This research used samples 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. The authors are grateful to the Leg 187 Shipboard Scientific Party and shipboard specialists for their help. We are grateful to Miguel Garcés, Jeff Gee, and Jay Miller for their constructive reviews and helpful comments that greatly improved the manuscript. We thank N. Ishikawa of Kyoto University for the use of the MicroMag and thermomagnetic balance, M. Fukuhara of Okayama University of Science for the use of the MPMS, and H.-Y. Yang of National Cheng Kung University for the use of the JEOL JSM-840A SEM. We also thank S.-F. Ou for helping measure rock magnetic properties and H.-D. Jiang for his technical assistance with BSE imaging. This study was supported by NSC grants NSC89-2611-M-110-028-ODP and NSC90-2611-M-110-006-ODP to Y.-H.S.