Abstract: Sequence Stratigraphy of Upper Cretaceous Alluvial Plain Facies, Tuscaloosa Formation, Alabama

David T. King Jr.

Tuscaloosa alluvial-plain facies in central and eastern Alabama were affected strongly by Cenomanian (96-92 Ma) eustatically induced base-level changes, and thus two third-order stratigraphic sequences were developed. Regional climatic and local tectonic changes also affected the regional drainage basin, and as a result numerous parasequence (fourth-order) subdivisions occur within each sequence. Third-order alluvial-plain sequences are bounded by regional-scale disconformities with incised valleys and by mature lateritic paleosols. Fourth-order parasequences are bounded by surfaces of thalweg scour and by immature lateritic paleosols.

Alluvial-plain ("red-bed") facies include humid (colluvial) fans, meandering- and braided-stream channels, well-drained floodplains (including immature paleosols), poorly drained floodplains (including shallow lacustrine deposits), and mature paleosols. The total thickness of these facies averages 100 m, but varies significantly according to basement paleotopography of underlying Piedmont crystalline rocks.

Distinctive third-order eustatic effects on Tuscaloosa sedimentology include gradient-driven changes in (1) channel morphology, (2) stream capacity and competence, and (3) bedload

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas