New synchrotron X-ray data on biotic synthetic and natural calcium carbonates from the Large cave of Arcy-sur-Cure (Yonne, France)
Résumé
The Large cave of Arcy-sur-Cure is well known as well as for its prehistoric paintings and for its limestone concretions. Unfortunately, formation of calcite layers has totally or partially obstructed paintings. The phenomenon of calcium carbonate (CaCO3) growth in karstic environment is very common and could be occurred in pure abiotic conditions or combined with microbiological influence. In the frame of the still on-going restoration project, this study focuses on the role of microorganisms in the formation of the calcite layer. From extracted bacteria from natural calcite samples taken in the cave, we tested their ability to start calcite growth. These synthetic samples have been investigated by means of synchrotron-based methods and more particularly by X-ray diffraction and then compared with natural samples from the cave. The biotic samples reveal the presence of crystalline carbonate phases and amorphous calcium phosphate phase. Interpretation of these data enables us to draw up conservation measurements and further express recommendations for the future.