Date of Thesis
Honors Thesis (Bucknell Access Only)
Bachelor of Science
Mary Beth Gray
structural geology, Bear Valley strip mine, faults, fold, strain, kinematic analyses, Shamokin Pennsylvania
Centimeter- to millimeter-scale fault data were collected over a fold and analyzed in order to gain insights into folding mechanisms and how folds accommodate strain. Strip mining of semi-anthracite coal in the east-central Pennsylvania Valley and Ridge Province uncovered superb exposures of Alleghanian folds in the Bear Valley Strip Mine, approximately 2 km southwest of Shamokin, PA. Among these folds is the iconic Whaleback anticline, defined by folded Pennsylvanian Llewellyn Fm. sandstone. The north anticline is adjacent to and north of the Whaleback. The north anticline is a non-plunging to gently east-plunging, upright, open, third-order fold capped by a ~30-cm-thick carbonaceous silty shale layer that directly overlies the sandstone exposed on the Whaleback. The fault array in the exposed carbonaceous silty shale outer arc of the north anticline is the focus of the study. To understand the significance of the faults on the north anticline, pavement mapping and scanline mapping techniques were implemented. The orientation, slip lineation, shear sense, net slip, and the amount of bed-parallel extension of over 300 faults were recorded in order to quantify strain and fault kinematics. This study found that all faults extend bedding regardless of position on the fold or the strike of the faults. Principal incremental shortening and extension axes rotate with bedding across the fold. The two average extensional fault orientations have an acute angle bisector that is subparallel to bedding. The average fault orientations are 080, 21S and 261, 41N (when bedding is rotated to horizontal). The relationships between bedding, fault orientations, and kinematic axes across the north anticline suggest that the faults formed during (rather than before or after) folding. When compared to two common fold models, the strain pattern produced by the north anticline extensional fault array may be best categorized as a combination of tangential longitudinal strain and flexural flow.
Cush, Kylie Grace, "Insights into Folding Mechanisms From Fault Analyses On the North Anticline, Bear Valley Strip Mine, Shamokin, PA" (2017). Honors Theses. 403.