TECTONIC SUBSIDENCE ANALYSIS AND SEDIMENT PROVENANCE EVOLUTION OF THE LATE PALEOZOIC OQUIRRH BASIN, UTAH

The Oquirrh Basin is a Pennsylvanian to early Permian mixed clastic and carbonate basin exposed in northwestern Utah. The basin is the northwestern-most expression of the Ancestral Rocky Mountains (ARM) orogeny, and locally contains up to 9 km of sediment. The subsidence history and tectonic drivers of the basin are poorly constrained. To better understand the subsidence and tectonic history of the Oquirrh Basin, tectonic subsidence analysis was performed on 11 published stratigraphic sections across the basin. Two phases of tectonism are interpreted to have occurred on either side of the basin, forming distinct depocenters during the middle Pennsylvanian and early Permian. Pennsylvanian subsidence is interpreted as a flexural response to a crustal load east of the basin coeval with the ARM, whereas Permian subsidence in the western part of the basin may be related to the uplift and unconformity sequence documented in the Antler Overlap basins of northeastern Nevada.

To test links between sediment provenance and tectonism, 34 thin-sections were analyzed from 8 locations in a northwest to southeast transect across the basin. Samples are from sandstone packages in the Butterfield Peaks, Bingham Mine, Curry Peak, Freeman Peak, Kirkman, and Diamond Creek Formations. Gazzi-Dickinson point counting was used to determine composition and provenance. Samples fell into three compositional categories: quartz arenite, sublitharenite, and quartz wacke indicating cratonic interior and recycled orogenic provenances. Petrographic analysis of middle Pennsylvanian sediments revealed very well sorted, finer-grained sandstones in the southeast and northwest part of the basin versus moderately well sorted, coarser-grained sandstones near the Cortez-Uinta Axis in the center of the basin. Permian sediments have decreasing sorting of grains and increasing variability in grain size toward the southeast. Published paleocurrent data indicate a prevailing southward ocean current suggesting sediment derivation from the stable Laurentian craton and Wyoming shelf to the north throughout rather than the Uncompahgre basement uplift to the southeast or the remnant Antler uplift complex to the west. The northern source interpretation is consistent with this study and will be further tested with U-Pb detrital zircon analysis.