岐阜県八百津町の木曽川泥流堆積物から採取された埋没樹木の加速器14C年代

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The Kisogawa Volcanic Mudflow Deposit (kmf), derived from the Ontake Volcano, has been found to be distributed on terraces around the Ontake Volcano down to the northeastern part of the Nobi Plain, along the Kiso River for a distance of more than 144km. Therefore, the kmf has been used as a key bed for comparing and correlating the upper Pleistocene of mountainous regions with those of coastal regions in Central Japan.Six wood trunks have been collected from the kmf and two wood chips from the clay bed immediately overlaid by the kmf, at Nishikoori, Yaotsu-Cho, Gifu Prefecture. The sampling site is located in the east end of the Minokamo Basin, as shown in Fig. 1, where the kmf constitutes the upper part of the Middle Terrace Deposits of the Kiso River (Figs. 2 and 3).Radiocarbon ages of the wood samples have been measured by a Tandetron accelerator mass spectrometer at the Dating and Materials Research Center, Nagoya University. 14C ages of six wood samples from the kmf range from 48, 750 to 51, 840yrs BP, except for a rather younger age of 43, 520yrs BP (KD-4; Table 1). The average of the older five dates is 49, 850±420yrs BP. The two wood chips from the clay layer below the kmf show 14C ages of 47, 280 and 51, 980yrs BP (Table 2), which are almost equal within margins of error to those of the log samples from the kmf. Based on these dates, it is concluded that the kmf was formed about 50, 000 years ago. This study, resulting in a much older 14C age of the kmf than the age generally accepted (ca. 27, 000yrs BP), enforces a revision of the chronology of Late Pleistocene deposits and tephras, which have been accumulated on terraces along the Kiso River and buried under the Nobi Plain.
日本第四紀学会の論文

岐阜県八百津町の木曽川泥流堆積物から採取された埋没樹木の加速器14C年代

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