Solutional features and cave deposits related to hypogene speleogenetic processes in a littoral cave of Mallorca Island (western Mediterranean)

Abstract

The Cova des Pas de Vallgornera, located in the southern part of Mallorca Island (western Mediterranean) and developed in Upper Miocene reefal carbonate limestones, is an exceptional coastal cave because of its particular morphological features and the presence of deposits with uncommon mineralogies. Littoral mixing dissolution processes represent the most important speleogenetic mechanism to be considered in the eogenetic karst platform, where it develops; nevertheless, part of the cave consists of an extensive network of galleries that show morpho-sedimentary features pointing up to a possible participation of hypogene speleogenesis. The morphological assemblage of the cave illustrates besides the typical coastal karstification, a noticeable meteoric water recharge along with a possible deep recharge of hypogenic character. Features consisting in upwards solutional channels are abundant, including a complete morphologic suite of rising flow supporting the involvement of hypogene speleogenetic processes. Furthermore, the presence of vents and some related speleothems, such as crusts and cave rims, together with Mn and Fe-rich deposits hosting several minerals not observed until present in other caves of the region must be highlighted. Given the monotonous surface geology around the cave, it is suspected that ascending Sr, Ba, Mn, and Al-rich hypogene solutions may have reacted with the host rock to form this unique mineral assemblage. These deep-seated speleogenetic and mineralogical phenomena could be associated with the feeble geothermal anomalies existing currently in the Llucmajor platform, related to SW–NE faults which delimitate the subsidence basin existing in the southern end of Mallorca Island.