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Sediment Routing and Provenance of Deep Marine Sandstones in the Late Paleozoic Oquirrh Basin, Utah


The Oquirrh Basin is a Pennsylvanian to early Permian mixed clastic and carbonate basin 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. Depositional facies range from shelf carbonates to deep marine turbidites, debrites, and hybrid flow deposits, with a general deepening from basin initiation to the early Permian; however, the tectonic drivers and sediment source(s) for 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. Unlike other ARM basins, no basin-bounding fault or highland has been identified. 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. 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 parts of the basin versus moderately well sorted, coarser-grained sandstones in the basin center. Permian sediments have decreasing sorting and increasing variability in grain size toward the southeast. Published paleocurrent data indicate a prevailing southward ocean current suggesting sediment derivation and transport from the Laurentian craton to the north throughout. This is consistent with a lack of an identified basin-bounding highland. The northern source interpretation will be further tested with U-Pb detrital zircon analyses. This study adds to our understanding of sediment routing and facies distribution in rapidly-subsiding marine basins, critical inputs for basin and reservoir modeling.