Search

Since the publication of the European archaeomagnetic field model SCHA.DIF.3k in 2009, the number of paleomagnetic data derived from archaeological materials such as baked clays and volcanic rocks coming from Europe has increased by about 90% for directions and around 180% for intensities. Taking advantage of this increase, here we provide an updated regional archaeomagnetic model, called SCHA.DIF.4k, for the European continent and adjacent areas and now covering the last four millennia. To model the three geomagnetic elements, declination, inclination, and intensity, we use the regional R‐SCHA2D technique in space and temporal basis of cubic splines. A critical selection of the archaeomagnetic and volcanic data available in a spherical cap of 30° centered at 40°N latitude and 10°E longitude has been considered. In addition, in order to better constrain the behavior of the archaeomagnetic field during the last centuries, we include the historical data of the HISTMAG compilation. The new regional model allows us to better define the paleomagnetic field over Europe as well as to generate new paleosecular variation curves for archaeomagnetic dating purposes. Using these curves, the dating precision has been estimated for the last 4 kyr. As expected, results show that it strongly depends on the data uncertainties, the temporal data distribution and the behavior of the geomagnetic field itself. In addition, the use of the full vector geomagnetic field, instead of the directional information exclusively, provides more precise archaeomagnetic dating results. Plain Language Summary: The Earth's magnetic field is generated by complex fluid movements located in the outer core and envelops our planet protecting us against the solar wind. For this reason, the geomagnetic field plays an important role to sustain our life. During the last decades, a worldwide network of observatories and satellites provided an accurate picture of the geomagnetic field changes. Moreover, thanks to the ability of some rocks preserving the ambient geomagnetic field, it is possible to know its past evolution at geological time scales through the so‐called paleomagnetic data. For the Holocene, the paleomagnetic information derived from certain archaeological artifacts and lava flows provides snapshots of the past geomagnetic field (or paleofield) and thus, they can be used to reconstruct it at local and global scales. Europe is the continent with a high density of paleomagnetic data for the last four millennia. Taking advantage of this, here we provide a regional reconstruction of the geomagnetic field for this period valid for Europe and adjacent areas. This new model is a useful tool to analyze the paleofield behavior. In addition, it can be used as an improved tool for dating archaeological remains and volcanic rocks from the target region. Key Points: An updated archaeomagnetic regional model for Europe for the last 4,000 yearsA better knowledge of the spatial and temporal past evolution of the European geomagnetic fieldThe regional model can be used as a tool for archaeomagnetic dating in Europe [ABSTRACT FROM AUTHOR]

The chronology of the Late Bronze Age and the earliest stages of the Iron Age in the Mediterranean is an important topic of debate since the study of both local social dynamics and trade and colonial activity around the Mediterranean requires obviously well-established chronological frameworks. However, the exact chronology of the Early Iron Age in the Mediterranean region is still a problematic issue today since different, and in some cases unbalanced, sources of information (historical texts, material culture sequences, and radiocarbon dating results) are used. The NE Iberian Peninsula is not an exception and different time periods are proposed in the literature for the Early Iron Age. Here, and in order to provide a new and an independent input to feed this debate, we apply the archeomagnetic dating method to four archeological hearths from the Sant Jaume Complex, a set of several Early Iron Age archeological sites located in the north-eastern part of the Iberian Peninsula. The archeomagnetic dating results suggest that the abandonment of the studied structures (that can be linked to the abandonment of the archeological sites) most probably occurred before 650 BC, and therefore invalidate the age commonly ascribed to the Early Iron Age sites in this area. Our study provides, hence, new evidences that the traditional view of human settlement development in the NE Iberian Peninsula should be revisited. [ABSTRACT FROM AUTHOR]

Over the last years new evidences of several short-lived regional maxima of the geomagnetic field intensity at various times and locations have been defined. These features have important implications both for geomagnetic field modeling and for Earth's dynamo simulations. However, the nature, extent and underlying causes of these variations are still poorly understood. The major constraint for an adequate description of these important features is the absence of continuous detailed records and the current limited availability of precisely dated geomagnetic field recorders. In this context, archeological materials from superimposed strata covering long sequences of occupation provide a powerful tool to investigate the temporal variability of geomagnetic field strength at decadal and centennial time scales. In this work we report the archeomagnetic study of 79 potteries from Southeastern Spain collected in 14 different stratigraphic units. The chronological framework of the studied collection, ranging from the 9th to the 12th centuries, is based on historical/archeological data such as written sources and well-established typological and archeometric documentation on ceramics found on reference contexts in the area. Additionally, two radiocarbon dates obtained from two different stratigraphic units confirm the proposed chronological intervals. From classical Thellier and Thellier experiments including partial thermoremanent magnetization (pTRM) checks and TRM anisotropy and cooling rate corrections, height new high-quality mean intensities were derived. The new data provide an improved description of the sharp abrupt intensity decay that took place in Western Europe after the 800 AD intensity maximum, the most significant geomagnetic field intensity feature observed in Europe over the last two millennia. The new results confirm that several rapid intensity changes (with rates higher than 10 μT/century) took place in Western Europe during the recent history of the Earth. The comparison between the regional curve of Western Europe and the SHA.DIF.14k global field model predictions suggests that the 800 AD event observed in Europe is probably controlled by non-dipolar geomagnetic sources. [ABSTRACT FROM AUTHOR]

Abstract: Available archaeomagnetic data indicate that during the past 2500yr there have been periods of rapid geomagnetic field intensity fluctuations interspersed with periods of almost constant field strength. Despite Europe being the most widely covered region in terms of archaeomagnetic data the occurrence and the behaviour of these rapid geomagnetic field intensity changes is under discussion and the challenge now is to precisely describe them. The aim of this study is to obtain an improved description of the sharp intensity change that took place in western Europe around 800 AD as well as to investigate if this peak is observed at the continental scale. For this purpose 13 precisely dated early medieval Spanish pottery fragments, four archaeological French kilns and three collections of bricks used for the construction of different French historical buildings with ages ranging between 335 and 1260 AD have been studied. Classical Thellier experiments performed on 164 specimens, and including anisotropy of thermoremanent magnetisation and cooling rate corrections, gave 119 reliable results. The 10 new high-quality mean archaeointensities obtained confirm the existence of an intensity maximum of ∼85μT (at the latitude of Paris) centred at ∼800 AD and suggest that a previous abrupt intensity change occurred around 600 AD. Together with previously published data from western Europe that we deem to be the most reliable, the new data also suggest the existence of two other abrupt geomagnetic field intensity variations during the 12th century and around the second half of the 13th century AD. High-quality archaeointensities available from eastern Europe indicate that very similar geomagnetic field intensity changes occurred in this region. European data indicate that very rapid intensity changes (of at least 20μT/century) took place in the recent history of the Earth''s magnetic field. The results call for additional high-quality archaeointensities obtained from precisely dated samples and for a selection of the previously published data if a refined description of geomagnetic field intensity changes at regional scales is to be obtained. [Copyright &y& Elsevier]

Abstract: New archaeointensity results have been obtained from the study of four ceramic collections coming from four different archaeological sites in Greece. The ages of the ceramic fragments, based on archaeological constrains and radiocarbon analysis, range from 2200 BC to 565 AD. Low-field magnetic susceptibility versus temperature reveals a good thermal stability for most of the samples. However, for some samples the thermomagnetic curves are not reversible indicating mineralogical changes during heating. Isothermal remanent magnetisation (IRM) acquisition curves and thermal demagnetisation of three orthogonal IRM components have also been performed. The rock magnetic results identify magnetite and/ or Ti-magnetite as the main magnetic carriers in the studied samples. Classical Thellier experiments with regular partial thermoremanent magnetisation (pTRM) checks have been conducted on 125 specimens belonging to 34 independent ceramic fragments. Only 61 archaeointensity determinations (at specimen level) that correspond to linear NRM–TRM plots were used for the calculation of the site mean archaeointensities. The effect of the anisotropy of the thermoremanent magnetisation (TRM) and cooling rate upon TRM intensity acquisition have been investigated in all specimens. The maximum difference between the TRM anisotropy corrected and uncorrected intensities is around 30% at specimen level confirming that the TRM effect can be very important in ceramic samples. Cooling rate correction factors determined per specimen are up to 10% with only one exception that reaches 35%. Despite the moderate success rate of archaeointensity determination (around 50%) reliable mean site intensities have been obtained, with in situ intensities ranging from 53.6±4.1 to 69.3±3.9μT, corresponding to virtual axial dipole moments from 9.2±0.7 to 11.9±0.7×1022 Am2. The new data are reasonably consistent with other available data for the studied region as well as with the SV reference curves for Greece and the South Balkan Peninsula, and the regional and global geomagnetic field models. Combined with previously published data from the area, they confirm that important changes of the Earth’s magnetic field intensity occurred in Greece during the last five millennia. For some periods, the available archaeointensity data for the Balkan area show a large dispersion, even for data corresponding to high quality intensity standards, whereas for other periods their limited number prevents an accurate description of geomagnetic field intensity changes. This evidences the need of new reliable and well dated archaeointensity data in order to obtain a robust description of geomagnetic field intensity changes during the last five millennia in this area. [Copyright &y& Elsevier]

SUMMARY New full-vector archaeomagnetic data for North Africa recovered from the study of six kilns, five from Tunisia and one from Morocco, are presented. Archaeological and historical considerations, along with three radiocarbon dates, indicate that the age of the kilns ranges between the 9th and 15th centuries AD. Rock magnetic analyses showed that the principal magnetic carriers are magnetite and low Ti titanomagnetite, along with variable contributions of thermally stable maghemite and a high coercivity phase with low unblocking temperatures. The magnetic mineralogy of the studied material is thermally stable and behaves ideally during archaeointensity experiments. Stepwise alternating field demagnetization isolated a single, stable, characteristic remanence component with very well defined directions at both specimen and structure levels. Mean archaeointensities have been obtained from successful classical Thellier experiments conducted on between five and eight independent samples per kiln. Thermoremanent magnetization (TRM) anisotropy and cooling rate effects upon TRM intensity have been investigated. The results showed that these effects are low for four of the six studied kilns, with differences between the uncorrected and corrected means of less than 3 per cent. For the other two structures differences between the uncorrected and corrected mean site intensities are 4.4 per cent and 5.8 per cent. These results highlight the necessity for TRM anisotropy and cooling rate corrections in archaeomagnetic studies if accurate archaeointensities are to be obtained. The new results suggest that high intensities occurred in Northwest Africa during the 9th century. Although more data are clearly needed to define this period of high intensity, the results are in agreement with the available European archaeointensity data. A comparison between the new data, other available archaeomagnetic determinations in nearby locations, and palaeosecular variation (PSV) curves derived from the regional SCHA.DIF.3k and global ARCH3K.1 geomagnetic field models shows good agreement between the new data and directional results derived from the models. However, some differences are observed between geomagnetic field models intensity results and available archaeointensity data for the studied regions. This highlights the need for new data for unexplored regions such as North Africa. The new data presented here better constrains the evolution of the geomagnetic field during historical times in this region. They represent a new step towards the construction of a reference PSV curve for Northwest Africa. Once established, this curve will represent a new dating method for this region. [ABSTRACT FROM AUTHOR]

In this study, we present new archaeointensity results from Italy in order to enrich the reference dataset with high-quality intensity records from this area that is still poorly covered in terms of intensity data. The new data were obtained from palaeointensity experiments performed on 79 samples collected from six archaeological sites with ages ranging from 700 BC to 1600 AD. The samples, prepared from pottery and brick fragments, were analyzed using the classical Thellier method including the correction for the anisotropy of thermoremanent magnetization (TRM) and for cooling rate dependence upon TRM acquisition. Strict quality criteria were applied to the obtained results to select only the most reliable intensity determinations. The accepted results were obtained from one single component pointing through the origin in Zijderveld plots and linear Arai plots without any evidence of magnetochemical alteration. The rejected experiments correspond to samples showing more than one component of magnetization or clear mineralogical changes during the Thellier experiments. The new data were compared with other archaeointensity records from Italy and nearby countries. They help to improve the intensity curve for Italy, even though there are still several time periods poorly covered by archaeointensity records. It is clear that more data are needed to reconstruct the detailed evolution of the geomagnetic field intensity in Italy and investigate the existence of the intense, short-lived, regional intensity maxima, identified in other regions. [ABSTRACT FROM AUTHOR]