GEOLOGY OF THE 1:24,000 WADLEY SOUTH, ALABAMA, QUADRANGLE

The geology of the 1:24,000 Wadley South, Alabama, Quadrangle has the second highest mapping priority in the State of Alabama due to rapid development along the US-280 corridor (State of Alabama Geologic Mapping Advisory Committee, 2013). Detailed geologic mapping is needed for: (1) planning, development, environmental concerns, and for Source Water Protection studies as required by the Alabama Department of Environmental Management; (2) further characterization of precious metal and aggregate resources; and (3) addressing basic research questions concerning geologic evolution. Investigations of the study area were aimed at addressing several problems of Appalachian orogenic evolution. Objectives for this research are: (1) to map and characterize lithologies and clarify their distributions; (2) to analyze structures and fabrics, and; (3) to synthesize the geological history. Key findings are five-fold; (1) Brevard zone lithologies in the Wadley South Quadrangle are not easily separated into individual map units as depicted on 1:24,000-scale maps due to their gradational nature and subtle lithologic variation. (2) Formation of first generation D₁ structures accompanied Neoacadian lower-to middle-amphibolite-facies metamorphism of eastern Blue Ridge units, upper-greenschist to lower- amphibolite-facies metamorphism of the Jacksons Gap Group, and upper-amphibolite-facies metamorphism of rocks of the Inner Piedmont. (3) Early-syn D₁ fabrics and contacts are truncated along the Katy Creek fault, implying juxtaposition of the Dadeville Complex and Jacksons Gap Group during syn- to late-stage metamorphism. An inverted metamorphic gradient may be associated with the Katy Creek shear zone, suggesting formation during down heating associated with thrust emplacement of the overlying Dadeville Complex. (4) Plastic reactivation of the Brevard shear zone under middle-greenschist facies conditions during Alleghanian movement is recorded in meso- and microstructures preserved in retrograde mylonites associated with the Abanda shear zone. (5) The presence of cataclasite along the northwest side of the Alexander City and Abanda faults marks the final translation of the Eastern Blue Ridge and Jacksons Gap Group under supra-ductile-brittle conditions during the Mesozoic rifting of Pangea.