Guano-derived morphologies and associated minerals in Cova de sa Guitarreta, Llucmajor, Balearic Islands

Abstract

Cova de sa Guitarreta is located in the southern part of Mallorca Island (western Mediterranean). It was formed presumably by hypogenic processes in Upper Miocene reefal calcarenites. The cave hosts an important breeding bat colony during the end of spring and early summer. Its microclimate is influenced by the presence of a thermal water phreatic pool (27.7ºC) and by the bat population residing in cave during the reproductive season. The morphological bat-related features include bat claws and thumb marks scratches, along with several others linked to bat excreta and aggressive leachates from guano. From a mineralogical point of view, the cave hosts a remarkable cave mineral association linked to guano; among the nine phosphates identified, three of them are reported for the first time in Mallorcan caves (newberyite, struvite, and whitlockite). Particularly interesting is the dichotomy between struvite and newberyite: the first one occurs when the cave is occupied by bat colonies (spring-summer), whereas during the colder seasons, the transformation of metastable struvite into the more stable newberyite occurs. Caves with seasonal cyclical occupation of bat colonies could provide a new field for the study of guano-related mineral assemblages.