GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 170-7
Presentation Time: 9:00 AM-6:30 PM


CUSH, Kylie G. and GRAY, Mary Beth, Geology and Environmental Geosciences, Bucknell University, Lewisburg, PA 17837,

Strip mining of coal in the east-central Pennsylvania Valley and Ridge province uncovered superb exposures of Alleghanian folds in the Bear Valley Strip Mine. Among these folds is the Whaleback Anticline, defined by folded Pennsylvanian Llewellyn Fm. sandstone. The focus of our study is the north anticline, adjacent to and north of the Whaleback. The north anticline is a non-plunging to gently E-plunging, upright, open, third-order fold capped by a ~30-cm-thick shale layer that directly overlies the sandstone exposed on the Whaleback. The shale is extensively faulted at the cm scale in contrast with wider spaced, higher displacement faults in the underlying sandstone layer exposed on the Whaleback. At present, we have measured more than 200 faults with mm- to cm-scale displacements. To understand the significance of these faults on the northern anticline, we mapped pavements at the cm scale and inventoried faults encountered on scanlines oriented normal and parallel to the fold axis. Bedding planes in the shale are littered with plant fossils, making it possible to determine fault displacements. We recorded the orientation, slip lineation, shear sense, net slip, and the amount of bed-parallel extension of faults in order to quantify strain and fault kinematics. On the north anticline, all faults extend bedding regardless of position on the fold or the strike of the faults. Fault densities and bed-parallel stretch values are highest on fold-normal transects. The geometric and kinematic relationships between the fault populations and dip domains across the fold will be assessed in an effort to examine strain patterns on this fold. Our findings will then be compared with those from the underlying Whaleback sandstone to examine lithological controls on the strain distribution. As part of a multidisciplinary study of the Bear Valley Strip Mine fold train, these findings ultimately will be used to test models of strain distribution as they relate to curvature and fold mechanics.