Geomagnetic intensity variations in Western Europe over the past 1700 years: Contributions and limitations of intensity dating of archeological ceramics (Invited)
Résumé
Archeomagnetic dating of in situ fired structures is particularly developed in France thanks to a well-established directional variation curve encompassing the past 2000 years and to the strong integration of this technique into the French archeological fabric (Le Goff et al. 2020). Conversely, dating studies based on the use of archeointensity alone are still scarce, as more generally in the European sphere where archeomagnetic research is particularly active. The acquisition of a large set of intensity results in France and North Italy derived from the analysis of precisely dated sets of archeological ceramic fragments has however made it possible to recover the variations in geomagnetic intensity over the past 1700 years with an unprecedented precision, offering new dating perspectives. We present first a short overview of the intensity research we carried out over the past 15 years using the Triaxe protocol. Two independent modeling approaches are used to construct intensity variation curves using our data, combined with a selection of previously published results within a 700 km radius of Beaune in Burgundy and re-examined based on cooling rate correction. The first algorithm developed by Thébault and Gallet (2010) yields rather smooth intensity variations, while the second proposed by Livermore et al. (2018) shows more abrupt variations with sometimes stronger amplitudes. The dating potential of these two variations curves is then illustrated for three medieval pottery workshops using two different procedures: either by comparing the intensity value to be dated with the reference intensity variation curves or by analyzing the marginal posterior probability distribution of the age values derived from the Bayesian method of Livermore et al. (2018). For France, where the data are numerous and consistent, the dating results are similar regardless of the method adopted. There, archeointensity investigation of displaced materials has become an effective means to obtain original chronological constraints, which help, when integrated into an archeological scheme, to determine the period of activity of pottery installation, paving the way for a wide range of complementary research on Medieval pottery.