Late Devonian--Early Mississippian Correlations Central Wasatch Mountains, Utah: ABSTRACT

Abstract

Strata of Late Devonian age have been recognized west of the Wasatch Front (Pinyon Peak Limestone and City Creek Limestone) and a few miles east of the Wasatch Mountains in the western Uinta Mountains (Pinyon Peak Limestone?). These consist commonly of a basal sandstone or shale a few feet thick which grades upward to a dolomite sequence that ranges in thickness from 50 to 300 feet. This succession is in turn overlain by the Madison Limestone (Mississippian). On the west this contact is conformable but on the east it is unconformable. In the Wasatch Mountains, sandstone or shale a few feet thick rests on older rocks (mostly of Cambrian age) and changes upward through about a 3-foot interval into medium to dark gray dolomite about 50-150 feet thick, which in turn is over ain conformably by the Madison Limestone. These pre-Madison rocks were tentatively correlated with the Formation (Devonian) by earlier workers on the basis of stratigraphic position and lithologic character. Subsequent workers of the U. S. Geological Survey have reported corals of Mississippian affinity from the exposures in American Fork Canyon and have thus assigned a Mississippian age to these strata. Restudy of several of the Wasatch Front exposures disclosed well preserved molds of the brachiopod Cyrtospirifer whitneyi(?) in the basal sandstone in the Big Cottonwood Canyon area. This fossil is generally considered to be of Late Devonian age and has been collected from the Pinyon Peak Limestone in the western Uintas and in the areas west of the Wasatch. Thus the Mississippian age assigned to these rocks on the basis of corals is questionable. Moreover, a Late Devonian age is more consistent with a regional stratigraphic correlation on the basis of physical evidence. Therefore the Jefferson (?) of the Wasatch is here correlated with the Pinyon Peak Limestone of the areas east and west. End_of_Article - Last_Page 261------------