The major pre-Mississippian unconformity in Rock Canyon, central Wasatch Range, Utah

Abstract

In central Utah, the major pre-Mississippian unconformity is fairly well understood at most of the localities where it is recognized. However, the unconformity is more enigmatic in Rock Canyon of the central Wasatch Range. At this locality, dolomitization of most pre-Mississippian rocks obscures stratigraphic identification of Devonian and older units. The absence of any identifiable angular relationship further complicates resolution. Because of this, both identification of the stratigraphic level of the unconformity and, consequently, its magnitude remain controversial. Large-size dolomite samples taken in Rock Canyon at closely spaced intervals for the 3.6-m directly below definite Upper Devonian rocks yield microfossils, including conodonts, in the uppermost 1.6-m of that interval that indicate no unconformity exists between the Cambrian Maxfield Limestone and the Upper Devonian-Lower Mississippian Fitchville Dolomite at the horizon previously identified as unconformable. Rather, an unknown thickness of dolomitized Upper Devonian Pinyon Peak Formation and probable older rock (possibly Bluebell Dolomite and Victoria Formation) occurs between the top of definite Maxfield and base of the Fitchville. The identification of the unconformity horizon remains unknown. Our preliminary work outlines a promising procedure for future understanding of the magnitude and stratigraphic level of the unconformity.