GEOLOGIC MAPS OF THE GRANT, LANGSTON, HOLLYWOOD, SCOTTSBORO, STEVENSON, SWEARENGIN, AND WANNVILLE 7.5-MINUTE QUADRANGLES, NORTHEAST ALABAMA

Supported in part by the U.S. Geological Survey's STATEMAP Program, the Geological Survey of Alabama has recently completed geologic mapping of seven 7.5-minute quadrangles in northeast Alabama. The quadrangles include urban and industrial growth corridors associated with the Appalachian Development Highway System and the projected route of the Memphis-Atlanta Interstate Highway. The area includes the southeast flank of the Nashville dome on the northwest and folds and thrust faults at the leading edge of the Appalachian thrust belt on the southeast. Stratigraphic units recognized include the Cambrian-Ordovician Knox Group; the Ordovician Stones River Group, Nashville Group, Inman Formation, Leipers Limestone, and Sequatchie Formation; Silurian Red Mountain Formation; Devonian Chattanooga Shale; Mississippian Maury Formation, Fort Payne Chert, Tuscumbia Limestone, Monteagle Limestone, Hartselle Sandstone, Bangor Limestone, and Pennington Formation; Pennsylvanian Pottsville Formation; and Quaternary alluvium and terrace deposits.

The structure of the area is dominated by the northwest-verging Sequatchie anticline, which shares a gently dipping common limb with the Sand Mountain syncline to the southeast. The steeply dipping northwestern forelimb of the anticline is cut by the southeast-dipping Sequatchie fault. Significantly, the new mapping has demonstrated the presence of northwest-dipping thrust faults (backthrusts) and associated southeast-verging folds in the hanging wall of the Sequatchie fault in this area. Additionally, a klippe of Fort Payne Chert structurally overlying the Monteagle Limestone northwest of the Sequatchie fault in the Wannville quadrangle is reminiscent of klippen mapped along strike near the Alabama-Tennessee state line (Milici and Finlayson, 1983).