APPLICATION OF NON-SEISMIC METHODS TO ANALYZE AND MODEL THE GEOMETRY OF THE NORTHERN MARGIN OF THE ONION CREEK SALT DIAPIR, PARADOX BASIN, UTAH

The Onion Creek salt diapir lies within the Paradox Basin of Utah where it forms part of a series of salt walls that separate the Paradox Basin into smaller sub-basins. One of these sub-basins has a series of anomalous tight folds occurring on the northern side of the Onion Creek diapir within the Permian Cutler Group Undifferentiated. These folds are thought to be associated with a shallow detachment horizon (less than 300m depth) with three possible origins:1) a weak shale layer within the Cutler Group, 2) a salt shoulder, or 3) a salt namakier. I use gravity and magnetics methods to better determine the extent and geometry of the Onion Creek salt body in order to constrain the origin of the detachment horizon. Since the salt is less dense than the Cutler Group siliciclastics, gravity methods are some of the best at defining the extent of salt in the subsurface, while magnetic methods help delineate the more highly magnetic Cutler siliciclastics. My initial results from gravity data show a low gravity anomaly over the diapir and then a gradual increase in gravity readings as more of the Cutler Group covers the salt. Initial magnetics data displays a similar trend with a low over the diapir with values that generally increase with more Cutler sediment cover. These initial datasets will be used to create a series of 2D cross section models that can be compiled to create a 3D salt geometry model that may be applied to other salt diapirs. Previous cross sections do not show a salt shoulder or namakier which changes the implication on the structure at Onion Creek with new gravity and magnetic data. If also found in other salt basins, knowing these salt geometries are key to developing a safe, effective, and high-recovery drilling plan.