Vegetative and lithologic response to the Paleocene-Eocene Thermal Maximum in the Hanna Basin, Wyoming

The Paleocene-Eocene Thermal Maximum (PETM), a rapid global warming event ~56 million years ago, caused by a large release of isotopically-light carbon into earth’s atmosphere and oceans, provides geologic parallels to anthropogenic climate change. This study focuses on vegetation changes within channel and overbank depositional sequences before, during, and after the PETM in the Hanna Basin, southeastern Wyoming, U.S.A. At each site, lithological descriptions were made, bulk carbon isotope samples were evaluated, and vegetation structure was assessed using reconstructed Leaf Area Index (rLAI) measurements. Our results indicate a meandering channel and closed canopy environment before the PETM, and a swampy, densely forested environment after the PETM. During the PETM, warmer temperatures and drier conditions decreased vegetation structure, causing a shift to braided fluvial systems. Our data demonstrates that the PETM had a significant impact on terrestrial landscapes.