STRUCTURAL GEOLOGY OF THE TRANSYLVANIA FAULT ZONE IN THE APPALACHIAN THRUST BELT, BEDFORD COUNTY, PENNSYLVANIA

Transverse zones cross strike of thrust belt structures as large-scale alignments of cross-strike structures. Frontal ramps form perpendicular to the direction of thrust translation and cut up-section across bedding. Frontal ramps generally extend for some distance along strike and end abruptly. Where a lateral ramp ends along strike, displacement is transferred across strike to another frontal ramp by way of a lateral ramp, a zone of displacement transfer, or a transverse fault. The cross-strike structures laterally connect the ends of frontal ramps across strike.

The Transylvania fault zone is a set of discontinuous right-lateral transverse faults striking at about 270º across Appalachian thrust-belt structures approximately along latitude 40º N in southern Pennsylvania. The beds were deformed by folding and thrusting during the Alleghanian orogeny. The rocks are semi-independently deformed on opposite sides of the transverse faults, indicating transverse fault movement during folding and thrusting. Near Everett, Pennsylvania, the Breezewood fault intersects the Everett Gap fault, which strikes at 290°. The Everett Gap fault ends westward where it intersects the Friends Cove thrust fault. Farther west in the footwall of the Friends Cove fault, the Bedford fault extends westward to an intersection with the Wills Mountain thrust fault. Both the Everett Gap fault and the Bedford fault terminate westward at a thrust fault, whereas other discontinuous fault segments end within thrust sheets.

Mapping of the Everett West 7.5-minute quadrangle depicts the Breezewood transverse fault, Everett Gap transverse fault, Friends Cove thrust fault, and Bedford transverse fault. Palinspastic restorations of balanced cross sections on either side of the fault zone are used to compare thrust fault displacement. A cross section north of the Everett Gap transverse fault shows an anticline that is not broken by a thrust fault. A cross section south of the transverse fault shows the Friends Cove thrust fault. The east-dipping hanging wall of the Friends Cove fault corresponds to the east limb of the anticline north of the Everett Gap transverse fault; however, the east-dipping panels are dextrally offset. Comparison of the cross sections shows that the Everett Gap transverse fault moved obliquely, dextrally and vertically.