13 February 2018
S-C fabric in limestone, Camerino, Italy
Posted by Callan Bentley
My field assistant sidles up to an outcrop showing a scaly texture:
This is outside of Camerino, Italy, in the central Apennines, on a small road near Morro. The outcrop here is adjacent to an old hermitage. The limestones here are early Cenozoic, probably the Scaglia Variegata, and they have been thrust up and over Miocene-aged turbidites that floor the Camerino Basin. The scaly pattern in the outcrop behind my son is a nice example of a distributed S-C fabric: two foliation surfaces which form in many rocks subjected to shearing stresses. The direction these structures “lean over” reveals the kinematics that formed them (left/west over right/east). Here’s a detail, followed by an annotated copy:
This thrusting was the process that built the Apennines up into a gnarly mountain range, but they were followed in time and space by a series of extensional faults, like those responsible for the recent devastating earthquakes in the region.
A few more shots showing these lens- to lozenge- to sigmoidal-shaped blebs of limestone:
Though the limestones are early Cenozoic in their depositional age, the structural fabric here was imposed later, probably in the Miocene, contemporaneous with the turbidites that fill the basin to the east.