THE EARLY PALEOGENE HERREN FLORA: AN INVESTIGATION INTO THE EARLY CENOZOIC HISTORY OF THE PACIFIC NORTHWEST

A locality in north-central Oregon, the informally named “Herren Formation,” has tremendous potential to fill a crucial gap in the PNW record because it is estimated to be Paleocene in age and contains fossiliferous sediments interbedded with datable igneous rocks. The over-arching goals of my research are to (1) analyze leaf bearing beds in the “Herren Fm” to document the paleoecology and estimate paleoclimate, (2) compare the “Herren Fm” to other hothouse Early Paleogene sites from the US continental interior and Alaska, and (3) compare the “Herren Fm” to PNW sites throughout the Cenozoic. This work tests the hypothesis that the Paleocene PNW climate was more tropical than present day, with higher amounts of precipitation, and therefore the vegetation was more diverse and less even than other contemporaneous areas on the continent.

Previous work has put conflicting ages to the “Herren Formation;” the fossil leaf assemblages suggest a Paleocene age, whereas prior correlation to the Clarno Formation suggests a middle-late Eocene age. My field investigations are aimed at mapping the fossil-bearing sediments and collecting samples from all available leaf bearing beds. Once the full paleobotanical and paleoecological data are collected, I will compare spot samples within a stratigraphic level and between stratigraphic levels within the “Herren Fm.” Floral diversity will be gauged via rarefaction, evenness via rank abundance curves and Pielou’s J, and composition via ordination analyses. Once floral ecology and composition, herbivory, and climate (LMA and LAA analyses) for the “Herren Fm” have been established, comparisons can be made to previously studied sites to better understand how vegetation in the PNW has changed over time and how the “Herren Fm” differs from Early Paleogene sites in the US continental interior and Alaska.