, Bumpnose Limestone, Forest Hill Sand, and Marianna Limestone and its Mint Spring Marl Member of the Vicksburg Group. Based on planktonic foraminifera (last occurrences of Turborotalia cerroazuensis cocoaensis (Cushman) and Hantkenina alabamensis Cushman), the Jackson-Vicksburg Stage boundary and the Eocene-Oligocene boundary have been placed at the top of the Yazoo Clay. Recently, other works have placed the Eocene-Oligocene boundary both below and above the Yazoo-Red Bluff contact. Further, the Eocene-Oligocene boundary has been described as a maximum marine flooding surface at the Yazoo-Red Bluff contact. The depositional sequence consists of transgressive systems tract deposits (Pachuta), condensed section deposits (Shubuta and lower Red Bluff/Bumpnose), and highstand systems tract deposits (upper Red Bluff/Forest Hill). Recently, other works have interpreted the Yazoo-Red Bluff/Forest Hill contact as a sequence boundary and have interpreted the maximum marine flooding surface as occurring lower in the Shubuta, with the upper Shubuta beds being, assigned to the highstand systems tract of the Yazoo-Red Bluff depositional sequence. By utilizing sequence stratigraphic analysis and chronostratigraphic correlation, these recent findings can be reconciled with the interpretation that the Jackson-Vicksburg Group boundary is time-transgressive and corresponds to a maximum marine flooding surface only in strata of the easternmost Gulf Coastal Plain.

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas