PALEOCENE TO EOCENE CLIMATE CHANGE IN CENTRAL UTAH: CHEMO- AND LITHOSTRATIGRAPHY OF THE FLAGSTAFF FORMATION, CENTRAL UTAH

The Early Paleogene Flagstaff Formation on the Wasatch Plateau of central Utah preserves a ca. 300 meter thick sequence of palustrine and lacustrine limestone and dolostone. These rocks formed during a climatically dynamic interval of Earth's history, and contain important sedimentological and geochemical records of Early Paleogene greenhouse climate. We have studied the stable carbon and oxygen isotope geochemistry of sample suites from 3 local stratigraphic sections in conjunction with observations from field studies, petrography, and x-ray diffraction analysis. Integration of lithological and isotopic evidence indicates the presence of a persistent lateral paleoenvironmental gradient among our study sites and a secular drying trend represented in all 3 study sections. Existing age constraints indicate that the desiccation of Lake Flagstaff occurred during a multi-million year interval of global climate warming that was punctuated by extreme, transient (~200 kyr) warmth during the Paleocene-Eocene Thermal Maximum (PETM). Our analysis suggests that changes in the aerial extent and chemistry of Lake Flagstaff can largely be attributed to climatic changes affecting the lake basin and document a multi-million year reduction in precipitation:evaporation ratios similar to that previously reported from sites in Wyoming to the north. Although the correlation of the PETM within the Flagstaff Fm. remains unclear, existing constraints are consistent with this event having corresponded to the maximum lowstand of Lake Flagstaff, perhaps providing evidence for regional climatic drying during this episode of global warmth.