Effects of contemporaneous orogenesis on sedimentation in the Late Cretaceous Western Interior Basin, northern Utah and southwestern Wyoming
During the Late Cretaceous, northern Utah and southwestern Wyoming were affected by contractional deformation driven by subduction of the Farallon plate. Deformation from the Sevier Orogeny resulted in the eastward propagation of thrust sheets and associated foredeeps. Shallowing of the subduction angle resulted in tectonic partitioning of the precursor Sevier foreland basin by exhumation of basement-cored uplifts. Lastly, long-wavelength dynamic subsidence is indicated by regional isopach patterns. This study combines outcrop lithofacies, paleocurrent measurements, detrital zircon geochronology, biostratigraphy, and stratigraphic correlations to examine the impact of changing tectonic regimes on provenance, basin geometry, and stratigraphic architecture. Data span the Coniacian to Maastrichtian (89-66 Ma) transition from thin-skinned deformation in the Wyoming segment of the North American Cordillera. Regional isopachs based on integration of new and published stratigraphic correlations constrain the timing of the changing subsidence patterns. During the deposition of the upper Baxter Formation (~88-83 Ma), a westward-thickening stratigraphic wedge characterized the foredeep developed by lithospheric flexure by thrust-belt loading. By the deposition of the Blair Formation (~83-81 Ma), the depocenter had shifted away from the thrust belt, with no evidence of a Sevier foredeep. The depocenter continued to migrate eastward during the early-mid Campanian (~81-77 Ma). Exhumation of the Wind River, Granite, and Uinta Mountains was initiated by the late Campanian – Maastrichtian (~74-66 Ma), based on local flexural thickening. Detrital zircon maximum depositional ages and biostratigraphy support that the Maastrichtian Hams Fork Conglomerate is deposited above the Moxa Unconformity adjacent to the thrust belt. The Moxa Unconformity bisects the fluvial Ericson Formation in the distal basin. The Hams Fork, however, is younger than the upper Ericson Formation, and instead equivalent to the upper Almond Formation. Therefore, the hiatus associated with the Moxa Unconformity continues for several million years longer in the fold belt than in the distal basin, with Ericson equivalents onlapping towards the west. Detrital zircon data also indicates varying sediment sources from the proximal to distal parts of the basin, with distal samples containing a southern source. This likely includes erosion and recycling of older Cretaceous strata mantling basement uplifts during Laramide partitioning of the basin.