RISE OF THE COLORADO PLATEAU: LEVERAGING CLIMATE MODELS, STRATIGRAPHY, AND CARBONATE CLUMPED-ISOTOPE THERMOMETRY TO DISENTANGLE TECTONIC AND CLIMATIC SIGNALS FROM THE MIOCENE BIDAHOCHI FORMATION, NAVAJO NATION, AZ, USA

Uplift of the Colorado Plateau (CP) in western North America influenced the regional climate and landscape. The cause and history of CP rise to modern elevation of ~2 km above sea level are debated - some argue that most uplift occurred during or after the Laramide Orogeny (~80-20Ma), while others argue that most uplift occurred in the past ~20Ma due to mantle dynamics. To test these hypotheses, we aim to reconstruct the depositional elevation of the 16-6 Ma Bidahochi Formation, located on the southern CP. Since temperature systematically decreases with altitude, we use carbonate clumped isotope thermometry (T-Δ₄₇) to infer the elevation history. This approach requires accounting for other factors that influence temperature beyond elevation, such as the global mean temperature drop of ~7-10°C across the Miocene Climate Transition (ca. 14 Ma), regional climate dynamics, and the carbonate depositional environment. We leverage recent advances in carbonate clumped isotope geochemistry, global climate modeling, and lacustrine carbonate sedimentology to better control for these variables. We sampled carbonates at high resolution from consistent lithofacies in the most profundal parts of the Bidahochi basin to control for environmental changes. Based on calculations using 1-D lapse-rates and a local sea-surface temperature record, we would expect 3-5°C cooling in the Bidahochi record due to climate change in the absence of uplift. However, preliminary T-Δ₄₇ data indicate a larger than predicted by both the global mean and our calculations, which could imply significant regional uplift. We present T-Δ₄₇ data, along with preliminary Δ₄₈ data to evaluate and correct for potential disequilibrium effects on the temperature record. We also present lake proxy-system and global circulation model (CESM2.3) simulations to deconvolve the effects of climate and tectonics on the temperature record. Our results aim to clarify whether the Bidahochi basin has maintained its current elevation or experienced substantial uplift over the past ~16 Ma. (Fieldwork on the Navajo Nation was conducted under a permit from the Navajo Nation Minerals Department. Any persons wishing to conduct geologic investigations on the Navajo Nation must first apply for, and receive, a permit from the Navajo Nation Minerals Department, P.O. Box 1910, Window Rock, Arizona 86515, and telephone # (928)871-6587.)