Abstract

Sheep Mountain Anticline is a basement cored, doubly-plunging, asymmetric fold on the east limb of the Bighorn structural basin. The trend of the anticline parallels that of the Bighorn Mountain uplift located 20 miles to the east. The fold is cut by the Bighorn River perpendicular to the fold hinge, providing excellent exposure of Upper Paleozoic strata in the core of the fold. Field mapping of Sheep Mountain and associated folds north of the Bighorn River was undertaken to determine detailed fold geometries and observe deformation mechanisms operative within the sedimentary units. The pervasive nature of the bedding plane slip mechanism and related minor thrusting, combined with absence of features to suggest extension in the hinge area, presents evidence for regional compression of the sedimentary sequence during Laramide folding. A proposed model for deformation of rigid Precambrian basement rock along a reverse fault at the core of Sheep Mountain Anticline is consistent with evidence for regional compression of overlying sedimentary strata.