DIULIO, AMANDA A., Colorado State University, Earth Resources Dept., Fort Collins, CO

ABSTRACT: Regional Thrust Kinematics in West-Central Wyoming and the Origin of Johan Field

The Sevier orogeny (120-50 my) and the Laramide orogeny (75-35 my) were active synchronously for 25 my. Discordance, between the resulting structures suggests a significant difference in the principle stresses and strains. Laramide structures are basement involved and trend northeast-southwest. However, Sevier structures are thin-skinned, penetratively deformed and trend north-south.

The Laramide Gros Ventre Range and the Sevier Wyoming thrust Belt converge at a 45 degree angle and bound the Hoback Basin in west-central Wyoming. This relationship creates the ideal location to study thrust belt and foreland structures interaction and their roles in the formation of hydrocarbon traps.

Johan Field, located in the Hoback Basin, is a large, combined structural and stratigraphic hydrocarbon trap producing gas from overpressured sandstones. The gas-bearing compartments are sealed structurally by bounding faults related to the regional structural kinematics and stratigraphically by shale. Understanding the origin of these faults is critical to understanding how hydrocarbons were trapped in Johan Field.

I will collect fault orientation and slip direction data on well-exposed areas in the Gros Ventre Range and the Wyoming thrust belt. These will be compared to three dimensional fault orientations and slip directions in Johan Field, determined by restoring depositional surfaces using 3-D seismic data and 3-D restoration software from Geo-Logic Systems. Comparing fault orientations and slip sense within these three domains will determine if the faults are the result of the combination of two stress fields acting synchronously or the result of a specific stress field related to either thrust belt or basement-involved structures.

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