HR: 0800h
AN: PP11A-1437    [Abstracts]
TI: 45,000 Years of Peat Accumulation at Lynch's Crater, Australia: REE and Pb Isotope Records and Environmental Change
AU: * Kylander, M E
EM: malin.kylander@imperial.ac.uk
AF: Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ United Kingdom
AU: Muller, J
EM: joanne.muller@jcu.edu.au
AF: School of Earth Sciences, James Cook University, James Cook Universit, QLD 4811 Australia
AU: Weiss, D J
EM: d.weiss@imperial.ac.uk
AF: Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ United Kingdom
AU: Wust, R
EM: raphael.wust@jcu.edu.au
AF: School of Earth Sciences, James Cook University, James Cook Universit, QLD 4811 Australia
AB: To date inorganic geochemical proxies in peat cores have been successfully, used to assess climate change. For example, work in Spain used [Hg] variations to delimit warmer/cooler climate periods while an Indonesian record used dust flux changes to identify a Younger Dryas-like event. Climactic studies have been limited by the temporal coverage of available cores. The core retrieved from Lynch's Crater is unique in the length of the record (45,000 years) and in its Southern Hemisphere location. We present a study that examined the potential of REE and Pb isotopes as proxies for climate change in peat deposits. While the immobility of Pb in peat bogs is well established, less is known about REE. Past research suggests REE are more mobile in acidic, organic rich environments. In our core we find REE are immobile based on the (1) lack of high [REE] horizons with changing pH; (2) high correlation between individual REE (r²>0.93, except Eu) suggesting no significant fractionation; and (3) relatively unchanging REE patterns the length of the 13 m record. We suggest that REE can identify changes in source areas and provide indications of changing environmental conditions. Eu/Eu*_PAAS variations in volcanic (1.19-1.38) and non-volcanic (0.96-1.09) (locally collected) source rock groups indicates that the former dominates peat REE. Volcanic rocks show decreasing importance between ~32-10 ky BP which we tentatively suggest shows greater influence of long distance sources outside the Atherton basaltic province. Pb three isotope plots support this interpretation with more unradiogenic signatures (²⁰⁶Pb/²⁰⁷Pb=1.18-1.23) representing the volcanic rock group. Decreases in (La/Lu)_Profile between ~35-24 ky BP to 0.66 from a baseline value of ~0.90 are likely associated with non atmospheric inputs from a local source (e.g., run off) and transport of large sized particles to the deposit.
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 1637 Regional climate change
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005