What is the maximum geomagnetic field strength in Western Europe circa 1000 BC? An investigation of geomagnetic spikes and archaeomagnetic jerks.
Final Report Abstract
Fourty new mean archaeointensity data were obtained on five fireplaces from Central France and on 35 pottery sets from archaeological sites close to Munich and dated between 1400 and 400 BCE. The sets of ceramic fragments come from graves, pits and wells dated by ceramic and metallic artefacts, radiocarbon and dendrochronology. Rock magnetism analyses show that the remanent magnetization is mainly carried by almost pure magnetite. The Thellier-Thellier experiments with correction of the effects of anisotropy and cooling rate were completed using Triaxe and multispecimen (MSP-DSC) protocols. Around 60 per cent of the studied specimens provide a reliable archaeointensity result after selection using stringent criteria. The 40 new average data are very consistent with the previous data and quadruples the Western Europe database between 1400 and 400 BCE. The new Western Europe secular variation curve was built using a Bayesian framework. It points out a double oscillation of the geomagnetic field strength. After a period of low secular variation from 1400 to 1200 BCE, the intensity increased to ~70 µT around 1000-900 BCE. It decreased to ~50 µT near 800 BCE and then increased again up to ~90 µT at 600 BCE, before to decrease rapidly in the fifth and fourth century BCE. The trend of the secular variation with two intensity maxima is similar to the one observed in the Near East and in the Caucasus. But unlike these regions there is yet no evidence of the short-term geomagnetic spikes. The difference of more than 2.10^22 A.m^2 between the Virtual Axial Dipole Moment records of Western Europe, Near East and Central Asia highlights a strong departure from an axial dipole field from ~1400 and even more from ~1000 to ~700 BCE. This could constitute a further proof of the Levantine Iron Age Anomaly, which would superimpose on an increase of the axial dipole moment and on a tilt of the dipole. But the respective parts of these different processes to explain the fast and high intensity secular variation in Western Eurasia remain unclear.
Publications
- (2018) Improvements in Archaeomagnetic Dating in Western Europe from the Late Bronze to the Late Iron Ages: An Alternative to the Problem of the Hallstattian Radiocarbon Plateau. Archaeometry 60 (4) 870–883
Hervé, G.; Lanos, P.
(See online at https://doi.org/10.1111/arcm.12344) - 2016. Archaeointensity study of five Late Bronze Age fireplaces from Corent (Auvergne, France), Journal of Archaeological Science: JAS Reports, 7, 414-419
Hervé, G., Chauvin, A., Milcent, P-Y. & Tramon, A.
(See online at https://doi.org/10.1016/j.jasrep.2016.05.018) - Intensity of the geomagnetic field as a relative and absolute dating tool : archaeomagnetic study of Bavarian potteries from 1300 to 400 BC, International Symposium on Archaeometry, Kalamata (Grèce), 15-21 mai 2016
Hervé, G., Fassbinder, J., Gilder, S., Metzner-Nebelsick, C., Westhausen, I.
- New evidence of a fast secular variation of the geomagnetic field circa 1000 BCE : archaeomagnetic study of Bavarian potteries. AGU Fall Meeting 2016, San Francisco, 12-16 décembre 2016
Hervé, G., Fassbinder, J., Gilder, S., Metzner-Nebelsick, C., Schnepp, E., Geisweid, L., Putz, A., Reuss, S., Riedel, G., Westhausen, I. & Wittenborn, F.
