CHARACTERIZATION OF SYNDEPOSITIONAL DEFORMATION IN THE PERMIAN CUTLER FORMATION, NORTHERN MARGIN ONION CREEK DIAPIR, PARADOX BASIN, UT

The Permian undifferentiated Cutler Fm. on the northern margin of Onion Creek Diapir, Paradox Basin, UT has a series of syndepositional growth synclines. The structural and stratigraphic variations in this area were documented by subdividing the Cutler into 30 stratigraphic units of fluvial and eolian facies and mapping unit thickness & facies changes using tablet based field mapping, measured sections, and drone based photogrammetry. The most common structures are syndepositional folds exhibiting growth strata, onlap and angular unconformities between units and the concentration of channelized conglomeratic sandstones in synclines. Folds trend parallel to the diapir margin and curve to match changes in azimuth of the margin. Fold wavelengths increase from 5 to 400 m with distance from the salt-sediment interface. Tighter folds are older and nearer to the diapir margin and more open folds are younger and more distal to the margin. At 600 m distance from the exposed diapir margin beds dip uniformly away from the diapir and do not record folding. A few radial faults are observed extending away from the diapir margin and locally cut older fold geometries (units 1-8) but are buried by younger Permian Cutler facies (units 9-30). Radial faults are generated by doming associated with diapir rise. Synclines form heterogenous microbasins that record Permian aged deformation along the diapir margin. The upward increase in fold wavelength and thickness suggests deformation occurred over a shallow detachment surface.

We interpret that shallow detachment to represent a salt shoulder (abrupt inward step of the diapir margin) marked by the cessation of salt movement in that area of the diapir and termination of radial fault growth. We infer Permian-aged gravity-driven folding across an inclined salt shoulder. This contrasts with previous interpretations of deformation either being post-depositional and influenced by regional compression or salt withdrawal or as being a salt wing.