Variations in shortening style as a function of mechanical stratigraphy inferred from 3D seismic reflection data, northern Paradox Basin, UT

Abstract

The Paradox basin, located in eastern Utah and western Colorado, was first drilled for oil in 1891. That discovery resulted in decades of geologic investigation and industry exploration efforts that are still ongoing today. Substantial work has been done to characterize the well-exposed surface geology and extensive well log and core data from the basin. The Paradox basin has undergone multiple stages of deformation, the expression of which is complicated by the presence of a thick, interbedded sequence of evaporites and shales within the Paradox Formation that responds to these deformational events in a unique way due to the distinctive mechanical weakness of this unit. The Paradox Formation is comprised of 29 cycles of interbedded salt and shale that were deposited during the Pennsylvanian in the foredeep basin southwest of the Uncompahgre uplift. Terrestrial clastic sediments shed off the uplift during the Permian and Triassic, causing differential loading of the salt and leading to the formation of salt walls and salt anticlines sub-parallel to the uplift. The basin was largely structurally quiescent during the Jurassic, then the salt structures were modestly reactivated in shortening during the late Cretaceous Laramide Orogeny. Post-Laramide, salt-wall parallel faults experienced normal offset, followed later by erosional removal of nearly 2 kilometers of sedimentary section, which led to the exposure of the salt walls to the surface, causing dissolution and additional faulting. However, questions remain about the geological history of the basin that would be best resolved by additional insight into the subsurface geometry of the basin elements illuminated by 3D seismic reflection data.