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Since the establishment of direct estimations of the Earth's magnetic field intensity in the first half of the nineteenth century, a continuous decay of the axial dipole component has been observed and variously speculated to be linked to an imminent reversal of the geomagnetic field. Furthermore, indirect estimations from anthropologically made materials and volcanic derivatives suggest that this decrease began significantly earlier than direct measurements have been available. Here, we carefully reassess the available archaeointensity dataset for the last two millennia, and show a good correspondence between direct (observatory/satellite) and indirect (archaeomagnetic) estimates of the axial dipole moment creating, in effect, a proxy to expand our analysis back in time. Our results suggest a continuous linear decay as the most parsimonious long-term description of the axial dipole variation for the last millennium. We thus suggest that a break in the symmetry of axial dipole moment advective sources occurred approximately 1100 years earlier than previously described. In addition, based on the observed dipole secular variation timescale, we speculate that the weakening of the axial dipole may end soon.

This study presents new archaeomagnetic results from 33 combustion structures (kilns and hearths) from the archaeological sites of Castelinho, Crestelos, Olival Poço da Barca and Fonte do Milho in NE Portugal. The age of the investigated structures ranges from 1210 BC to 200 AD according to calibrated radiocarbon dating, thermoluminescence dating and archaeological constraints. Stepwise thermal and alternating field demagnetization isolate a single, stable, characteristic remanence component with very well defined directions. Rock magnetic analyses suggest low-Ti titanomagnetite/maghemite as the main magnetic carrier of the remanence. Mean directions are well grouped in most structures. The effect of thermoremanent anisotropy on mean directions has been evaluated and was found to be important. Inclination increases of between 2° and 13° after applying the anisotropy correction at specimen level. This highlights the requirement of evaluating this effect on the directions of small and flattened thin kilns and hearths. The 31 new directional data improve both the temporal and spatial distribution of the Iberian archaeomagnetic dataset from Late Bronze Age to Roman Times. Finally, a new directional palaeosecular variation curve for Iberia for the last twelve centuries BC is proposed. The curve has been computed using the bootstrap method and includes data coming from sites within 900 km of Madrid. The new palaeodirectional secular variation curve for Iberia is consistent with the Western European palaeosecular variation curve and with the prediction of regional European models., The authors are Grateful to the Spanish Research Project CGL2014-54112-R which has supported the field and laboratory costs, as well as the post-doctoral contract of APO.

A detailed rock-magnetic and archaeomagnetic investigation were carried out on seven pottery fragments (49 specimens) found within the burial of an individual with the most body/dental modifications and prestige elements found so far in the ancient Teotihuacan city. The skull of this 35 to 40 years old woman (at the time of death) shows an intentional cephalic modification with frontal-occipital compression. This is very uncommon within the Teotihuacan population and indicating the southern provenance (Oaxaca or Maya area). The age estimations, based on relative datings, placed the archaeological context between 350 and 400 CE. The magnetic mineralogy experiments were characterized by a single remanence component, occasionally accompanied by a soft overprint, probably of viscous origin and Curie temperatures between 540 °C and 565 °C. Only twelve specimens, belonging to two distinct pottery fragments, yielded reliable determinations meeting very strict selection criteria. The values retrieved from both fragments are statistically undistinguishable. The absolute age estimation of the Tlailotlacan Woman archaeological context obtained in this study contradicts the early estimations and indicates a late time interval between 650 and 800 CE corresponding to the decline of Teotihuacan, where the social differences of their inhabitants became much more evident.

The understanding of the paleosecular variations (PSV) of the geomagnetic field in South America is still biased by the scarcity of data. Especially, the recent geomagnetic PSV is characterized by the large growth of the South Atlantic Magnetic Anomaly (SAMA) during the last centuries, first documented by the geomagnetic model gufm1 (Jackson et al., 2000). A large amount of data is required to understand the time and geographic distribution of this primary feature, and the Andean Pleistocene and Holocene volcanoes are an excellent recorder of instant local changes in SV. Here we present a preliminary study from 18 paleomagnetic samples collected during 2015 on what it was supposed to be the 1750 or the 1957–58 AD lava flow on the Llaima Volcano (38.692° S; 71.729° W), one of the most active centers of the Chilean Andes, in the Southern Volcanic Zone. A detailed paleomagnetic study was performed in order to recover the Declination and Inclination of the geomagnetic field, obtain the paleointensity and define the magnetic mineralogy. AF demagnetization until 1 T yielded an average vector at Dec/Inc 2.3°/-33.1° with α95 of 2.4°. This direction is carried by titanomagnetite grains with 40–45% ulvospinel as revealed by thermomagnetic curves. Paleointensity estimates were obtained following the IZZI-Thellier protocol. Seven specimens from 5 samples provided reliable results (success rate of 35%), giving an average paleointensity for these specimens of 30.88 ± 2.39 μT. The full magnetic vector obtained here was compared to archaeomagnetic reference curves and the IGRF suggest that the lava flow has the age of 1957–58 AD.

Landscape geophysical survey around the small upland ‘henge’ at Yarnbury, Grassington, North Yorkshire revealed few anthropogenic features around the enclosure but did identify a small rectangular structure in the same field. Sample trenching of this feature, radiocarbon and archaeomagnetic dating proved it to be an earlier Neolithic post and wattle structure of a type that is being increasingly recognised in Ireland and the west of Britain. It is the first to be recognised in the Yorkshire Dales and it is argued that the Dales may have been pivotal in the Neolithic for east–west trade as well as pastoral upland agriculture.

A través de la datación arqueomagnética de Guachimontones de Teuchitlán, Jalisco, se contribuye a la cronología prehispánica del Occidente de México. A partir de 16 muestras arqueomagnéticas (81 especímenes en total) de hornos, pisos quemados y no quemados recolectados en 2005 y 2010, se hicieron mediciones para determinar la dirección media de cada muestra en el Laboratorio de Paleomagnetismo de la UNAM (Ciudad de México y Campus Morelia). Se obtuvieron dataciones arqueomagnéticas con α95 < 10° para el 88% de las muestras y corresponden a las épocas de ocupación del sitio. Este estudio aporta 2 nuevos datos a la curva de variación de Mesoamérica, registra modificaciones arquitectónicas en una edificación y apoya la teoría de reocupación del sitio hacia el periodo Epiclásico (450-900 d. C.). ENGLISH: This study contributes to the pre-Hispanic chronology of Western Mexico through archaeomagnetic dating of the archaeological site Guachimontones (Teuchitlán, Jalisco). Systematic magnetic measurements were carried out to determine the mean direction of each sample at the UNAM paleomagnetism laboratories (Mexico City and Campus Morelia). Sixteen analyzed samples (81 specimens in total) come from furnaces, burned and unburnt floors, collected between 2005 and 2010. Archaeomagnetic dates with precision parameter α95 < 10° were obtained for 88% of the samples, and corresponds to the site occupation periods. This study thus contributes new and reliable data to the reference variation curve of Mesoamerica in addition to documenting architectural modifications in the building sequence at Guachimontones and supporting the theory of reoccupation of this site during the Epiclassic period (450-900 A.D.).

For the global time stationary geomagnetic core field, a new modeling concept for Holocene archeomagnetic data is presented. Major challenges consist of the uneven data distribution, missing vector field components and non-linear relations between observations and the geomagnetic potential. Instead of a truncated spherical harmonics approach, we propose a fully Bayesian, Gaussian process based model. Inherently, the Bayesian approach provides location dependent uncertainties.The geomagnetic potential is assumed to be a Gaussian process whose covariance structure is given by an explicit kernel function, including several hyperparameters. For this kind of non-parametric models, the full Bayesian posterior is numerically intractable. Instead, we propose an approximate computation using a Bayesian update system. In a first step, the full vector records are used to obtain, within Laplace approximation, a rough field estimate. This estimate serves as a point of linearization for the non-linear observations. The approximate posterior is then given by a Gaussian mixture. Marginals for all relevant parameters and the field itself can be computed. We are able to quantify the impact of data coverage on uncertainty reduction.

SUMMARY During the last decade, rapid or extreme geomagnetic field intensity variations associated with rates greater than the maximum currently observed have been inferred from archeomagnetic data in the Near-East and in Western Europe. The most extreme events, termed geomagnetic spikes, are defined as intensity peaks occurring over a short time (a few decades), and are characterized by high variation rates, up to several μT yr–1. Magnetic flux expulsion from the Earth’s outer core has been suggested as one possible explanation for these peaks but has not yet been examined in detail. In this study, we develop a 2-D kinematic model for magnetic flux expulsion whose key control parameter is the magnetic Reynolds number Rm, the ratio of magnetic diffusion time to advection time. This model enables the tracking of magnetic field lines which are distorted and folded by a fixed flow pattern. Two processes govern the magnetic evolution of the system. The first is the expulsion of magnetic flux from closed streamlines, whereby flux gradually concentrates near the boundaries of the domain, which leads to an increase of the magnetic energy of the system. If the upper boundary separates the conducting fluid from an insulating medium, a second process then takes place, that of diffusion through this interface, which we can quantify by monitoring the evolution of the vertical component of magnetic induction along this boundary. It is the conjunction of these two processes that defines our model of magnetic flux expulsion through the core–mantle boundary. We analyse several configurations with varying flow patterns and magnetic boundary conditions. We first focus on flux expulsion from a single eddy. Since this specific configuration has been widely studied, we use it to benchmark our implementation against analytic solutions and previously published numerical results. We next turn our attention to a configuration which involves two counter-rotating eddies producing an upwelling at the centre of the domain, and comprises an upper boundary with an insulating medium. We find that the characteristic rise time and maximum instantaneous variation rate of the vertical component of the magnetic field that escapes the domain scale like $\sim R_m^{0.15}$ and $\sim R_m^{0.45}$, respectively. Extrapolation of these scaling laws to the Earth’s régime is compared with various purported archeointensity highs reported in the Near-East and in Western Europe. According to our numerical experiments magnetic flux expulsion is unlikely to produce geomagnetic spikes, while intensity peaks of longer duration (one century and more) and smaller variation rates appear to be compatible with this process.

The progressive southward reoccupation of territories of the Iberian Peninsula by the Christian kingdom against the Muslims from the eighth century AD onwards is a well-known process. However, there are few well-dated sites of this period, especially in the northern plateau of Spain. Here we report the full vector archaeomagnetic dating of two hearths from the archaeological site of La Pudia I (Caleruega, Castile-and-Leon, Spain). Both hearths were archaeomagnetically investigated in order to date their last use linked to the abandonment of the site. The archaeomagnetic direction was analysed through thermal (TH) and stepwise alternating field (AF) demagnetization of the natural remanent magnetization (NRM). Pseudo-single domain slightly substituted magnetite was identified as the main magnetic carrier. Thellier–Coe type absolute archaeointensity determinations were carried out on 48 samples from both hearths. The mean directions obtained were independently analysed both at sample and at specimen levels yielding very similar results but statistically distinguishable at 95% confidence level. The archaeomagnetic dating was carried out by comparing the mean directions and archaeointensity values of both hearths with the SHA.DIF.14k geomagnetic field model. The results obtained are in agreement with the archaeological context, suggesting that the abandonment of the archaeological site took place between the end of ninth century and the first half of the eleventh century AD. These results provide one of the first evidences of independently well-dated sites of the Christian conquest in the Iberian northern plateau at the onset of the Early–High Middle Ages.

International audience; In Western Eurasia, the first millennium BCE is characterized by the fastest secular variation of the Earth Magnetic Field observed over the last millennia and by a geomagnetic anomaly centered on the Middle East. On the global scale, the variation of the dipolar field during this period remains poorly constrained because of the lack of data in other geographical areas. Here, we presented 23 new mean archaeointensity data on ceramic sherds dated between 1500 BCE and 200 CE from Chalcatzingo archaeological site in Central Mexico. Archaeointensities were determined using the classical Thellier‐ Thellier protocol with corrections for TRM anisotropy and cooling rate effects. Our work doubles the number of high‐quality archaeointensity data in Mexico during the considered period. Using a Bayesian approach, a new secular variation curve was calculated at Mexico City between 1500 BCE and 200 CE after selection of Mexican archaeointensity data. After a period of oscillations of the intensity between 20 and 40 μT from 1500 to 300 BCE, the curve shows a large maximum `~65 μT in the second century BCE. The corresponding VADM varied between ~4.0 and ~11.0 × 1022 Am2, which highlights further that the intensity of the geomagnetic field could vary at regional scale over a larger range as previously thought. However, this amplitude variation may be overestimated, as it does not take into account the fast directional variation observed at this time.

Archaeomagnetic directions of 141 archaeological structures have been studied from 21 sites in Austria, 31 sites in Germany and one site in Switzerland. Characteristic remanent magnetization directions obtained from alternating field and thermal demagnetizations provided 82 and 78 new or updated (12 and 10 per cent) directions of Austria and Germany, respectively. Nine of the directions are not reliable for certain reasons (e.g. displacement) while three of the features are not well dated. Apart from this some updated age information for the published databases is provided. Rock magnetic experiments revealed magnetite as main magnetic carrier of the remanences. The new data agree well with existing secular variation reference curves. The extended data set covers now the past 3500 yr and a lot of progress were made to cover times BC with data. Here enhanced secular variation is observed manifested in declinations with values up to 70��. The new data will allow for recalculation of archaeomagnetic calibration curves for Central Europe from mid Bronze Age until today. �� 2019 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society.

Understanding the chronology of Norse settlement is crucial for deciphering the archaeology of many sites across the North Atlantic region and developing a timeline of human-environment interactions. There is ambiguity in the chronology of settlements in areas such as the Northern Isles of Scotland, arising from the lack of published sites that have been scientifically dated, the presence of plateaus in the radiocarbon calibration curve, and the use of inappropriate samples for dating. This novel study uses four absolute dating techniques (AMS radiocarbon, tephrochronology, spheroidal carbonaceous particles and archaeomagnetism) to date a Norse house (the “Upper House”), Underhoull, Unst, Shetland Isles and to interpret the chronology of settlement and peat which envelops the site. Dates were produced from hearths, activity surfaces within the structure, and peat accumulations adjacent to and above the structure. Stratigraphic evidence was used to assess sequences of dates within a Bayesian framework, constraining the chronology for the site as well as providing modelled estimates for key events in its life, namely the use, modification and abandonment of the settlement. The majority of the absolute dating methods produced consistent and coherent datasets. The overall results show that occupation at the site was not a short, single phase, as suggested initially from the excavated remains, but instead a settlement that continued throughout the Norse period. The occupants of the site built the longhouse in a location adjacent to an active peatland, and continued to live there despite the encroachment of peat onto its margins. We estimate that the Underhoull longhouse was constructed in the period cal. AD 805–1050 (95% probability), and most probably in cal. AD 880–1000 (68% probability). Activity within the house ceased in the period cal. AD 1230–1495 (95% probability), and most probably in cal. AD 1260–1380 (68% probability). The Upper House at Underhoull provides important context to the expansion and abandonment of Norse settlement across the wider North Atlantic region.

Temporal variations of Earth\'s magnetic field provide a great range of geophysical information about the dynamics at different layers of the Earth. Since it is a planetary field, regional and global aspects can be explored, depending on the timescale of variations. In this thesis, the geomagnetic field variations for the last two millennia were investigated. For that, some improvement on the methods to recover the ancient magnetic field intensity from archeological material were done, new data was acquired and a critical assessment of the global archaeomagnetic database was performed. Two methodological advances are reported, comprising: i) the correction for microwave method of the cooling rate effect, which is associated to the difference between the cooling times during the manufactory of the material and that of the heating steps during the archaeointensity experiment; (ii) a test for thermoremanent anisotropy correction from the arithmetic mean of six orthogonal samples. The temporal variation of the magnetic intensity for South America was investigated from nine new data, three from ruins of the Guaraní Jesuit Missions and six from archaeological sites associated with jerky beef farms, both located in Rio Grande do Sul, Brazil, with ages covering the last 400 years. These data combined with the regional archaeointensity database, demonstrates that the influence of significant non-dipole components in South America started at ~1800 CE. Finally, from a reassessment of the global archaeointensity database, a new interpretation was proposed about the geomagnetic axial dipole evolution, where this component falls constantly since ~700 CE associated to the breaking of the symmetry of the advective sources operating in the outer core. Variações temporais do campo magnético da Terra fornecem uma grande diversidade de informações geofísicas sobre a dinâmica das diferentes camadas da Terra. Por ser um campo planetário, aspectos regionais e globais podem ser explorados, dependendo da escala de tempo das variações. Nesta tese, foram investigadas as variações do campo geomagnético para os dois últimos milênios. Para isso, aprimoramentos nos métodos de aquisição da intensidade geomagnética registrada em materiais arqueológicos foram realizados, bem como a aquisição de novos dados e uma avaliação crítica da base de dados arqueomagnética global. Dois novos avanços metodológicos são aqui propostos, sendo eles: i) correção para o método de micro-ondas do efeito da taxa de resfriamento, que está associada à diferença entre os tempos de resfriamento durante a manufatura do material e o das etapas de aquecimento durante o experimento de arqueointensidade; (ii) teste para correção da anisotropia termorremanente a partir da média aritmética de seis amostras posicionadas ortogonalmente umas às outras durante o experimento de arqueointensidade. A variação temporal da intensidade magnética para a América do Sul foi investigada a partir de nove dados inéditos, sendo três provenientes das ruínas das Missões Jesuíticas Guaraníticas e seis de sítios arqueológicos associados a fazendas de charque, ambos localizados no Rio Grande do Sul, Brasil, com idades que cobrem os últimos 400 anos. Esses dados, combinados com o banco de dados regionais de arqueointensidade, demonstram que a influência significativa de componentes não-dipolares do campo magnético na América do Sul começou em ~1800 CE. Finalmente, a partir de uma reavaliação do banco de dados globais de arqueointensidade uma nova interpretação foi proposta a respeito da evolução do dipolo axial geomagnético, sugerindo que essa componente está decrescendo constantemente desde ~700 CE devido à quebra da simetria das fontes advectivas que operam no núcleo externo.

Holocene geomagnetic field models are used to study processes in Earth's core, millennial scale variations in solar activity and to relatively date geological and archaeological archives. Constructing models from magnetic field directions and intensities stored in archaeological artefacts, igneous rocks and sediment records is challenging due to the sparse data distribution and the large chronological and magnetic uncertainties associated with the data. In addition, data from sediment records are further complicated by the effects of post-depositional remanent magnetisations (pDRMs) that lead to a magnetic signal which is smoothed and offset in time. Here we present a new probabilistic modelling approach that addresses these problems by co-estimating the geomagnetic field and the age of the data as well as accounting for the effects of pDRM and systematic directional errors in the sedimentary data. The use of a flexible Student's t-distribution in the likelihood function removes the need for outlier rejection which may otherwise lead to excessive smoothing of the model when applied to data with uncertain ages. A final ensemble of models is obtained through Hamiltonian Monte Carlo simulation of the posterior distribution. The modelling approach is tested and evaluated using synthetic data generated from the prior with an equivalent spatial and temporal distribution to the real data and corrupted with realistic noise.

We report new results from frontier research that relates the methodology and knowledge of geophysics (geomagnetism) with archeology and the data will represent a valuable contribution to both disciplines. A detailed magnetic survey was performed on limekilns from the northern Yucatan peninsula. We used Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) Spectroscopy to determine the temperature of calcination in order to select limekiln samples that were heated above the Curie temperature for common magnetic minerals. Using rock-magnetism, we identified the main carrier of remanent magnetization to be multi-domain or large pseudo-single domain low titanium titanomagnetite. Alternating magnetic field demagnetizations delivered reliable archaeomagnetic directions. Our summary of 12 limekiln ages shows a large span from 707 to 1900 yr AD. Such a wide time range signifies that Maya used limekilns in the Yucatan peninsula area in the Late Classic period (600 AD), and that some of these limekilns were reused in the Colonial period. From a geophysical point of view, information can be used about the behavior of the Earth's magnetic field in the recent historical past in Mesoamerica. In this context, the hundreds of Mayan limekilns which are distributed in large areas, open great opportunities to contribute to both archeology and geomagnetic field fluctuations during the past two millennia.

Dating analysis of potsherds from three of the six units recently excavated in the Tingambato archaeological site, central-western Mexico, was carried out employing two regional intensity Paleosecular Variation Curves (PSVC) and the global model SHA.DIF.14k. A complete evaluation of the ceramic fragments' magnetic characteristics was done to determine the samples' magnetic carriers and their capacity to provide reliable archaeointensity data. The presence of two magnetization components in five analyzed potsherds provides two snapshots of the Earth's magnetic field intensity behavior at different temporalities. Intensity values were obtained following strict quality criteria, including cooling rate and anisotropy corrections. The principal causes of failure in archaeointensity experiments are associated with the alteration of the magnetic mineralogy during the heating of the specimens and with the presence of multidomain grains. Intensities within the established quality criteria were obtained for four out of the eleven ceramic fragments analyzed. The dating exercise shows a better correspondence of the intensity values with the regional curves than with the global model, especially for the temporal range between AD 400–1200, for which both regional curves are in good agreement. The obtained archaeomagnetic ages had a good correspondence with the radiocarbon ages reported in previous studies. By determining two archaeointensity values in one of the studied potsherds: one associated whit its fabrication and the other related to the fire (after which the site is supposed to be abandoned), archaeomagnetic ages of the probable end of Tingambato occupation were estimated.

In the present study we report on archaeomagnetic and luminescence results from three ceramic kilns unearthed in a workshop during the subway (METRO) excavations in Thessaloniki (N. Greece) as well as from a small kiln at Ierissos (Chalkidiki). The first settlement is situated in the western part of the city where several similar workshops were excavated in the past. The archaeological information attributed a possible Ottoman age to these structures and placed their last use after the 14th century CE. The other small kiln is one of the rare “in situ” remains within the settlement reported as “Medieval Ierissos”. A total of fifty-five hand samples were retrieved from the four kilns and studied following established archaeomagnetic protocols in order to define the full vector of the magnetization. Additionally thermoluminescence (TL) experiments have been performed on the same material for the Thessaloniki kilns and the obtained ages converge and refine the archaeological ones. At Ierissos optically stimulated luminescence (OSL) experiments on five samples revealed the firing history of the structure. The combination of archaeological and/or TL-OSL information allowed to define four new full vector recordings for the improvement of the secular variation curves during the second millennium CE where intense variations of the Geomagnetic Field are reported from several places in Europe. The new data, together with recently published ones for the first millennium CE, allow to update the directional reference curves, poorly constrained for this period.

Today's knowledge about paleomagnetic secular variations in (southern) Africa is extremely limited. Here, we derive paleomagnetic records from independently radiocarbon dated sediment records from three maars in Madagascar: Andraikiba and Amparihibe are terrestrial maars located on the main island of Madagascar and on a small island in the Northwest, whereas Crater Lake is a maar which has an open connection to the Indian Ocean. Studied through alternating field demagnetization of u-channel samples, characteristic remanent magnetization (ChRM) directions document similar inclination and declination patterns in two of the archives for the past 2,500 years (except for the last 400 cal BP). These new data are the first allowing to test the reliability of previous records which often suffer from low resolution and other obstacles. This will further allow to start to distinguish between robustly confirmed paleomagnetic secular variation data for this region from potentially problematic data. Considering a much lower resolution and a shorter covered time interval of archaeomagnetic data from La Reunion, South Africa, Botswana and Zimbabwe the temporal successions of maxima and minima reveal a coherent picture. Although slightly shifted in time, similarities also exist to the global geomagnetic field reconstruction model SHAWQ2k ( Campuzano et al., 2019 ) which includes the above mentioned data. Surprisingly also similarities, though only in declination, are observed to the CALS3K.4 model ( Korte and Constable, 2011 ) which is used as Northern Hemisphere biased model example. In contrast to this, no declination similarities but remarkable inclination similarities are observed to a lake record from Lake Malawi. An analog inclination pattern is also observed in a record from the Makran Accretionary Wedge which is ∼5,000 km to the north of the investigated sites. Interestingly the spatial distribution of archives showing these inclination similarities resembles the spatial distribution of inclination anomalies detected in model predictions. PSV similarities over such a large area are suggestive of a large-scale core dynamic origin independent of westward drift of non-dipole field components often associated with PSV records. This study emphasizes the potential of maar lakes in Madagascar for paleo reconstructions but also suggests that shallow marine and marine-brackish systems should be avoided if possible when trying to expand the (South) African paleomagnetic database.

Here we report a detailed archaeomagnetic and rock-magnetic study of a pottery kiln from Burgos (Spain) to reconstruct its burning conditions and date its last use and abandonment age. During the course of a rescue archaeological excavation carried out in 2015 in the center of Burgos city, a medieval pottery workshop was discovered. Two well-preserved kilns appeared and archaeomagnetic analyses were performed on one of them. In addition to a large amount of pottery remains, some numismatic and documental evidences provided a general chronological estimation, but the abandonment age of the workshop remains unknown. On the basis of the existing archaeological information we carried out an archaeomagnetic study in order to date its last use. 69 archaeomagnetic samples were collected from the combustion chamber and the kiln's fire tunnel. Stepwise alternating field and thermal demagnetization of the natural remanent magnetization (NRM) were carried out to retrieve the mean direction. Additional experiments consisted in the acquisition of isothermal remanence (IRM), low-field magnetic susceptibility and its anisotropy as well as thermomagnetic curves. Despite the high temperatures expected in the combustion chamber, it appeared that the bricks´ samples from the fire tunnel exhibit the most successful directional results. Magnetite and variable contributions of hematite are the main ferromagnetic minerals observed in the thermomagnetic curves. The type of lithology studied, its previous magnetic history and their location in the kiln strongly condition the observed directional and rock-magnetic results. Additionally, AMS data revealed the manufacturing fabric of the fire tunnel's bricks, showing moderately high anisotropy degrees, but not enough to casts doubts on the directional NRM record. In order to test the reproducibility of the dating results, archaeomagnetic dating was carried out using different geomagnetic field models and the Iberian paleosecular variation curve. The small differences observed in the dating results are mainly due to the density and type of input data of these records. The combination of the archaeomagnetic analyses with the archaeological and documental suggests that last kiln's usage took place during the first half of the XVIth century CE. Overall, this paper illustrates how the combination of archaeological data and archaeomagnetic analyses may improve our understanding about the manufacturing processes, use and age of abandonment of archaeological combustion structures., European Social Fund (Operational Programme for Castilla y León) and the Junta de Castilla y León (Consejería de Educación). Authors also thank the support of the project CGL2016-77560-C2 financed by Spanish Ministry of Economy and Competitiveness (MINECO) and European Fund of Regional Development (EFRD), the project BU235P18 funded by Junta de Castilla y León and EFRD, and the projects PID2019-108753GB-C21 and PID2019-105796GB-I00 financed by Agencia Estatal de Investigación (Spain) [AEI /10.13039/501100011033].

The paper presents an overview of the current state of investigation of heated and heat-treated artefacts from Pleistocene sites, the methods frequently used in such investigation, and the main goals of similar research. Heated artefacts should be targeted in pre-excavation (mostly by non-destructive surficial methods), excavation (e.g., primary visual estimation, archaeomagnetic measurements in situ), and the post-excavation phases (a range of analytical methods). Apart from distinguishing heated artefacts, we are frequently able to date them directly, distinguish deliberately heated artefacts, assess the role of heat treatment on different Pleistocene sites, and draw conclusions about the spatial organization of such sites based on the distribution of heated artefacts. Successful heat treatment made stone knapping easier, enabled pressure flaking and the formation of sharper edges. The main causes of such improvements are the closing of pores due to the formation of new bonds, the appearance of fluid inclusions with high-velocity crack propagation, and potentially neo-formed iron oxides or other fluxes in the siliceous matrix. In view of recent research, the recrystallization of silica matter or the positive role of microcracks within the siliceous matrix are less probable causes of improved flakeability. Heat treatment was a type of technological and symbolic adaptation of modern humans to the frequently hostile environments of the Pleistocene as the two spread together over the world before the onset of the Holocene. The oldest dates of the technique currently come from the Near East. Though it might have spread from there to some parts of Eurasia, polycentric invention of heat treatment in the Pleistocene must be assumed. Independent centres of development of the technique are probably southern Africa, South America or Australia – relatively isolated regions where technological influence from other areas is not evidenced.

There is a significant lack of geomagnetic field strength (archaeointensity) measurements for many archaeological time periods in the United Kingdom (UK). This not only makes past geomagnetic secular variation difficult to model but also limits the development of archaeointensity dating. This paper presents the first archaeointensity study on UK Neolithic material. In this study, twenty-five sherds of Neolithic Grooved Ware pottery from the Ness of Brodgar, Orkney, UK, some with direct radiocarbon dates, were subjected to a full archaeomagnetic investigation with the aim of increasing the amount of archaeointensity data for the UK. Both thermal Thellier and microwave palaeointensity experiments were used to determine which technique would be most suitable for British Neolithic pottery. Three successful archaeointensity results between 35 and 40μT were obtained using thermal Thellier method, which is consistent with the limited data available within a 15° radius and geomagnetic field model predictions from the same time. We separated the results into four different types with an intention of explaining the behaviours that determine the likelihood of achieving an acceptable archaeointensity estimate. The feasibility of obtaining geomagnetic field strength information during the UK Neolithic from ceramics has been demonstrated and the results provide a solid basis for improving our knowledge of geomagnetic secular variation during archaeological time in Britain.

Variations of the Earth's geomagnetic field during the Holocene are important for understanding centennial to millennial-scale processes of the Earth's deep interior and have enormous potential implications for chronological correlations (e.g., comparisons between different sedimentary recording sequences, archaeomagnetic dating). Here, we present 21 robust archaeointensity data points from eastern China spanning the past ∼6 kyr. These results add significantly to the published data both regionally and globally. Taking together, we establish an archaeointensity reference curve for Eastern Asia, which can be used for archaeomagnetic dating in this region. Virtual axial dipole moments (VADMs) of the data range from a Holocene-wide low of ∼27 to "spike" values of ∼166 ZAm2 (Z: 1021). The results, in conjunction with our recently published data, confirm the existence of a decrease in paleointensity (DIP) in China around ∼2200 BCE. These low intensities are the lowest ever found for the Holocene and have not been reported outside of China. We also report a spike intensity of 165.8 ± 6.0 ZAm2 at ∼1300 BCE (±300 y), which is either a prelude to or the same event (within age uncertainties) as spikes first reported in the Levant.

The archaeomagnetic studies of ceramics from the Hermonassa multilayer archaeological monument in the Taman Peninsula provided the data on the intensity of the main geomagnetic field in the past. The data for the interval from VIII to XX centuries A.D. demonstrate a well pronounced decreasing trend in the geomagnetic field intensity during this time. Three stages, each lasting for a few centuries, are distinguished in the variations of the centennial average field which slightly varies within each stage and generally decreases from 70 to ~45 μT during the entire period from VIII to XX centuries A.D. The variations of the geomagnetic field in the interval from XII to XVII centuries A.D. have a form of quasi-harmonic oscillations with a characteristic time of about 300 years.

Geophysical Journal International New archaeomagnetic direction result from China and its constraints on paleosecular variation of the geomagnetic field in Eastern Asia Journal: Manuscript ID Manuscript Type: Date Submitted by the Author: Complete List of Authors: Keywords: Geophysical Journal International Draft Research Paper n/a Cai, Shuhui; Institute of Geology and Geophysics Chinese Academy of Sciences, ; University of California San Diego Scripps Institution of Oceanography, Tauxe, Lisa; Scripps Oceanographic Institution, Deng, Chenglong; State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Qin, Huafeng; Institute of Geology and Geophysics, State Key Laboratory of Lithospheric Evolution Pan, Yongxin; Institute of Geology and Geophysics Chinese Academy of Sciences Jin, Guiyun; Shandong University, School of History and Culture Chen, Xuexiang; Shandong University, School of History and Culture Chen, Wei; The Sichuan Provincial Cultural Relics and Archeology Research Institute Xie, Fei; Hebei Province Institute of Cultural Relics Zhu, Rixiang; Institute of Geology and Geophysics Chinese Academy of Sciences Archaeomagnetism < GEOMAGNETISM and ELECTROMAGNETISM, Palaeomagnetic secular variation < GEOMAGNETISM and ELECTROMAGNETISM, Palaeomagnetism < GEOMAGNETISM and ELECTROMAGNETISM

Archaeomagnetic dating is probably one of the most known applications of magnetic methods to archaeology but there are others still underutilized and of particular interest to Palaeolithic archaeology. Here, we report a novel application of archaeomagnetism as a technique to determine temporal diachronies among combustion features from the same surface within palaeolithic palimpsests. The approach is based on the subtle directional changes of the Earth's magnetic field through time (secular variation, SV) and on the ability of burned materials to record such variations under certain conditions. Three Middle Palaeolithic hearths from level O (ca. 55 ka BP) at the Abric Romaní rock-shelter (NE Spain), were archaeomagnetically investigated. The studied surface (black homogeneous carbonaceous facies), recorded the magnetic enhancement produced by fire with a tenfold increase in concentrationdependent magnetic parameters in the uppermost centimetre with respect to its unburned or deeper counterparts. Pseudo-single domain (PSD) Ti-low titanomagnetite was identified as the main remanence carrier. The irreversibility of thermomagnetic curves suggests that these samples did not undergo enough high temperatures as to record a full thermoremanence (TRM). Additionally, the occasional occurrence of maghaemitized magnetite is interpreted as an indication of a thermochemical remanent magnetization (TCRM), making these samples unsuitable for absolute palaeointensity determinations. Two well-defined (a95 < 5 ) and statistically indistinguishable archaeomagnetic directions were obtained with their mean directions within their respective confidences circles at the 95% level. The lack of directional changes and the similarity in the magnetic properties suggest that these hearths recorded simultaneously or closely confined in time the Earth's magnetic field direction at the time of cooling. These results agree well with archaeological evidence which indicates a synchronic occupation of this activity area. The possibility of determining temporal differences among combustion features in prehistoric sites arises as a promising tool in palimpsest dissection studies and may help to reconstruct occupation patterns of prehistoric groups. The practical limits of the method are discussed as well as its potential to identify post-depositional mechanical alteration processes., Spanish Ministry of Economy and Competitiveness, (MINECO) and European Regional Development Fund (projects CGL2012-38481 and CGL2012-32149)

Red colored paintings contain small amount of antiferromagnetic hematite grains. When the red pigment is applied to the wall, these grains are free to move and they align their magnetic moment with the Earth's magnetic field. The resulting magnetization is called pictorial remanence. Here, we evaluate the usefulness of natural remanent magnetization carried by mural paintings in archaeomagnetism in order to try to estimate whether it may be used as a reliable dating tool. Moreover, we report a first ever attempt to analyze samples of cave paintings.

This paper presents results of an archaeomagnetic study of slag from four Early Bronze (EB) Age copper production sites in the Faynan Copper Ore District and the northern Arabah Valley (modern Israel and Jordan). The results provide age constraints for metallurgical activities at these sites. Together with previously published data, they indicate copper production around ca. 2900 cal. BCE (EB II-III transition) and between ca. 2600-1950 cal. BCE, spanning the later part of the EB III and the entire EB IV period. These data strongly suggest a direct link between Faynan and the Old Kingdom of Egypt, which is reflected in the most significant phase of copper production and trade in the northern Arabah prior to the Iron Age, and in a settlement wave in the Negev Highlands. In addition, the results indicate that during the late EB II copper was smelted up to 40 km away from the mines. This is evident at the unique cultic site of Ashalim, located on the main road between Faynan, southeast of the Dead Sea, and the settled areas in the core of Canaan.