Abstract

The northern Paradox Basin evolved during the Late Pennsylvanian–Permian as an immobile foreland basin: the result of flexural subsidence in the footwall of the evolving Uncompahgre Ancestral Rocky Mountain Uplift. During the Atokan-Desmoinesian (~313.4–305.6 Ma), a thick sequence of evaporites was deposited in the foreland basin, interfingering with course clastics in the foredeep and carbonates around the basin margins. Cyclic deposition of the evaporites produced a repetitive sequence of primarily halite (~71%), with minor clastics, organic shales, and anhydrite. Sediment loading of the evaporites subsequently produced a series of linear salt walls up to 4500 m high. Seismic, well and published data define the proximal Cutler Group (Permian) as a basinward prograding unit that caused underlying mobile salt layers to flow in the same direction, i.e., towards the southwest. Faults at the top Mississippian level (base salt), inherited from Precambrian basement lineaments, localized the development of linear salt walls along a NW-SE trend. A crosscutting NE-SW basement trend was also important in controlling facies variations in original salt deposition and the abrupt termination of salt walls. The presence or absence of halite within the Paradox Formation subsequently exerted a strong control on the stratigraphic geometry of the progradational Cutler units.