*Adam David Sproson¹、Toshihiro Yoshimura¹、Shigeyuki Wakaki²、Tsuyoshi Ishikawa³、Naohiko Ohkouchi¹ (1.Biogeochemistry Research Center, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan、2.National Museum of Japanese History, 117 Jonai-cho, Sakura City, Chiba Prefecture 285-8502, Japan、3.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology 200 Monobe Otsu, Nankoku City, Kochi 783-8502, Japan)