New constraints on geomagnetic field intensity variations in the Balkans during the Early Byzantine period from ceramics unearthed at Thasos and Delphi, Greece (original) (raw)
Physics of the Earth and Planetary Interiors
The archaeointensity records from Greece present several gaps in the prehistoric period among which the ones in the third and second millennia BCE (Early and Middle Bronze Age) are not justified by the abundance of relevant settlements in the broader Greek area. Their excavations yielded numerous collections of pottery and ceramics, well-studied to a big extent from archaeological and archaeometric point of view. We collected six groups of fragments dated from 2200 BCE to 1500 BCE which were subjected to a classical archaeomagnetic study. The material response to the experiments was mostly satisfactory, and the archaeointensity was calculated both with Thellier-Thellier and multispecimen protocols. These results, complemented by the ones recently published for the period 1500-900 BCE, and plotted versus the existing secular variation curves for Greece and relevant geomagnetic field models allow the recovery of a smooth V-shape already suggested for 2 the Middle East. Nevertheless, we only observed a slight intensity maximum around 1900-1800 BCE while the minimum suggested for the Near East around 1800 BCE is probably shifted to an earlier period.
GREEK ARCHAEOMAGNETIC INTENSITIES: SOME ASPECTS OF RELIABILITY AND GEOPHYSICAL IMPLICATIONS
Archaeointensity results from Greece for the last 2000 yr have been obtained using thermal and alternating field (AF) demagnetisation techniques. Most of the samples consisted of tiles and bricks derived from Byzantine churches which were epigraphically dated. The accuracy of the dating of the samples (to within a few years) and the comparison of the two techniques for measuring geomagnetic intensity combine to provide a good basis from which to derive meaningful conclusions -i.e. (i) About 70% of the archaeointensity measurements, made by the two methods, were highly compatible, differing less than t7% from their mean. In 60% of the cases, the AF technique yielded higher palaeointensity results than that for thermal demagnetization. The results for the thermal and AF techniques are discussed in accordance with reliability criteria and attention is drawn to the reliability of archaeointensity data in general. (ii) An overall similarity of the intensity trend was observed for the last 400 years between the AF, the thermal demagnetization and a modelled intensity curve derived from the spherical harmonic coefficients since AD 1600. (iii) A decrease of Intensity amounting to 40% is noted in the new data for the period since AD 400, and (iv) a non-dipole disturbance was noted at around AD 1300 in southern Greece, where the intensity changed by about 30% within a period of 30 years or so.
Geomagnetic field variations as determined from bulgarian archaeomagnetic data
Surveys in Geophysics, 1994
The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I , the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed.
Surveys in Geophysics, 1998
The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I (Kovacheva and Toshkov, 1994), the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed.
W. S. Downey, I. Liritzis, 2013
Archaeointensity results were obtained from ceramic sherds incorporated in the 'mortar' of two Rhodian Byzantine churches. Samples were analysed using a modified Thellier method with samples orientated so that the Natural Remanent Magnetization is at right angles to the applied laboratory field. Only a few samples showed high magnetic stability and an archaeointensity result was obtained from ceramic sherds (tilebrick) from the lower interior walls of the church (Afandou Ka-tholiki). Comparison with the Geomagnetic Field Variation plot indicated the probability density of possible dates between ~1000 to ~1500 AD. a date, broadly consistent with historical records.
Journal of Radioanalytical and Nuclear Chemistry, 2001
Archaeomagnetic studies in Bulgaria have a long history and the well established secular variation curves of the three elements of the ancient geomagnetic field (declination, inclination and intensity) for the last 8000 years enable the dating of archaeological features of burnt clay, independently of other methods. The determination of ancient palaeointensity is the most difficult characteristic and requires very cautious evaluation of the suitability of the burnt clay material. The present paper is an overview of the methodological progress in studying the suitability of the materials for archaeomagnetic investigations. The main rock-magnetic methods and summary of the most common results are presented involving the archaeomagnetic practice in the palaeomagnetic laboratory in Sofia. In addition, supplementary information obtained by magnetic measurements, which can be helpful for archaeology, are discussed. An example of archaeomagnetic dating procedure is also presented.
Geomagnetic Research of the Archaeological Site Isar Marvinci, Republic of North Macedonia
Природни ресурси и технологии
In this paper the results of the geophysical investigation on the archeological site Isar-Marvinci are presented. The results show low changes in the magnetic field and the local gradient, as it is an archeological site where there are no buildings and structures built of baked bricks that cause larger magnetic changes in the magnetic field over 100 [nT] or more [nT]. Small anomalies of the magnetic gradient probably indicate graves that have been confirmed by illegal diggers, whose presence can be seen on the ground.
First archaeomagnetic results and dating of Neolithic structures in northern Greece
Studia Geophysica et Geodaetica, 2012
Archaeomagnetism in Greece has continuously developed during the last decades. Numerous studies have provided high quality data and accurate secular variation curves for the direction and intensity of the geomagnetic field have been constructed. The Greek Secular Variation Curves (SVCs) cover the last 8 millennia for intensity and 6 millennia for direction. The coverage of the archaeological periods remains uneven, with several gaps, mostly in the directional dataset, with only two results for periods older than 2500 B.C. In the present contribution, the first archaeomagnetic results from Neolithic settlements in northern Greece are presented. For the present study, samples were collected from three different archaeological sites: burnt structures in Avgi (Kastoria) and Vasili (Farsala) and one oven from Sosandra (Aridaia). The natural remanent magnetization (NRM) grouping of all specimens indicated that the majority of the samples were burnt in situ, providing thus a reliable direction of the ancient field. Magnetic cleaning (both alternating-field and thermal) revealed the presence of one stable component of magnetisation. Rock magnetic experiments (acquisition of isothermal remanent magnetization (IRM), thermal demagnetisation of the IRM, thermomagnetic curves) have been performed on pilot samples indicating that low coercivity magnetic minerals such as magnetite or Timagnetite are prevailing. The mean directions (declination D, inclination I and parameters of the Fisherian statistics), which arose from the three sites are as follows:
Archaeomagnetic studies in kilns from N. Greece
2010
Archaeomagnetism combines the magnetic properties of baked materials with Archaeology. The archaeomagnetic method can be applied to any kind of permanent-in situ or displaced-burnt structures, such as kilns, ovens, hearths, burnt floors, tiles, bricks and pottery fragments, the latter for intensity measurements only. In this study we present the latest archaeomagnetic results from archaeological sites which are distributed in N. Greece (Polymylos, Sani, Thesssaloniki). The Natural Remanent Magnetization (NRM) and the magnetic susceptibility of the samples have been initially measured. The samples have been subjected to magnetic cleaning (AF and Thermal demagnetizations) and this procedure revealed the characteristic component of the ancient magnetic field. Rock magnetic experiments such as acquisition of the Isothermal Remanent Magnetization (IRM) and thermomagnetic analysis have been performed in pilot samples in order to identify the main magnetic carriers. Finally the secular variation curves for Greece and the SCHA.DIF.3K model were used in order to date these archaeological structures. This dating improved or modified the estimated archaeological ages.