QUANTIFYING STRESS CONDITIONS OF DEFORMATION BAND FORMATION ADJACENT TO SALT STRUCTURES, SOUTHERN UTAH, USA

Deformation bands are ubiquitous in the Jurassic sandstones of the Paradox Basin of southern Utah, and research into them has been driven in part due to their porosity reduction in potential reservoir rocks. The Pennslyvanian Paradox Formation consists of evaporites which have mobilized to form salt diapirs, which have a strong influence in the surface topography in the region. Deformation bands in the Jurassic sandstones near salt diapirs have been described in detail, however, the stress conditions of their formation have tended to be described qualitatively. Here we present a quantitative study of the stress conditions required for deformation band formation. Various types of deformation bands have been recognized in the region; however, we focus on cataclastic deformation bands in the Upper Jurassic Moab Member of the Curtis Formation, which occur as semi-planar zones of reduced grain size and porosity. Grain size and porosity analyses of both deformation bands and undeformed host sandstones allow for a quantification of the mean and differential stresses required to form deformation bands. The results of these analyses, in addition to in-situ location, orientation, and thickness measurements, indicate relatively high stresses are required for cataclastic deformation bands to form. Furthermore, spatial data indicates strain accommodated by deformation bands is highest near salt diapirs and decreases exponentially away from the salt bodies. We use this data to interpret the deformation bands to have formed as a result of high stress conditions experienced during salt diapirism.