Geology of the Tassaro valley


This is a brief introduction to the geology of the Tassaro valley.

Sedimentary rocks

The Rio Tassaro valley is characterized by the prevalent presence of sedimentary rocks belonging to the sandstone and marl group. The sandstones of the valley are made up of fine debris, with a predominantly sandy component of marine origin, subsequently lithified and cemented by calcium carbonate. Marls, on the other hand, originate from sediments which are also of marine origin, but of a silty and clayey type. The sandstones form thick banks, which in some cases can reach a thickness of several metres, interspersed with thinner levels of marl that emerge.

Val Tassaro and Tassobbio

The entire sandstone and marl complex of Val Tassaro stratigraphically overlies extensive clay deposits, which emerge in the valley floor of the Tassobbio stream. Due to the greater resistance to erosion of sandstones compared to clays, high vertical walls frequently form at the points of contact between the two types of rocks which, in particular conditions, give rise to waterfalls, such as that of the Tassaro below Scalucchia or steep cliffs, like the one on which the fortress of Crovara stood.

Rocce ofiolitiche e calanchi presso Piagnolo

The age of rocks

The sandstones date back to the Tertiary period and are several tens of millions of years old, while the underlying clays, however, are older and date back to the Mesozoic period (about 80-100 million years ago).


Fossil finds are not very frequent within the sandstones and marls of the Tassaro Valley, as the sediments were formed in environments exposed to frequent landslides of the ancient marine slopes. Only at the marly outcrops or at the contact between the arenaceous and marly layers are fossilized traces of the passage of ancient limivorous organisms or “casts” of gastropods, bivalves and solitary corals found with a certain frequency. Much more frequent are the so-called “bottom footprints”, that is, the “petrified” traces of the currents resulting from underwater landslides.