Geological map
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Permian volcanic tuff sample, cut and polished. Fragments of rock torn from the volcanic duct during the eruption are immersed in a finer matrix originally consisting of ash. Photo: Museo cantonale di storia naturale |
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Distribution of the seas and emerged lands in the Permian period and position of the rock formation area of Mount Caslano (starred). |
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During the Permian period, the rock formation environment of Mount Caslano probably resembled the volcanic landscape of the current Atacama desert (Bolivia). Photo: Marco Antognini 1995 |
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Moving from the Carboniferous to the Permian period, the rock formation environment of Mount Caslano migrated northwards, approaching a tropical latitude. The warm-humid climate that had favoured the development of the carboniferous forests thus gave way to persistent aridity, that deeply marked the landscape.
During the Permian period, the landscape was also marked by intense volcanic activity around 280 million years ago.
Extending over 50 square kilometres from the western slope of Monte Generoso to Valganna (Italy), through Monte San Giorgio and the Morcote peninsula, a succession of volcanic rocks a thousand metres thick covered the gneiss of the Variscan base.
Red or purple coloured rocks, often known as «porphyries», extracted in the past mainly for road surfacing.
Those visible here, in the panel, have that origin: they are volcanic tuffs, produced by the fall and consolidation of ashes, lapillus and fragments of rock torn from the volcanic duct by the violence of the eruption. |
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Section of volcanic tuff observed under a microscope in polarised light. Prismatic crystals of feldspar are dispersed in a matrix composed of volcanic ash. Photo: Museo cantonale di storia naturale |
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At the beginning of the Triassic period, the waters of the Tethys Ocean began to wash from the east the region occupied by the rocks of Mount Caslano. They first formed large river deltas, where sands and gravel from the erosion of Permian volcanoes accumulated.
The resulting rocks, arenites and conglomerates from the prevailing reddish tones, sometimes contain rare fossils that document the subsequent passage, in the Middle Triassic period, to a real coastal marine environment. These rocks belong to the Servino and the Formation of Bellano and constitute the rocky outcrops observable above the footpath, about twenty metres uphill from this panel.
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Servino / Formation of Bellano Conglomerate Sample (Lower Triassic - Middle), consisting of small pebbles of volcanic rock immersed in a sandy matrix and cemented together. Photo: Museo cantonale di storia naturale |
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