1. Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan (e-mail: tyamaguchi@kochi-u.ac.jp)
2. Department of Earth Science, Tohoku University, 6–3 Aramaki, Aoba, Aoba-ku, Sendai 980-8578, Japan
3. Tohoku University Museum, Tohoku University, 6–3 Aramaki, Aoba, Aoba-ku, Sendai 980-8578, Japan