This research was supported by the CNR (ODP-Italy) and by the "Ricerca di Ateneo" grants (Università degli Studi di Genova). We wish to thank the Master, Crew, and Scientific Party of Leg 168 for the wonderful cooperation. We thank L. Cortesogno and G. Lucchetti for the helpful discussion. We also thank L. Negretti (SEM technician, Università di Genova) and A. Cucchiara (XRD technician, Università di Genova) for their invaluable analytical help. P.M. thanks P. Spadea because she convinced and gave me the opportunity to participate in Leg 168, an unforgettable experience. The authors wish to thank the reviewers J. Allan and J. Alt for comments that helped to improve the paper.