Sulfuric acid caves of Italy: A review

In Italy, especially along the Apennine Chain, numerous active and inactive sulfuric acid speleogenetic (SAS) caves have been documented in the last two decades. Here we present an overview of these peculiar hypogene systems, illustrating their main geomorphological and mineralogical features, and the microbial signatures observed in the active underground environment. SAS caves are widely distributed in the northern and central Apennines, whereas they are less abundant in the southern Apennines, in the Apulian foreland, in Sicily and in Sardinia. Their location is significantly influenced by lithological and structural rock properties, as they occur in carbonate areas where acidic fluids, deriving from the interactions with deep-seated sulfates and/or sulfides, rise through deeply rooted geological structures. Geomorphological observations demonstrated sub-horizontal maze passages to be one of the most favorite arrangements for SAS caves, whereas gypsum, sulfur and alunite supergroup minerals are the most typical sulfuric acid by-products. The δ34 S results demonstrated the deepseated H2S sources to be mainly related to the interaction between Triassic evaporites and hydrocarbons.