Speleogenesis in highly geodynamic contexts: The quaternary evolution of Monte Corchia multi-level karst system (Alpi Apuane, Italy)

The Mt. Corchia karst system is one of the most important and famous caves in the World. Different from many other large caves, here the geological structure has had only a minor role on the vertical, multi-level pattern of the cave. A detailed geomorphic and morphometric analysis of the cave and a preliminary study of cave sediments, along with new datings of speleothems, allow us now to depict the multistage evolution of this cave, which produced at least three major paleo-phreatic levels related to different base-level stages. The analysis of the directions of cave passages shows that the three main phases have different orientations, which can be attributed to the different surface morphology during speleogenesis in former times.Chronological constraints and geomorphic features suggest that the upper part of Mt. Corchia Cave developed during the end of Pliocene in a stage of favourable climatic conditions and with a moderate tectonic uplift-rate. The morphological features and the nature of sediments in the upper paleo-phreatic level at 1350-1450 m above present sea level (apsl) imply the occurrence of a wide allogenic catchment area. This drainage pattern persisted also in the following stage, during a significant but slow lowering of the base level, which allowed the formation and the intense vadose rearrangement of the epi-phreatic network around 1100-1250 m apsl. An uplift stage in the Early Pleistocene caused the capture of the basins and the loss of allogenic feeding. A third epi-phreatic level was formed at around 900 m (apsl) when the catchment area was reduced to the present extent of carbonate rock, more than 1 Ma ago. The recent evolution is due to rapid uplift and to the progressive incision of surrounding basins, which led to the lowering of the local base level and to a readjustment of the cave system in order to adapt to a new equilibrium with the present elevation of the springs.