Archaeomagnetism is an area of research that utilises the magnetic properties of archaeological materials to date past human activity. This research aimed to use the evidence of past geomagnetism, as recorded by archaeological and geological materials, to identify and characterise short timescale changes in the Earth¿s magnetic field. This contribution to the discipline focused on the first millennium BC, as there is evidence that during this time the Earth¿s magnetic field experienced rapid changes in direction. This work focused on an established weakness in archaeomagnetic studies, i.e. the application of archaeological information to assign a date range to the magnetic directions. The date ranges for 232 magnetic directions from 98 Iron Age sites were reviewed and a programme of fieldwork produced 25 new magnetic directions from 11 Iron Age sites across Britain. The approach developed in this thesis has made significant improvements to the data examined, which represent the prehistoric section of the British secular variation curve (SVC). These data have been incorporated into the British archaeomagnetic dataset that now comprises over 1000 magnetic directions and will be used to generate future British SVCs. The potential of the near continuous records of geomagnetic secular variation from British lake sediment sequences to SVCs was explored. This showed that these sediments have recorded the relative changes in the Earth¿s magnetic field but the dating and method of constructing the British master curve requires revision. As SVCs are predominately used as calibration curves for archaeomagnetic dating, this work provides a foundation for a revised and extended British SVC. This revision would be to the mutual benefit of studies in archaeology and archaeomagnetism, as the latter could potentially enable highresolution dating of Iron Age material, providing a viable alternative to radiocarbon dating.

Archaeomagnetism is an area of research that utilises the magnetic properties of archaeological materials to date past human activity. This research aimed to use the evidence of past geomagnetism, as recorded by archaeological and geological materials, to identify and characterise short timescale changes in the Earth¿s magnetic field. This contribution to the discipline focused on the first millennium BC, as there is evidence that during this time the Earth¿s magnetic field experienced rapid changes in direction. This work focused on an established weakness in archaeomagnetic studies, i.e. the application of archaeological information to assign a date range to the magnetic directions. The date ranges for 232 magnetic directions from 98 Iron Age sites were reviewed and a programme of fieldwork produced 25 new magnetic directions from 11 Iron Age sites across Britain. The approach developed in this thesis has made significant improvements to the data examined, which represent the prehistoric section of the British secular variation curve (SVC). These data have been incorporated into the British archaeomagnetic dataset that now comprises over 1000 magnetic directions and will be used to generate future British SVCs. The potential of the near continuous records of geomagnetic secular variation from British lake sediment sequences to SVCs was explored. This showed that these sediments have recorded the relative changes in the Earth¿s magnetic field but the dating and method of constructing the British master curve requires revision. As SVCs are predominately used as calibration curves for archaeomagnetic dating, this work provides a foundation for a revised and extended British SVC. This revision would be to the mutual benefit of studies in archaeology and archaeomagnetism, as the latter could potentially enable highresolution dating of Iron Age material, providing a viable alternative to radiocarbon dating. / Available full-text since June 30th 2013, at the end of the embargo period. / Lab data and appendices 3 and 4 are unavailable online.

L’objectif de ce travail est l’amélioration des courbes de variation séculaire de la direction (inclinaison I et déclinaison D) et de l’intensité (F) du champ magnétique terrestre en Europe occidentale durant le premier millénaire av. J.-C. 47 fours, foyers et lots de tessons céramiques ont été étudiés pour constituer de nouvelles structures de référence. La datation du moment d’acquisition de l’aimantation a été définie en analysant l’ensemble des informations archéologiques et chronométriques disponibles sur les sites. 39 nouvelles archéodirections ont été obtenues après désaimantations thermique et par champ alternatif. Les 18 archéointensités ont été déterminées par le protocole de Thellier-Thellier et généralement corrigées des effets de l’anisotropie et de la vitesse de refroidissement. Les courbes de variation séculaire françaises, construites par moyenne mobile et par la statistique hiérarchique bayésienne, ont été étendues jusqu’en 1500 av. J.-C. pour la direction et jusqu’en 800 av. J.-C. pour l’intensité. L’inclinaison a une variation non monotone entre 65 et 75° entre 1500 et 0 av. J.-C. Les variations de la déclinaison et de l’intensité sont très fortes avec un maximum en 800 av. J.-C. (30° pour D et 90 µT pour F) et un minimum (-5° pour D et 60µT pour F) en 250 av. J.-C. L’interprétation géomagnétique de la variation séculaire est difficile en raison des lacunes des jeux de données de référence hors Europe. Ces nouvelles courbes plus fiables améliorent la datation archéomagnétique au premier millénaire av. J.-C. et étendent son application à l’âge du Bronze final. Du fait de la forte variation séculaire, le premier âge du Fer est la période la plus propice. / This study aims to improve the Western Europe secular variation curve of the direction (inclination I and declination D) and the intensity (F) of the Earth’s magnetic field during the first millennium BC. New archaeomagnetic reference data were obtained from 47 kilns, hearths and sets of pottery sherds with precise magnetization acquisition ages determined through a comprehensive review of available archaeological and chronometric informations. 39 new archaeodirections were computed after thermal and alternating field demagnetizations and 18 new archaeointensities were determined by the Thellier-Thellier protocol with anisotropy and cooling rate corrections. The new French secular variation curves, built using hierarchical bayesian statistics, were extended to 1500BC for the direction and to 800BC for the intensity. Inclination vary non-monotonously (between 65 and 75°) between 1500BC and 0AD. Variations in declination and intensity are very strong with a maximum at 800BC (30° for D and 90µT for F) and a minimum at 250BC (-5° for D and 60µT for F). Interpreting the geomagnetic significance of this strong variation is hindered by the scarcity of data outside Europe. However it provides a useful marker for reliable archaeomagnetic dating in Western Europe during the Iron Age, especially during the Early Iron Age thanks to the strong secular variation. The new directional curve also allows the extension of archaeomagnetic dating to the Final Bronze Age.