1. Potential of archeomagnetism as a dating tool for archeology: Examples from France Maxime Le Goff 1, Yves Gallet 1, Nicolas Warmé 1,2, Agnès Genevey 3 IPGP 1, INRAP 2, C2RMF 3

2. Archeomagnetic sampling following Thellier’s technique

3. « Big » sample inductometer at Saint Maur IPGP Laboratory Magnetic measurements

4. Methodology : The directional results are determined and selected viscosity experiments on the basis of viscosity experiments (Thellier, 1981) By vectorial substraction VRM and TRM 1)Direct position during 15 days measurements 2) Inverse position during 15 days measurements

5. Example of archeomagnetic results (Rungis, France) TRM VRM Mean TRM direction: D=-0.7°, I=70.6°,  95 =0.4° (N=14) 2000 fichier RUN06.AMZ

6. A reference directional curve is needed Archeomagnetic dating

7. Bucur, PEPI, 1994 Changes in direction of the Earth’s magnetic field in France as deduced from archeomagnetic data Sliding window of 80 years shifted every 25 years Thellier, PEPI, 1981

8. Age distribution of the French archeomagnetic results selected by Bucur (1994)

9. Constructing a reference curve taking into account the non-homogeneous age distribution of the data The mean directions (i) are estimated using the bivariate extension of Fisher’s statistics (  w j T j ) For each time window (i), intercepted data (j) are weighted following the proportion of time contained in the window (0< w j <1) Each individual datum is defined by a direction (D, I, k, N) and an age bracket A total weight is obtained for each time window (  wi ) The width of the window is step-by-step increased until the minimum weight required is attained

10. (Le Goff, Gallet, Genevey, Warmé, PEPI, 2002) Comparison between the French curves constructed using moving windows of varying (double line) and fixed (dashed line) duration Weight and duration of each time window considering a threshold value of 2.5

11. Determining an archeomagnetic age…  The angular distances between the respective means allow to determine an archeomagnetic age bracket at 95%  We can also estimate the probability P (in %) of making an error if an undated archeomagnetic direction is assumed different from any sliding window direction Use the rejection test developed by McFadden and McElhinny (1990) Modified in order to compare a Fisherian mean (to be dated) and non Fisherian means (ellipses defining the reference curve)

12. but low quality high quality Perfect agreement Archeomagnetic dating still possible Circumvent a contradiction…

13. Dating the end of use of a Roman water conduit (Rungis, France) supplying the south of Paris Water conduit kiln

14. Age of the oven found in Rungis Archeomagnetic age: AD 625-725 (more probable: AD 685-725)

15. The case of a kiln found with a filling containing several tens of Roman and some undetermined potsherds Has this kiln a Roman age ? (Argenteuil, France)

16. No, the kiln is Merovingian (AD 625-725)

17. The story of a domestic kiln… 1) Excavating a ditch 2) Digging the kiln in silt 3) Heating the kiln 4) Cooking meals 5) Abandonment of the kiln And digging a new one

18. Is there a significant time interval between several domestic kilns sharing the same working area ? Site of Marines (Val d’Oise, France) 1 m

20. Dating of 4 kilns same archeomagnetic age: AD 705-895 (more probable: AD 705-845)

21. Constraining the historical change in the use of kilns: Site of Marines Archeomagnetic ages at 95% Most probable archeomagnetic ages Nb. Structures 500600700800900 1000 Age (AD) Individual to group 500600700800900 1000 Isolated kilnNon isolated Kiln

22. Conclusions : The archeomagnetic dating technique is already operational in France, But We still need additional well-dated archeomagnetic directions to define better the reference archeomagnetic secular variation curve.