Date of Award
This study characterizes the deformational history of a ~ 700 m long exposure in the Upper Devonian Irish Springs member of the Catskill Formation in the southern Valley and Ridge province. The study area is located along the west shore of the Susquehanna River in the hinge of the Pennsylvania salient. The sandstones, siltstones, and shales contain 3rd and 4th order folds, conjugate wedge faults, thrust faults, joints, cleavage, and grain-scale finite strain indicators. This suite of structures records a complex deformational history similar to the Bear Valley sequence of progressive deformation (Nickelsen, 1979) observed 40 km to the ENE. Analysis of the orientations of structural features from successive stages of the progressive deformation is used to constrain the orientations of the maximum shortening direction (MSD) and to distinguish between a single-stage (Gray and Stamatakos, 1997) and two-stage (Wise, 2004) model for the development of the Pennsylvania salient. Consistently oriented MSDs ranging from ~335° to 351 °at the study area parallel findings 100 km to the NW in the hinge of the salient at the Appalachian structural front (Spiker and Gray, 1997). This is distinctly different from the CW rotations of MSDs seen in the Reading Prong (e.g. Gray and Mitra, 1993) and CCW rotation of MSDs in the Blue Ridge (e.g., Nickel sen, 2009), suggesting that the hinge of the Pennsylvania salient coincides with an axis of no rotation of MSDs, consistent with the single-stage model (Gray and Stamatakos, 1997).
Wills, Marci Allison, "A Study of Progressive Deformation in the Hinge of the Pennsylvania Salient; Southern Valley and Ridge Province, Perry County, PA" (2010). Dickinson College Honors Theses. Paper 100.