Fault chronology and uplift history of the southern Wind River Range, Wyoming: Implications for Laramide and post-Laramide deformation in the Rocky Mountain foreland
The stratigraphy, provenance, and structural involvement of tectogenic sedimentary rocks along the southern and western margins of the Wind River Range in western Wyoming record a complex Laramide and later uplift history and identify the timing and position of individual faulting events. The chronology of these events is (1) main uplift of the range by displacement on the Wind River fault between 90 and 49 to 50 Ma, (2) the formation of reverse faults in the hanging wall of the Wind River fault ca. 50 to 51 Ma, (3) sagging of the toe of the Wind River fault into sedimentary fill of the Green River basin between 46 and 23 Ma, (4) uplift of the core of the range along reactivated Precambrian shear zones between 30 and 23 Ma, and (5) collapse of the southern part of the range along normal faults beginning at 13 Ma. The sedimentary record of uplift and erosion indicates that erosion and basin fill kept pace (or caught up) with uplift, so that by the end of the Laramide, there was little topographic relief between the crest of the range and the adjacent Green River basin. The present topography of the range, characterized by a high-level erosion surface and distinct crestal ridge, derives from uplift of the erosion surface by the late Laramide reverse faulting, post-Laramide uplift of the crest of the range, and Neogene exhumation. Initial uplift of the range as early as 110 Ma and prior to displacement on the Wind River fault suggests either a pre-Laramide event of unknown origin or that Laramide crustal shortening began nearly 35 m.y. earlier than commonly assumed.