Testing Some Models of Foreland Deformation at the Thermopolis Anticline, Southern Bighorn Basin, Wyoming

The Thermopolis anticline is a typical structure in the Rocky Mountain foreland, southern Bighorn Basin, Wyoming. Photogeologic interpretation of Landsat Thematic Mapper data, in combination with the evaluation of topographic, bore hole, seismic reflection, and field data were used to analyze structure and constrain tectonic models. The anticline is near-concentric, asymmetric with a southwest sense of vergence, and plunges to the northwest. The steeply dipping to overturned southwest limb of the fold is cut at the surface by several thrust faults dipping northeast. Approximately 25% of the stratigraphic section on the southwest limb is missing due to faulting. Two east to northeast-striking, basement-controlled compartmental faults segment the anticline into three blocks that apparently deformed simultaneously but probably independently from one another. Slickensides indicate a dominant southwest tectonic transport direction. Additionally, subtle northeast-trending folds are superposed on the dominant northwest structural trend. Structural patterns at Thermopolis anticline can be explained using models that propose a single phase of northeast Laramide compression, combined with shear-zone deformation.