We express our special thanks to Drs. I. Koizumi and M. Lyle for their encouragement and support throughout the course of this study. We also express our sincere thanks to staff of ODP Leg 167 cruise and of the ODP Gulf Coast Repository for their assistance with sampling and data collection. Thanks also go to Mr. Takayama for his assistance in the laboratory and Dr. R. Behl for his discussion. This study is partly supported by the Grant-in-Aid for Scientific Research of the Ministry of Education, Science and Culture of Japan No. 08458141.