2022 Fiscal Year Final Research Report
Re-evaluation of the potential for Uranium series dating using marine mollusks samples based on high-resolution uranium and thorium isotopes measurements
| Project/Area Number |
19K14805
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| Research Category |
Grant-in-Aid for Early-Career Scientists
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| Allocation Type | Multi-year Fund |
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| Review Section |
Basic Section 17030:Human geosciences-related
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| Research Institution | The University of Tokyo (2021-2022)
Rissho University (2020)
Kyushu University (2019) |
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Principal Investigator |
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| Project Period (FY) |
2019-04-01 – 2023-03-31
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| Keywords | U/Th dating / Marine mollusks / Radiocarbon |
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| Outline of Final Research Achievements |
U/Th dating is a powerful tool used for age determination throughout the Late Quaternary. Suitable marine samples for U/Th dating are largely restricted to well-preserved corals, with distributions limited to tropical and temperate regions. Some previous studies have approached the use of U/Th dating with marine mollusks, the results of which indicate U/Th dating potential. However, mechanisms of the uranium uptake process and closed-system U/Th dating for marine mollusk shells are still unclear. In this study, modern and fossil Turbo sp. samples, which are widely distributed along the Japanese archipelago, are evaluated to reveal the uranium distribution in the shells and explore the potential of U/Th dating using mollusks based on high-resolution uranium concentration measurements. Our results suggest variable uptake of uranium isotopes into mollusk shells, and highlight that it is important to define criteria for choosing mollusk species for U/Th dating around Japan.
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| Free Research Field |
Paleoclimatology
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| Academic Significance and Societal Importance of the Research Achievements |
U/Th年代測定に使用可能な生物化石は石サンゴ類に限られており、放射性炭素年代測定の限界を超える5万年以前の高精度年代決定が重要な課題となっている。造礁サンゴに比べ、貝はその分布域が熱帯域から高緯度域に渡り、U/Th年代測定に使用可能な貝試料を見つけることができれば、高精度年代決定可能な地理的・時代的範囲が大幅に拡大することが期待される。本研究ではTurbo sp.を用いて、貝試料中のウラン分布の偏在要因を考察し、得られるU/Th年代値について試算した。本研究成果は貝試料に取り込まれるウラン濃度の挙動を解明し、 U/Th 年代測定可能な種の選定指針の確立に向けた重要な知見である。
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