ADDRESSING STRUCTURAL AND STRATIGRAPHIC ISSUES WITHIN THE ROANOKE RECESS FOR SEAMLESS BEDROCK GEOLOGIC MAPPING IN THE LEWISBURG 30 X 60 MINUTE QUADRANGLE

The Roanoke recess marks the junction of the Central and Southern Appalachians where structural and stratigraphic features distinctive of each blur, resulting in varied interpretations of deformation history and stratigraphic architecture. Ongoing 1:24k bedrock geologic mapping of the Paint Bank, Glace, Alleghany, and Potts Creek 7.5-minute quadrangles within the Roanoke recess documents: potential fold overprinting relations, horses within the St. Clair thrust previously unrecognized at 1:100k, and stratigraphic inconsistencies within the Upper Silurian-Lower Devonian and Upper Devonian-Lower Mississippian. Reconciling structural and stratigraphic complexity will aid in seamless mapping across state lines for the Lewisburg 1:100k compilation.

In the Paint Bank, Glace, and Alleghany quadrangles, the NE-striking St. Clair thrust juxtaposes Middle-Upper Ordovician carbonates and siliciclastics in the hanging wall over Silurian-Mississippian siliciclastics in the footwall syncline. Deformation in the fault zone is characterized by tight NW-vergent asymmetric folds and horses comprised of Upper Ordovician carbonate and Silurian sandstone. In the footwall, deformation is characterized by open NW-vergent folds with curved hinge lines that transition between Southern (~70°) to Central (~30°) Appalachian trends along strike. As the St. Clair thrust trends to the northeast within the Alleghany quadrangle, cross-strike faulting imbricates fold hinges top-to-the-SW. Similar deformation is observed in the Potts Creek quadrangle where fold hinges trending ~070° are imbricated to the SW and interfinger with folds trending ~050° forming domal structures.

Previous 1:100k mapping suggests the Upper Devonian Hampshire Formation extends into the Glace quadrangle; however, we find that fluvial facies characteristic of the Hampshire Formation terminate north of our study area. The Silurian Keefer and Williamsport Sandstones have collectively been called the “Eagle Rock sandstone” to the northeast, but these distinct sandstones can be traced southeastward from Paint Bank to Narrows, Virginia and are separated by 30-45 feet covered interval. Structural compression causes the removal of the less competent interbeds; thus, "Eagle Rock" is a structural package and not a true stratigraphic unit.