Geologic Structure of Southeastern Utah

Abstract

Southeastern Utah, lying within the Colorado Plateau, is characterized by several types of structural features, including (a) huge asymmetrical upwarps, (b) domes associated with laccolithic intrusions, (c) the southern edge of the Uinta Basin structural depression, (d) a north-trending zone of normal faults at the west edge of the plateau, and (e) a group of numerous folds, faults, and faulted folds that are found in a limited area near Moab. Folding has occurred in the region several times since the end of the Mississippian, but the principal deformation that is reflected in the structure of the surface rocks took place at the end of the Cretaceous or early in the Tertiary and was therefore related to the Laramide orogeny. The large domical uplifts have a northerly tren and are strongly asymmetric, with the steep limb toward the east; they were formed at the end of the Cretaceous, possibly as a reflection in the surface rocks of more or less vertical uplifting along deep-seated reverse faults. The group of numerous smaller folds, faults, and faulted anticlines in the part of the region near Moab also is believed to have been formed near the end of the Cretaceous; the deformation is obviously related to the presence of the plastic salt-bearing beds of the Pennsylvanian Paradox formation beneath the surface rocks, because the structural features of this type near Moab are typically developed only within the area underlain by the Paradox formation and because the salt-bearing beds have been intruded into the overlying rocks at the crests of some of the fo ds. Events in the Tertiary structural history of the region include the intrusion of igneous rocks in four isolated mountain groups, the downwarping of the Uinta Basin, and the development of the zone of normal faults at the west edge of the plateau; it is not possible to determine the order of these events, or to determine whether they represent different modes of expression of one period of crustal disturbance.