Sulfuric acid speleogenesis in the Majella Massif (Abruzzo, Central Apennines, Italy)

Abstract

Many active and inactive hypogene sulfuric acid cave systems are known along the Apennines, Italy. The Cavallone-Bove cave system is located in the external part of the central Apennine Chain, in the Majella Massif, and opens at 1470 m asl along the Taranta Gorge (South of Chieti). The presence in these caves of peculiar geomorphological features, such as feeders, rising channels, megacusps, cupolas, and replacement pockets, offers evidence of rising acidic fluids. The secondary mineral deposits, including meter-size white gypsum deposits, alunite, jarosite, black layers of iron‑manganese oxides and hydroxides, along with a rare association of authigenic rutile-ilmenite minerals indicate a sulfuric acid origin. Stable isotope analyses of sulfates further confirm a sulfuric acid speleogenetic (SAS) origin of these minerals and, in general, of the whole cave system, with H2S coming from the bacterial sulfate reduction of deep-seated Triassic evaporites interacting with hydrocarbons. Alunite dating demonstrates this water table SAS cave to have been active at least until 1.52 ± 0.28 Ma. All the evidence suggests that Cavallone-Bove is an ancient sulfuric acid karst system that was uplifted <1 km above pre-existing base level. The age of speleogenesis further suggests that tectonic uplift of this area was as high as 670 m My−1 over the last 1.5 Ma.