A03_09

The dating of dolomitic mortars with uncertain chronology from Müstair Monastery: sample characterization and combined interpretation of results

Caroselli M¹, Hajdas I², Cassitti P³

¹SUPSI, Mendrisio, Switzerland, ²ETH, Ion Beam Physics Lab. , Zurich, Switzerland, ³Foundation Pro-Kloster St. Johann , Müstair, Switzerland

To obtain scientific data regarding the chronology of archaeological structures, lime mortar radiocarbon dating has often demonstrated to be a decisive method. However, it is well known that certain chemical-mineralogical characteristics of the mortars can greatly influence the results. Among other issues, the dating of magnesian mortars can be particularly difficult because of the combined slaking, setting and hardening reactions of the calcium and magnesium phases, typical of these mortars. The formation of numerous mineralogical phases depending on reaction conditions adds further complexity to the dating method, which deserves to be studied with further detail. During the project "Mortar technology and construction history of Müstair Monastery" thanks to the presence of numerous mortar fragments belonging to different construction phases, the first experiments in this regard had yielded encouraging results. An additional 5 samples from buildings with controversial chronology, thought to belong approximately to the 9th, 12th and 15th centuries, were selected, prepared and radiocarbon dated. The data obtained were discussed by integrating preliminary petrographic and chemical characterization analyses of the mortars with archaeological information and excavation records. The results provided a better understanding of the potential and limitations of dating dolomitic mortars coming from archaeological context.