NEW PALEOCLIMATE CLAMP ANALYSES OF THE LATE EOCENE FLORISSANT FOSSIL BEDS, CENTRAL COLORADO

The Florissant Formation in central Colorado is a highly fossiliferous upper Eocene shale and siltstone lacustrine succession punctuated by volcanic events represented by volcanic ash and tuff layers. Plant and insect micro- and macrofossils within these deposits help document the magnitude of Cenozoic climate change in the southern Rocky Mountains. Previous taxonomic and leaf physiognomic paleoclimate studies on the Florissant flora have generally yielded warm temperate climates, with mean annual temperatures (MAT) between 9 and 18 ºC and mean annual precipitation values ranging from about 30 to 80 cm. However, lack of a modern analog for the Florissant flora and fauna gives rise to divergent climate estimates depending on methodology. Here, we report new paleoclimatic estimates based on a fossil leaf assemblage within Florissant Fossil Beds National Monument at Site 9, an exposure that has yielded the most diverse set of morphotypes yet analyzed from a single site within the formation. Here, we employ the Climate Leaf Analysis Multivariate Program (CLAMP) to estimate paleotemperature and paleoprecipitation values including warm month mean temperature (WMMT), cold month mean temperature (CMMT), growing season precipitation (GSP), and length of the growing season (LGS). We analyze stratigraphically binned, time-transgressive sample collections through the section as well as overall climate estimates for the entire Site 9 leaf flora. Preliminary CLAMP results show a mean annual temperature around 11-12 ºC, a ~7-month long growing season, and growing season precipitation of ~150 cm. The Florissant Site 9 paleoflora illustrates a temperate late Eocene climate, generally corroborating earlier leaf physiognomic paleotemperature estimates but indicating higher precipitation. Additionally, paleoclimate estimates of Florissant allow for estimates of paleoelevation, which facilitates a better understanding of the timescale of the Rocky Mountain uplift.