First report on the sinkhole phenomena in the Sicilian evaporites (Southern Italy)

In Sicily Messinian evaporite rocks are widespread covering a total area over 1000 km2. The main evaporite areas develop in central and southern part of the island; small evaporitic basins occur in west, north and south-eastern Sicily. The evaporites consist of asuccession of carbonates, gypsum and salts, with many intercalations of clays, marls and carbonates. The succession lies on clayey, marly-sandy deposits of Upper Serravallian Lower Messinian and it is overlain by different lithotypes like pliocenic calcarenitic, marly and clayey deposits, pleistocenic clayey and arenitic rocks. In the evaporitic successions karst phenomena are widespread and generally occur in “exposed karst” conditions able to create well developed surface landforms, ranging in size from micron to kilometers, and underground systems. Where evaporites are covered by insoluble rocks a number of sinkholes like subsidence and cover dolines occur. These forms can develop in sandstones, clays or marly-lime stones, show different shape and size and can hold a little permanent pond. Beside the depressions linked to karst processes, in Sicily the sinkholes are also connected to the mining activity. Anthropogenic sinkholes are located in the Caltanissetta, Enna and Agrigento areas, in correspondence of abandoned salt mines; they can develop in gypsum rocks or in clayey deposits overlaying salt layers, or they may affect waste domes of the mines. Sinkhole diameters vary from some meters to about 300 m and depth may be up to 70 m. In this note distribution, typology and genetical mechanism of sinkhole occurring in evap oritic areas of Sicily are illustrated