THE JUNIATA CULMINATION AND ITS SIGNIFICANCE IN THE DEFORMATION HISTORY OF THE PENNSYLVANIA SALIENT, APPALACHIAN MOUNTAINS

Two competing models exist for the formation of the Pennsylvania salient, a widely studied area of pronounced curvature in the Appalachian mountain belt. The viability of these models can be tested by compiling and analyzing the patterns of structural orientation data collected in the center of the salient within the Juniata Culmination. Outcrops of Paleozoic sedimentary rocks contain 3^rd and 4^th order folds, conjugate faults, joints, conjugate en echelon gash vein arrays, spaced 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). Orientation analysis of successive stages of the progressive deformation at 19 discrete locations throughout the Valley and Ridge and southern Appalachian Plateau of Pennsylvania are used to constrain orientations of the maximum shortening direction (MSD) and establish whether these orientations have rotated during progressive deformation in the Juniata Culmination. One end member model (Gray and Stamatakos, 1997) predicts a NW-directed maximum shortening direction and no rotation through time in the Culmination. Alternatively a model by Wise (2004) requires a two-stage development of the Culmination involving NW-directed maximum shortening overprinted by WNW-directed maximum shortening. The available structural data from the Juniata Culmination do not suggest progressive, uniform patterns of rotation. Rather, they largely indicate uniform, parallel shortening directions consistent with the Gray and Stamatakos (1997) model.