Detailed study and measurement of 30 stratigraphic sections, and reconnaissance of numerous other sections of Permian marine rocks of the eastern half of Nevada, western half of Utah, and central to south-central Idaho indicate that certain revisions in nomenclature are justified. This area in the eastern Great Basin contains excellent sections of Late Paleozoic marine rocks, most of which contain diagnostic fusulinid faunas. Within the Permian system representatives of the Wolfcampian, Leonardian, and Guadalupean time-equivalents are areally extensive. In most of eastern Nevada and part of western Utah a widespread regional disconformity separates Permian from Pennsylvanian rocks, and commonly this is represented by absence or truncation of strata of medial to late Pennsylvanian age. This disconformity is slight or missing in the Oquirrh Formation of Utah and southern Idaho, the Wood River Formation of central Idaho, and certain limestones and related sedimentary rocks of east-central Idaho.

The Ferguson Mountain Formation, mostly Wolfcampian in age but locally of late Virgilian age at the base and early Leonardian age at the top, is of wide areal extent and at its type locality in eastern Elko County, Nevada, contains one of the most prolific Wolfcampian fusulinid faunas in the eastern Great Basin. It is conformably overlain by the Pequop Formation, Leonardian in age, also rich in fusulinids. The Pequop is unconformably overlain by the Loray Formation, a dolomitic and gypsiferous sequence laid down in retreating epeiric seas. The Park City Group includes, in ascending order, Kaibab Limestone, Plympton Formation, and Gerster Formation. These are of late Leonardian to Capitanian age. The Indian Canyon Formation comprises sandy, cherty, and dolomitic rocks beneath the Gerster and above the Plympton, but was not originally included in the Park City Group.

In southern Nevada, basin facies include the Bird Spring Formation (Pennsylvanian), conformably overlain by the Spring Mountain Formation (Wolfcampian and Leonardian age). Shelf facies to the east consist, in ascending order, of: Callville Limestone (Pennsylvanian), and Pakoon Limestone (Wolfcampian), Queantoweap Sandstone, Hermit Formation, Coconino Sandstone, Toroweap Formation, and Kaibab Formation (the last two are of Leonardian to early Wordian age). Kaibab Formation also is in the basin. Permian rocks in this area, and to the north, are disconformably overlain by early Triassic sedimentary rocks (Moenkopi or Thaynes Formations).

Carbonates predominate in the stratigraphic sections and are bioclastic, matrix, micritic, detrital, and combined types. Sediments accumulated in different repositories of the miogeosyncline; with varying degrees of tectonism in the Antler-Sonoma orogenic belt on the west, intra-geosynclinal highlands, and shelves to the east, numerous lithologic associations formed, including evaporites.

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