Unit U3C is siliceous nannofossil chalk with calcareous diatomite interbeds. Deformational structures were observed in the first core at Site 1040. Deformation bands and distributed fractures are common in the upper 20 mbsf and discontinuous throughout Unit P1. Many of these may be drilling-induced, particularly all stratal disruptions. Both brittle and plastic deformation structures are common from the surface to 370 mbsf.
Plastic deformation is associated with soft, sticky clay and severe drilling disturbance.
Therefore, original plastic deformation cannot be identified although it may have existed within these clay-rich intervals. From 340-350 mbsf, we find that fracture networks, stratal disruption, veins, and incipient scaly clay structures are common. Locally, a very intense fracture fabric is formed. From 350-360 mbsf, brittle deformation gives way to plastic deformation in sticky clays. Throughout Unit P1, cores are highly disrupted by drilling, with evidence of both flow-in and intensive torque transfer to the cores.