Evolution of Karst Caves in the Alpi Apuane (Italy): Relationships with the Morphotectonic History

Abstract

The study of the geomorphic features of the karst caves in the Alpi Apuane can give a notable contribution to the understanding of the morphotectonic history of this part of the Apennines in the Pliocene and Quaternary periods. The geomorphic analysis of cave systems and relict caves suggests three major development phases. The first phase, represented by relict phreatic caves at more than 1400 m a.s.l., developed in a landscape very different from the present-day one, with a base level 800–1000 m higher than now. This phase acted mainly in the M. Corchia Complex, where the occurrence of fluvial infills with non-metamorphic sandstone suggests that this cave began to be formed when the Alpi Apuane were bounded on N and E by highlands of non-metamorphic rocks. Such a morphotectonic framework probably existed in the Late Pliocene, before the tectonic collapse of the intermontane basins surrounding the Alpi Apuane (Serchio and Magra basins). During this phase, a closed basin of 20–30 km² drained allogenic waters towards the Corchia Complex, allowing the development of a wide level with large epi-phreatic conduits. The second and more important development phase gave rise to most of the phreatic caves, which are now located between 750 and 900 m in altitude. These caves can be related with the plain surfaces, now found at an altitude of about 900–1000 m, which can be interpreted as remnants of pediments or base-level plains, developed during an early Quaternary phase of tectonic standstill. The third phase of karst evolution was responsible for the formation of the phreatic conduits now found between 500 and 650 m a.s.l. On the NE side of Apuane, this generation of caves is still active, while on the seaward side, the karst base level, corresponding to the main karst springs, was affected by a further lowering due to a Late Quaternary regional uplift.