Tectonic Influence of the Transcontinental Arch on Sediment Provenance: Detrial Zircon Geochronology of the Middle Cambrian Flathead Standstone, Bighorn Mountains, Wyoming

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Abstract We report the results of detrital zircon U-Pb analysis from the middle Cambrian Flathead Sandstone from two locations in the eastern Bighorn Mountains of Wyoming and their implications for post-rift tectonics in western Laurentia. The Flathead Sandstone U-Pb zircon age spectra shows prominent age peaks at ~1.8 Ga and minor age peaks at ~2.7 Ga. Detrital zircon samples taken across the extent of the Flathead Sandstone have a much higher proportion of Archean grains nearer to the basal unconformity and further to the west, and age spectra overall get progressively younger in samples taken higher in the section and further east and south. The 2.7 Ga signature observed in the Bighorn Mountains is largely absent from the Wyoming Province rocks and is likely derived from the Superior Province. Proterozoic zircons are sourced from the east and southeast in the Trans-Hudson and Yavapai Province rocks exposed in the Transcontinental Arch. The differences in age spectra between samples correlated to their spatial and temporal differences likely reflects subsidence along the passive margin and progressive southwestward-advancing uplift of the Transcontinental Arch during Flathead deposition. Subsidence, denudation and burial of Wyoming Province rocks and uplift of those exposed in the Transcontinental Arch led to the removal of the Wyoming Province as a source terrane by the time of Flathead Sandstone deposition in the Bighorn Mountains. The Transcontinental Arch was a significant contributor to detrital zircons across Laurentia, and concurrently acted as a barrier to sediment dispersal from more distal and younger Proterozoic terranes to the east and south into northwestern Laurentia.

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