報告書番号

U99063

タイトル（和文）

OSL法･TL法･ESR法による段丘堆積物の年代測定 --光曝実験と年代既知段丘堆積物の年代測定による検討--

タイトル（英文）

Studies on applicability of terrace sediment dating by OSL, TL and ESR methods - Illumination tests and dating of age-known terrace sediments -

概要 （図表や脚注は「報告書全文」に掲載しております）

光ブリーチング仮説に基づく石英を用いた段丘堆積物の年代測定を光曝実験と年代既知試料への適用により検討した．OSL法は，数千年の若い河成段丘堆積物への課題は残るが，概ね段丘堆積物へ適用できる見通しを得た．TL法では，TLが実験的に光に対して消えやすい成分と消えない成分に分離でき，消えやすい成分だけを使うと海成段丘堆積物に対して適用できる可能性を得た．ただし，河成段丘堆積物に対する適用は難しい．石英の代表的な信号を用いたESR法については，堆積過程における完全な光ブリーチングが期待できず，海成・河成段丘堆積物共に適用が難しい．さらに，これらの年代測定では，地質時代を通じての含水比の変動の寄与が大きく，試料採取・手法の選択において堆積物の運搬・沈着過程を考慮する必要があることがわかった．

概要 （英文）

We investigate the applicability of the luminescence dating methods for terrace sediments based on the assumption of the complete optical bleaching of some radiation defects in quartz grains in the processes of erosion, transportation and/or sedimentation. At first, we have carried out illumination tests. The illumination tests show that the Ti signal is more light-sensitive than E1' and Al signals, and is bleached completely by illumination. This result shows that the TL consists of the light-sensitive component and the residual one, and that we can obtain the intensity of a light-sensitive component easily by illumination tests.Then, we tried to date late Quaternary marine/river terrace sediments, whose age had been already estimated from geological information, using OSL, TL of light-sensitive component and ESR Ti signal. Ages obtained by the OSL and TL methods are in good agreement with geologically estimated ages. We found that variation in pore water content over time was of major significance in age determinations for these sediments, on account of their history of deposition underwater, with subsequent uplift and drainage. However, the ESR method fails to date marine terrace sediment, because we were not able to determine how the bleaching of the ESR Ti signal proceeded in antiquity.Furthermore, we have carried out OSL dating of late Quaternary river terrace to verify its applicability. Samples from the recent riverbed show a weak OSL and gave very young ages. OSL ages obtained from sand-lenses in terrace gravel layers show a good agreement with ones estimated by stratigraphic data. OSL ages obtained from flood plain deposits are older than geologically estimated ages. This was attributed to the mixing of different age grains by incomplete optical bleaching due to the inundation process. Analyses of OSL from single quartz grains confirmed that these sediments were composed of grains having a wide range of palaeodoses. Therefore, we concluded that the OSL method is adaptable for marine and river terrace sediments, and that the TL method is probably appropriate for dating of the marine terrace sediments. Furthermore, the process in transportation and deposition of sediments should be considered for dating of sediments.

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