A hypogenic cave system with late-stage condensation-corrosion and epigenic overprinting (Toirano, Liguria, Italy)

Description

The Toirano karst system is located in the Ligurian Alps, in the dolostones of Middle Triassic age, around 4.5 km inland from the coast (Borghetto Santo Spirito). It comprises different caves, among which the most important are, from the higher altitudes to the Varatella brook below, Colombo Cave (247 m asl), Upper Santa Lucia (215 m asl), Lower Santa Lucia (201 m asl), and the Bàsura Cave (186 m asl), the last two connected by an artificial tunnel and equipped for cave visits. Bàsura Cave is mainly known for the presence of cave bear bones and the footprints of Upper Paleolithic Man (12,000 years B.P.). Walking through the various environments and passages of the cave it is immediately clear that there is a very large variety of speleothems and morphologies. This geodiversity places Toirano caves among the most interesting and unique karst features of Italy. Up to only a couple of years ago, the genesis of the cave system was attributed to the action of underground rivers that would have created the complicated network of phreatic and vadose passages following the main tectonic features of the area. A more detailed investigation of the morphologies and sedimentary deposits, however, together with the presence of an active low thermal sulfidic spring (located on the important regional normal Mt. Carmo fault) only 500 m south of the caves and 100 m below the lowest passages in Bàsura Cave, favors the hypothesis of a hypogenic origin of the caves, by rising waters that followed the main vertical structural flow pathways that characterize the area. Many walls and roofs are sculpted with rising features (cupola

Abstract

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