Structural chronology of the Alleghanian orogeny in southeastern West Virginia

The trend change between central and southern Appalachian structures is sharply defined in southeastern West Virginia. There, N30°-35°E trends coincident with major central Appalachian folds, such as the Browns Mountain anticline, end abruptly at N60°E-trending southern Appalachian structures along the St. Clair fault. Analysis of local and regional folds, cleavage, bedding-perpendicular stylolite seams and bedding, and fault slickenlines reveals that layer-parallel shortening, directed N10°-30°W, occurred in nonfolded Greenbrier Group (Mississippian) carbonates well into the present Appalachian Plateau area. This structural event is early and is associated with the evolution of southern Appalachian folds and faults south of the St. Clair fault. Central Appalachian folds and mesoscopic structures were superimposed on this early layer-parallel shortening fabric. This structural chronology indicates that southern Appalachian folds and faults predated the development of central Appalachian structures in the region.