Eight thousand years of geomagnetic field intensity variations in the eastern Mediterranean

Abstract

Twenty new intensity determinations of the ancient geomagnetic field have been obtained from groups of potsherds and brick fragments from Syria. These artifacts, archeologically well dated from ∼6000 B.C. to approximately A.D. 1200, have been analyzed using the Thellier and Thellier [1959] method as modified by Coe [1967]. Intensity values have been corrected for the effects of anisotropy of thermal remanent magnetization and cooling rate. Our results indicate that field intensities were moderate in Syria from ∼6000 B.C. to ∼3500 B.C., with values of ∼30–40 μT. There was a significant increase in intensity by a factor of 2 from ∼3500 B.C. to ∼700 B.C., which was interrupted by a moderate decrease between ∼2550 B.C. and ∼1750 B.C. During more recent periods, our results show an intensity minimum approximately A.D. 200 and a maximum around the tenth century. Comparison with different data sets from the eastern Mediterranean and central Asia shows that geomagnetic field intensity variations were consistent at this large regional scale, at least over the last 5 millennia.

Remanence anisotropy effect on the palaeointensity results obtained from various archaeological materials, excluding pottery

“…10(a) indicate that the values of the correction factors do not depend on the angles between the NRM directions and the direction of maximum axes of the TRM anisotropy ellipsoids. This lack of systematic dependence on α is supported by the random directions of the K max (TRM) for a given structure, reported recently by Gomez-Paccard et al (2006) based on their study of baked clay materials from pottery kilns. The same is also evident from the 3D-plot in Fig.…”

“…This is linked with the shape-related magnetic fabric for bricks and tiles and with the mechanically produced one for baked clay ovens' floors. The similarity in the TRM anisotropy evaluated at two temperatures is even better revealed in case of pottery having the highly expressed 'easy plane' of magnetization (Genevey et al, 2003).…”

“…Furthermore, in an archaeomagnetic study of Danish materials from bricks, a few ceramics, and burned clay from furnaces, Gram-Jensen et al (2000) proved the negligible influence of the remanence anisotropy estimated by TRM anisotropy tensor, as has been done in the present study. In a more recent paper, Genevey et al (2003) estimated the TRM anisotropy correction on the palaeointensity from both pottery and bricks from Syria. The obtained correction factor for bricks was found to cluster between 0.98 and 1.02 for 70% of the specimens, which is in excellent agreement with the results shown in this study.…”

First archeointensity results from Portuguese potteries (1550-1750 AD)

“…Directional and intensity data obtained from these materials have been used to produce reference curves for the past few millennia. Reference curves (also called master curves), which reveal the variations in the intensity of the geomagnetic field are now available for several regions, including North America, Meso-America, Eastern Asia, Eastern and Western Europe (e.g., Kovacheva, 1997;Yu et al, 2000;Morales et al, 2001;Bowles et al, 2002;Genevey et al, 2003;Soler-Arechalde et al, 2006; see also the compilations of Valet, 2003;Perrin and Schnepp, 2004;. Archeointensity data for Western Europe are concentrated on archeological sites from France (e.g., Chauvin et al, 2000;Gallet et al, 2002;Genevey and Gallet, 2002;Gallet et al, 2005) while only few results are available for the Iberian Peninsula (Kovacheva et al, 1995;Gómez-Paccard et al, 2006).…”

Arqueomagnetismo e datação arqueomagnética: princípios e métodos

“…Este tipo de abordagem é válido apenas para uma determinada região do planeta. Atualmente, as curvas de referência estão disponíveis para os últimos 2.000 a 3.000 anos em várias regiões do planeta, incluindo a América do Norte (Stenberg 1989;Labelle e Eighmy 1997;Yu et al 2000), América Central (Morales et al 2001;Bowles et al 2002;Soler-Arechalde et al 2006), Leste da Ásia (Cong e Wei 1989), Leste e Oeste da Europa (Bucur 1994;Kovacheva 1997;Kovacheva et al 1998;Chauvin et al 2000;Genevey e Gallet 2002;Genevey et al 2003;Kovacheva et al 2004;Schnepp e Lanos 2005;Gómez-Paccard et al 2006). Existem também compilações globais, como aquelas de Valet (2003); e Korte et al (2005).…”