Abstract

Realms of sedimentation of Permian rocks include basins, troughs, platforms, and shelves within or adjacent to the Cordilleran miogeosyncline. Peripheral tectonic uplands (Antler and Sonoma orogenic belts on the west, Utah-Wyoming and other shelves on the east), as well as intrageosynclinal positive areas (Northeast Nevada high, Western Utah high, Southern Nevada high, Emery uplift, and others), varied in degrees of tectonism and thus provided different types of detritus and material removed in solution to accumulate in the several depocenters. Oquirrh, Wood River, Bird Spring, Ely, Hamilton-Elko, Ferguson, Pequop-Diamond Creek, Montello-Sublett, Ruby, and Park City basins are the more negative parts of the geosyncline, whereas several shelves and the Riepe Spring, Collville, Pakoon, and Kaibob platforms identify the less negative repositories. Starved basins of relatively short geologic duration were present locally.

The study area, embracing western Utah, eastern Nevada, and a part of southern Idaho, is about 300 mi (483 km) wide in an east-west direction and about 525 mi (845 km) long north-south. The Permian includes slightly more than 17,000 ft (5,182 m) of sedimentary rocks in northwestern Utah, but thins to featheredges toward the orogenic belts on the west and the craton on the east. Most basinal accumulations exceed 5,000 ft (1,524 m), and many aggregate 6,000–10,000 ft (1,829–3,048 m). Rocks include a vast spectrum of limestone, dolostone, orthoquartzite, siltstone, sandstone, mudstone, gypstone, redbeds, and minor shale. They are of Wolfcampian, Leonardian, and Guadalupian ages. Fusulinids and some corals are abundant and are excellent guide fossils in Wolfcampian and Leonardian rocks, whereas mollusks (including some ammonoids), brachiopods, sponges, and conodonts hove stratigraphic value in younger sedimentary rocks. Conodonts in particular ore of index and correlation value in Guadalupion rocks.

During Wolfcampian time a thick sequence of orthoquartzite and shelly limestone accumulated in the Oquirrh, Wood River, and Hamilton-Elko basins, whereas bituminous carbonate rocks formed in the Ferguson basin. Clean carbonate sediments and various arenites typified the shelves and platforms. The Leonardian was a time of diversification into deeply subsiding troughs, basins, and areally extensive shelves and platforms; orthoquartzite, limestone, dolostone, some evaporites, redbeds, and related sediments formed. During Guadalupian time basinal carbonate rocks accumulated locally. Very cherty mudstone and carbonate sediment formed in other depocenters, whereas patch reefs, redbeds, sandstone, and evaporites were deposited in other depositional realms. Ochoan rocks, as identified elsewhere by certain ammonoids and advanced fusulinaceans, ore not recognized in the eastern Great Basin, but it cannot be stated with assurance that they ore absent. Lower Triassic nonmarine (and marine) rocks disconformably overlie Permian rocks in several places within the study area.

Oil is produced in limited quantity from Permian rocks within the study area in Utah, and hydrocarbon shows in wells have been very common. This vast area, however, has not been tested adequately. It is a structurally complex area, and exploration for oil and gas will be hazardous and costly.

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