A study on accurate age determination of volcanic eruptions by high-precision 140 dating and a wiggle matching analysison charred wood from volcanic deposits

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Six wood samples were collected from Baitoushan Volcano in 2001 and two charred wood trunks were detected to have barks by careful inspection. The larger one of the two, with 102 annual rings, was used for ^<14>C dating. The annual rings were divided into 82 samples. The outer 20 annual rings were divided every two years because of narrow annual rings. From 21^<st> to 92^<nd> each annual ring was separated. Annual rings inner than 92^<nd> ring were broken and could not be separated. We have analyzed 35 samples out of 82 : approximately every three annual rings. The charcoal samples were processed by AAA treatments and converted to graphite in a routine method. The ^<14>C, ^<13>C and ^<12>C were measured with a HVEE Tandetron at Nagoya University. The obtained dates were compared with the INTCAL98 ^<14>C calibration data by wiggle matching. We obtained a probability distribution of one clear peak that corresponded to the time when the mixture of the outermost two rings was grown most probably in 935 cal AD, with errors of +8 and -5 years. This results implies that the eruption of Baitoushan Volcano had no relation with the fall of the Bo-hai State in AD926.ext, tephras from the Ulleung Island were studies chronologically. The U-Oki tephra is commonly accepted to have deposited in Japan at around 9.3-9.6 kaBP. The tephra layers U1, U2, U3 and U4 have been recognized on the Ulleung Island and their horizons were upper than the AT tephra (2.5 kaBP). During the survey at the Ulleung Island in 2002 and 2003, carbon samples for ^<14>C dating were collected from U2 (charred wood), U3 (organic soil) and U4 (charred twigs and organic soil). ^<14>C ages obtained for these layers were 5 kaBP for U2, 7.5-8.0 kaBP for U3 and 10-12 kaBP for U4. These results imply that the U-Oki tephra in Japan corresponds to U4. This is a really new finding, because the U-Oki tephra has been believed to correspond to U2.