APPLICATION OF RARE EARTH ELEMENT(REE) SIGNATURE ANALYSIS AT PLEISTOCENE LOCALITIES IN FOSSIL LAKE, OREGON

Fossil Lake is located in south central Oregon and comprises a (< 20 m thick) sequence of lacustrine sediments, deposited during the late Pleistocene. The sediments were divided into distinct lithologic units (by JEM). Bones from Pleistocene mammals, fish, birds as well as eggshells, were collected for REE analysis from all these stratigraphic units from the Fossil Lake localities. The study at Fossil Lake focused on recognizing the uniqueness of the REE Signatures within lithological units less than 1 meter thick and also measuring the lateral extent of the signatures within an ephemeral, lacustrine environment. REE signatures (ratios) of fossils from various lithological units were distinctly different from one another, as determined by Statistical Analysis. Fossils were found to have unique signatures specific to their unit, regardless of species, diet, or bone material type. A rabbit skeleton from a burrow within the uppermost unit had an REE Signature identical to those of fish bones from the sediments surrounding the burrow. Therefore, the REE signature was not affected by diet of the organisms but was acquired during early diagenesis and reflects the burial environment of the organism. The period between burial of the fish and rabbit must have been less than the interval required for REE incorporation (ca. 10,000 to 30,000 years). Samples collected from a gravel unit over a 16-kilometer distance show the same signature. This indicates that a REE signature may have a significant lateral extent within this fresh-water environment. Additionally, through the use of this technique, bones of unknown provenance were assigned to a specific unit. Each suite of fossils from each of the eight lithological units can be differentiated on the basis of REE Signatures. This study further proves that fossils having questionable provenance, due to lost or incomplete records, may be identified using REE Signature analysis.