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- Amino acid racemization and radiocarbon age of a Mammoth molar fossil from eastern Siberia(Proceedings of the 16^<th> Symposium on Researches Using the Tandetron AMS System at Nagoya University in 2003)
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We measured D/L aspartic acid ratios and radiocarbon ages of a Mammoth molar fossil collected from Bykovsky Peninsula, eastern Siberia and animal bone fossils collected from the shell mound excavated at Awazu submarine archeological site, Shiga, Japan. Four parts of dentin, enamel, cement and root in the molar fossil were measured. The ^<14>C ages of gelatin collagens are dated 〜36,000 BP for the dentin and 〜37,000 BP for the cement and root, while those of XAD-treated hydrolysates are dated 〜35,000 BP for the dentin and cement and 38,750 BP for the root. The gelatins have 1000〜2000 year older ages than the XAD-treated hydrolysates, expect for the root part. It might be due to that the gelatins contain foreign organic carbon with older ^<14>C age than the fossil, or that the XAD-treated hydrolysates are contaminated by modern carbon. The latter is possible, and the age of the Mammoth molar could be 〜37,000 BP. The D/L aspartic acid ratio of the molar fossil is low, and it suggests that amino acids in the Mammoth molar have not racemized since it was dead and buried. This result is well consistent with the fact that it was preserved in the permafrost. In animal bone fossils from Awazu submarine archeological site, amino acids racemization is observed and the average of D/L aspartic acid ratio is about 0.11. The average temperature, to which samples had exposed, is estimated to 13.2±1.1℃, using the D/L ratios and ^<14>C age of 4,500 BP (Minami and Nakamura, 2000). Because it is hard to think that there was large environmental change at Lake Biwa during last 4,500 years after the samples were sank, the animal bone fossils had not experienced large environmental change about temperature since it was buried. In this study, we suppose that the rate of amino acid racemization in a fossil depends on only temperature. However, it is also dependent on other environmental factors such as pH, existence of water and amino acid composition in a fossil. More study is needed to obtain reliable the average temperature.
名古屋大学加速器質量分析計業績報告書 15 52-65, 2004-03