Date of Thesis
Bachelor of Science
Mary Beth Gray
grain-scale strain analysis
Three-dimensional strain analyses were conducted to investigate grain-scale strain patterns on an iconic fold, providing insights into folding mechanisms. The "Whaleback" anticline within the Appalachian Valley and Ridge province displays superb exposures, allowing for detailed examination of a single folded sandstone layer in the Pennsylvanian Llewellyn Formation. The Bear Valley Strip Mine (BVSM), near Shamokin, Pennsylvania, was mined to extract semi-anthracite coal primarily from the Mammoth coal seam. When the mine was abandoned in the 1950's, it was not reclaimed and a single folded sandstone layer directly beneath the Mammoth coal seam was left exposed throughout the mine. As part of a preliminary study of grain-scale strain on the Whaleback, thirty-nine mutually perpendicular thin sections were prepared from 13 oriented hand samples along three axis-normal transects. Two-dimensional bulk rock finite strain was calculated using the normalized Fry method. Three-dimensional finite strain ellipsoids were then calculated for each sample site. In the plane of bedding, finite strain ratios range from 1.05 ± 0.02 to 1.24 ± 0.03. Normal to the fold axis, finite strain ratios range from 1.04 ± 0.02 to 1.21 ± 0.03. Finite strain ellipses in the plane of bedding are generally elongate sub-parallel to the fold axis. In fold-axis normal profiles, finite grain strain ellipses appear to be sheared towards the hinge of the fold. Octahedral shear values (εs) of strain ellipsoids range from 0.07 to 0.18 and are consistent with low magnitudes of 2D strain. Our preliminary study of strain patterns on the Whaleback anticline suggests that flexural flow occurred during folding.
Monfort, Eric Michael, "A Study of Three-Dimensional Grain-Scale Strain on the Bear Valley Strip Mine Whaleback Anticline Using Normalized Fry Analysis, Shamokin, PA" (2016). Honors Theses. 351.