Notes on the Stratigraphy of the Moab Region, Utah

Abstract

Results of work near Moab, Utah, by U. S. Geological Survey field parties in 1926 in part accord with and in part differ from current interpretations. In the Salt Valley anticline lower Mississippian rocks occur as limestone boulders in a conglomerate of unknown age. The oldest rocks in place at the surface are Pennsylvanian (Hermosa formation), sharply separated from the Permian by contained marine faunas. The Permian formations (Rico and Cutler) are not sharply separated. The former contains marine limestones; the latter, tongues of white sandstone that increase southwestward and at top the sandstone member (De Chelly?) locally known as the White Rim. The Lower Triassic Moenkopi formation, including in Green River Valley a marine limestone member, rests with unconformit upon Cutler and is in turn overlain unconformably by Upper(?) Triassic Shinarump conglomerate. Shinarump grades upward into the Chinle formation and is not recognizable as a separate unit at many localities, especially toward the east. A group of Jurassic(?) formations, including Wingate and Navajo sandstones separated by the Todilto(?) formation, rests unconformably upon the Chinle. The formations of the group are conformable and have arbitrary common boundaries. The succeeding Carmel and Entrada formations (Upper Jurassic) are similar to this group. The Carmel formation may overlie the Navajo sandstone with unconformity. Summerville formation (Upper Jurassic) intertongues with the underlying Entrada sandstone so that Entrada lithology extends higher toward the east. Summerville is sep rated by an unconformity from the overlying Salt Wash sandstone member of the Morrison formation (Cretaceous?). Dakota(?) sandstone (Upper Cretaceous) rests unconformably upon the Morrison formation and is succeeded by the Mancos shale. The stratigraphy would seem to indicate the following events in the history of the region: Possibly folding and erosion between lower Mississippian and Pennsylvanian; folding and erosion at the close of the Permian; erosion and possibly folding between Lower and Upper Triassic, and between Upper Triassic and Jurassic(?) (Wingate); possibly erosion preceding Upper Jurassic (Carmel); erosion between Upper Jurassic and Cretaceous(?) (Morrison), and between Cretaceous(?) and Upper Cretaceous. End_Page 785------------------------------