Origen bacteriano de espelotemas tipo moonmilk en ambiente karstico (Cueva de Altamira, Cantabria, España)

Abstract

Moonmilk subaerial speleothems of Altamira Cave are constituted by a network of needle-fiber calcite crystals (NFC) and active microbial filaments. These recent deposits allow us the observation of the first evolution stages, as well as defining microclimatic and hydrochemical conditions of mineral precipitation. In previous works, the origin of the NFC has been determined being associated to fast mineral precipitation related with evaporation and criodesiccation processes. From our data, an evolutionary model has been proposed for this type of deposits. The stable microclimatic conditions of the cave, with air humidity close to saturation, lead us to conclude that their origin doesn't have to be related with these processes. Also it has been proven that the NFC of monocrystallyne rods type is generated by means of calcitization of microbial filaments. On the other hand, epitaxial cements and polycristalline chains are related with organic activity and inorganic processes in a confined aqueous environment developed inside the biofilm.