Abstract: The Cacapon River Fault, Morgan County, West Virginia

Stuart L. Dean, Peter Lessing, Byron R. Kulander

Cacapon Mountain anticlinorium is one of the major positive structures west of the Great Valley in West Virginia and extends from Fulton County, Pennsylvania to Rockingham County, Virginia. The anticlinorium is asymmetrical to the west, with numerous folds and faults in Silurian and Devonian strata superimposed on it. Typical of these structures are Piney Ridge anticline, South Fork anticline, and Cacapon River fault. Cacapon Mountain anticlinorium developed as major folding proceeded westward of the Great Valley, first with development of Ferrel Ridge anticlinorium, then Sleepy Creek anticlinorium, and finally the Cacapon Mountain structure.

Early faulting above the Martinsburg detachment horizon generated complex folds and faults in the overlying Silurian, Devonian, and Mississippian section, with development of the Cacapon River splay fault from the Martinsburg detachment. Development of Cacapon Mountain anticlinorium as a fault bend anticline occurred through longitudinal ramping from a decollement horizon in Lower Cambrian Waynesboro Formation shales to the upper detachment level seated in shales of the Upper Ordovician Martinsburg Formation. Emplacement of the Cacapon Mountain structure folded the previously formed Cacapon River fault, with subsequent erosion exposing this feature in a narrow window on the northwest flank of the mountain in the Ridge quadrangle. Cacapon River fault re-emerges west of the window and i s trace trends southwest to northeast close to the outcrop of Devonian Oriskany Sandstone across Morgan County.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas