NEW INTERPRETATION OF THE LATE ALLEGHENIAN STANLEY FAULT SYSTEM WITHIN THE VALLEY AND RIDGE OF PAGE COUNTY, VIRGINIA

New, detailed, 1:24,000 scale geologic mapping of the Stanley 7.5 minute quadrangle, Page Valley, Virginia has provided an updated interpretation of the Stanley Fault and its significance as a late Alleghenian thrust system. Bound to the west by the Massanutten Synclinorium and to the east by the Blue Ridge Anticlinorium, Page Valley comprises the eastern half of the Great Valley and is predominately underlain by Early Ordovician carbonates of the South Fork Anticline (Sarros, 1995). The area is transected by the Stanley Fault, mapped by King (1950) as a high angle reverse fault with oblique-slip displacement. Reinterpreted by Sarros (1995), the Stanley Fault was mapped as a complex system of several low angle, west-directed thrusts. This previous mapping in the Stanley area interpreted carbonate breccias within the Beekmantown Group as indicators of thrust movement. However, these breccias consist of large angular clasts showing no internal deformation and absence of other typical fault fabrics. In addition, there is a distinct absence of breccia in known fault outcrops. This led to our reinterpretation of the breccias as paleokarst features characteristic of the upper Beekmantown Group in proximity to the Knox Unconformity. New detailed mapping of lithologic relationships and structural features in the Stanley quadrangle suggest that the Stanley Fault is a more restricted system of low to moderate angle, northwest directed thrusts that place Late Cambrian carbonates over Early Ordovician carbonates. Northwest-directed thrusting is indicated by isoclinal folding in the hangingwall proximal to the fault, in contrast to broad folding within the footwall. The Stanley Fault trends southwest-northeast, cutting across both the Valley and Ridge and Blue Ridge, suggesting late Alleghenian movement. Future work will focus on the Stanley Fault in the Big Meadows quadrangle to the east, where the fault may have reactivated a section of the basal Blue Ridge thrust system.