Abstract

New and compiled U-Pb detrital zircon ages (n = 495) and sandstone petrographic compositions (n = 45) indicate a largely similar provenance throughout deposition of the Paleocene and lowermost Eocene Wasatch Formation in the Piceance Creek basin of northwest Colorado, U.S.A. Age spectra are dominated by Cretaceous- and Precambrian-age zircons from fluvial sand bodies composed of compositional litharenites and feldspathic litharenites. Our comparison with age spectra from other geologic formations exposed in surrounding Laramide uplifts indicates the Wasatch Formation is most similar to Upper Cretaceous fluvio-deltaic and marine strata of the Mesaverde Group, Mancos Shale, and their equivalents. Age spectra and paleodrainage directions from the lower Paleogene Wasatch and underlying Ohio Creek formations suggests recycling of these strata off the Sawatch and Uncompahgre uplifts from south and southeast of the basin. The data are inconsistent with previous hypotheses that Yavapai–Mazatzal crystalline basement in the Sawatch Range and Mesozoic eolianites in the Uncompahgre uplift contributed significant sediment to the basin. Based on these provenance insights and estimates of maximum depositional ages from detrital-zircon ages and biostratigraphy it appears that exposure and erosion of sedimentary strata of the Sawatch Range began between 65 and 60 Ma. This timing is significantly younger than the previously hypothesized ∼ 72 Ma unroofing of the crystalline basement in the uplift. Furthermore, we find no provenance evidence that sediment was transported across the Douglas Creek arch into the Piceance Creek basin from the Uinta basin. Thus, we infer this subdued Laramide structure was sufficient to block sediment dispersal from the paleo–California River system, which contemporaneously deposited ∼ 3000 km³ of sediment, transported from the magmatic arc, in the Uinta basin.