The potential of historic rock avalanches and man-made structures as chlorine-36 production rate calibration sites

Samples from three medieval rock avalanches from the French (Le Claps, Mont Granier) and Austrian Alps (Dobratsch) and a man-made structure, i.e. the Stephansdom in Vienna, have been analysed for in-situ produced ³⁶Cl by accelerator mass spectrometry (AMS). All four sampling sites of independently known exposure duration turned out to be not appropriate as calibration sites for the determination of the ³⁶Cl-production rate from Ca. Indeed, the determination of short exposure ages for dating rock avalanches and man-made structures by ³⁶Cl is hindered dramatically by inheritance, especially for samples characterized by high ^natCl-concentrations. Generally, there are hints that the theoretical calculation of ³⁶Cl-production from epithermal and thermal neutron-capture on ³⁵Cl is highly underestimated in all existing models, thus, asking for particular precaution if working on high-Cl samples for any project. Hence, this work evidences that potential high inheritance, even for samples reasonably shielded before exhumation, has to be considered especially when dealing with recently exposed surfaces such as glacially polished rocks, alluvial terraces, fault scarps etc.