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^<14>C age of buried stump preserved in dammed lake sediments of Koinami in Yatsuo Town, Toyama City, central Japan(Proceedings of the 20^<th> Symposium on Chronological Studies at the Nagoya University Center for Chronological Research in 2007)

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  • 富山市八尾町小井波の埋没根株の^<14>C年代とその応用地質学的意義(第20回名古屋大学年代測定総合研究センターシンポジウム平成19(2007)年度報告)

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Koinami in Yatsuo Town, Toyama City, central Japan is located on a small flat basin along the Besso River surrounded by ridges about 600-800 m in altitude, south of the Toyama Plain. The ENE-WSW trending fault to the south of Koinami is the boundary between the Miocene Nirehara and Iwaine Formations to the north and the Tetori Group and the Funatsu Granite of Hida belt to the south. Many landslides are developed within the area underlain by the Iwaine Formation composed of volcanic and volcaniclastic rocks. One of the landslides, 500 in width and 800 m in length, dammed the Besso River and the dammed lake was filled in to form the Koinami flat basin. The buried forest composed of many stumps, about 2-5 m in diameter, were recovered from the lake sediments during the land improvement in 1977-79, one of which yields the AMS ^<14>C age of 2475±30 BP. It is between the Final Jomon and Early Yayoi periods. Wood pillars with mortises were also recovered during the improvement, although the occurrence and the relationship with the stump-bearing formations are unclear. We couldn't determine the inducing cause of the landslide from the geomorphological and geological information now obtained from this area. If the slide was caused by an earthquake, the Atotsugawa fault is the most probable candidate causing the trigger earthquake for this landslide on the basis of the recurrence interval and the last event of the active fault.



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