Structurally controlled development of a sulfuric hypogene karst system in a fold-and-thrust belt (Majella Massif, Italy)

We documented the deformation in the southeastern domain of the Majella anticline (Central Apennines, Italy) to highlight timing and structural characteristics of different fracture sets affecting the outcropping Cretaceous- Miocene ramp carbonates. An isolated and inactive hypogene karst system produced by sulfuric acid (Cavallone- Bove cave system) was studied following a multidisciplinary approach. Our findings suggest that deeprooted, sub-vertical strike-slip fault zones reaching the H2S source rocks were the main vehicle for ascending acidic fluid flow. Linkage and intersection of these faults by splays in extensional stepovers and pre-orogenic normal faults permitted ascending fluids to reach multiple recharge points (feeders) near the paleo watertable. In proximity to the oxygenated groundwater, where H2SO4 was produced, lateral dissolution focused along bedding planes and zones of localized deformation (fracture clusters) characterizing the hinge of the anticline. We conclude that structural position in the anticline and large-offset, vertically extended strike-slip fault zones control the localization of efficient permeability pathways and represent first order controlling features for fluid flow in the fold-and-thrust belt. This study provides insights into the understanding of time-space evolution, geometry, and pattern of sulfuric hypogene karst systems in folded carbonates, whose prediction is critical for fractured and karstified reservoirs.