1. Department of Earth and Planetary SciencesKyushu University, 744 Motooka Nishiku Fukuoka 819‐0395 Japan
2. Department of GeologyUniversity of Johannesburg, PO Box 524 Auckland Park Johannesburg 2006 South Africa
3. Kochi Marine Core CenterKochi University Nankoku Kochi Japan
4. Global Exploration DivisionINPEX CORPORATION, Akasaka Biz Tower 5‐3‐1 Akasaka, Minato‐ku Tokyo 107‐6332 Japan
5. Department of GeologyNational Institute of Polar Research, 10‐3, Midori‐cho, Tachikawa‐shi Tokyo 190‐8518 Japan