THREE NEW GEOLOGIC CROSS-SECTIONS IN THE APPALACHIAN PLATEAU AND VALLEY AND RIDGE PROVINCES OF THE SOUTHERN APPALACHIAN BASIN, WEST-CENTRAL TO NORTHEASTERN ALABAMA

The U.S. Geological Survey (USGS) is currently creating three new geologic cross sections each running northwest to southeast from 1) Pickens County to Greene County in west-central Alabama, 2) Fayette County through Tuscaloosa County to Bibb County in central Alabama, and 3) Cullman County through Blount and Etowah Counties to St. Clair County in northeast Alabama. They will be the 7th, 8th, and 9th in a series of USGS Appalachian Basin geologic cross sections. Other sections in this series span the northern and central parts of the basin. These new cross sections are 35, 57, and 45 miles (56, 92, and 72 km) long, perpendicular to the structural trend of the Appalachian Mountains. Stratigraphic correlations between 17 wells in the new cross sections were based on gamma ray well logs, core, and mud logs. Published geologic cross sections; stratigraphic correlation charts; and oil, gas, and coal reports were also used to interpret structural and stratigraphic relationships of the study area.

The new cross sections display important structural features including: (1) normal faulting of crystalline basement rocks in the Birmingham graben and adjacent horst blocks; (2) semi-horizontal decollement faults that bend upward and intersect the surface; (3) ductile duplex “mushwad” structures composed of thick sequences of highly contorted weak shales above a regional decollement and below competent carbonate roof rocks of a thrust ramp; (4) the Greene-Hale-Perry-Bibb depositional margin, where Devonian to Silurian black shales were explored for oil and gas; and (5) thick sequences of coal-bearing Pennsylvanian rocks in the Warrior and Cahaba coal basins in Fayette, Tuscaloosa, and Bibb Counties. The new cross sections provide information about the structural and stratigraphic framework that is useful for exploration of petroleum exploration (for example coal-bed gas and Devonian shale gas in Chattanooga and Floyd Shales); potential carbon dioxide storage in sandstone, salt, and carbonate formations; and the dynamics of fluid flow in the southern Appalachian Basin. Potential users and stakeholders of this project include companies and scientists involved in energy exploration and production, ecology, and climate change, members of academia, local, state, and federal governments, and the general public.