MANCINI, ERNEST A., Geological Survey of Alabama, and Univ. of Alabama, Tuscaloosa, AL; and BERRY H. TEW, Univ. Alabama, Tuscaloosa, AL

ABSTRACT: Geochronology, Biostratigraphy, and Sequence Stratigraphy of Upper Paleocene (Tuscahoma Sand) and Lower Eocene (Hatchetigbee Formation) Strata of the Eastern Gulf Coastal Plain

In the eastern Gulf Coastal Plain, the Paleocene-Eocene Epoch boundary (ca. 54 ma) coincides with the lithostratigraphic contact of the upper Paleocene Tuscahoma Sand with the lower Eocene Hatchetigbee Formation. Both of these units are included in the Wilcox Group. Planktonic foraminifera diagnostic of the Selandian Stage Morozovella velascoensis Interval Zone have been recovered from the Greggs Landing Marl and Bells Landing Marl Members of the Tuscahoma Sand, whereas species indicative of the Ypresian Stage M. subbotinae Interval Zone have been recovered from the Bashi Marl Member and calcareous sands in the unnamed member of the Hatchetigbee Formation. In addition, palynological studies of the predominantly nonmarine strata of the uppermost Tuscahoma ("upper Tuscahoma") and margin l marine strata of the lowermost Hatchetigbee ("Bashi lowstand sand unit") indicate late Paleocene and early Eocene ages, respectively.

Two unconformity-bounded depositional sequences are recognized in the middle and upper parts of the Tuscahoma Sand. The lower sequence (type 1), here designated the Tejas A-Gulf Coast (TAGC) 2.2 sequence, includes strata from the base of the Greggs Landing Marl Member to the base of the Bells Landing Marl Member; and the upper sequence (type 2), the TAGC-2.3, encompasses strata from the base of the Bells Landing Marl Member of the Tuscahoma to the top of the upper Tuscahoma. The lower Tucahoma (below the Greggs Landing Marl Member) consists of parasequences of alternating marl and silty clay that are included in the underlying type 1 TAGC-2.1 sequence, which also includes the Nanafalia Formation. The contact between the Tuscahoma Sand and the Hatchetigbee Formation is disconformable a d corresponds to a type 1 sequence boundary in the study area. Above this boundary, the Hatchetigbee comprises a type 1 depositional sequence, the TAGC-2.4. Discontinuous lowstand sand ("Bashi lowstand sand unit") is overlain by the Bashi Marl Member of the lower Hatchetigbee. Parasequences of alternating calcareous sand and silty clay characterize the upper Hatchetigbee beds.

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