KEY PERMIAN SECTION, CONFUSION RANGE, WESTERN UTAH

Abstract

Approximately 10,000 feet of Permian strata, mainly of marine origin, and in some beds abundantly fossiliferous, is well exposed and readily accessible in the northern part of the Confusion Range, western Utah. Because of their strategic location between the better known sections of southern Nevada, southern Utah, and central Utah the exposures in the Confusion Range are of especial importance for the light they shed on Permian problems in the western United States. Pennsylvanian and Lower Permian limestones of undetermined total thickness are correlated with the similar Bird Spring formation of southern Nevada and with the Oquirrh formation of the Wasatch Mountains in central Utah. The Bird Spring limestone is overlain by 2500 feet of relatively unfossiliferous limy sandstones, impure limestones, and calcareous shales prevailingly of drab colors. Discontinuous lenses of red sandstone occur in the upper part. This unit tentatively is correlated with the Supai formation and associated elastics of the Grand Canyon region, although the lithologic facies is quite different. Approximately 2000 feet of massive limestone containing Dictyoclostus ivesi s.l. in the upper part is correlated with the Kaibab limestone of the Colorado Plateau. At the top of the Permian sequence is 4555 feet of richly fossiliferous interbedded cherty limestone and calcareous shale. The contained fauna is that of the Phosphoria formation of the middle and northern Rocky Mountains. There is no apparent intermingling of Kaibab and Phosphoria faunal types. The Permian succession is overlain with angular unconformity by red shales and interbedded limestones of the Lower Triassic. Silty red limestones some hundreds of feet above the base of the Triassic contain an abundance of Meekoceras . Interpretation of the succession in the Confusion Range confirms a discovery by Baker and Williams (1940) of Phosphoria strata directly above Kaibab equivalents in the Wasatch Mountains. It seems clear that the entire Phosphoria formation is younger than the Kaibab.