A chemical weathering and paleoclimatic reconstruction of the early Cambrian environment of the Wyoming Craton from the Wind River Canyon, WY paleosol on the Great Unconformity

The weathering of continental rocks during the Precambrian-Cambrian transition contributed to the carving of the Great Unconformity and coincided with increasing biodiversity during the early Cambrian world. We use an early Cambrian paleosol exposed in the Wind River Canyon of Wyoming where it is buried by the overlying mid-Cambrian Flathead Sandstone to assess the paleo-weathering environment and constrain paleoclimate conditions on the Wyoming Craton in early Cambrian. The ∼ 3 m thick paleo-weathering profile is characterized by complete plagioclase weathering and moderate alkali feldspar weathering with maximum CIA (Chemical Index of Alteration) and PIA (Plagioclase Index of Alteration) reaching 69 and 98, respectively. Higher K concentrations toward the upper part of the profile associated with the authigenic precipitation of sericite clay minerals suggest that modest post-burial K-metasomatism may have overprinted the weathering profile. Our results suggest that the saprolite was developed under a mean annual paleoprecipitation and paleotemperature comparable to modern temperate environments. Geochemical characteristics of this paleosol formed during the final chapter of the Precambrian suggest intensive chemical weathering in the presence of elevated atmospheric CO2 concentration, forming a saprolite profile similar to other, previously described Cambrian and Precambrian-aged paleosols from the North American Craton.