Accelerator Mass Spectrometry 14C Dating of Lime Mortars: Methodological Aspects and Field Study Applications at CIRCE (Italy)

Centre for Isotopic Research on Cultural and Environmental heritage (CIRCE) has, recently, begun an intensive testing campaign on the feasibility of Dead Carbon (DC) suppression by means of a purification procedure applied to a series of laboratory test mortars. Observed results confirmed the overall successful character of the proposed methodology encouraging its accuracy testing on real samples by comparing mortar radiocarbon dates with other materials of known or constraint age. In this study, some 14C measurements performed on archaeological mortars will be discussed and compared with independently estimated (i.e. radiocarbon dating performed on organic materials found in the same study site) absolute chronologies of 2 Spanish sites. Observed results confirm the overall agreement of the mortar isolated fractions dates with the chronological reconstruction for both examined sites. Moreover several authors reported the possibility to obtain accurate radiocarbon dating results of mortar matrices by analyzing lime lumps: binder related particles of different sizes composed exclusively by calcium carbonate. Hence, in this paper, preliminary data for the absolute chronology reconstruction of the Basilica of the cemetery complex of Ponte della Lama (Canosa di Puglia, Italy) based mostly on lime lumps will, also, be discussed. Accuracy of the procedure will be quantified by comparing 14C data on mortar lime lumps from a funerary inscription of known age found nearby the basilica, in the same site context. For this study site, a comparison between absolute chronologies performed by lime lumps, laboratory purified lime lumps and charcoal (when found) will, also, be shown. Observed results evidence how pure lime lumps dating may introduce sensitive aliquots of DC leading to systematic overestimations of the examined sample ages while laboratory pretreatment procedure allow unbiased dating.