Morphological and mineralogical evidence for ancient bat presence in Cova des Pas de Vallgornera (Llucmajor, Mallorca, Western Mediterranean)

Cova des Pas de Vallgornera is a unique karst cave located at the Llucmajor coastal platform that stands out not only because of its length, more than 78 km, but also for its particular morphological suite, richness and variety of speleothems and mineral infillings. Although the mineralogy of speleothems and minerals related to hypogene morphologies has been studied and described, the existence of minerals derived from guano deposits was still poorly investigated. The cave hosted bat colonies until the collapse of its natural entrances, circa 2.4 My ago, since then until its discovery in 1968, the cave remained sealed. These particular environmental conditions, kept along millennia, helped the interaction of guano-related leachates with the bedrock and clay deposits provoking dissolution and mineral precipitation. Moreover, thanks to the discovery of guano-associated cave minerals, it has also been possible to determine the presence of morphologies related to ancient guano deposits. In this paper, we report on features caused by bat's biomechanical erosion, bat claws and bat thumb marks and the influence of geobiological modifications caused by guano deposits on stalagmites and fallen boulders, haystack-shaped stalagmites, stalagmites covered in niches and crypto-corrosion features on fallen boulders. In addition, an array of guano-related minerals is reported, being phosphates the most abundant mineral group identified, underlining the broad presence of fluorapatite from all the studied sites. Among the oxides and hydroxides, nordstrandite, gibbsite and todorokite are especially common. Finally, connections between microclimatic conditions in the cave and the location of bat roosting and breeding sites are discussed.