NEW GEOLOGIC CROSS SECTION FROM GREENE COUNTY, WEST-CENTRAL ALABAMA, TO BIBB COUNTY, CENTRAL ALABAMA, SHOWING THE REGIONAL STRUCTURAL AND STRATIGRAPHIC FRAMEWORK OF THE VALLEY AND RIDGE PROVINCE IN THE SOUTHERN APPALACHIAN BASIN

The U.S. Geological Survey (USGS) has created a new geologic cross section running from southwest to northeast from Greene County in west-central Alabama, through Hale and Perry Counties, to Bibb County in central Alabama. It will be the seventh in a series of USGS Appalachian Basin geologic cross sections. This new geologic cross section is 69 miles (111 km) long, running parallel to the structural trend of the Appalachian Mountains. Stratigraphic correlations between eight wells were based on gamma ray well logs, core, and mud log records. Previously published geologic cross sections; stratigraphic correlation charts; and oil, gas, and coal exploration reports for oil, gas, and coal were also used to interpret the structural and stratigraphic relationships of the study area.

The new cross section displays several 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 to the northwest and intersect the surface; (3) ductile duplex “mushwad” structures, composed of thick sequences of highly contorted weak shales that overlie a regional decollement and underlie competent carbonate roof rocks of an overlying thrust ramp; (4) the Greene-Hale-Perry-Bibb Synclinorium, where Devonian to Silurian black shales have been explored for oil and gas; and (5) a thick sequence of coal-bearing Pennsylvanian rocks in the Cahaba coal basin in Bibb County. The cross section provides information about the structural and stratigraphic framework that can be used for exploration of petroleum systems (e.g., coal-bed methane in Alabama coal basins and Devonian shale gas in the Chattanooga and Floyd Shales); potential CO₂ storage reservoirs in sandstone, salt, and carbonate formations; and the dynamics of fluid flow in the southern Appalachian Basin.