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Potential of archeomagnetism as a dating tool for archeology: Examples from France

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. Archeomagnetic sampling following Thellier’s technique. Magnetic measurements.

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Potential of archeomagnetism as a dating tool for archeology: Examples from France

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  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 IPGP1, INRAP2, C2RMF3

  2. Archeomagnetic sampling following Thellier’s technique

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

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

  5. Example of archeomagnetic results (Rungis, France) VRM 2000 TRM fichier RUN06.AMZ Mean TRM direction: D=-0.7°, I=70.6°, a95=0.4° (N=14)

  6. A reference directional curve is needed Archeomagnetic dating

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

  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 Each individual datum is defined by a direction (D, I, k, N) and an age bracket For each time window (i), intercepted data (j) are weighted following the proportion of time contained in the window (0< wj <1) The mean directions (i) are estimated using the bivariate extension of Fisher’s statistics ( wj Tj ) 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. 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 (Le Goff, Gallet, Genevey, Warmé, PEPI, 2002)

  11. Determining an archeomagnetic age… 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) • 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

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

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

  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 (Argenteuil, France) Has this kiln a Roman age ?

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

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

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

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

  20. Constraining the historical change in the use of kilns: Isolatedkiln Non isolated Kiln Individual to group Archeomagnetic ages at 95% Nb. Structures 500 600 700 800 900 1000 Most probable archeomagnetic ages Nb. Structures 500 600 700 800 900 1000 Site of Marines Age (AD)

  21. 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.

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