Evolution of minibasin stratigraphy adjacent to the Pine Ridge salt diapir; Paradox Basin SE Utah

Abstract

The architecture of salt-controlled minibasins affects the distribution of hydrocarbon elements within a system, and may be different across associated minibasins adjacent to salt bodies. Therefore, it is vital to accurately correlate stratigraphic sequences in adjacent minibasins, as mistakes can be costly. This can be a difficult task in salt-controlled basins due to the transient nature of the evaporites, which in turn affects accommodation and depositional patterns. The task is complicated in areas with sparse data density. This can be seen in two previously published papers over the Pine Ridge salt diapir, SE Utah, which have conflicting interpretations due to lack of subsurface control. One interpretation is based on well data, while the other is based on 2D seismic data. This study incorporates a 3D seismic dataset, regional 2D seismic lines, well data, and field data over the Pine Ridge Diapir, allowing a detailed analysis of minibasin stratigraphy both temporally and spatially. Our dense dataset in this study suggests that the evolution of the Pine Ridge diapir was significantly different to that of the Salt Valley salt wall to the north. Depositional geometries at Pine Ridge show that the salt rise rate was equal to the sediment accumulation rate. A lack of supra-salt faults indicates that the salt body was consistently below the surface, and did not experience salt dissolution or extension during its evolution. Salt geometries and isopach stacking patterns give insight into the evolution of the diapir. During interpretation it was determined that salt movement was not significant during the formation of the early to mid-Pennsylvanian evaporites, and continued to be quiescent into the late Pennsylvanian. However, rapid movement occurred during deposition of the lower Cutler beds, leading to drastic thickness changes across the minibasin. Salt movement generally stayed consistent for the rest of the diapir passive growth history with the exception of a few increases of diapir rise rate versus aggradation during the deposition of the White Rim, Moenkopi, and Chinle formations. The findings at the Pine Ridge salt diapir can be applied to other salt diapirs in similar tectonic settings.