ISOTOPE GEOCHEMISTRY OF LACUSTRINE DEPOSITS IN THE CRETACEOUS CEDAR MOUNTAIN FORMATION, EASTERN UTAH

Lakes provide excellent archives of the terrestrial record due to their rapid response to accommodation and sediment supply, resulting in enhanced sensitivity to climate and tectonic changes. Cretaceous lacustrine deposits in the Cedar Mountain Formation of eastern Utah provide a unique opportunity investigate paleoclimate parameters of the terrestrial record in the western United States. Samples were collected from “Lake Carpenter” lacustrine sequence located near Moab, Utah and investigated using petrographic observations and stable isotopes.

Petrographic observations and bulk XRD indicated that carbonate samples are calcitic and/or dolomitic. Different carbonate phases were microsamples using a mm scale diamond coated bit and analyzed on a Thermo Gasbench II connected to a Thermofinnigan Delta +XP isotope ratio mass spectrometer. Preliminary isotopic carbon values on calcareous samples for the upper section are generally depleted while the lower section is generally enriched, ranging from -2.47‰ to 7.38‰ VPDB. Oxygen isotopes range from -1.9‰ to 6.11‰ VPDB.

Future work will be focused on completing stable isotope analysis on remaining calcareous and dolomitic samples. Clumped isotope paleothermometry provide temperature of formation for these carbonates and can be coupled with stable isotopes to infer whether the isotopic signatures of carbonate samples are primary or secondary. If paleothermometry results indicate unusually high temperatures, it can be concluded that late burial diagenesis may have altered these carbonates. Stable isotopes from primary carbonate samples will provide reliable data to infer paleoclimate parameters.