In this locality on the crest of Col de San Colombano, we can study nice examples of synsedimentary deformation on deep-sea sediments. This outcrop exposes a sequence of radiolarian chert that was folded on the seafloor while still mostly unconsolidated. In addition, the sequence contains a house-sized limestone olistolith.
The crest exposes the contact of pillow basalts to radiolarites of Cretaceous age. The radiolarites are deformed in a heterogeneous way: For example, we observed folded layers sandwiched between undeformed layers above and below. This is usually interpreted as synsedimentary deformation, like slumping or submarine sliding of unconsolidated sediments. Correspondingly, the radiolarites in the upper part of the outcrop contain a tens-of-meters-sized block of limestone. This olistolith represents a sedimentary mass-wasting event, where the block rolled or slid down a submarine slope. At some point, the block smashed into the layers of radiolarian mud, causing some of the observed deformation in the radiolarites.