Abstract The Oquirrh Basin of central and northwestern Utah was a major downwarp in the Cordilleran miogeosyncline during the Pennsylvanian and Permian. During Late Mississippiantime its forerunner was the Great Blue depocenter in which accumulated from 800 to 1,400 m of dark, gray to black, dense, siliceous and sparsely fossiliferous limestone and calcareous siltstone with minor dark-gray shale units. The Great Blue basin was subovate, and covered about 7,500 sq km area in the eastern part of the miogeosyncline. The following reasons indicate a deep-water origin for most of the limestone of the Great Blue Formation: (1) areally extensive distribution of mostly homogeneous dark colored, argillaceous and siliceous limestone; (2) within the thick succession of this limestone, a monotonous repetition of laminated to thin-and medium-bedded strata is characteristic; numerous strata range from millimeter- to centimeter-thin units; (3) rocks are siliceous and contain substantial amounts of black iron monosulfide, as well as cryptocrystalline varieties of pyrite and/or marcasite; (4) within all sections studied, flysch-like arrangement of strata is typical; some units display graded bedding; (5) most of the formation in outcrops near Provo, Utah, is sparsely fossilferous to nonfossiliferous; forms include a depauperate fauna of thin-shelled chonetid brachiopods; (6) some sections contain exotic blocks of coral-bearing limestone interpreted to have been gravity-driven downslope into deeper waters of the sedimentary basin; (7) some of the shale units contain the trace fossil Scalarituba missouriensis Weller (particularly those shales containing the exotic limestone blocks mentioned above); this trace fossil is a form common in deep to intermediate waters of the Mississippian and Pennsylvanian, particularly in the deep-water part of the Oquirrh Basin. As herein interpreted, the Great Blue depocenter was the forerunner of the Oquirrh Basin. The latter was a deep-water depocenter during parts of the Pennsylvanian and Permian. Accordingly, this downwarped segment of a part of the eastern Cordilleran miogeosyncline subsided locally to possibly bathyal depths during Late Mississippian time. Considerable quantities of terrigenous material were swept from the craton on the east and northeast and the Emery uplift and Uncompahgre highland to the southeast. This material moved downslope into deeper waters to accumulate with carbonate material to form impure argillaceous limestone. Siliceous, clayey, and argillaceous lime mud derived from the northeast Nevada highland of Nevada and Utah, the western Utah highland, and Antler orogenic belt in Nevada entered the western side of the Great Blue depocenter.

Abstract Mississippian, Pennsylvanian, Permian and Lower Triassic strata in the eastern Great Basin aggregate almost 12,250 m (40,000 ft) of dominantly marine clastics and carbonates that accumulated in the eastern part of the miogeosynclinal belt of the Cordilleran geosyncline. Subsidence and hypersubsidence created depocenters in the Oquirrh, Sublett, Arcturus, Park City, Bird Spring and other sedimentary basins within this region. Late Paleozoic (Antler and Sonoma) and early Mesozoic (ancestral Sevier) tectonism within and west of but adjacent to the miogeosynclinal belt controlled contrasting realms of clastic and carbonate sedimentation within and near these basins. Various highlands in western and northwestern Utah, in eastern and northeastern Nevada, in southern Nevada, and in orogenic belts (Antler and Sonoma) lying still farther west were stripped, in some instances into their Precambrian cores, to provide some sediment to the adjacent mobile depocenters. The Emery, Uncompahgre, and Kaibab uplifts southeast of the miogeosynclinal belt also were source areas at times. However, the continental craton to the east and northeast provided most of the sediment which makes up the abnormal thickness of clastic strata in the basins described. Sediment derived from Precambrian and younger rocks in Wyoming, Montana, and Alberta was transported southerly, then westerly, and dumped into the various depocenters. Although the Sonoma orogeny was a major tectonic event farther west during Late Permian and Early Triassic times, the transition from Permian to Early Triassic was not marked by major deformation in the eastern part of the miogeosynclinal belt Only a paraconformity marks the Permian-Triassic boundary at many places in the miogeosynclinal belt, although significant disconformities are present locally. Up to 1225 m (4000 ft) of Lower Triassic sediments accumulated during the waning stages of deposition, but by mid-Triassic time a major tectonic reversal occurred. The region that had been a negative mobile belt since late Precambrian time was then uplifted, whereas the region east of the Las Vegas-Wasatch hinge line became negative, and the hinge line was the fulcrum. The Cordilleran geosyncline was destroyed before the end of the Triassic, and throughout much of the Late Triassic, Jurassic, and Cretaceous some of its sediments were stripped away, to be recycled and deposited in the Rocky Mountain geosyncline to the east. The tectonic behavior of the Las Vegas-Wasatch hinge line thus controlled sedimentation over a large region throughout Paleozoic and Mesozoic time.