Abstract

Southeastern Alabama stratigraphy, as shown in selected borehole records, includes a Cenozoic section (0 to ~1200 ft thick), an Upper Cretaceous section (~2300–3300 ft thick), and an immense clastic section (more than 6000 ft thick), including unnamed and/or poorly known Lower Cretaceous, Jurassic, and Triassic (?) stratigraphic units. Typical Upper and Middle Jurassic units of the Alabama and Mississippi Gulf Coastal Plain—the Werner Formation, the Louann Salt, the Norphlet Formation, the Smackover Formation, and the Haynesville Formation—are not present in the study area. Instead, directly below the Upper Cretaceous stratigraphic section lies an unnamed Lower Cretaceous clastic interval that consists of several hundred feet of high-frequency fining-upward sand sequences and sandy clays. Below that unit, lies several hundred feet of the Cotton Valley Group, an Upper Jurassic to Lower Cretaceous, fine- to coarse-grained clastic unit. Below the Cotton Valley lies an unnamed, Upper Triassic (?)–Upper Jurassic stratigraphic unit comprised of coarse- to fine-grained clastics, which is estimated to be about 2250 ft thick. The lower part of this unnamed unit is a relatively thin, Upper Triassic (?)–Lower Jurassic clastic unit, which is a clastic red-bed sequence (probably the Eagle Mills Formation). The probable Eagle Mills lies unconformably upon the local Paleozoic basement.