EARLY EOCENE LEAF FOSSILS OF THE DENVER BASIN, CO: PALEOCLIMATIC INTERPRETATIONS AND COMPARISONS WITH OTHER EARLY EOCENE FLORAS

Sedimentary rocks in the Denver Basin of central Colorado contain a multitude of leaf fossil assemblages that range in age from 69 to 54 Ma. The younger and less abundant of these megafloras are from of the early Eocene ‘D2’ sequence of synorogenic sediments, and most of them are constrained to a distinctive paleosol and adjacent arkosic sands near the base of the D2 layer. Most of these floras are relatively understudied compared to older floras, but there are chemostratigraphic data to suggest that the basal paleosols and sands were deposited during the beginning of the Paleocene Eocene Thermal Maximum (PETM) climatic event. Therefore it is important to describe the nature of the D2 leaf assemblages, and to compare them with PETM floras from other areas. For this study leaves from six leaf sites were morphotyped and described to create a comprehensive database of D2 leaves in the Denver Basin. Paleoclimate data will be calculated using Leaf Margin Analysis and Leaf Size Analysis to determine mean annual temperature and precipitation, respectively during early D2 (and presumably early PETM) time. The Denver Basin Eocene floras will also be compared to published floras of contemporaneous age from the Bighorn Basin, WY and Golden Valley Formation, ND. Such a comparison will hopefully lead to a better understanding of regional climate change and regional vegetation change during the PETM warming event.