The Cedar Mountain Formation (Lower Cretaceous) in the Gunnison Plateau, central Utah
Malcolm P. Weiss, Michael G. Roche, 1988. "The Cedar Mountain Formation (Lower Cretaceous) in the Gunnison Plateau, central Utah", Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Christopher J. Schmidt, William J. Perry, Jr.
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Along the southeast flank of the Gunnison Plateau, southwest of Sterling, Utah, red and violet mudstones, some of which contain limy nodules and “gastroliths,” and inter-bedded sandstones, conglomerates, and thin limestones, have long been considered a possible correlative of the Jurassic Morrison Formation, and are often mapped as “Morrison(?).” The lower 134-m interval is now known to conformably underlie strata containing fossils of Cretaceous age (Albian-Cenomanian); it contains limy nodules, oncolites, limestone beds, and bright red mudstones, and is assigned to the Cedar Mountain Formation of Early Cretaceous age. The upper part of the sequence underlies sandstone like the Sanpete Formation, and is assigned to an as-yet unnamed basal unit of the Indianola Group, of which the Sanpete was heretofore the lowest formation recognized. The names Morrison and Morrison(?) are abandoned for outcrops in central Utah.
The very limited areas of outcrop of these units in the deformed east front of the Gunnison Plateau are identified and described, in revision of earlier published work. Exposures of the Cedar Mountain Formation at the north end of the Gunnison Plateau and along its west flank are described for the first time; they show an irregular trend of southward thinning. Substitution of Cedar Mountain for the lower part of the Morrison(?) means that true Morrison strata (i.e., Jurassic) do not occur in central Utah and that there is a record of Lower Cretaceous terrestrial sedimentation in central Utah from near Thistle, 35 km (22 mi) northeast of the plateau, through the Gunnison Plateau, and down to Salina Canyon, 25 km (16 mi) south of the plateau. Under this new interpretation the earliest stages of the Sevier Orogeny are represented by the Cedar Mountain Formation (lower part of the former Morrison? Formation); this interval probably is Early Cretaceous in age rather than Jurassic.