Date of Graduation

Summer 2022


Master of Natural and Applied Science in Geography, Geology, and Planning


Geography, Geology, and Planning

Committee Chair

Matthew McKay


The Porter Gap 7.5–minute quadrangle in eastern Alabama contains portions of the undifferentiated sedimentary Knox Group of the Valley and Ridge province, the metamorphic Talladega Group of the western Blue Ridge, and the metamorphic Ashland Supergroup of the eastern Blue Ridge. Three major faults separate the rock units, including the Talladega-Cartersville fault, the Hillabee thrust fault, and the Hollins Line fault. Deformation and metamorphism of rocks within the Talladega Group occurred during the middle to late Mississippian (~334–320 Ma) recorded by stretched pebbles within the Cheaha Quartzite member of the Lay Dam Formation. Stretched pebbles within the Cheaha Quartzite have been elongated north-south and flattened east-west, suggesting an east-west deformational force acting on the rocks. Elongation was likely during the metamorphism of the Talladega Group. The beginning of deformation can be estimated using the youngest Talladega Group member, the Erin Slate (360-350 Ma), and the faulting of the Hillabee thrust onto the Talladega Group (∼350 and 320 Ma). The overall estimate for deformation time is ~359-325 Ma during an Acadian-Alleghanian Transition. Two hypotheses could explain the deformation patterns of the pebble elongation: subregional faulting of the Hollins Line fault and a regional deformation from an Appalachian-wide stress field.


Blue Ridge, southern Appalachians, Appalachian-wide stress field, Porter Gap, Talladega Group, Cheaha Quartzite

Subject Categories

Geology | Tectonics and Structure


© Tessa Mills

Open Access