THE APPALACHIAN THRUST BELT BENEATH THE COVER OF THE MESOZOIC-CENOZOIC COASTAL PLAIN IN WESTERN ALABAMA AND EASTERN MISSISSIPPI

The exposed southern Appalachian foreland thrust belt trends northeast to southwest and extends beneath the cover of the Mesozoic Cenozoic Gulf Coastal Plain in western Alabama. The subsurface Appalachian thrust belt continues southwest across western Alabama and into east central Mississippi, where it truncates the frontal structures of the Ouachita thrust belt. For the subsurface thrust belt, drill cuttings and cores, geophysical well logs, and seismic reflection profiles support construction of balanced cross sections and a regional palinspastic map. Well data and seismic reflection profiles enable stratigraphic correlation from the outcrop to the subsurface. The new cross sections and palinspastic map, along with those of the exposed thrust belt (Thomas and Bayona, 2005), provide a regional palinspastic reconstruction from Georgia southwestward to east central Mississippi.

The frontal structure of the exposed thrust belt, the relatively low amplitude Sequatchie anticline, ends southwestward northeast of the Gulf Coastal Plain onlap. Farther southwest, the thrust front is defined by the Jones Valley fault and Blue Creek splay. The high-amplitude frontal ramp of the Jones Valley fault apparently ends southwestward at a lateral ramp near the Coastal Plain onlap; and farther southwest, the frontal structure may be a continuation of the Blue Creek fault, which extends to east-central Mississippi. Seismic reflection profiles suggest a similar arrangement of a lateral ramp and a leading splay along the subsurface trace of the Helena fault, at the southeastern trailing cutoff of the Jones Valley thrust sheet. Well and seismic data define the trace of the Talladega fault at the trailing edge of the sedimentary thrust belt.

Along the Alabama-Mississippi border, a separate frontal structure, the subsurface Pickens-Sumter anticline, is in a structural position similar to and aligned with the Sequatchie anticline. The Pickens-Sumter anticline ends northeastward along strike via a displacement gradient in Alabama, and it ends southwestward at a lateral ramp in Mississippi.