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U-series dating and open-system processes in fossil corals from Henderson Island, South Pacific.

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Andersen M.B.1 , Stirling C.H 2

1Bristol Isotope Group, Department of Earth Sciences, University of Bristol, Parks Road, Bristol, United Kingdom (morten.andersen@bris.ac.uk)

2Department of Chemistry, University of Otago, PO Box 56, Union Place, Dunedin
New Zealand

 

In this study we present high-precision U-series ages for fossil corals sampled from fossil reefs on Henderson Island, an emergent coral atoll in the South Pacific. Fossil corals from this locality significantly pre-date the last glacial cycle, with coral development occurring during the warm interglacial/interstadial conditions of Marine Isotope Stage (MIS) 7.5 (230-245 ka), 9 (303-339 ka) and MIS 15 (575-620 ka) (Stirling et al., 2001, Andersen et al., 2006, Andersen et al., 2008). The fossil corals on Henderson Island generally show relatively little evidence of open-system U-Th isotopic alteration in comparison to reefs of comparable age at other localities. However, open-system U-Th behaviour in some corals is evident and replicate U-series analyses of multiple sub-samples from the same coral show that U-Th heterogeneity, resulting from diagenetic disturbance of the U-series isotopes, cannot be solely accounted for by any of the current open-system U-series models of diagenesis. To address this issue, a series of different fossil coral cleaning methods prior to chemical processing have been tested, together with investigations of the surrounding carbonate matrix hosting the samples. These tests may yield a better understanding of the processes occurring within these coral reefs and, in turn, may have broader implications for the pronounced U-Th open-system behaviour occurring generally in fossil corals of all ages and localities.

 

Andersen M. B. (2006) High-precision U-series measurements in the marine environment Ph.D thesis, ETH Zurich.

Andersen M. B., Stirling C. H., Potter E. K., Halliday A. N., Blake S. G., McCulloch M. T., Ayling B. F., and O'Leary M. (2008) High-precision U-series measurements of more than 500,000 year old fossil corals. Earth and Planetary Science Letters 265, 229-245.

Stirling C. H., Esat T. M., Lambeck K., McCulloch M. T., Blake S. G., Lee D. C., and Halliday A. N. (2001) Orbital forcing of the marine isotope stage 9 interglacial. Science 291(5502), 290-293.

Last updated: September 9, 2009
 


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