Analysis of the Structural Geology in the South Desert of Capitol Reef National Park, Utah

Jurassic units within the Utah transition zone in the South Desert region of Capitol Reef National Park were examined to determine styles of tectonic deformation. Using field evidence along with descriptive, kinematic, and dynamic analyses, as well as gravity and magnetic data, it was determined that a principal deformation zone (PDZ) exhibiting right-handed strike-slip occurs in that area. Stereographic analyses of cataclastic and non cataclastic deformation bands and joints in the Entrada Sandstone and the Salt Wash Member of the Morrison Formation, as well as folds in the Carmel formation, suggest a mechanism involving an unrecognized forcing structure, such as a strike-slip basement fault that does not exhibit significant vertical displacement nor surface offset. This implies that the basement rock has been faulted and possibly affected the structural character of the overlying sedimentary rocks. Orientation of principal stress directions within the South Desert has changed over time from Jurassic to Tertiary. These changes in principal stress directions between the San Rafael Swell and Miners Mountain were recorded in the deformation bands of the Salt Wash Member of tile Morrison Formation, indicating a positioning of strain along the eastern front of the Sevier fold-and-thrust belt. The principal stress directions changed from SW-NE during Laramide, to E-W during Sevier, and finally to N-S during Basin-and-Range