Speleogenesis of Sulfuric Acid caves in southern Italy

The main objectives of this research are: a) to investigate the main processes involved in sulfuric acid speleogenesis (SAS) of Italian caves, b) to estimate the dissolution-corrosion rate in several active SAS systems of southern Italy, and c) to contextualize landscape evolution using subhorizontal cave levels in the central-southern Apennine Chain. SAS caves formed in hypogene conditions (i.e., rising fluids), and are influenced by H2S-rich waters, which gain their acidity in deep-seated settings. The geological situation of Italy allows it to host ~25% of the worldwide known SAS caves, located along the the Apennine Chain, Apulia, Sicily and Sardinia. Geomorphological and mineralogical investigations can be used to identify inactive SAS environments, and recognize the conditions in which they originated. The most common geomorphological features refer to unconfined settings, which likely influenced the speleogenesis in the last stages of void formation, and are therefore, well-preserved. Peculiar suites of secondary byproducts including gypsum, sulfur, alunite, natroalunite, and jarosite strongely contribute to clarify cave speleogenesis. Sulfur stable isotopes may contribute to elucidate the source of H2S, which in Italy seems to be mainly related to bacterial sulfate reduction of Triassic evaporites interacting with hydrocarbons and/or organic matter. Moreover, gypsum and alunite dating may help to pin down the chronology cave speleogenesis. Active SAS caves show waters undersaturated with respect to gypsum and calcite and atmosphere composed of degassing hypogene H2S, CO2 and CH4. These special conditions promote the growth of microbial biofilms, composed of extremophile communities of bacteria and archaea able to arrange themselves into special structures. Active SAS caves can be used as laboratories to study the dissolution-corrosion rate, and calculate weight variation over time. Finally, subhorizontal SAS levels and alunite ages can help in understanding the uplift and erosion rates of the mountain hosting the cave system.