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Geologic Mapping of Ice Cave Peak Quadrangle, Uintah and Duchesne Counties, Utah With Implications for Lower Mississippian Stratigraphy and Laramide Faulting


Geologic mapping (1:24,000 scale) of the Ice Cave Peak quadrangle, Uintah and Duchesne Counties, Utah has produced a better understanding of the geologic structures present in the quadrangle and helped to clarify nomenclature used for Lower Mississippian strata in northeastern Utah. Map units in the quadrangle range in age from late Neoproterozoic to Quaternary and include good exposures of Paleozoic rocks (Mississippian to Permian), limited exposures of Mesozoic rocks, and good exposures of Tertiary strata (Duchesne River Formation and Bishop Conglomerate) produced by Uinta Mountain uplift. Lower Mississippian strata along the south flank of the Uinta Mountains have typically been mapped as Madison Limestone. Our mapping suggests that the Madison may be subdivided into an upper unit equivalent to the Deseret Limestone and a lower unit separated by a phosphatic interval equivalent to the Delle Phosphatic Member of the Deseret Limestone found farther west. We propose extending the use of Deseret Limestone with the Delle Phosphatic Member at its base into the south-central Uinta Mountains, but maintaining the use of Madison Limestone for the lower unit. This usage makes the Madison in the Uinta Mountain area more consistent with its usage to the north in Wyoming. A zone of northwest-trending faults, called the Deep Creek fault zone, occurs mainly east of the Ice Cave Peak quadrangle. However, our mapping shows that this fault zone extends into the quadrangle. Most of these faults are strike-slip faults as documented by mapping and kinematic indicators, and cut the folded hanging-wall sedimentary rocks of the Basin boundary thrust fault. These faults may be part of an en echelon fault system that is rooted in the upper Neoproterozoic and reactivated during Laramide deformation above a possible transfer zone between segments of the buried Basin boundary thrust.