STRATIGRAPHIC FRAMEWORK OF FLORAL LOCALITIES IN THE JOHN DAY BASIN

Fossil-bearing strata in the John Day Basin include four stratigraphic units (Clarno, John Day, Mascall, and Rattlesnake units) that span much of Cenozoic time (50–5 Ma). During the deposition of all four units, local and regional volcanism contributed high amounts of volcaniclastic sediments that buried ancient ecosystems (plants, animals, and soils). Therefore, strata in the John Day Basin contain a wealth of paleontological information regarding the evolutionary and climatic changes that occurred during much of the Cenozoic, along with radiometrically dated/datable tuff layers. Workers in the John Day Basin have collected and analyzed fossil vertebrates and plants for over a century. Vertebrate paleontologists have collected mammalian fossils from over 400 localities, most of which are associated with dated tuff layers. Paleobotantists have collected and described many new species from over 100 fossil plant localities in the area. However, most of the previous paleobotanical studies have emphasized the taxonomic descriptions of plant taxa, rather than the stratigraphic occurrences of the plant localities. In order to study floral, faunal and climatic dynamics through time, existing fossil leaf localities need to be placed in a stratigraphic and temporal framework that utilizes diagnostic marker beds, and the well-constrained chronology available from numerous dated tuff layers. Here we present the stratigraphic placement of Cenozoic-aged floral localities on a new master composite section measuring ~2200 m thick. This new section is a compilation of existing stratigraphic data from multiple authors that have worked in the area. Vertical placement of the leaf localities on this section are based on previously published data and new field measurements. This composite section will serve as the basis of all future paleobotanical and vertebrate studies involving biostratigraphy, climate change, and floral and faunal comparisons through time.