ANALYSIS OF THE STRUCTURAL GEOLOGY IN THE SOUTH DESERT OF CAPITOL REEF NATIONAL PARK, UTAH

The northern boundary of Capitol Reef National Park near Torrey, Utah is located within the Utah transition zone, which exhibits overlapping tectonic styles. Mesoscopic structures in this transition zone record the interplay and overprinting of Sevier, Laramide, and Basin and Range tectonic styles.

In Jurassic rocks, outcrop-scale structures, including deformation bands, joints, faults and folds, were mapped in various formations within the South Desert of Capitol Reef National Park. Large and small-scale deformation bands, void of any slickenlines, and joint sets were mapped in the Entrada sandstone and the Salt Wash Member of the Morrison Formation. Large and small-scale folds were mapped in the Carmel and Summerville Formations. Stereographic projections of the deformation bands in the Salt Wash Member of the Morrison Formation display an oblique northwest-southeast transpression.

While deformation bands have been described over broad areas of southern Utah, the major exposures have always been found in conjunction with larger structures, particularly Laramide monoclines. The deformation bands described here are significant in that they appear to have developed in the absence of a larger "forcing" structure. This raises two possibilities: firstly, that there is a hitherto unrecognized mechanism for forming deformation bands in southern Utah or secondly, there is an unrecognized "forcing" structure such as a Laramide strike-slip fault that does not exhibit significant vertical displacement.