New archeointensity data from French Early Medieval pottery production (6th–10th century AD). Tracing 1500 years of geomagnetic field intensity variations in Western Europe

Abstract

a b s t r a c tNineteen new archeointensity results were obtained from the analysis of groups of French pottery fragments dated to the Early Middle Ages (6th to 10th centuries AD). They are from several medieval ceramic production sites, excavated mainly in Saran (Central France), and their precise dating was established based on typo-chronological characteristics. Intensity measurements were performed using the Triaxe protocol, which takes into account the effects on the intensity determinations of both thermoremanent magnetization anisotropy and cooling rate. Intensity analyses were also carried out on modern pottery produced at Saran during an experimental firing. The results show very good agreement with the geomagnetic field intensity directly measured inside and around the kiln, thus reasserting the reliability of the Triaxe protocol and the relevance of the quality criteria used. They further demonstrate the potential of the Saran pottery production for archeomagnetism. The new archeointensity results allow a precise and coherent description of the geomagnetic field intensity variations in Western Europe during the Early Medieval period, which was until now poorly documented. They show a significant increase in intensity during the 6th century AD, high intensity values from the 7th to the 9th century, with a minimum of small amplitude at the transition between the 7th and the 8th centuries and finally an important decrease until the beginning of the 11th century. Together with published intensity results available within a radius of 700 km around Paris, the new data were used to compute a master curve of the Western European geomagnetic intensity variations over the past 1500 years. This curve clearly exhibits five intensity maxima: at the transition between the 6th and 7th century AD, at the middle of the 9th century, during the 12th century, in the second part of the 14th century and at the very beginning of the 17th century AD. Some of these peaks are smoothed, or nearly absent when the selection of the data is extended to a 1250 km radius around Paris. The apparent regularity in the occurrence of intensity maxima, with a recurrence of $250 years, is particularly intriguing and might reflect a new characteristic of the secular variation, at least in Western Europe. It clearly requires further investigation and in particular the acquisition of new data from older periods.

Reconstructing the Geomagnetic Field in West Africa: First Absolute Intensity Results from Burkina Faso

“…Genevey et al 30. observed in their Western European master curve five prominent peaks in the last 1500 years, with a recurrence of 250 years.…”

“…Comparison with several palaeosecular variation curves has also been made (Fig. 3a): the master curve for Western Europe30 (GEN; Fig. 3a), the Western European Bayesian and Bootstrap curves2 (GBA and GBO, respectively; Fig.…”

“…3b,c), the SW-European/W-African curve31 (KIS; Fig. 3d), the Balkan curve for Eastern Europe130 (BAL; Fig. 3e), the bootstrap intensity variation curve for the Middle East32 (GAL; Fig.…”

“…KOR: Data from this study, corrected for cooling rate. These data are compared to: ( a ) GEN: Western European curve30. ( b ) GBA: Bayesian curve for Western Europe2.…”

Investigating the archaeointensity determination success of prehistoric ceramics through a multidisciplinary approach: new and re-evaluated data from Greek collections

“…For example, new evidence of short-lived regional maxima intensity episodes has been recently recovered but the spatial and temporal variation of these features is still poorly understood (e.g. Shaar et al 2011;de Groot et al 2013;Genevey et al 2016;Gómez-Paccard et al 2016). One of the most important constraints for the accurate description of the geomagnetic field strength evolution in the past is the absence of continuous records due to the limited availability of well-dated archaeological material suitable for archaeointensity determinations.…”