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X Congreso Geológico de España, 5-7 Julio 2021, Vitoria - Gasteiz, Reciente estudios arqueomagnéticos han detectado una caída en la intensidad del campo en torno al 3000 BP (Shaar et al., 2016). Este fenómeno se ha observado en distintas partes del mundo, como en Israel, Europa, y Corea. El principal objetivo de este estudio es ampliar nuestro conocimiento acerca del comportamiento espacial y temporal de dicho evento en la región de Asia central durante el I milenio AEC. Para esto se ha utilizado el protocolo de paleointensidad de Thellier en el tratamiento de 141 fragmentos cerámicos procedentes del sur de Uzbekistán. Los experimentos de magnetismo de rocas indican que los principales portadores magnéticos de las muestras son la magnetita y la titanomagnetita. Los resultados obtenidos confirman una caída drástica de la intensidad entre el 400 y el 100 AEC en la zona de Asia central. Por último, se han comparado los valores del Momento Dipolar Virtual Axial (VADM) con el valor del momento dipolar obtenido a partir del modelo global SHA.DIF.14k (Pavon-Carrasco et al., 2014).

Recent studies indicate the existence of rapid fluctuations of the geomagnetic field intensity over the last 3000 years. These features have been observed during the first millennium BCE in the Mediterranean area (from Western and Central Europe to the Near East), and in other regions as the Canary and the Azores Islands, China and Korea. Nevertheless, due to the difficulty to obtain precise secular variation intensity curves, the spatial and temporal extension of these events, and the potential link between the different regional events observed are still under discussion. In this study, we focus on the rapid intensity decrease that seems to take place in central Asia during the second half of the 1st millennium BCE. We present 51 new archeointensity from South Uzbekistan, obtained by Thellier-Thellier method, also, rock magnetism experiments have been conducted in order to identify the principal magnetic minerals responsible for the magnetization. The results of those experiments show that the maghemite and/or magnetite, in some cases with low titanium content, are the main magnetic carriers. New data together with 73 previous archaeointensity data, allow us to better defined geomagnetic field intensity changes in South Uzbekistan between 600 BCE and 600 CE. The results indicate a rapid drop out in intensity between 500 BCE and 200 BCE with a minimum of 37.2 µT around 200 BCE ¿ 50 CE. A comparison with different VADMs values available for different regions indicates that similar intensity trends are observed during this period at the continental scale. Finally, the results are compared with Axial Dipole Moment estimations derived from different global models, suggesting that this sharp continental decrease is controlled by non-dipolar sources.

Reunión MAGIBER XI Portugal ,Condeixa a Nova (4 al 6 de septiembre de 2019), The geomagnetic field is a global feature with an important regional character. Its temporal and spatial variation can be observed from direct measurements such as satellites and logbook available since the 17th century. In order to know the behaviour of the geomagnetic field further in the past indirect measurements are needed. These indirect measurements (called paleo or archeomagnetic data) are based on the study of the remanent magnetization acquired by the iron oxides present in certain rocks and archaeological materials when heated at high temperatures (Néel, 1955)., This work was supported by two R&D&I projects, CERAC (HAR2016-75133-C3-1-P) led by V. Martínez and J.M. Gurt, and CONCERAC (HAR2016-75133-C3-3-P) led by E. Ariño, all funded by the Spanish Ministry of Science, Innovation and Universities. V. Martínez worked on this paper through the post-doctoral research contract Ramón y Cajal (RYC-2014-15789). M. Gómez-Paccard thanks to RYC-2013-14405. This congress was funded by Red de trabajo y laboratorios MAGIBERII (CGL2017-90632-REDT).

Tis Article contains errors in the Discussion section.

AGU Fall Meeting 2019 in San Francisco, 9 – 13 December 2019, Recent archeomagnetic studies provide new evidences for rapid variations of the intensity of the geomagnetic field in the last millennia. In particular, during the first millennium BC, one of the biggest jerks of the geomagnetic field took place. This phenomenon has been observed in the Near East, Israel and Georgia, Germany and Western Europe. The main purpose of this work is to study the behaviour of the geomagnetic field intensity in Central Asia during the first millennium BC, a region and period of time for which very few high- quality paleointensity data are available. For this purpose, an archaeomagnetic study has been conducted over a collection of 68 ceramic fragments coming from three archaeological sites in the south of Uzbekistan: Kampyr Tepe, where samples from three different sites have been studied: the Citadel (-262 ± 113 BC), the ceramic workshop (-150 ± 50 BC) and the Lower City (-129 ± 41 BC); Kurganzol (-325 ± 75 BC); and Termez, where samples came from different stratigraphic units with ages between 350 BC and 350 AD. The Kurganzol collection has been dated by a variety of archaeological and historical constraints, while the Kampyr Tepe and Termez ceramics were dated by 8 different radiocarbon analyses. During the first stage of this work, rock magnetism experiments have been conducted on 43 samples in order to identify the principal magnetic minerals responsible for the remanent magnetization. The results show that magnetite and/or Ti-magnetite are the main magnetic carriers. In a second stage, we have conducted paleointensity experiments following the Thellier classical methodology, including the TRM and cooling rate corrections necessary to ensure the reliability of paleointensity estimations. The new results, together with prior high-quality data, confirm that the geomagnetic field underwent a steep dropout in intensity between 600 BC and 100 BC in Central Asia. Finally, the VADM values have been compared with the dipolar moment variation predicted by several global geomagnetic models. This comparison indicates that the VADM values are higher than global model estimations, which might indicate the strong influence of non-dipolar sources upon the rapid decrease observed.

Reunión MAGIBER XI Portugal ,Condeixa a Nova (4 al 6 de septiembre de 2019), A precise description of the evolution of the past geomagnetic field is important for the development of global and regional models, which can be applied to explain and predict the Earth’s magnetic field evolution and also can be used to archaeomagnetic dating. Few archaeomagnetic data before the third millenium BC are available in Europe, mainly due to the scarcity of appropriate archaeological remains for this time period. Recent archeomagnetic studies have demonstrated that burnt anthropogenic cave sediments related to stabling areas, also called fumiers in French archaeological terms, can provide a reliable record of the past geomagnetic field directions (Carrancho et al., 2009, 2013). The systematic archeomagnetic study of these materials combined with the available archaeomagnetic directions for this time interval, most of them derived from Eastern Europe, allowed the first European paleosecular variation curve for the Neolithic (Carrancho et al., 2013). Despite this improvement, more data, especially for Western Europe, are needed in order to better describe the evolution of the geomagnetic field in the past., The projects “Les Comunitats Prehistòriques del Massís de Garraf Nord. Fase 2. (CLT009/18/00034)”, “GEOMED (CGL2015-63888-R)” and the network ”MAGIBER-II (CGL2017-90632-REDT)” are acknowledged. Some of the authors are members of the consolidated research group 2017SGR596 of the Generalitat de Catalunya and the Geomodels Research Institute.

Coastal wetlands have been proposed as highly threatened by the ongoing and future climatic change, including projected sea-level changes as an additional forcing factor compared to more inland locations. The limited knowledge generated to date in this topic has been primarily focused in those areas attaining a high population density in the present-day, and rarely deals with long-term (>50 years) dynamics. Here we present the first Holocene palaeoecological study carried in the Orinoco Delta, in NE Venezuela. The record presented here, PATAM18_A12 (9º 30’ N - 62º 41’W, 13 m bsl), contains sediments from the last 6200 years and is located in a river-shore swamp dominated by the palm Mauritia flexuosa. This palm is very abundant in the region, and forms both extensive monospecific and mixed vegetation communities along the river courses. Current human occupation is almost restricted to small settlements of the Warao indigenous culture (known as the boat people), closely related to the use of M. flexuosa (which they refer to as the “tree of life”), and other palm species present in the zone. The results show the occurrence of three well-distinguished palynological zones: (i) from 6200 to 5200 cal yr BP, characterised by mangrove and other taxa related to salinity, low (negative) values of magnetic susceptibility and magnetic grain size, absence of transported clays, and the highest macrocharcoal particles abundance; (ii) from 5200 to 2950 cal yr BP, marked by a replacement of the mangrove vegetation by a more inland mixed-swamp forest community with low levels of charcoal, and (iii) from 2950 cal yr BP to present-day, characterised by the establishment of the current vegetation community, dominated by M. flexuosa, and an increasing trend in the charcoal curve since the last 700 years. Climatic changes have been proposed as the key driver influencing the vegetation succession recorded. The stabilisation of the sea-level that occurred during the mid-Holocene would have favoured the transgression of the coastal line, with the migration of the mangrove vegetation seawards. Around 2800 years ago, the decrease of the ENSO variability registered in the close Cariaco record likely influenced the expansion of the Mauritia palm community. It is suggested that in our location, the inhabiting human populations were differently influenced by these environmental changes. First, the disappearance of the coastal resources could have favoured the land abandonment, whereas the increase in the abundance of the palm might be influential for the arrival of other inland cultures that were previously used to manage Mauritia. This sequence shows the importance of the ecosystem services for the location inhabitants, highlighting the abandonment of the mid-Holocene culture coeval with the disappearance of its ecosystem. These results also provide information about the sensitivity or resilience in facing external stressors of both humans and vegetation, and will be valuable tools for managing the future of this ecosystem. Project refs.: 2014 BP-B-00094 and IJCI-2015-24273.

Improving geomagnetic field reconstructions clearly poses a high-priority challenge in Earth Sciences today. A better characterization of the variation of the geomagnetic field strength at centennial to millennial time scales is particularly crucial to disentangle the long-term evolution of the Earth´s dipole moment, a global characteristic of our planet. Here we present new high-quality archeointensities for Central Asia, a vast and rather poorly known region in terms of geomagnetic field intensity fluctuations. These new data are obtained from the study of 26 pottery fragments from Termez, a great urban and Buddhist religious center in ancient Bactria (south Uzbekistan) during the Kushan period. The samples have been collected in several sectors related to different stages of the occupation as demonstrated by 14C analysis: 1) two sectors in the alluvial plain (AC2 and AC1), dated to the Greco-Bactrian (from the 3rd to the 1st centuries BC) and the nomadic Yuezhi (≈1st century AD) periods respectively; 2) sector RC at the Tchingiz Tepe fortress, dated to the Kushan and Kushano-Sassanian periods (from the 2nd to the 4th centuries AD). The classical Thellier method including regular partial thermoremanent magnetization (pTRM) checks and TRM anisotropy and cooling rate corrections has been used for archeointensity determination. The new data obtained shed new light on the past fluctuation of geomagnetic field strength in Central Asia. In addition, a critical revision of archeointensity data from Central Asia is presented. Selected high-quality archeointensities are finally compared with regional and global geomagnetic field reconstructions.

Trabajo presentado en la X Reunión de la Comisión de Paleomagnetismo de la Sociedad Geológica de España, celebrada del 14 al 17 de septiembre de 2017 en el valle del río Grío, Zaragoza (España), En este trabajo se presenta una actualización de la base de datos direccional de Iberia para los últimos 3000 años (Gómez-Paccard et al., 2006) y el primer catálogo de intensidad para este periodo. En direcciones, la base de datos ha aumentado en más de un 80%, incluyendo más de 10 resultados direccionales no publicados hasta la fecha. En intensidades, este estudio representa un aumento de más del 50% en la cantidad de datos de calidad disponibles (si nos referimos al primer milenio a.C., se cuadruplica el número de datos), entendiendo datos de calidad como aquellos que cumplen los siguientes criterios: a) que el número de especímenes empleados para la determinación de la paleointensidad sea igual o superior a 4; b) que el protocolo empleado sea Thellier (Thellier y Thellier, 1959) o derivados; c) que la anisotropía de la imanación termorremanente haya sido investigada y corregida. Toda esta información ha permitido desarrollar nuevas curvas de variación paleosecular de declinación, inclinación e intensidad de Iberia para los tres últimos milenios. Se ha empleado el método bootstrap (Thébault y Gallet, 2010) incluyendo la jerarquía asociada a la información estratigráfica cuando estaba disponible. Las nuevas curvas direccionales no presentan grandes diferencias con las anteriormente publicadas (Fig. 1), aunque se incrementa su precisión. En intensidad las principales diferencias aparecen en el primer milenio a.C. y en el posible doble máximo en torno a 600-800 años d.C, que no es recogido por esta curva. Las nuevas curvas de variación paleosecular suponen una mejora en las posibilidades de la datación arqueomagnética en la península ibérica

Trabajo presentado en la X Reunión de la Comisión de Paleomagnetismo de la Sociedad Geológica de España, celebrada del 14 al 17 de septiembre de 2017 en el valle del río Grío, Zaragoza (España), En años recientes, las bases de datos de medidas arqueomagnéticas y volcánicas han crecido significativamente, aproximadamente un 40% en el caso de medidas direccionales y un 25% en medidas de intensidad. La mayor densidad de datos paleomagnéticos en Europa, en comparación con el resto del globo, permite desarrollar modelos regionales que cubran sólo esta zona, que se beneficien de una mayor resolución espacial y de la ausencia de influencia de outliers medidos fuera de la región. En este trabajo, se presenta un modelo regional de campo geomagnético actualizado que cubre los últimos tres milenios en Europa. El modelo ha sido obtenido utilizando la técnica R-SCHA-2D, que permite modelar el campo geomagnético sobre una porción en forma de casquete de la superficie de la tierra, aplicando métodos de regularización con significado físico. El campo magnético terrestre varía en el tiempo de forma continua, sujeta a observación directa sólo en la época reciente. Sin embargo, las medidas arqueo- y paleomagnéticas permiten conocer la naturaleza del campo geomagnético a lo largo de miles de años, aunque sólo en lugares e instantes puntuales. La modelización geomagnética permite generar reproducciones continuas del campo, mediante el ajuste de conjuntos de funciones matemáticas que representan el potencial magnético (Pavón-Carrasco et al. 2009, 2014, Constable et al., 2016). Uno de los usos más extendidos de los modelos de campo es la datación arqueomagnética, ya que permiten ubicar una medida en un tiempo dado según el grado de acuerdo con el modelo. Figura 1. Histogramas de las diferencias residuales entre el modelo y El conjunto de datos de partida está basado en la base de datos GEOMAGIA50.v3 (Brown et al., 2015), extendida utilizando la base de datos ArchaeoInt (Genevey et al., 2008). También se han utilizado datos de estudios recientes aún no incorporados a las bases de datos. La metodología de elaboración del modelo está basada en el método RSCHA-2D, descrito por Thebault 2008), que permite modelar campos vectoriales derivados de un potencial sobre un casquete esférico, y mejora el método clásico SCHA, descrito por Haines (1985). La modelización regional de datos DIF (declinación, inclinación, e intensidad, que resultan de medidas arqueo- y paleomagnéticas) conlleva varios problemas: el campo dipolar (que representa más del 90% del total) sólo puede ser representado regionalmente con armónicos de muy alto grado. Este obstáculo se puede sortear modelando sólo las diferencias locales entre el campo y un campo dipolar aproximado. Por otro lado, ya que los valores de declinación, inclinación e intensidad dependen de los coeficientes del modelo de forma no lineal, el problema debe ser linealizado antes de ser resuelto por inversión lineal. Finalmente, el problema inverso, en general, requiere añadir regularización para obtener soluciones con significado físico. Esto significa buscar una solución que minimice una norma elegida, que en nuestro caso es una combinación lineal de dB²r/dt² y B²r. Figura 2. Curvas de variación secular ubicadas en París para los últimos 3000 años, generadas con el modelo del presente estudio, comparadas con datos cercanos (a 900 km o menos de París, relocalizados vía polo), y con el modelo global SHA.DIF.14K. El modelo obtenido presenta un buen compromiso entre la suavidad temporal y espacial y el error rms respecto a los datos. Además, se ha estimado su error estadístico mediante una técnica bootstrap. Esto facilita su uso como herramienta de datación, permitiendo obtener no sólo una fecha estimada, sino también intervalos temporales de confianza para la datación.

Trabajo presentado en la International Conference on Rock Magnetism, celebrada en Utrech (Países Bajos) del 10 al 14 de julio de 2017, We present the first update of the archaeomagnetic data catalogue for the Iberian Peninsula covering the last 3000 years. The first archaeomagnetic data compilation for Iberia was published in 2006, including 63 archaeomagnetic directions and making possible the generation of the first directional Palaeosecular Variation Curve (PSVC) in Iberia. Since then, the number of directional data has increased by more than 80%, of which around 20% have been studied in this work. Regarding archaeointensity data, we present 20 new high quality archaeointensities, in addition to previously published ones (about 100 data), by creating the first archaeointensity catalogue for Iberia spanning the last 3000 years. The different qualities of the data included in this Iberian dataset have been evaluated following different palaeomagnetic criteria, such as the number of specimens analysed, the laboratory protocol applied and the kind of material studied. The improvement of the database is especially notable for the first millennium BC (about 50% of the new included data), a period for which there was not possible to develop an intensity palaeosecular variation curve due to the lack of high quality archaeointensity data. This new compilation of archaeomagnetic data has provided enough new information to generate the first PSVC of the geomagnetic full vector for Iberia for the last three millennia, which have been obtained by hierarchical bootstrap method using only selected high quality data from the catalogue in order to obtain the most reliable secular variation curve. No important differences between these curves and those calculated from regional and global geomagnetic field models are registered, with the most notable discrepancies observed in the intensity curve and during the first millennium BC. These new PSVCs offer a comprehensive view of the variations of the geomagnetic field in Iberian Peninsula and is suitable as a Master Curve in the archaeomagnetic dating technique for archaeological combustion structures located in this region.

Trabajo presentado en la European Geosciences Union General Assembly, celebrada en Viena (Austria), del 23 al 28 de abril de 2017, In 2006, the first Iberian archaeomagnetic catalogue for the last 3000 years was presented, including 63 archaeomagnetic directions coming from Spanish archaeological sites. Since then, several archaeomagnetic studies have been carried out in order to cover the main temporal gaps present in this catalogue: the first millennium BC and the Late Roman – High Middle Ages. In this work, the first update of this catalogue is proposed. The directional database has increased by more than 80% (around 50 new data), of which more than 10 palaeodirections come from new studies that had not been previously published. The improvement of the database is especially notable in the first millennium BC, representing more than 50% of the available data in the first directional catalogue for Iberia (around 30 directions). This updated database has provided enough new information to generate a revised directional Palaeosecular Variation Curve (PSVC) for Iberia spanning the last three millennia using the bootstrap technique. This new PSVC offers a comprehensive view of the evolution of the geomagnetic field in this region and is suitable as a Master Curve in the archaeomagnetic dating technique for archaeological combustion structures located in the Iberian Peninsula.

Trabajo presentado en la European Geosciences Union General Assembly, celebrada en Viena (Austria), del 23 al 28 de abril de 2017, In 2006, the first Iberian archaeomagnetic catalogue for the last 3000 years was presented, including 63 archaeomagnetic directions coming from Spanish archaeological sites. Since then, several archaeomagnetic studies have been carried out in order to cover the main temporal gaps present in this catalogue: the first millennium BC and the Late Roman – High Middle Ages. In this work, the first update of this catalogue is proposed. The directional database has increased by more than 80% (around 50 new data), of which more than 10 palaeodirections come from new studies that had not been previously published. The improvement of the database is especially notable in the first millennium BC, representing more than 50% of the available data in the first directional catalogue for Iberia (around 30 directions). This updated database has provided enough new information to generate a revised directional Palaeosecular Variation Curve (PSVC) for Iberia spanning the last three millennia using the bootstrap technique. This new PSVC offers a comprehensive view of the evolution of the geomagnetic field in this region and is suitable as a Master Curve in the archaeomagnetic dating technique for archaeological combustion structures located in the Iberian Peninsula.

Trabajo presentado en la X Reunión de la Comisión de Paleomagnetismo de la Sociedad Geológica de España, celebrada del 14 al 17 de septiembre de 2017 en el valle del río Grío, Zaragoza (España), The rate of production of cosmogenic isotopes, such as 14C or 10Be, plays an important role in our understanding of the solar-terrestrial relationship since radionuclides records stored in polar ice cores and tree rings offer the unique way to reconstruct changes in the solar total irradiance during the Holocene (see Usoskin, 2017, for a review). To accurately determine past solar activity, the effect of the variability of the geomagnetic field upon the production of cosmogenic radionuclides needs to be properly considered since the Earth´s magnetic field greatly modulates the rate of isotope production in the atmosphere. Up to now, it has been assumed that the long-term time variation of isotope production rate is mainly modulated by changes in the geomagnetic field whereas the solar magnetic field dominates shorter time wavelengths (Snowball and Muscheler, 2007; Usoskin et al., 2016). Here we reanalyse this assumption by demonstrating that the geomagnetic field also exerts a strong modulation of high-frequency (periods of ∼800 yr) atmospheric radiocarbon production rates that are currently being wrongly associated to solar activity. Specifically, we identify for the first time a clear and robust coherence, in terms of amplitude and phases, between the production rate curve directly derived from the geomagnetic field reconstruction derived from the SHA.DIF.14k global model (PavónCarrasco et al., 2014) and the original isotope production curve for the Holocene (Steinhilber et al., 2012). Our results provide a new vision of the mechanisms causing the observed isotope production variability and, hence, are crucial to re-evaluate past solar forcing and use it as a benchmark to test links between climate and total solar irradiance in the next generation of climate models.

Trabajo presentado en la International Conference on Rock Magnetism, celebrada en Utrech (Países Bajos) del 10 al 14 de julio de 2017, Improving geomagnetic field reconstructions clearly poses a high-priority challenge in Earth Sciences today. A better characterization of the variation of the geomagnetic field strength at centennial to millennial time scales in the southern hemisphere is particularly crucial to disentangle the long-term evolution of the Earth's dipole moment, a global characteristic of our planet. Here we present new high-quality archeointensities obtained from the study of four collections of well-dated pottery fragments from La Puna (Northwest Argentina). The classical Thellier method including regular partial thermoremanent magnetization (pTRM) checks and TRM anisotropy and cooling rate corrections has been used for archeointensity determination. The new data obtained shed new light on the past fluctuation of geomagnetic field strength in South America, a rather poorly known region in terms of geomagnetic field intensity fluctuations. In addition, the results confirm that TRM anisotropy corrections are an essential requirement when studying past geomagnetic field strength from the archeomagnetic study of pottery fragments. Future geomagnetic field reconstructions do well to have the TRM anisotropy requirement in mind when trying to unravel geomagnetic field variations from pottery-based archeointensity data, both at regional or global scales.

PROJECT AIMS: The paucity of palaeoecological data is acute in the Neotropics, where the low number of good quality records (with reliable dating and continuous sedimentation) prevents the development of a regional understanding of the vegetation and climate dynamics. Within the Neotropics, low wetlands are particularly poorly known due to the scarcity of potential archives. We present here an ongoing project designed to improve the understanding of wetland forests' responses to changes in climatic and human variability by studying their long-term dynamics. The project will focus on specific scales for maximising the accuracy of the outputs: I) the geographic area (northern South American wetlands), and ii) the time period (last 6 kyr). The region has been chosen because of the occurrence of globally important big wetland areas dominated by the palm Mauritania flexuosa and the perceived threats to the fluvial-linked systems. Within this broad area, two specific locations have been chosen that represent the northern limit of M. flexuosa current distribution. Time frame has been selected to allow: i) the comparison between intervals with and without human activity, and ii) covering the establishment of Mauritania which will allow a better understanding of the current trends (communities in expansion or reduction). The knowledge of past interactions between wetlands, seasonality changes and human practices will provide new insights into how this poorly understood community could face future projections of climatic and land use changes. In addition, emphasis will be placed on studying what influenced the composition of modern plant communities, to analyse their sensitivity to external drivers and to identify the occurrence of irreversible tipping points or thresholds in the recent past. The research will be addressed by using a combination of indicators (proxies) of past environmental change in sedimentary sequences, including: vegetation (pollen), erosion/run-off/sedimentation (palaeomagnetism, XRD), and human impacts (non-pollen palynomorphs, charcoal particles). Funding project reference: 2014 BP-B-00094.

Trabajo presentado en la X Reunión de la Comisión de Paleomagnetismo de la Sociedad Geológica de España, celebrada del 14 al 17 de septiembre de 2017 en el valle del río Grío, Zaragoza (España), Estudios recientes realizados en distintas regiones como Oriente Medio o Europa (Gallet et al., 2003; Shaar et al., 2016, Gómez-Paccard et al., 2016, entre otros) han mostrado que el campo magnético terrestre ha experimentado en el pasado reciente fuertes sacudidas de su intensidad en escalas de tiempo multidecadales. Debido a la escasez de datos de paleointensidad de alta calidad, las características y orígenes de estos eventos no están aún claros. El objetivo principal que nos proponemos en este trabajo es investigar la variabilidad temporal y espacial de los dos máximos de intensidad más importantes ocurridos en Europa durante los últimos milenios: el máximo del final de la edad del Bronce y la fluctuación rápida del periodo Romano tardío (Ertepinar et al., 2012; Gómez-Paccard et al., 2016). Para ello se obtendrán nuevos datos de intensidad a partir de hornos, hogares y cerámicas procedentes de 35 contextos arqueológicos de la zona del Mediterráneo de cronología bien determinada y correspondiente a los periodos mencionados. Para obtener datos de intensidad de alta calidad se aplicará el método clásico de Thellier (Thellier y Thellier, 1959) incluyendo tests de alteración (los llamados pTRM checks), y se realizarán las correcciones de anisotropía de la termoremanencia y de la velocidad de enfriamiento. Este método se basa principalmente en calentar y enfriar los especímenes a diferentes temperaturas en presencia de un campo magnético controlado y uniforme de intensidad conocida. Este proceso se repite dos veces por cada temperatura, uno aplicando el campo en el eje Z positivo y otro en negativo. Cada dos etapas de temperatura se realizará un pTRM check con el objetivo de investigar si se generan o destruyen minerales debido a procesos químicos producidos durante el calentamiento de las muestras en el laboratorio. Se estudiarán varias muestras por contexto y varios especímenes por muestra. Los nuevos datos que se obtendrán cumplirán, por tanto, estándares estrictos de calidad. También se realizarán estudios de magnetismo de rocas con el fin de identificar los principales minerales portadores de la magnetización. En este trabajo se mostrarán los resultados preliminares de paleointensidad obtenidos para tres localidades estudiadas en Grecia: Dikili-Tash (DT), Mochlos (MLO) y Velika (VE) y se expondrá las implicaciones de los resultados obtenidos en el contexto del estudio de las variaciones rápidas de intensidad.

Trabajo presentado en la International Conference on Rock Magnetism, celebrada en Utrech (Países Bajos) del 10 al 14 de julio de 2017, One of the most important applications of the study of geomagnetic field variations in the recent past is archeomagnetic dating. This method is based on the comparison between well-established regional geomagnetic field secular variation curves or models and the archeomagnetic signal acquired and preserved by well-heated archeological structures. In this work we illustrate how this method can provide a powerful tool to date archeological remains that can not be properly dated by other archeological and geochronological methods. In particular, we present the archeomagnetic study of several archeological kilns sampled in two archeological sites from the Eastern part of the Iberian Peninsula. The studied kilns clearly correspond to the First Iron Age, period that has been classically dated in the Iberian Peninsula between 675 and 575 BC based on ceramic typology studies. However, new archeological evidences challenge this classical view since the impressive number of cultural and technological advances recently discovered in different archeological excavations can be hardly ascribed to this very short interval of time, suggesting that the First Iron Age in this region corresponds probably to a longer period of time. In order to test this hypothesis we apply here the archeomagnetic dating method and present the dating results obtained from both regional secular variation curves and geomagnetic field models.

Trabajo presentado en IAPSO-IAMAS-IAGA Assembly, celebrada en Cape Town (Sudáfrica), del 27 de agosto al 1 de septiembre de 2017, The production rates of cosmogenic isotopes, such as 14C and 10Be, are directly modulated by the strength of the Solar and Earth magnetic fields. Changes in the isotope production rate during the Holocene are estimated mainly from isotopic sampling in tree and ice cores, while the past evolution of the geomagnetic field can be recovered from well‐dated rock samples containing magnetic minerals than can be used to obtain the so‐called paleomagnetic data. However, no indirect measurements provide the past solar activity. Estimates of solar forcing play an important role in understanding paleoclimatic temperature reconstructions and as boundary conditions in simulations with climate models due to its influence to modify the energy balance of the Earth. Nowadays, different studies consider that both magnetic fields affect the production rate at two different timescales: the long‐term modulation is associated to changes in the geomagnetic field and the shorter variations to the past solar activity. However, the most recent palaeomagnetic reconstructions developed during the last years provide a new picture with higher temporal resolution of the past variations of the strength of the Earth’s magnetic field. In this work, we revisit the connection between the past evolution of the Earth’s magnetic field and the production rates of 14C and 10Be for the Holocene by means of the more complete paleomagnetic database and the most recent geomagnetic reconstructions.