GEOLOGICAL HISTORY

La ricchezza geologica dell’Altipiano del Calisio è conosciuta fin dall’antichità dai suoi abitanti e dai signori della vicina Trento. Alcune risorse del sottosuolo hanno avuto un ruolo molto importante nello sviluppo di questo territorio.

Il nome stesso deriva dai giacimenti d’argento coltivati nel Medioevo da minatori di origine germanica, i canòpi, che estraevano il prezioso metallo per conto del Principe Vescovo: con l’argento del Calisio si coniava allora la moneta di Trento. Al loro lavoro dobbiamo il paesaggio lunare che caratterizza l’area centrale dell’Ecomuseo, crivellato da migliaia di pozzi e chilometri di stretti cunicoli. Dal Calisio proviene anche il Rosso Ammonitico, la roccia utilizzata per costruire la città di Trento fin dall’Età romana. I famosi cubetti di Porfido con cui sono lastricate strade e piazze, provengono dal lembo settentrionale dell’Ecomuseo, nel territorio di Albiano e Fornace.

The history of the territory of the Ecomuseum begins about 280 million years ago (Lower Permian) when the lava and the ashes of a huge caldera (a volcanic crater) settled down to a thickness of more than 2 km, giving rise to the Atesino Volcanic Group, which include the porphyry.

At the end of the volcanic phase (about 260 million years ago – Upper Permian), the sea advanced from the East, invading a large part of the area currently occupied by the Alps: the territory of Argentario, as well as much of Trentino, was represented by a vast and arid plain valley cut through by lazy rivers.

Over the next millions of year the sea continued to move and our territory first became a salt lagoon (Bellerophon Formation – Upper Permian), then about 250 million years ago (Lower Triassic) a coastal plain shaken by the waves in which sand, clay and limestone that gave rise to Werfen Formation were settling. These rocks would later be enriched by argentiferous galena veins, from which the plateau will be named.

After a long period made of incessant drops and rises of the seabed, some 215 million years ago most of Trentino became a mudflat regularly invaded by water: in this environment full of mollusks and algae the Principal Dolomite, the rock that constitutes Cima Calisio, were deposited.

Between 170 and 125 million years ago, we find the Calisio at the bottom of an ocean, where high layers of limestone deposited between Upper Jurassic and the beginning of the Cretaceous. They formed what today we call “Pietra di Trento”, Trento stone, (red ammonite and majolica), a rock rich in fossils (i.e. the ammonites) with which many buildings and the public sidewalks were built.

During the Cretaceous, began the movements that led to the formation of the Alps (alpine orogeny): the deposits in Calisio came from the northern Alps, the portion of chain that had formed first, and they gave rise to the Red Scale in which the Fersina river will dig the Forra of Ponte Alto.

During the Eocene, about 50 million years ago, the sea was shaken by a series of underwater eruptions that led to the formation of effusive volcanic rocks (basalt of Val Lagarina), located in the area between Martignano and Cognola, famous for the production of fine wines for whose production, neighboring lands are less suitable.

Above these volcanic rocks that were on the surface of the water, calcareous organisms went on depositing: they constitute the present nucleus of the anticline of Calisio, that is the fold at the Dos Calmuz with which a long history of 220 million years ended.

Today, the plateau is entirely covered with an uneven layer of debris deposited by retreating glaciers and rivers formed between one glaciation and the other. The underlying rocks often carry traces of ice passage, such as rounded boulders of porphyry (rocky rocks) around Lake Santa Colomba.