Abstract

In southwestern Utah the Kaibab and Toroweap formations provide the opportunity to study the last Paleozoic deposition in the transition zone between the Colorado Plateau and Basin and Range provinces. The Toroweap Formation contains three members that represent a marine transgression separated by two regressions. The lowest is the Seligman Member that contains interbedded siltstone, gypsum, and limestone. Above the Seligman Member is the Brady Canyon Member that is composed of thick-bedded fossiliferous limestone. The upper member of the Toroweap Formation is the Woods Ranch Member that contains gypsiferous siltstone and gypsum near the bottom, a limestone tongue in the middle that thickens to the north, and gypsiferous siltstone at the top. This tongue is called the Hurricane Cliffs Tongue. The conformable contact between the Toroweap and Kaibab formations is placed at the base of a massive limestone cliff above the slope forming siltstones and limestones of the Woods Ranch Member.

Two members of the Kaibab Formation are present in southwestern Utah. They represent deposition during a transgression followed by a regression. The lowest is the Fossil Mountain Member that is composed of fossiliferous limestone that contains numerous chert nodules. Above the Fossil Mountain Member is the Harrisburg Member that contains siltstone and gypsum near the bottom, a limestone near the middle, and alternating siltstone and limestone near the top. A disconformity, along which lens-shaped conglomerate bodies of the Rock Canyon Conglomerate were deposited, marks the contact between the Kaibab and Moenkopi formations.

In southwestern Utah the Toroweap and Kaibab formations are exposed along the Hurricane Cliffs from the Utah-Arizona stateline to Kanarraville, Utah (Fig. 1). They are also exposed in the Harrisburg, Washington, and Bloomington domes (Price Hills) in the St. George Basin. Excellent exposures are present in the Beaver Dam Mountains and the Virgin Gorge. Southwestern Utah is considered to be in the transition zone between the Colorado Plateau and the Basin and Range Provinces. However, during the Permian, this area was part of a broad shelf between the Cordilleran Geosyncline and the Transcontinental Arch across which Permian seas fluctuated. There was no distinct Wasatch-Las Vegas line during the Permian in this area. Exposures of the Kaibab and Toroweap formations provide information on the stratigraphic framework of the Permian shelf during the early Permian Period.

Objectives of this study are to: 1) differentiate between the Kaibab and Toroweap formations in southwestern Utah, 2) subdivide the Kaibab and Toroweap formations into members, 3) discuss the carbonate and clastic petrology of these formations, and 4) determine the depositional environments of the members of the Kaibab and Toroweap formations.