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AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 11. (November)

First Page: 1976

Last Page: 2007

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

Author(s): C. Dennis Irwin (2)

Abstract:

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.

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