Understanding deformation band formation across a range of length scales in the Paradox Basin, Utah

Abstract

In evaporite basins, salt flow can drive complex deformation of high porosity sedimentary units adjacent to salt and this has been demonstrated by recent numerical modeling studies, however field evidence of this deformation has remained elusive. Detailed analysis of high-porosity wall and cover rocks adjacent to a large salt-cored anticline in Salt Valley, UT yields three observable deformation band gradients. A long-wavelength gradient of steeply dipping normal/shear bands is recognized along structural transects up to 5 km away from the Salt Valley anticline axis. A shorter-wavelength (5–60 m) deformation band gradient shows band density increasing toward similarly-oriented brittle normal faults. A third gradient of intense compactional deformation banding is recognized adjacent to the salt diapir. Importantly, cement phases are undamaged in these bands, indicating that they likely experienced plastic critical-state deformation prior to cementation. The steeply-dipping deformation bands and normal faults are interpreted to be broadly contemporaneous and result from outer arc extension of the Salt Valley anticline; the dense compactional band network adjacent to salt likely accommodated compression during diapiric rise contemporaneous with folding. This integration of field and petrologic studies with forward modeling makes a critical step toward developing predictive models for deformation band formation in hydrocarbon systems.