Oblique Convergence During Northeast-Southwest Laramide Compression Along the East-West Owl Creek and Casper Mountain Arches, Central Wyoming

Abstract

Understanding the diversity of structural trends in the Laramide foreland of the conterminous United States is important to understanding the location, geometry, and fracturing of hydrocarbon reservoirs. East-west basement-cored arches in central Wyoming are oblique to the average northwesterly trend of foreland faults and folds. Tectonic models predict that these arches formed by one of the following mechanisms: north-south-directed thrust faulting; sinistral strike-slip faulting; or northeast-southwest-directed, oblique-slip thrust faulting. In the eastern Owl Creek Mountains, average slip directions given by slickenline directions trend from N37°E to N57°E. Geometric analysis of conjugate faults and stress inversion of minor fault data indicate nearly horizontal compression trending between N48°E and N65°E. In the east-west Casper Mountain structure, more limited minor fault data are consistent with the northeast-southwest compression seen in the eastern Owl Creek arch and indicate an additional stage of extension by normal faulting. The northeast-southwest compression documented by minor faults suggests oblique thrusting with a component of sinistral strike-slip on the underlying, east-west-striking Owl Creek and Casper Mountain thrusts. In this area of the Laramide foreland, east-west arches probably formed during a single stage of oblique slip on thrust ramps connecting northwest-trending arch culminations. This conclusion indicates that trap geometries and reservoir characteristics of foreland hydrocarbon accumulations are dependent on their obliquity to the regional stress field.