Abstract

The Wind River uplift extends in a general northwest-southeast direction for approximately 200 km across west-central Wyoming, and was formed during the Laramide orogeny by crustal-scale thrusting and associated folding in response to northeast-southwest regional horizontal compression. The gentle back limb of the Wind River uplift dips approximately 10-20 degrees to the northeast, into the Wind River basin. Developed on this "dip slope" are several smaller-scale structures that share similarities to the larger-scale structure and are therefore used to define further the structural style of the Wind River region.

The fold-thrust and related thrust models of foreland deformation best fit the basement-involved structural geometries of the Wind River uplift, the Sweetwater Crossing-Winkleman line of folding, and Red Canyon anticline; whereas, Windrock Ranch anticline and other minor flank structures are formed by detachment and thrusting in the sedimentary section. These flank structures are strongly asymmetric toward the southwest, exhibiting an "out-of-the-basin" vergence, or, in other words, a vergence up the flank of the Wind River dip slope. Characteristics of parallel (or concentric) folding, including overall geometric fold habit, and the occurrence of associated volumetric crowd structures, can be observed throughout the region.

A multi-order structural continuum was observed in the Wind River region, including small megascopic structures, outcrop-size to km-scale features, mountain uplifts and associated basins, and perhaps even the entire foreland itself. Despite pronounced differences is size, structures throughout the continuum are quite similar to one another.

Strain and stress data are supportive of the overall structural style. The maximum regional compressional strain in the Wind River region trends northeast-southwest, based on the well-expressed northwest-southeast trend of folding. Local strains determined by calcite-twin analysis show more variability, but are generally a reflection of complex internal strain conditions within the three-dimensional fold geometries. Evidence indicates that episodes of layer-parallel compression and layer-parallel shear played important roles during fold development.