CONCLUSIONS

Based on the acquisition of a deep-tow seismic profile calibrated at Site 897, we have clearly imaged reverse faulting associated with the existence of a serpentinized PR located within the OCT zone. The main conclusions of this study are:

1. The Pasisar deep-tow seismic system is a useful tool to image deep seismic features such as acoustic sedimentary sequences and tectonic features.
2. Seismic unconformities calibrated with Site 897 biostratigraphic unconformities allow us to define a mean vertical velocity in the sedimentary column of 1820 m/s.
3. The major reverse fault that develops within the synsedimentary Miocene deformation zone merges with the eastern flank of a serpentinized PR identified by drilling.
4. Site 897 cores show that the surface of the PR underwent a late shear deformation event. As the process of serpentinization facilitates a lubricant role, we suggest that the synsedimentary reverse fault has a downward prolongation along the eastern flank of the PR and within the whole brittle crust.
5. As reverse faulting is preferentially located where serpentinized PRs exist, reverse faults located at the base of passive continental margins could help to recognize and locate the OCT, as in the Tagus Abyssal Plain.