ABSTRACT: Post-Eocene West-Stepping Thrust Faulting in the Utah-Wyoming Thrust Belt: Implications for the Genesis of the Cretaceous Interior Seaway

Art Berman

Field relations suggest that thrust faulting began in western Wyoming and eastern Utah with movement on the Absaroka thrust, possibly during the Late Cretaceous. It seems likely that the Darby thrust became active shortly thereafter. Intraplate deformation of the Absaroka package occurred during or after the Eocene, resulting in belts of folds and faults along the Commissary, Tunp, and Crawford trends. This Absaroka intraplate deformation resulted from compression produced by movement on the Ogden thrust to the west. The Ogden thrust is exposed along the Wasatch fault between Ogden and Salt Lake City, Utah, and extends as far east as the Devil's Slide area, west of Croyden, Utah. This thrust has not previously been recognized. The Precambrian crystalline rocks of the Wasa ch Mountains are carried on the Ogden thrust along with Paleozoic and Mesozoic sedimentary rocks that crop out east of the range. The Willard thrust moved after the Ogden and initiated still farther to the west. The Willard includes Proterozoic and lower Paleozoic rocks not recognized on any of the more easterly thrust sheets. The unique occurrence of oil and gas within the Absaroka package is related to many factors including its initial geometry and the remigration of fluids associated with the post-Eocene modification of this geometry. The source of pre-Maestrichtian sediments to the Cretaceous Interior Seaway becomes problematic as a result of this analysis, as does the assumption that the seaway was a foredeep related to flexural loading by the thrust belt.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990