Early Tertiary Stratigraphy of Part of Central Utah

Abstract

Between Peterson Creek and Gooseberry Creek, SE. of Salina, Utah, a 7,800-ft.-thick section crops out that records post-Laramide events from the latest Cretaceous to early middle Tertiary. The preservation of this section is the result of a consistently low structural position through recurring regional uplifts of adjacent areas. The description of this Tertiary section supplements the excellent record of Laramide events obtained by studies of the complete Cretaceous section in the Wasatch plateau area. The section described begins with the North Horn formation, which records piedmont and succeeding lowland environments during contemporaneous orogenic activity farther W. The upper North Horn lacustrine shale sequence indicates the first inundation of this area by the early Tertiary Uinta Lake. The lake remained continuously while the Flagstaff limestone, Colton shale, and Green River shale and limestone were deposited, a continuous Paleocene to middle Eocene section totaling more than 2,300 ft. The lake withdrew because of post-Green River, pre-Crazy Hollow (late middle Eocene) positive movements, and erosion removed varying thicknesses of Green River prior to deposition of fluvial Crazy Hollow shale and sandstone. Central Utah was inundated again in the late Eocene by a lake. Volcanic activity on the S. or SW. at this time caused a fairly steady rain of fine pyroclastic material during deposition of the Bald Knoll formation; increased activity provided coarser debris for the Dipping Vat formation (new name). The late Eocene lake withdrew, and mudflows and conglomeratic tuffaceous sandstone of the Bullion Canyon volcanics were deposited. These sediments were derived from erosion of nearby volcanoes and represent the last of a nearly continuous sedimentary succession in central Utah from Jurassic to middle Tertiary. Igneous extrusives (Bullion Canyon lava flows) covered almost all the subject area in the early middle Tertiary. Stratigraphic relations indicate that monoclinal folding (Wasatch and Gates Creek monoclines) preceded and that high plateau normal faulting postdated the Bullion Canyon lava flows.