Oquirrh Basin Research Articles

Sediment routing and provenance of shallow to deep marine sandstones in the late Paleozoic Oquirrh Basin, Utah

The Oquirrh-Wood River Basin is a Pennsylvanian to Permian clastic and carbonate basin in northwestern Utah and southern Idaho, USA. The basin is commonly considered the northwesternmost expression of the Ancestral Rocky Mountains (ARM). Basin fill is locally up to 9 km thick. Facies range from shelf carbonates to deep marine debrites, and generally deepen from basin initiation to the beginning of the Permian. Unlike other ARM basins, no basin-bounding fault or highland has been identified as the source of these thick deposits and the tectonic drivers of basin subsidence are poorly understood.Tectonic subsidence analysis was performed on 10 stratigraphic sections across the basin, resulting in a two-phase tectonism model. Pennsylvanian subsidence is interpreted as being related to strike-slip deformation; whereas Permian subsidence in the western part of the basin may be related to the uplift and unconformity sequence documented in northeastern Nevada.Detrital zircon geochronology and thin section point counts are relatively uniform in Middle Pennsylvanian and early Permian samples, suggesting local tectonism did not alter dominant sediment routing patterns. Oquirrh Group sandstones are compositionally mature and contain sparse feldspar or lithic grains, leading to the interpretation that sample sediments were derived from recycled orogenic sources. UPb ages on detrital zircons from three Pennsylvanian and three Permian samples suggest sediment was overwhelmingly derived from multiple Laurentian basement provinces to the north and east, consistent with interpretations from the Wood River Basin. Paleocurrent data indicate a prevailing southward ocean current, suggesting a combination of sediment recycling and sediment transport across Laurentia from orogenic highlands in the northeast to the Oquirrh-Wood River Basin throughout the late Paleozoic.

Tectonic Analysis of the Pennsylvanian Ely‐Bird Spring Basin: Late Paleozoic Tectonism on the Southwestern Laurentia Margin and the Distal Limit of the Ancestral Rocky Mountains

AbstractDuring Pennsylvanian to Early Permian time, much of southwestern Laurentia experienced broad deformation far from the nearest plate boundaries. The bulk of this deformation is known as the Ancestral Rocky Mountains orogeny, which consists of several basement uplifts and proximal basins north and northwest of the Ouachita‐Marathon suture. The Ely‐Bird Spring basin formed during this time, located between the classic Ancestral Rocky Mountains and the complex and poorly constrained western Laurentian margin. In this study, we used tectonic subsidence curve analyses to evaluate the tectonic style of basin subsidence in this basin and several northern Ancestral Rocky Mountains basins. The Ely‐Bird Spring and Wood River basins have convex upward and stair‐stepped tectonic subsidence curves similar to curves from migrating foreland basins. These curves, combined with sedimentological and structural data, are consistent with these basins forming due to loading from the west and northwest as part of the complex western Laurentian plate boundary, not due to classic Ancestral Rocky Mountains tectonics. The other northern Ancestral Rocky Mountains basins have much steeper and more linear subsidence curves, similar to foreland basins with fixed loads. However, the Oquirrh basin, in particular, displays a large amount of subsidence far from hypothesized tectonic drivers of deformation. A combination of transmitted stress from both the western Laurentia margin and traditional Ancestral Rocky Mountains tectonism explains the anomalously large subsidence in the Oquirrh basin. Therefore, transmitted stresses from more than one side of western and southern Laurentia are required to explain the observed pattern of deformation.

An alternative interpretation for the map expression of “abrupt” changes in lateral stratigraphic level near transverse zones in fold-thrust belts

The map expression of “abrupt” changes in lateral stratigraphic level of a thrust fault has been traditionally interpreted to be a result of the presence of (1) a lateral (or oblique) thrust-ramp, or (2) a frontal ramp with displacement gradient, and/or (3) a combination of these geometries. These geometries have been used to interpret the structures near transverse zones in fold-thrust belts (FTB). This contribution outlines an alternative explanation that can result in the same map pattern by lateral variations in stratigraphy along the strike of a low angle thrust fault. We describe the natural example of the Leamington transverse zone, which marks the southern margin of the Pennsylvanian–Permian Oquirrh basin with genetically related lateral stratigraphic variations in the North American Sevier FTB. Thus, the observed map pattern at this zone is closely related to lateral stratigraphic variations along the strike of a horizontal fault. Even though the present-day erosional level shows the map pattern that could be interpreted as a lateral ramp, the observed structures along the Leamington zone most likely share the effects of the presence of a lateral (or oblique) ramp, lateral stratigraphic variations along the fault trace, and the displacement gradient.

The long-term burial and exhumation history of basement blocks in the footwall of the Wasatch fault, Utah

Thermochronologic studies of the Santaquin and Farmington Canyon crystalline basement complexes, exposed in the footwall of the Wasatch fault in Utah, provide rare opportunities to investigate the long-term tectonic, burial, and exhumation history of this region. Both complexes underwent amphibolite-facies metamorphism at ∼1700 Ma, followed by a complex pressure-temperature-time history. By 740–770 Ma, exhumation had brought both complexes to the surface from a depth of ∼9–10 km (3–3.5 kbar), followed by reburial by passive margin, Oquirrh Basin, and foreland basin sedimentation from Neoproterozoic through early Cretaceous time. The final structural pathway to present-day surface exposure of both complexes began in early Cretaceous time, with crustal contraction along the Sevier belt and resultant structural stacking. Structural breaching of the thrust culminations and final cooling of the crystalline complexes occurred as a result of Tertiary through Holocene extension and accompanying normal faulting. Inferred exhumation rates for the last 10–15 my are on the order of 0.3–0.6 mm/yr, although recent slip rates across the Wasatch fault appear to be several times higher. This suggests that: (1) periods of enhanced slip on the Wasatch fault from Miocene to present time may have been punctuated by periods of quiescence; and (2) the fault now may be experiencing an episode of rapid slip. Alternatively, strain may have been partitioned into multiple fault strands at a boundary between the Provo and Nephi segments.

The Oquirrh Basin Revisited

The upper Paleozoic succession in the Oquirrh basin is unusually thick, up to 9300 m, and consists mainly of a Pennsylvanian-middle Permian sedimentary package located within the Cordilleran miogeocline of northwestern Utah. Previous workers have suggested a tectonic origin for the Oquirrh basin that is incompatible with the basin location in both time and space. There is no evidence for Pennsylvanian and Lower Permian tectonism in the middle of the miogeocline. Thermal evidence from the Mississippian Mission Canyon shale does not support the implied deep burial of the crustal sag models of basin formation. Stratigraphic and facies evidence indicates a growth fault origin for the basin. Regional isopach maps and facies maps are powerful tools in interpreting depositional environments and in reconstructing fold-and-thrust belts. However, the location of measured sections relative to the location of the growth fault needs special consideration for these tools to be effective in reconstructing a thrusted growth fault basin. The Charleston-Nebo thrust may have essentially reversed the movement on a growth fault. Thick Oquirrh basin sedimentary rocks may not be required to balance structural sections across this thrust fault. A thin-skinned, extensional growth fault origin for the Oquirrh basin implies that the Cordilleran miogeocline did not participate in the Pennsylvanian north-vergent uplifts of the Ancestral Rocky Mountains.

Carboniferous biogeography of the bryozoanArchimedesin North America

The fenestrate bryozoan genus Archimedes apparently originated and then diversified in Early Carboniferous seas of eastern North America. Its highest species richness and greatest abundance are reached in uppermost Lower to lowest Upper Carboniferous (Chesterian) rocks of eastern North America. Following the unconformity that marks the mid‐Carboniferous eustatic event, however, it is known in North America only in Upper Carboniferous basinal deposits of the Oquirrh Mountains and in nearby regions of Utah and Nevada. It is hypothesized that Archimedes’ life‐history patterns caused the biogeographical change: dependence on fragmentation as a means of recruitment did not allow Archimedes to keep up with its rapidly migrating preferred back‐barrier environment during the numerous eustatic transgressive and regressive cycles that caused the shoreline to sweep across North America during the Late Carboniferous. The persistence of Archimedes in the Oquirrh Basin and vicinity is inferred to have resulted from its...

Characteristic trace-fossil associations in oxygen-poor sedimentary environments

Research Article| August 01, 1988 Characteristic trace-fossil associations in oxygen-poor sedimentary environments A. A. Ekdale; A. A. Ekdale 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 Search for other works by this author on: GSW Google Scholar T. R. Mason T. R. Mason 2Department of Geology and Applied Geology, University of Natal, Durban 4001, South Africa Search for other works by this author on: GSW Google Scholar Geology (1988) 16 (8): 720–723. https://doi.org/10.1130/0091-7613(1988)016<0720:CTFAIO>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation A. A. Ekdale, T. R. Mason; Characteristic trace-fossil associations in oxygen-poor sedimentary environments. Geology 1988;; 16 (8): 720–723. doi: https://doi.org/10.1130/0091-7613(1988)016<0720:CTFAIO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The sedimentologic record of oxygen-poor depositional environments typically includes trace fossils produced by deposit-feeding organisms. We propose an oxygen-controlled trace-fossil model in which increasing oxygen concentration of interstitial water in sediment parallels a transition from fodinichnia-dominated through pascichnia-dominated to domichnia-dominated trace-fossil associations. In certain places, such as parts of the late Paleozoic Oquirrh Basin in Utah, this model provides a reasonable alternative to the more traditional, depth-controlled model of trace-fossil distribution. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Preliminary Basin Analysis of Late Pennsylvanian-Permian Wood River Basin, South-Central Idaho: ABSTRACT

Stratigraphic correlation of partly coeval tectonostratigraphic units in the Smoky and Boulder Mountains, west and north (respectively) of Ketchum, Idaho, allows for reconstruction of the Late Pennsylvanian-Early Permian Wood River basin. These tectonostratigraphic units contain calcareous sandstones, silty limestones, and carbonaceous siltites and shales of the Wood River Formation (units 6 and 7 - Virgilian-Wolfcampian), Grand Prize Formation (Wolfcampian(.)), and Dollarhide Formation (Wolfcampian). Interpretation of sedimentary facies, petrologic characteristics, and structural relations suggests contiguous deposition of these units in a westward deepening basin in shallow shelf, outer shelf to upper slope, and lower slope to basin environments, respectively. In the Wood River basin, vertical facies changes within each formation are similar to lateral facies changes progressively westward between formations, as suggested by palinspastic reconstructions. Upsection and to the west, thick sequences of calcareous sands give way to fine-grained carbonaceous sediments, suggesting a deepening of depositional environments through time. Regional sea level rise, basin subsidence, or both, during Virgilian to early Wolfcampian time, is suggested by deepening-upward facies transitions in rocks of both the Wood River basin of central Utah and Oquirrh basin of northern Utah. Both basins evolved from shallow to moderate depth shelf-and-slope environments to more restricted, deeper watermore » environments. Paleogeography and basin development are relatively well constrained in the Oquirrh basin, but is more tentative in the Wood River basin where a lack of biostratigraphic control and structural complexities permit only tentative paleogeographic reconstruction.« less

Lithostratigraphy and Conodont Biostratigraphy of a West Canyon Limestone Equivalent (Upper Mississippian-Middle Pennsylvanian) in Southeastern Idaho: ABSTRACT

Upper Mississippian to Lower-Middle Pennsylvanian limestones and calcareous sandstones, which overlie the Manning Canyon Formation, crop out in the Albion, Sublett, and Bannock Ranges and the Black Pine, Deep creek, and Samaria Mountains, and have been assigned to various formations and groups. Five carbonate and two siliciclastic lithofacies are recognized: bioclastic packstones to grainstones; whole-fossil wackestones to muddy packstones; bioturbated, arenaceous mudstones to wackestones; oncolite packstones to grainstones; bryozoan framestones; calcareous quartz arenites to sublithic arenites; and calcareous shales. The lithologies are interpreted as being deposited on a barrier shoal carbonate ramp along the eastern margin of the Oquirrh basin and are time-equivalent to the West Canyon Limestone of northwestern Utah.

Shallow-Water Clastic Sediments of Great Blue Formation and Manning Canyon Shale, Oquirrh Basin, Utah: ABSTRACT

An east-west belt of clastic sediments in the Mississippian Great Blue Formation and Manning Canyon Shale thickens and coarsens westward and contains terrestrial plant and palynomorph assemblages. These clastic sediments were derived from the Antler highlands in central Nevada. The depositional axis of the clastic belt or proto-Oquirrh basin is probably related to a basement weakness that controlled the east-west-trending Uinta basin. The geometry of the belt is illustrated by isopach maps and cross sections. An isopach map of the total Mississippian clastics in eastern Nevada and Utah and an east-west cross section through the Oquirrh basin demonstrate that the clastics thicken and coarsen westward and indicate a western source. A north-south cross section illustrates ho the clastic sediments were restricted to the east-west clastic belt. In contrast to previous interpretations that assumed that the clastic sediments were shed westward from the craton into deep water, field evidence suggests that they were shed eastward from the rising Antler mountains into very shallow water. Terrestrial plants preserved in shales and sandstones of the Great Blue Formation and the Manning Canyon Shale suggest that the clastic sediments were deposited in a transitional environment such as lagoons, distal flood plains, and deltas. Palynomorph assemblages in the shales lack marine forms and also indicate shallow-water deposition. In addition, surface gamma-ray patterns of measured sections are typical of transitional facies sequences such as deltas and nearshore environments. End_of_Article - Last_Page 934------------

Climatic and Structural Controls of Stacked Algal Lime Mud Mound Development in Oquirrh Group (Pennsylvanian and Permian), Deep Creek Mountains, Southeastern Idaho: ABSTRACT

Oquirrh Group rocks comprise the uppermost of a series of allochthons exposed in southern Idaho. The basal unit of the Oquirrh Group, the West Canyon Limestone (Atokan), is composed largely of lime mudstone and fossiliferous lime wackestone with the exception of a coarse qaurtzarenite and lime mudstone clast debris flow that originated from syndepositional faulting. Overlying this unit are unnamed cyclic back-mound siltstones, sandstones, cherts, and fossiliferous wackestones and packstones that thicken southward from 270 to an estimated 1,000 m of noncyclic strata of similar lithologies. Cyclic, thinly stacked algal lime mud mounds are inferred to have developed in Desmoinesian time. In Virgilian time, syndepositional faulting controlled the development of thickly stacke (700 m) algal, lime-mud mounds. To the north and west, cyclic back-mound lithofacies consist of siltstone, sandstone, chert, lime mudstone, and fossiliferous wackestone and packstone. Similar but noncyclic fore-mound lithofacies are greatly thickened southward suggesting that syndepositional faulting controlled sedimentation. In Wolfcampian time, cyclic, stacked bryozoan algal lime mud mounds (300 m thick) developed. Thin tabular lime mud mounds developed in cyclic back-mound lithofacies. Similar fore-mound lithofacies thickened in a southerly direction. As many as 50 cycles developed in Middle Pennsylvanian to Lower Permian rocks. Eustatic sea level changes caused by late Paleozoic glaciation controlled cyclic sedimentation. Syndepositional faulting in Atokan, Desmoinesian, and Virgilian times also had the effect of keeping the northern and eastern parts of the study area in the marine photic zone. This area may have constituted a paleohorst within the Oquirrh basin in Pennsylvanian and Permian times. End_of_Article - Last_Page 914------------

Carboniferous-Permian Boundary Sequence of Northern Oquirrh Basin, Idaho-Utah: ABSTRACT

The Carboniferous-Permian boundary occurs in the middle of the Oquirrh Group in the northern part of the Oquirrh basin, the largest basin formed east of the Antler tectonic belt during the middle Carboniferous. Good sequences of fusulinid faunas for the northern part of the basin are exposed in the Sublett and Deep Creek Ranges of southern Idaho, a position midway between the basin's bathymetric low and the basin edge. In the Sublett Range, Late Pennsylvanian-Early Permian fusulinids occur through 1,500 m of mixed quartose sands and limestones of the Trail Canyon Formation and basal part of the overlying Hudspeth Cutoff Formation. The Missourian interval is thin relative to the Virgilian interval. Near the base of the Trail Canyon Formation, possible Missourian fusulinid aunas appear containing Triticites and Eowaeringella, and extend through a 250-m section, which is overlain by a 400-m section with Virgilian fusulinids, including Triticites sp. aff. T. cullomenensis and T. sp. aff. T. subventricosus. The Carboniferous-Permian boundary occurs at about the top of the middle limy unit of the Trail Canyon Formation, and Wolfcampian fusulinids, including Schwagerina and Pseudoschwagerina, occur through 800 m of section. Pseudofusulinella is common through Virgilian and Wolfcampian interval on the western side of the Sublett Range, but has not been found in this interval on the eastern side. Leonardian fusulinids have yet to be found here, contrary to earlier published reports. End_of_Article - Last_Page 1010------------

Paleogeography and Structural Development of Late Pennsylvanian-Early Permian Oquirrh Basin, Northwest Utah: ABSTRACT

Deposition in the late Paleozoic Oquirrh basin of northwest Utah produced as much as 7.5 km of limestone and sandstone. Study of Upper Pennsylvanian and Lower Permian lithofacies, trace fossils, and body fossils relative to a time framework determined by fusulinid biostratigraphy reveals a spatial mosaic of depositional environments which shifted through time. The Oquirrh basin changed in form from a broad, topographically subdued, shelf area in the Middle Pennsylvanian to a northwest-trending topographic basin in the Late Pennsylvanian. Water depths may have reached 300 to 400 m. Coarse conglomerates, commonly composed of older Oquirrh Group clasts, are common in latest Pennsylvanian and early Wolfcampian deep-water deposits. They record rapid lithification, uplift, and erosion of the margins of the trough, and imply that the Oquirrh basin was bounded by active northwest-trending high angle faults. The faults, with offset rates of about 25 cm/1,000 years, were apparently initiated in the Late Pennsylvanian, and became inactive by the late Wolfcampian. The upper Oquirrh Group records the passive filling of the remnant graben-like trough.The histories of the Oquirrh basin and of basement uplifts and yoked basins throughout the region to the south and east are similar. The northwest trend, high angle fault margins, and rapid structural development in the latest Pennsylvanian and early Wolfcampian demonstrate the Oquirrh basin's tectonic association with the regional deformation responsible for the Ancestral Rocky Mountains. End_of_Article - Last_Page 730------------

Conodont-Based Assessment of Thermal Maturity in Paleozoic and Triassic Rocks, Central Great Basin: ABSTRACT

Conodonts (marine apatitic microfossils) are of organic origin and have biostratigraphic value. They are used as mineral thermal indices that undergo visible color changes between 50 and 500°C. Using these changes, color alteration index (CAI) maps were compiled for Ordovician through Triassic Systems in Nevada and adjacent parts of Idaho, Utah, and California using more than 5,000 samples. The maps show three thermal intervals which generally correspond to: (a) the thermal window for oil generation (CAI 1 to 2); (b) the upper thermal interval for gas generation (CAI 2 to 4.5); and (c) the thermal cutoff for most hydrocarbon generation (CAI >4.5). The Great Basin is one of the most difficult areas in which to interpret thermal metamorphism in Paleozoic and Triassic rocks. Original burial metamorphic patterns are disrupted by thrust and normal faulting, masked by post-Triassic sedimentary and igneous rocks, and overprinted by post-Triassic thermal events. Nevertheless, maps show broad regional thermal patterns for Paleozoic and Triassic Systems which help delineate prospective areas for continued hydrocarbon and mineral exploration. In general, Ordovician through Triassic rocks west of 117°30^primeW longitude and most Ordovician through Pennsylvanian rocks north of 41°30^primeN latitude and west of 113°W longitude and in the Oquirrh basin have CAI values >4.5 and appear to be unfavorable targets for hydrocarbon exploration. Ordovician through Triassic rocks in central Nevada and Millard County, Utah, have regional moderate to low CAI values. This area, which includes the only two producing oil fields in Nevada, should provide a variety of hydrocarbon exploration targets. The Paleozoic and Triassic rocks of the Overthrust belt of southeast Idaho and Utah predictably have low to moderate CAI values. End_of_Article - Last_Page 719------------

Bathymetric Distribution of Trace Fossils in Upper Pennsylvanian and Lower Permian, Western Oquirrh Basin, Utah: ABSTRACT

Detailed study of the Oquirrh Group in Tooele and Box Elder Counties, Utah, has revealed a history of basin development during the Late Pennsylvanian and Early Permian. Trace fossils are of paramount significance in recognizing depositional environments in this sequence (a) because of uniform composition and uniform grain size and (b) because most megafossils were redeposited several miles or more from their initial growth sites. Middle Pennsylvanian littoral and inner-shelf limestones and quartz arenites form the base of the sequence studied. During Late Pennsylvanian time, the western Oquirrh basin area was primarily an outer-shelf environment. Trace fossils in shelf units are diverse, recording a variety of behavior patterns, and include Zoophycos, Teichichnus, and Helminthoida in the Hogup/Terrace Mountains and Zoophycos, Phycodes, Helminthoida, and Spirophycus(?) in the Grassy Mountains. Rapid subsidence in latest Pennsylvanian-earliest Permian time is marked by conglomerates and arenites that carried shallow-water fossils into the bathyal environments. End_Page 476------------------------------ Trace preservation is poor, but is typified by low diversity and high abundance. Uppermost Pennsylvanian turbidite deposits on Bovine Mountain contain Helminthoida and Chondrites; basal Wolfcampian rocks of the Grassy Mountains bear Helminthoida, Protopaleodictyon, and Lophoctenium. Upper Wolfcampian fetid, soft-sediment-folded, arenaceous siltstones locally yield indigenous fauna that suggests an off-shelf origin. In the Hogup and Grassy Mountains, Helminthoida is preserved, but in general the trace-fossil record is scanty in this interval. In Leonardian time, the Oquirrh basin filled to shelf depth, and a mixture of vertical and horizontal bioturbation again prevailed. End_of_Article - Last_Page 477------------

Stratigraphic Analysis of Upper Permian and Lower Triassic Strata in Southern Utah

Permian sedimentation in southwestern Utah was influenced by three principal depositional areas--the Oquirrh basin in north-central Utah, the Cordilleran geosyncline in eastern Nevada, and the Quemado-Cuchillo basin on the northern shelf of the Sonoran geosyncline in east-central Arizona and west-central New Mexico. Throughout Permian time, marine sediments and well-developed beach and continental eolian sandstone equivalents were deposited within these basins and on the surrounding shelves. Each of the three depositional sites appears to have exerted influence on sedimentation during a discrete period of geologic time. Thus, while one basin was the site of sedimentation, the other two basins were relatively quiescent. Remarkably similar beach and continental sandstone deposits are related to each basin, and all these sandstones extend to a common depositional area in southwest Utah where they are interlayered. Vertical juxtaposition or interlayering of littoral and beach sandstone facies that are related to three differing sedimentational basins has been responsible for most of the problems invo ving Permian nomenclature and correlation in the Colorado Plateau province. Stratigraphic analyses show that each continental sandstone facies has a basinal stratigraphic equivalent which consists primarily of interbedded carbonate with smaller amounts of sandstone and shale. The beach and basinal equivalents present are: Cedar Mesa Sandstone equivalent to Elephant Canyon carbonates; Organ Rock Shale equivalent to Meseta Blanca Sandstone and Yeso evaporites and carbonates; Coconino Sandstone, to upper De Chelly Sandstone; White Rim Sandstone (approximately upper 80 percent), to Toroweap Formation; and upper White Rim Sandstone, to lowermost (Gamma member) Kaibab Formation. Rock units underlying the Toroweap-White Rim Formations are younger toward the south. The Kaibab Formation is a stratigraphic continuation of the Franson Member of the Park City Formation in northern Utah and southwestern Wyoming and is inferred to be time-transgressive. The Permian-Triassic boundary is recorded by a pronounced unconformity in southwesternmost Utah. Northward, the break is less pronounced and is not recognizable in north-central Utah. Early Triassic sedimentation in southern Utah appears to record cyclic response to one major subsiding sedimentational area, the Cordilleran Triassic basin, apparently with characteristic onlap relations, and at least two and possibly three of the Early Triassic Moenkopi units are not present at the Moenkopi type section in northern Arizona. The southward continuation of the Woodside Formation from southwestern Wyoming to central Utah is now recognized. The Sinbad and Timpoweap Members of the Moenkopi Formation are shown to be the same stratigraphic unit. Subsurface control suggests that the Virgin Limestone Member extends into central Utah. Structurally, most of southern Utah appears to have been a slowly subsiding shelf throughout most of Permian and Early Triassic times.

Pennsylvanian and Permian Basins in Northwestern Utah, Northeastern Nevada and South-Central Idaho: REPLY

The Pennsylvanian and Permian basins in northwestern Utah, northeastern Nevada, and south-central Idaho are downwarped segments of the Cordilleran geosyncline superposed on a complex structural pattern of Precambrian and early and middle Paleozoic age. The Oquirrh basin contains Pennsylvanian and Lower Permian sedimentary rocks as much as 26,000 feet thick; the area of maximum sedimentation was in northwestern Utah. Three principal parts are recognized: a lower part of clastic limestone, sandy limestone, and minor shale; a middle cyclically bedded limestone and sandstone; and an upper sandstone, chert, and shale unit. The lower part was deposited in an offshore shallow-water environment; the middle and upper parts in offshore moderately deep water; these grade laterally both eastward and westward into shallow-water nearshore facies. The Permian Phosphoria basin was partly coextensive with the Oquirrh basin, but the area of maximum sedimentation was in northeastern Nevada and southern Idaho, where locally 3,500 feet of shale, cherty shale, chert, dolomite, and limestone accumulated. This facies was deposited in an offshore deep-water environment, favoring formation of thick sponge-spicule chert and cherty shale units; these grade southward and eastward into carbonates and shales that were deposited in a shallow nearshore environment. In Cretaceous time the Paleozoic and lower Mesozoic rocks of northeastern Nevada and western Utah moved eastward on great thrust plates that extended from southern Utah into Idaho. Movement took place on the Willard-Charleston-Nebo thrust belt in the Wasatch Mountains. Westward continuations of these thrusts crop out in northwestern Utah and eastern Nevada. Imbricate thrusts and tear faults within the upper plate have resulted in complex distribution of upper Paleozoic rocks.

Pennsylvanian and Permian Basins in Northwestern Utah, Northeastern Nevada and South-Central Idaho

The Pennsylvanian and Permian basins in northwestern Utah, northeastern Nevada, and south-central Idaho are downwarped segments of the Cordilleran geosyncline superposed on a complex structural pattern of Precambrian and early and middle Paleozoic age. The Oquirrh basin contains Pennsylvanian and Lower Permian sedimentary rocks as much as 26,000 feet thick; the area of maximum sedimentation was in northwestern Utah. Three principal parts are recognized: a lower part of clastic limestone, sandy limestone, and minor shale; a middle cyclically bedded limestone and sandstone; and an upper sandstone, chert, and shale unit. The lower part was deposited in an offshore shallow-water environment; the middle and upper parts in offshore moderately deep water; these grade laterally both eastward and westward into shallow-water nearshore facies. The Permian Phosphoria basin was partly coextensive with the Oquirrh basin, but the area of maximum sedimentation was in northeastern Nevada and southern Idaho, where locally 3,500 feet of shale, cherty shale, chert, dolomite, and limestone accumulated. This facies was deposited in an offshore deep-water environment, favoring formation of thick sponge-spicule chert and cherty shale units; these grade southward and eastward into carbonates and shales that were deposited in a shallow nearshore environment. In Cretaceous time the Paleozoic and lower Mesozoic rocks of northeastern Nevada and western Utah moved eastward on great thrust plates that extended from southern Utah into Idaho. Movement took place on the Willard-Charleston-Nebo thrust belt in the Wasatch Mountains. Westward continuations of these thrusts crop out in northwestern Utah and eastern Nevada. Imbricate thrusts and tear faults within the upper plate have resulted in complex distribution of upper Paleozoic rocks.

Oquirrh and Phosphoria Basins in Northwestern Utah, Northeastern Nevada, and Southern Idaho: ABSTRACT

The Oquirrh and Phosphoria basins in northwestern Utah, northeastern Nevada, and southern Idaho are downwarped segments of the Cordilleran geosyncline superposed on a complex structural pattern of Precambrian and early and middle Paleozoic age. End_Page 1878------------------------------ The Oquirrh basin contains Pennsylvanian and Early Permian sedimentary rocks as much as 26,000 feet thick; the area of maximum sedimentation was in west-central Utah. Three principal units are recognized: a lower unit of cyclically bedded bioclastic limestone and sandy limestone, a middle unit of interbedded limestone and quartzite, and an upper unit of quartzite. The lower and middle units were mostly deposited in an offshore shallow water environment; the upper unit in offshore moderately deep water; these grade laterally both eastward and westward into shallow nearshore facies. The Middle Permian Phosphoria basin was partly coextensive with the Oquirrh basin, but the area of maximum sedimentation was in northeastern Nevada and southern Idaho, where locally 3,500 feet of shale, cherty shale, chert, dolomite, and limestone accumulated. This facies was deposited in an offshore deep-water environment, favoring formation of thick sponge-spicule chert and cherty shale units; these grade southward and eastward into carbonates and shales that were deposited in shallow nearshore environment. In Cretaceous time the Paleozoic and early Mesozoic rocks of northeastern Nevada and western Utah moved eastward on great thrust plates that extended from southern Utah into Idaho. Movement took place on the Willard-Charleston-Nebo thrust belt in the Wasatch Mountains. Westward continuations of these thrusts crop out in northwestern Utah and eastern Nevada. Imbricate thrusts and tear faults within the upper plate have resulted in complex distribution of late Paleozoic facies. End_of_Article - Last_Page 1879------------

Permo-Pennsylvanian Stratigraphy of Western Colorado Plateau and Eastern Great Basin Regions

Subsiding basins and broad uplifts influenced the distribution of Permo-Pennsylvanian strata in the Colorado Plateau and eastern Great Basin. Within the area of study are the Pioche and Hamilton basins of eastern Nevada and the southern part of the Oquirrh basin of Utah. Uplifts include the Emery and Kaibab, their connection, the central Utah high, and the Snake Range uplift of east-central Nevada. The Manhattan geanticline which influenced deposition in the Hamilton and Pioche basins lay to the west of the area. Strata of Morrowan, Atokan, Virgilian, Wolfcampian and Leonardian ages are generally widespread over basins and adjoining shelves. Those of the Mississippian-Pennsylvanian transition, Desmoinesian, and Missourian ages are for the most part confined to basins. Facies changes across northwestern Arizona in Atokan and Virgilian strata show that the red beds of the lower Supai are equivalent to marine strata farther west. Probably the upper Supai is Late Wolfcampian; however, the westward facies change is less clear. Lower Wolfcamp carbonates seem to wedge out east of the Grand Wash. The Hermit Shale may be Leonardian in age, and the overlying Coconino, Toroweap, and Kaibab formations are assigned to the Leonard. In the Hamilton basin, Leonard strata are about 7100 feet thick. Correlation between shelf facies and their neighboring basins is complicated by Laramide thrust and tear faults which have moved the basinal facies eastward into juxtaposition with the shelf.