PALEOCLIMATE AND PALEOECOLOGY OF THE LATE EOCENE FLORISSANT FLORA USING DIGITAL LEAF PHYSIOGNOMY

Paleoclimate of the late Eocene Florissant flora of central Colorado has been studied for more than 60 years utilizing a variety of both taxonomic and physiognomic methodologies. These results facilitate a multiproxy perspective of likely climate envelopes that provide a broad scope of comparison with new methods. We applied Digital Leaf Physiognomy (DiLP) to a fossil leaf assemblage from a single locality in the middle shale unit of the Florissant Formation. This method differs from other physiognomic proxies (i.e., CLAMP) previously applied to the Florissant flora by measuring continuous leaf character variables, rather than categorical variables. DiLP variables show robust correlations with mean annual temperature and precipitation. Approximately 120 leaves representing forty dicotyledonous morphotypes, dominated by Cedrelospermum lineatum, Fagopsis longifolia, Quercus spp., Rhus spp., and members of Rosaceae and Fabaceae, were analyzed. Preliminary results from the DiLP analysis suggest the flora represents a cool temperate, relatively dry, shrubland/woodland to forested environment. The mean annual temperature (MAT) estimate (~9 °C) is cooler than previous estimates from Florissant, which range from 11-18 °C, but overlaps within error of previous CLAMP estimates. Leaf mass per area (M_A) was calculated for 26 morphotypes using measurements of leaf area and petiole width. The sampled flora shows a broad range of M_A estimates (54 – 161 g/m²), and the majority of species have high M_A values indicating that the flora was dominated by taxa with long-lived leaves. The distribution of M_A values at the site is most similar to the distributions of modern non-riparian temperate floras, suggesting a similar ecology for the Florissant flora. The correspondence of relatively cool MAT reconstruction, the occurrence of a palm macrofossil signifying lack of prolonged freezing, and the predominance of taxa with long-lived leaves indicates a relatively equable climate with low temperature seasonality.