Estudios arqueomagnéticos y de arqueointensidad en materiales arqueológicos quemados de la península ibérica y el Cáucaso

Resumo

The study of the variations of the Earth's magnetic field in burned archaeological materials is a valuable source of information, both archaeological (mainly as a dating technique) and geophysical (modeling of the Earth's magnetic field). This PhD addresses archaeomagnetic studies in burned archaeological materials, mainly from the recent prehistory, both from the Iberian Peninsula and the Caucasus. The objectives of this thesis are set out with this double perspective. From an archaeological point of view, the aim is to obtain archaeomagnetic datings, to improve the available secular variation curves (SVC) and to obtain new archaeomagnetic data to be included in geomagnetic models. From a geophysical point of view, the aim is to obtain new data about the variation of the Earth's Magnetic Field (EMF) in the Iberian Peninsula and in the Caucasus region, and to compare its behaviour in two areas located at the same latitude but different longitudes, the eastern and western margins of the Mediterranean. To achieve these objectives, burned archaeological materials from the Iberian Peninsula and the Caucasus region with a good independent chronological control have been studied, Chronologically, they cover prehistoric (Neolithic, Chalcolithic, Bronze Age and Iron Age) and historical (Roman Period and Middle Ages) periods. These materials consist of ovens, hearths, potteries, burned clay remains, and slags. Firstly, rock magnetic experiments were carried out to gain insight about the characteristics of the minerals that carry thermoremanence, their thermal stability and to preselect samples for archaeointensity experiments. These experiments mainly consisted of progressive isothermal remanent magnetization (IRM) acquisition curves, hysteresis loops, backfield curves and thermomagnetic curves. The high reversibility of the thermomagnetic curves (frequently observed) has turned out to be especially useful to select the most suitable samples to obtain good archaeointensity results. This analysis also allowed to interpret anomalous behaviours observed in the Arai diagrams obtained in archaeointensity experiments. Archaeomagnetic (directional) studies were also performed in all oriented combustion structures. These studies consisted of demagnetization experiments of the natural remanent magnetization (NRM) using both thermal (TH) and alternating field (AF) demagnetization. 6 mean directions have been obtained for the Iberian Peninsula and 9 mean directions for the Caucasus region. Thermal demagnetization has also been applied to non-oriented samples, such as pottery or burnt clay material. This has allowed to determine the properties of these materials to carry out archaeointensity experiments and obtain information of archaeological interest such as the determination of paleotemperatures. Archaeointensity experiments have been carried out using a multi-method approach (Thellier-Coe, Thellier-IZZI, multispecimen and pseudo-Thellier), that allows to increase the reliability of the results. After applying strict selection criteria, 30 mean absolute archaeointensity determinations have been obtained in materials from the Iberian Peninsula and 13 ones in materials from the Caucasus region. These results represent a significant increase in data of proven quality for these chronologies in both regions. After comparing directional and archaeointensity data obtained with the available geomagnetic models, 6 archaeomagnetic dates have been obtained for the Iberian Peninsula. For the Caucasus, 9 archaeomagnetic dates have been obtained, 6 based on the direction and 3 on the full vector (direction and intensity). In addition, the comparison of the archaeointensity data obtained from the 1st half of the I millennia BCE for the Iberian Peninsula and the Caucasus region has provided new evidence about the occurrence of the Levantine Iron Age Anomaly (LIAA), in both regions. The results confirm the existence of this anomaly in the Caucasus with greater antiquity and how it progressively migrated from the Levant area to the western Mediterranean. Archaeomagnetic data obtained from the studied materials of the Iberian Peninsula and the Caucasus region, will allow not only to improve the archaeomagnetic dating technique but also to increase the geomagnetic information of both regions. This is especially valuable for the Caucasus, where existing data are very scarce and of poor quality. Likewise, the application of magnetic techniques to the study of burned archaeological materials provides valuable information in order to reconstruct their formation, use and preservation processes.