We gratefully acknowledge the Ocean Drilling Program (ODP) for providing the samples used in this study. ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Tai-Chun Lin is appreciated for her assistance in processing samples. This study was funded by the Taiwan National Science Council (grants NSC88-2611-M-110-010-ODP and NSC89-2611-M-110-027-ODP to H.-L. Lin).