PALEOSTRESS AND FRACTURE ANALYSIS OF THE EASTERN BIGHORN MOUNTAINS AND WESTERN BLACK HILLS, POWDER RIVER BASIN

The Powder River Basin is a topographic and structural basin bounded to the west by the Bighorn Mountains in Wyoming and the east by the Black Hills Mountains in South Dakota. In accordance with the Plains CO₂ Reduction (PCOR) Partnership, we generated an extensive statewide compilation of existing structural data and collected new measurements on faults, fractures, and veins throughout the Powder River Basin. We collected oriented samples of calcite from veins within host rock Paleozoic limestones and sandstones throughout the Powder River Basin for laboratory analyses. We utilized calcite U-Pb geochronology to constrain the timing of vein emplacement (91.7 ± 4.6 Ma, Bighorn Mountains; 66.0 ± 11.0 Ma and 52.12 ± 0.5 Ma, Black Hills Mountains; 55.7 ± 1.8 Ma, Casper Arch Mountains). We additionally analyzed the samples in thin section for calcite twinning paleopiezometry. This will allow us to interpret both the magnitude and timing of shear stress on the flanks of the Powder River Basin.