Biogenic corrosion caused by bats in Drotsky's Cave (the Gcwihaba Hills, NW Botswana)
Résumé
Located in north-west Botswana, Drotsky's Cave is a vast cavity hosted within dolomite known for the discovery of archaeological strata dating back to the Late Stone Age. It is home to a colony of bats comprising several ten thousands of individuals who are responsible for the accumulation of a thick deposit of guano, on which we have conducted research in some of the deeper parts of the cavity. A detailed study of the morphologies of the dolomite walls and roofs demonstrates that part of the cave's speleogenesis is probably due to biogenic corrosion. This type of weathering and corrosion process is still poorly described in underground environments. However, it is now accepted that the role played by bats and their droppings on the condition of walls, their weathering, and the enlargement of galleries and chambers by condensation-corrosion processes, should be taken into account when considering the way deep networks evolve. In this article, we discuss the mechanisms of this biogenic corrosion in Drotsky's Cave, as well as their morphogenic impacts (the dissolution and recession of walls, the formation of lateral notches, arches, bell holes, and ceiling spherical cupolas), and the consequences for the wall retreat of conduits. Finally, we propose a new typological classification. The consequences of this biogenic corrosion are important for archaeological questions related to the taphonomy of archaeological remains in the buried deposits and the conservation of cave art. Because of the important impacts of guano on buried biological archaeological remains, such a population would have encouraged accelerated weathering, corrosion and dissolution of the walls, potentially contributing to the total, or partial, disappearance of any trace of human activity on the surrounding rocks.