Structural control on epigenic gypsum caves: evidences from Messinian evaporites (Northern Apennines, Italy)

Abstract We documented the relations among fractures, bedding, geological structures and the development of epigenic gypsum caves in the Bologna sector of the Northern Apennines, Italy. Different methods such as surface and subsurface surveys, aerial photo interpretation, structural analyses and hydrogeological observations were integrated to unravel different types of structurally-controlled epigenic gypsum karst speleogenesis. Data collected highlight a close relationship between the main directions of caves development and structural trends in the Northern Apennines (NW-SE and NE-SW). The results show that large offset faults (>10 m), bedding interfaces and anticline axes control the development of underground drainage basins and compartmentalize flow among adjacent areas. Furthermore, collapse hall morphology is mostly controlled by high-angle joints, bedding, and splay joints associated with bedding plane parallel faults, while the main structural weaknesses focus the surface flow, leading to a concentrated pattern of underground drainage and the formation of dominant conduits.