The PGNA was carried out at the Inter-University Laboratory for the Joint use of Japan Atomic Energy Research Institute facilities. We thank C. Yonezawa, H. Matsue, and H. Sawahata for their help in the PGNA. We also thank J. Ryan for his constructive comments, which improved the manuscript. This research used samples and data provided by the Ocean Drilling Program (ODP). The ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Founding for this research was supported by a Grant-in Aid from the Ministry of Education, Science and Culture of Japan (14740307) to T.S.