QUANTIFYING CLIMATE CHANGE OVER THE EARLY CRETACEOUS RUBY RANCH MEMBER OF THE CEDAR MOUNTAIN FORMATION, EAST-CENTRAL UTAH

The Ruby Ranch Member (RRM) of the Cedar Mountain Formation (CMF) in East-Central Utah was recently constrained using C-isotope chemostratigraphy to span C-isotopes associated with the late Aptian to early Albian (Ludvigson, G. A., et al. (2010). J. Sed. Res., 80(11), 955-974.; Ludvigson, G. A., et al. (2015). Cretaceous Res., 56, 1-24.). The RRM is characterized by calcrete horizons that are thought to occur across the C10 isotope excursion, accompanied by an aridification event hypothesized based on traditional carbonate stable isotope analyses (Ludvigson et al., 2015) and the region’s position in a depositional basin on the leeward rain shadow of the Sevier Orogenic belt. Our research objective is to quantify the extent of this aridity by use of clumped isotope paleothermometry and paleoprecipitation proxies. We determined the whole rock composition of 51 samples and temperature of formation of seven carbonate nodules collected across the C10 chemostratigraphic interval. Two weathering indices, CIA-K (Harnois, L. (1988). Sed. Geol., 55(3), 319-322.) and CALMAG (Nordt, L. C., & Driese, S. D. (2010). Geology, 38(5), 407-410.) were applied to data obtained from XRF spectroscopy. Using these proxies, we determined mean annual precipitation across the RRM at its type section. Precipitation values obtained through the CIA-K transform function for identified paleosol horizons ranged between 821 and 1338 cm/yr, and through the CALMAG transform function ranged between 918 and 1352 cm/yr. Precipitation values decreased overall during the C10 interval which may indicate increased aridity. Interestingly, precipitation values were not lowest during the C10 interval. Clumped isotope analyses provided Δ₄₇ values ranging from 0.546 to 0.687‰. Calculated paleotemperature values were between 28.4 and 67.9°C. Temperatures above 50°C are interpreted to be the result of burial diagenesis. Temperatures peaked after the C10 interval and decreased during it, indicating a potential for cooler, arid conditions. These results suggest that carbon cycle changes during the Cretaceous may have influenced paleoclimate conditions experienced in terrestrial settings.