Stable and Clumped Isotope Investigation of the Early Cretaceous Terrestrial Paleoenvironment in Eastern Utah
Lake basins are significantly more sensitive to climate and tectonic changes versus marine settings. This study focuses on a detailed isotope geochemical investigation of lacustrine deposits found in the Ruby Ranch Member of the Early Cretaceous Cedar Mountain Formation. The Early Cretaceous is characterized as a period of transitioning greenhouse climate. The objective of this study is to identify and quantify potential changes in paleoclimate reflected in the history of deposition of the "Lake Carpenter" through detailed petrographic, and stable and clumped isotope analyses of lacustrine carbonates. Additionally, chemostratigraphy is used to constrain the relative age of the Ruby Ranch Member immediately below the Lake Carpenter sequence.
Primary and secondary calcite carbon and oxygen isotope values of lacustrine carbonates range from -9.2‰ to 5.4‰ and -9.3‰ to -0.3‰, respectively. Dolomite carbon and oxygen isotope values range from -1.7‰ to 1.8‰ and -4.2‰ to -0.9‰, respectively. Paleothermometer temperatures range from 13.0°C +/- 2.2 to 33.2°C +/- 7.5. Carbon and oxygen enrichment of primary lacustrine carbonates and paleothermometer temperatures exhibit episodes of dramatic cooling and warmth during the late Aptian -- early Albian. Ruby Ranch Member 13Corg values of rock samples below the Lake Carpenter sequence range between -28.5 to -23.7‰ and have an average of -26.3‰. The chemostratigraphic curve correlates with the C8--C9 negative carbon isotope excursion interval and the "Kilian" and "Jacob" events associated with enhanced presence of light carbon. Approximate age constraint of this Ruby Ranch Member section is between 116 -- 113 Ma.