This research used samples and data provided by Ocean Drilling Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. This work was supported by a Grant-in-Aid for Scientific Research (no. 13640453) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. The authors thank Drs. Asahiko Taira and Hiroshi Kitazato of Japan Marine Science and Technology Center and Masanobu Yamamoto of Hokkaido University for their useful comments.