Oxygen Isotopic Composition of Fossil Horse Tooth Phosphate as a Record of Continental Paleoclimate

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Palaeogeography Palaeoclimatology Palaeoecology
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Feb 28
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Oxygen isotopic, elemental, and X-ray data are presented for a suite of 24 fossil horse teeth from Nebraska ranging in age from 18.2 to 8.5 Ma, to test the use of delta(18)O of enamel phosphate (delta(18)O(PO4)) as a quantitative record of continental climate. Modern equid teeth were analyzed to estimate a relationship between delta(18)O(PO4) and environmental water. Multiple samples of seven different fossil species from Burge Quarry, a similar to 12 Ma attritional fossil deposit, indicate that diagenetic overprints exist but can be detected by decreased P concentration and increased crystallinity relative to modern enamel. Isotopic variation for the pristine samples from Burge Quarry is +/- 1.5 parts per thousand (1 sigma, n=9), which may represent the resolution of the procedure within a stratigraphic horizon. There are no apparent correlations with body size, hypsodonty, or phylogeny. A range of 7 parts per thousand in delta(18)O(PO4) occurs over the 10 m.y. interval. A trend towards depleted delta(18)O(PO4) of about 4 parts per thousand corresponds to a depletion of up to 6 parts per thousand in delta(18)O of precipitation between 18.2 and 8.5 Ma, but the range of variation at Burge is large relative to the climate signal. Our results demonstrate that delta 6(18)O(PO4) should be useful in quantitatively reconstructing Cenozoic continental paleoclimate on 10(6)-year timescales. Isotopic variation due to taphonomic bias and the terrestrial rock record will likely obscure higher-order climate signals.


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