JUDGE, SHELLEY A., Ohio State University, Department of Geological Sciences, Columbus, OH

ABSTRACT: The Origin and Evolution of the Wasatch Monocline, Central Utah

The Wasatch monocline forms the western front of the southern Wasatch Plateau, one of the dominant structural features of the geology of central Utah. The monocline is a key tectonic element within the complex Mesozoic-Cenozoic framework of central Utah, because it coincides spatially with the eastern limit of both the Sevier fold-thrust belt and the Basin and Range province. The purpose of this research is to determine the age, origin, and evolution of the Wasatch monocline by combining both structural (fault and joint) and sedimentologic (paleocurrent and petrologic) analyses.

Structural studies are focused on mapping the distribution of contractional and extensional structures across and along the Wasatch monocline for comparison with model predictions. Mesoscopic structures (faults and associated vein fill) are being measured along several E-W profiles across the monocline. Preliminary fault analysis reveals that antithetic faults have an orientation slightly oblique to the axial trace of the monocline. In addition, fault striae show both dip-slip and oblique-slip motion. Taken together, these data document oblique shear and multiple slip events during monocline development. Ultimately, this structural data will establish the kinematic history associated with phases of monocline development.

Expression of the Wasatch monocline as a regional topographic high should have influenced sediment provenance and dispersal; therefore, paleocurrent and petrographic analysis of key stratigraphic units can be used to constrain the timing of monocline development. Field measurements, supplemented by data from the literature, illustrate dominant paleocurrent trends at each locality for specific time slices. Seven out of eleven localities show a mean paleocurrent to the NW, suggesting a regional paleoslope from the SE to the NW. At present, paleocurrent data are inconclusive, but regional patterns may indicate that the Wasatch monocline was a topographic high by the Early Oligocene.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid