Funding is requested to test the hypothesis that the d18O of the CO3 component of fossil bone apatite can be used as a paleoclimate proxy analogously to paleosol carbonate. Trace element, crystallinity, and sparse isotopic data suggest that (a) bone recrystallizes significantly during fossilization, (b) the d18O of the CO3 component of bone may correlate with local carbonates, and (c) recrystallization occurs on a similar time scale as pedogenesis. That is, alteration of bone, including isotopic alteration of bone CO3, appears to be a pedogenic process. If so, then the isotopic compositions of bone CO3 and paleosol carbonate should correlate, and fossil bone could be used as a paleoclimate proxy as an alternative to paleosol carbonate. Key to this proposal is comparison of coexisting paleosol carbonate and the CO3 component of fossil bone fragments. A collection of several hundred paleosols from the Oligocene John Day Formation, central Oregon, now housed at John Day Fossil Beds National Monument, uniquely provides the raw materials. Paleosol carbonate from each paleosol has already been analyzed by Retallack and coworkers, and data show isotope shifts that are both short-term (thousands of years) and long-term (millions of years). Outstanding age dating and stratigraphic contexts permit resolution of isotope shifts to tens of thousands of years (meters, stratigraphically). Most importantly, an estimated 50 of these paleosols also contain fossil bone fragments. Thus analysis of bone fragment compositions will readily permit comparison with coexisting paleosol carbonate. It is additionally important to identify the degree to which bone fragments adopt paleosol compositions. Compositional profiling will first be conducted with select (5-10) large bone fragments from the paleosol sequence to evaluate what portions of the bone are altered (e.g., the entire bone irrespective of bone type and location, cortical vs. cancellous bone, outer iuexposedlv vs. inner inprotectedll portions, etc.). These data will help define a sampling protocol that will then be applied to bone from the remaining paleosols. If bones are in fact isotopically altered, compositional comparison with paleosol carbonate will reveal whether bones are partially or completely altered to paleosol conditions. Preservation of short-term (thousands of years) variations vs. only longer-term trends will help define whether the time scale for alteration is indeed thousands of years, as suggested by trace element and crystallinity studies, or instead millions of years. Successful use of the CO3 component of fossil bone as a paleoclimate indicator would be especially beneficial in areas that are fossiliferous but lack paleosol carbonates (e.g., the Miocene of central Oregon). Other areas of the world that are fossiliferous, but perhaps not abundantly so, would become amenable to paleoclimate and tectonic research. A positive outcome would also foster greater synergy between stable isotope geochemists and paleontologists, as paleontological field prospecting crews are well trained to identify and collect fossil bone, but not paleosols or paleosol carbonates.
