NEW CROSS-SECTION IN CENTRAL ALABAMA ILLUSTRATING 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 in central Alabama. It will be the seventh in a series of USGS Appalachian Basin geologic cross-sections providing added insight into the regional structural and stratigraphic framework of the basin. This new 67 mile geologic cross-section runs parallel to the strike of the Appalachian Mountains, extending northeastward from Greene County, Alabama, through Hale and Perry counties, ending in Bibb County. Gamma ray and other well logs, including core and mud log records, from eight wells were used to correlate stratigraphic units from well to well. Previously published cross-sections, stratigraphic correlations charts, and oil, gas, and coal exploration reports were also utilized to interpret the structural and stratigraphic relationships in the geologic cross-section.

Major structural features shown in this new cross-section include: (1) bedding-plane detachment faults, which are associated with thrust fault ramps, (2) so-called “mushwad” structures, which are thick sequences of contorted weak shaley rocks overlying a regional decollement and underlying stiff roof rocks, (3) the Greene-Hale Synclinorium, where Devonian-aged black shale may be a hydrocarbon source, and (4) alternating anticlines and synclines in the Cahaba coal basin in Bibb County which contains numerous Pennsylvanian-age coal beds. Appalachian Basin geologic cross-sections published by the USGS are widely used to provide framework structural and stratigraphic information for research into petroleum systems (such as coal-bed methane in Alabama coal basins and Devonian shale gas from the Chattanooga Shale and other formations), potential CO₂ storage in sandstone, salt, and carbonate formations, and fluid flow dynamics across the southern Appalachian Basin.