New pollen data from four Oligocene floras in volcanic landscapes of Colo rado record important climatic shifts that reshaped the local flora and promoted the development of subarid vegetation types. We combined new pollen data with previous megafossil evidence to assess vegetation changes during the Eocene-Oligocene Transition (EOT). Pollen data are the basis for updating the list of flora identified at Creede. Local extinctions in response to lower sum mer rainfall abruptly removed many of the exotic woody taxa of eastern North American and Asian affinity. This loss was followed by the appearance of xeric shrubland taxa of the Ponderosa pinefir woodland and sagebrush flora that characterize the Colorado area today. Telltale genera appear and suggest an understory of shrubs such as Artemisia, Elaeagnus, Ribes, Ephedra, Jamesia, and Shepherdia. Poaceae are also present. Significantly, herbaceous taxa of the Asteraceae, Rosaceae, Cucurbitaceae, Euphorbiaceae, and Caryophyllaceae make their first appearances in the fossil record of Colorado here. The new Oligocene pollen data record a significant drop in summer rainfall and a climatic cooling at 33.8 Ma of several degrees that relates to the Oi1 glaciation in Antarctica. The particular taxa that continued after the EOT were a basis for estimating changes in soil moisture during this time. The condi tions in Colorado are reminiscent of Wolfe's "terminal Eocene event." This re markable shift precipitated the development of a local pollen and megafossil flora more "modern" in aspect (e.g., a larger proportion of extant local genera are present). The impressive floristic turnover was probably a response to the increasingly continental climate that embraced the area during the Oligocene.
Published estimates on the paleoclimate of the Florissant fossil beds site of Colorado (34.1 Ma) have led to extremely different estimates of paleoelevation. The purpose of this paper is to review the paleoclimate methods used and to add the coexistence approach (CA) method to estimate paleotemperature for the Florissant site. The basis of the CA method is the dependence on overlapping climatic requirements for different taxa in the flora and their nearest living relatives. These relationships tie the fossil identities to the actual plant habitats and climatic requirements of close relatives. Based on the CA method, we conclude that the mean annual temperature ranged between 14.3 and 18.2 °C. These results support the conclusions offered by several other studies that the Florissant was a warm temperate to subtropical flora, and they are consistent with recent conclusions by structural geologists as well as other studies, indicating that the Florissant site was deposited at a relatively low elevation, probably between 1 and 1.5 km.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.