Paleointensidad del campo geomagnético en Iberia en la época romana

Abstract

The evolution of the geomagnetic field in the Iberian Peninsula during the first millennium AD is still poorly constrained. In this study we report the archaeomagnetic full vector obtained from one combustion structure, GS kiln, recovered from the archaeological site La Genestosa (Salamanca, Spain). This archaeological site is located near the Portugal-Spain border (40.352º N, 6.772º W). It has been dated by archaeological evidences around the first century AD. A total 18 hand samples were recovered from the archaeological site consisting in two different groups of materials: tiles recycled to construct the sole furnace and typical burned clays. We present results from 11 specimens investigated from 11 hand samples. Specimens belonging to the first group (tiles) have relatively high values of natural remanent magnetization (NRM) and susceptibility while the second group of specimens is characterized by significantly lower values of NRM and susceptibility. The characteristic remanent manetization (ChRM) is carried by a low coercivity magnetic phase with Curie temperatures of 257– 573 ºC, ranging from Ti-high titanomagnetite/titanomagnemite to Ti-poor titanomagnetite/magnetite. Archaeointensity determinations were carried out by using the classical Thellier-Thellier protocol including pTRM checks (partial-TRM) and corrections for magnetic anisotropy. The effect of anisotropy of the thermoremanent magnetization (ATRM) on paleointensity analysis was systematically investigated although low ATRM corrections were obtained. Only 5 of the 11 samples have been considered to calculate the mean intensity while the other 6 were rejected because they did not accomplish the standard criteria of quality commonly used in paleointensity studies. The mean intensity obtained was 68.6 ± 5.2 μT, corrected for ATRM. The direction of the field at first century AD has also been determined from GS kiln (D = 0.78º; I = 55.4º; N = 11, α95 = 3.1°). The directional data agree with previous results while the intensity obtained is slightly higher than the one expected for the first century AD. However, it is important to notice that the mean intensity obtained is consistent with previous results within the error margins and with palaeosecular variations curves synthesize from regional models and with directional and palaeointensitiy data.Peer reviewe