The role of the Moonmilk speleothem in hypogeal archaeological sites

The moonmilk is a speleothem of microbial origin, usually formed by nanofibers of calcium carbonate, and found in karst caves. We discovered the presence of the moonmilk in the Etruscan hypogeal tombs of Tarquinia, a unique case of a biogenic activity resulting in protective rather than damaging a cultural heritage site. In fact, after 2,500 years, the Etruscan mural paintings in these hypogeal tombs were found well preserved under the white patina of the moonmilk. To study this phenomenon, we previous analyzed the calcite nanofibers of 5 tombs, together with their microbial communities. A deep investigation of the geology of this site was also conducted to unravel how the co-evolution of microorganisms and the rock contributes to this calcium carbonate deposition. The Etruscan tombs were carved in a yellow calcarenite, called macco, rich in calcium, produced 5 million of years ago, during the Pliocene. In Italy, a similar calcarenite rock is found in Puglia, in the south of Italy. This region is rich in karst caves and many of them harboring important archaeological remains. One of the most famous sites is the Lamalunga cave, near Altamura, Puglia, where a complete Neanderthal skeleton was discovered in 1993. We had the opportunity to take samples from this cave and we will present a comparative analysis of the calcarenite rocks and the microbial communities of the moonmilk from Tarquinia and Lamalunga archaeological sites, to investigate the geomicrobiological situation, as a part of a preservation project of archeological karst caves, to be ready, in the near future, to identify criticisms due to climate changes.