Marne of Puez
Between 131 and 65 million years ago, during the Cretaceous period, various
sediments were deposited that have been grouped together under the name of
Marne of Puez. These are friable and easily eroded rocks that produce
rounded-hill shapes now visible on the mountain plateaux.
Such deposits accumulated in a deep-sea environment. They prevalently consist of microscopic shells of plankton and numerous ammonite shells showing a genetic mutation in the shape of the spiral, that tends to unwind and open.
They also contain fine particles of clay and silt, as wells as sand-grain pebbles pointing to the arrival of detritus from the erosion of the first mountains of the Alpine Chain that was already forming underneath the sea.