Philip D. Gingerich, University of Michigan Biotic change in the Bighorn Basin, Wyoming, before, during, and after the Paleocene-Eocene Thermal Maximum (PETM): Consistent with orbital forcing? Philip D. Gingerich, University of Michigan The Paleocene-Eocene Thermal Maximum and the ETM-2, two global warming events during the early Eocene, occur at 100-kyr eccentricity maxima, suggesting both events were orbitally forced. The Bighorn Basin is the best place to determine if terrestrial climate and biotic change during the Paleocene-Eocene were orbitally paced because of its nearly continuous lithostratigraphic and biostratigraphic records. This hypothesis is being tested by combining high-resolution stratigraphic, isotopic, and faunal records over a > 1.8 Myr interval spanning the PETM and ETM-2. Preliminary results indicate trends in dispersed organic carbon (DOC) that occur on scales > 100 kyr, consistent with eccentricity periodicities. Finer scale trends in the DOC record coincide with fluvial facies change, which is not influenced solely by climate change. Understanding the lithological controls on DOC stable isotopes will be necessary in order to determine if higher frequency orbital periodicities influenced Paleogene climates and biotas. PETM Figure. Representative stratigraphic and DOC isotope record encompassing the PETM. Raw isotope values are in black and a smoothed trend in red. Most significant spectral peak occurs at 23 m (~50 kyr) and coincides with deposition of major fluvial sand, indicating a lithologic influence of DOC values in addition to climate influences.