9418210 Smith Climate change near the Eocene-Oligocene boundary was one of the most significant environmental changes of the Phanerozoic. The nature of this geologically abrupt global cooling, and hypotheses for its cause, have come largely from study of continuous marine stratigraphic records. In order to understand the dynamics of global climate change, it is essential to better understand the nature of the early Oligocene climatic deterioration on continents. To date, the interpretation of climate change at the time in North America has been based on scattered, and in some cases poorly dated, paleo-floras. Ambiguities remain, therefore, on age relationships of these climatically-sensitive floras and the extent to which differences between them represent true temporal change rather than variations in altitude and other environmental parameters between floral sites. We will study a sequence of fossil floras preserved in a single stratigraphic sequence, in north-central Oregon, where reconnaissance work suggests a record of the entire climate change. Detailed collection, study, and interpretation of these floras will be complemented by geologic mapping, sedimentological, and stratigraphic study to assure the stratigraphic framework of strata containing the fossils and the depositional environments (and thus environmental or taphonomic biases) represented by beds enclosing the floras. The paleofloras are hosted in volcaniclastic sediment interlayered with tuffs and lava flows that will be dated by 40Ar/39Ar method in order to constrain the chronology of the climatically- driven floral change in central Oregon.
