Monte San Giorgio today
The topography of Monte San Giorgio was created at the same time as the surrounding Alps, when, 95 millions years ago, the “African” plate began to move northwards, progressively compressing the “Eurasian” plate. The powerful push of the African plate caused a series of deformations within a collisional zone, including the area of Monte San Giorgio in its southern part. The ancient seabed was pushed upwards, emerging from the water and building the mountain we know today.
Quarries and mines
The bituminous shales of Monte San Giorgio have been exploited in mines above Besano since the first half of the 18th century. In 1830, studies were conducted on gas production from these shales for the street lightning of Milan, but this and other projects were quickly shelved. In 1861 Ticino’s government allowed several mines to open in the territories of Meride and Brusino, but these exploitation attempts also did not last very long.
The fossiliferous levels
The most important fossil beds occur in the central part of the stratigraphic series, within the carbonate sedimentary rocks of marine origin (limestone and dolomite) that were formed during the Triassic. So far, six particularly rich fossiliferous levels have been identified within a more then 600 metres thick succession of rocks dating from the Middle Triassic and covering a period of four million years (from 243 to 239 million years ago).
The Triassic period
At the beginning was the sea…
Throughout the Triassic (the geological period 252–201 million years ago) the landmasses that existed were combined into the one large supercontinent of Pangaea, surrounded by a vast ocean called Panthalassa. At the equator, an arm of this ocean intruded deeply into the centre of Pangaea forming an ancient sea called the Tethys, which divided Pangaea into Gondwana in the south and Laurasia in the north.
The lagoon of Monte San Giorgio
During the Middle Triassic (247–235 millions years ago) Monte San Giorgio was not the mountain we know today, but the bottom of a shallow sea located at the western margin of the Tethys. The environment was characterized by the presence of small islands and banks of fine sand. These separated the coast from the open sea, forming a lagoon or a more or less isolated basin.
Most spectacular of the fossils found at Monte San Giorgio are the reptiles represented by approximately 25 species of mostly marine taxa. These show different degrees of adaptation to aquatic life.
In addition to the famous reptiles, the deposits of Monte San Giorgio are especially rich in fish with approximately 50 species described so far. Many species are documented in different stages of growth and sometimes it is even possible to determine whether they were male or female.
The conodonts are a mysterious group of organisms that became extinct at the end of the Triassic. Only their tiny mouth elements, teeth-like fossils measuring from 0.1 to 4 mm, were known until the discovery of the first complete skeleton in 1983.
Molluscs and other marine invertebrates
In addition to the well-known reptiles and fishes, the fossiliferous deposits of Monte San Giorgio have also provided many species of marine invertebrates. These have been used to better understand the environmental conditions through this time interval and to more precisely date the vertebrate levels.
Recent studies by the Museo cantonale di storia naturale, Lugano, have focused on even the tiniest organisms that formed marine plankton, especially radiolarians (unicellular protozoans with siliceous shells a few tenths of a millimetre long), because they are excellent index fossils that can be used for precisely dating the age of the rocks.
In 1998, researchers at the University of Milan discovered the first fossil insect belonging to the group of Ephemeroptera: Tintorina, commonly known as the “mosquito” of Monte San Giorgio. The discovery of Tintorina is very important because it is the first finding of insects at MSG, and shows it was already highly diversified by the Middle Triassic.
The marine deposits of Monte San Giorgio also revealed fragments of terrestrial plants (small branches, leaves, cones), which suggest the presence of nearby mainland or islands.