Archeomagnetism is a discipline at the crossroads between paleo/geomagnetism and archeology. It is mainly based on the analysis of the magnetic properties of archeological materials made of fired clay, such as combustion structures (pottery kilns, domestic kilns, lime kilns, etc.) and ceramics (pottery, tiles or bricks) found during archeological excavations. When the dating of the studied artifacts is known to archeologists, these archeomagnetic analyses allow us to trace the geomagnetic field evolution in direction and/or intensity for a given region over the past millennia.
IPGP has a long tradition of research in archeomagnetism started in the 1930s by Emile Thellier. Our activity is carried out using instruments and experimental procedures developed in the laboratory. The applications of our research are both in geomagnetism, for a better understanding of the secular variation of the Earth’s magnetic field, notably in France but also in other regions of the world (Europe, Near East, Asia, South America) and in archeology, thanks to the possibilities of archeomagnetic dating.
Research activities in archeomagnetism are carried out on two distinct sites: directional measurements of the geomagnetic field are conducted at the National Magnetic Observatory in Chambon-la-Forêt (~100 km south of Paris), while measurements of geomagnetic intensities are performed in the Cuvier building, in Paris.
Measurements of archeo-directions are performed with an inductometer adapted to the decimetric size of the samples analyzed. The experimental protocol used, which is derived from the work of Emile Thellier, is based on magnetic viscosity experiments. A description of the method, which preserves the advantage of the high precision of the orientation of the samples made in the field, can be found in Le Goff et al. (2020).
Our archeointensity studies are carried out using a laboratory-built vibrating sample magnetometer called the Triaxe, which allows continuous measurement of the magnetization of a small volume sample (less than 1cm3) at varying temperatures up to 650°C, in field or in zero field. Our results are therefore obtained using an experimental protocol developed specifically to take advantage of the Triaxe’s capabilities (for its description, Le Goff and Gallet, 2004). Three such magnetometers are available at Cuvier, including one belonging to the Laboratoire d’Archéologie Moléculaire et Structurale (LAMS, Sorbonne Université).
Our work, carried out for the most part in close collaboration with LAMS (Agnès Genevey), is based on numerous collaborations established with different archeological research organizations (universities, departmental or regional archaeological services, museums, INRAP, Eveha, Archeodunum).
Read more about the history of the laboratory
The laboratory is particularly involved in the establishment and constant improvement of the reference curves of directional and intensity geomagnetic field variations in France over the past two millennia. Conducted without discontinuity since the work of Emile Thellier, this activity provides us with a reliable and accurate description of the geomagnetic secular variation for our country during this period. These results extend in time the direct geomagnetic records made in Western Europe in magnetic observatories for four centuries at most for the directions, but less than 200 years for the intensities. Beyond the detailed characterization of the secular variation, this work allows the use of archeomagnetism in France as a dating tool for archeological practice.
Our other archeomagnetic studies are focused on the geomagnetic intensity variations in the Near East (Syria, Israel, Iraq), Asia (Uzbekistan, Cambodia), Africa (Ethiopia) or in South America (Brazil, French Guyana). As a whole, they aim at tracing more precisely the regional and/or global behavior of the geomagnetic field over the past millennia, based on modeling methods developed in collaboration with our colleagues in geomagnetism.