Papers by Gwenael Herve
La datation archéomagnétique porte sur deux fours découverts dans la ville basse de Cumes, un fou... more La datation archéomagnétique porte sur deux fours découverts dans la ville basse de Cumes, un four de tuilier retrouvé dans la nécropole de la Porte médiane et un four de potier retrouvé près de la Cava greca. Les deux fours sont datés par la stratigraphie et la typochronologie entre le ve et le viie siècle apr. J.-C. Les échantillons, prélevés par carottage dans les briques des parois des fours, ont été analysés par désaimantation thermique et par le protocole de Thellier-Thellier. Les deux fours donnent de très bons résultats d’archéointensité et présentent un très bon regroupement des directions d’aimantation. La différence signi cative entre les deux archéointensités moyennes indique que la n du fonctionnement des deux fours n’est pas contemporaine. La datation archéomagnétique a été réalisée avec les prédictions à Cumes du modèle géomagnétique européen SCHA.DIF.3k. Le four de la Cava greca est daté entre 590 et 640 apr. J.-C. à 95 % de con ance. Au même niveau de confiance, le four FR59006 de la nécropole de la Porte médiane est daté entre 540 et 645 apr. J.-C. La seconde moitié du vie siècle apparaît la période la plus probable. Ces deux datations archéomagnétiques confortent et précisent les datations archéologiques. Nos résultats placent le fonctionnement des deux secteurs artisanaux à l’époque byzantine et documentent les réappropriations médiévales de la ville antique.
The archaeomagnetic study focuses on two kilns, unearthed in the lower city of Cumae, a tile kiln in the necropolis of the Median Gate and a pottery kiln at the Cava greca. The two kilns are dated between the Vth and the VIIth century AD by the stratigraphy and the typochronology. Archaeomagnetic samples, cored in the bricks of the kiln walls, were analyzed by thermal demagnetization and by the Thellier-Thellier protocol. The two kilns provide very good archaeointensity results and the directions of the thermoremanent magnetization are well grouped. The significant difference between the two mean archaeointensities indicates that the last use of the two kilns were not contemporaneous. Archaeomagnetic dating is performed with the predictions at Cumae of the European model of the geomagnetic field SCHA.DIF.3k. The kiln from the Cava greca is dated between 590 and 640 AD at 95 per cent of confidence. At the same confidence level, the kiln FR59006 from the necropolis of the “Median Gate” is dated between 540 and 645 AD. The second half of the VIth century appears the most probable dating. These two archaeomagnetic datings concur and precise the archaeological dating. Our results date the use of the workshops in the Byzantine period and document the medieval changes of the antique city.
… 2010, held 2-7 May …, 2010
Directional archaeomagnetic reference curves have been published for Austria and Germany some yea... more Directional archaeomagnetic reference curves have been published for Austria and Germany some years ago. Recent determination of new archaeomagnetic directions was mainly concentrated on time intervals with only sparse data. About 60 new directions have ...
Geophysical Journal International, 2011
Variations of the Earth's magnetic field during the first millennium BC in western Europe remain ... more Variations of the Earth's magnetic field during the first millennium BC in western Europe remain poorly constrained, especially archaeointensity changes. Three salt-kilns (MOA, MOB and MOC) sampled in Moyenvic (Lorraine, eastern France) have been studied to provide new reference data. Each kiln has been dated by radiocarbon to originate from the Early Iron Age or Hallstatt period (between VIII and Vth Century BC). Rock magnetic experiments and hysteresis results suggest the predominance of pseudo-single domain (PSD) Ti-poor magnetite. Archaeomagnetic directions obtained by thermal and alternating field demagnetizations have high mean inclination (close to 70 • ) and declination (between 19 and 31 • ). A first set of classical Thellier-Thellier experiments was conducted on 46 samples with a laboratory field almost parallel to the direction of the characteristic remanent magnetization (ChRM). Only 24 of these specimens present a linear NRM-TRM plot. For other specimens, NRM-TRM plots are concave-up with positive pTRM checks. The very large dispersion observed between the determined palaeointensity values suggests some artefacts have not been fully recognized. A second set of Thellier experiments was conducted on 34 sister specimens with the laboratory field applied quasi-perpendicular to the ChRM. In these cases, mineralogical evolutions during heating and chemical remanent magnetization acquisitions have been clearly recognized, despite positive pTRM checks. The concave-up shapes of NRM-TRM plots appear mainly due to mineralogical alteration rather than to the presence of PSD-MD grains. For the entire set of samples the success rate of the palaeointensity determinations is very low with 80 per cent of the samples rejected. Nevertheless, reliable mean archaeointensities have been obtained for two of the three kilns (MOA, 80.1 ± 14.5 µT and MOB, 86.6 ± 6.9 µT at the latitude of Paris). The high field strength and the archaeomagnetic directions determined, combined with previous published data, provide further evidence for important changes of the Earth magnetic field in Europe during the first half of the first millennium BC. These large variations of the geomagnetic field during the Iron Ages indicate that archaeomagnetism is highly suitable for dating of structures from this period.
Recent excavations at Corent (France) unearthed a vast Late Bronze Age settlement. The high densi... more Recent excavations at Corent (France) unearthed a vast Late Bronze Age settlement. The high density of fireplaces especially highlights it. The present study focuses on the archaeomagnetic study of five fireplaces. These ones were dated between 950 and 800 BCE by cross-dating of metallic and ceramic artefacts and by radiocarbon. The main objective of our study is to increase the archaeointensity database in Western Europe at the beginning of the first millennium BCE. The sampling was conducted on 64 fragments of baked clay and sherds from the fireplaces floor. The classical Thellier-Thellier protocol provides 48 successful archaeointensity results, yielding to five mean values between 58 and 69 μT at the site. Together with previously published results, our new data point out two successive maxima of the intensity of the geomagnetic field. The first maximum ~70 μT in the ninth century BCE and the second ~90 μT in ~ 700 BCE are separated by a ~45–50 μT minimum at ~800–750 BCE. The resulting fast variation of the field intensity will be very useful for archaeomagnetic dating purposes. As the direction of the geomagnetic field has also a strong variation during this period (Hervé et al. 2013a), archaeomagnetism promises to be a powerful dating tool to recover the historical processes at the transition between the Bronze and Iron Ages in Western Europe.
Hervé, G., Gilder, S., Marion, C.L., Osinski, G.R., Pohl, J., Petersen, N., Sylvester, P., 2015
La collection Bibracte est éditée par BIBRACTE, Centre archéologique Européen. Du nom antique de ... more La collection Bibracte est éditée par BIBRACTE, Centre archéologique Européen. Du nom antique de la capitale des Éduens, elle rassemble tout d'abord les résultats des recherches effectuées sur le site du Mont Beuvray et le territoire éduen, ensuite les actes des rencontres scientifiques organisées par le Centre archéologique, enfin des travaux majeurs relatifs à l'archéologie de l'Europe celtique. Le comité de lecture de la collection est constitué des membres du Conseil scientifique de bibracte. Études sur Bibracte -2 sous la direction de Vincent GUICHARD Collection Bibracte -24 BiBracte -Centre archéologique européen F -58370 Glux-en-Glenne 2014 Couverture : Estampage imitant un coin monétaire sur les anses d'une cruche découverte au Theurot de la Wivre (B2005.38.246.2 ; cliché Bibracte/A.Maillier 2009, n° 77208). Notice catalographique Guichard (V.) dir., Études sur Bibracte -2. Glux-en-Glenne : Bibracte, 2014 (Bibracte ; 24, ISSN 1281-430X) 378 pages, 275 illustrations, 27 planches, annexes. Premier élément date et référence bibliographique GuIChARD (V.) dir. -Études sur Bibracte -2. Glux-en-Glenne : Bibracte, 2014, 378 p., 275 ill., 27 pl. (Bibracte ; 24).
This study aims to improve the Western Europe secular variation curve of the direction (inclinati... more 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 Late Bronze Age.
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.
Hervé Gwenaël, Chauvin Annick & Lanos Philippe, 2013
To improve the geomagnetic field secular variation curve (SVC) of Western Europe during protohist... more To improve the geomagnetic field secular variation curve (SVC) of Western Europe during protohistoric times, archaeomagnetic directions of 39 archaeological kilns or hearths from France were investigated. The dating of each archaeological structure was established with archaeological or chronometric meth- ods. Thirty-seven of these structures are dated from the first millennium BC, one from the end of the sec- ond millennium BC and the last one from the fourth millennium BC. Thermomagnetic curves, unblocking temperatures and coercivities suggest that the main carrier of the remanent magnetization is a Ti-poor titanomagnetite. Archaeodirections were obtained by alternating field and thermal demagnetizations on almost 900 specimens. The anisotropy tensor of thermoremanent magnetization was determined for 35 structures and 22 mean archaeodirections were corrected for anisotropy. The new archaeodirec- tions are very consistent with previously published data. A new directional SVC was built using bivariate statistics with selected Western Europe data located within 1000 km of Paris. Selection criteria include the number of samples, the dating reliability and the accuracy of the mean archaeodirection. Resulting secular variation between 1500BC and 0AD mainly shows large changes in declination, while inclinations are bracketed between ﰀ65° and ﰀ75°. The declinations show a strong maximum with values ﰀ30–35° around 800–750BC, followed by a sharp decrease to values around 0° at 500BC and close to ﰁ7° around 250BC. The main features of the secular variation from 1500BC to 0AD appear to be a dominant westward drift and two major changes around 800 and 250BC. Compared to the global and regional geomagnetic models, the new reference data are better fitted by ARCH3k_cst.1 and SCHA.DIF.3k than by ARCH3k.1 and CALS3k.4 models. The strong variation of the archaeodirection between 1000 and 500BC makes archaeomagnetism very useful for dating purposes.
Hervé Gwenaël, Chauvin Annick & Lanos Philippe, 2013
In order to extend the secular variation curve (SVC) of archaeointensity in Western Europe to the... more In order to extend the secular variation curve (SVC) of archaeointensity in Western Europe to the first millennium BC, we studied 24 kilns and hearths in place, 2 displaced hearths and 6 sets of pottery sherds from French archaeological sites. Archaeological artefacts, radiocarbon and dendrochronology dated the acquisition of the thermoremanent magnetization (TRM) carried by the studied objects. Rock magnetism experiments suggest that the main carrier of the magnetization is a Ti-poor titanomagnetite. Archaeointensity was determined by the Thellier-Thellier classical protocol with pTRM-checks. A strict criteria set was applied to select only the most reliable results with linear NRM-TRM diagrams (55% of total specimens). This study demonstrates that pottery sherds with two TRMs give reliable archaeointensities in the low-temperature interval, if the NRM-TRM diagram is adequately adjusted. Eighteen new mean archaeointensities (14 corrected from the anisotropy of TRM and 16 from cooling rate) were computed. The comparison with previously published Western Europe paleointensities show a strong dispersion between data primarily due to their variable quality. Western Europe data were weighted following the archaeointensity protocol, the number of specimens per site and the type of studied materials, in order to better highlight the secular variation of archaeointensity during the first millennium BC. The SVC, built with sliding windows of 160 years shifted every 50 years, presents (at Paris) a maximum of 90µT around 800BC and a minimum of 60µT around 250BC. These archaeointensity maximum and minimum correspond to cusps of the geomagnetic field direction in Western Europe. This new curve is consistent with Mesopotamian and Eastern Europe data. The archaeointensity secular variation in Western Europe predicted by global geomagnetic models CALS3k.4, ARCH3k.1 and ARCH3k_cst.1 is smoother than our SVC. We used our directional dataset (Hervé et al., 2012a) to build a new Western Europe VGPs and VDMs mean curves. Comparison with the predictions given by the global models points out a possible persistent non-dipole fields effect over Europe between 1000BC and 600-500BC. Finally, we note that the strong variations of intensity of the geomagnetic field (with a mean decrease rate per century close to 6µT) will be useful for archaeomagnetic dating purposes.
Hervé Gwenaël, Schnepp Elisabeth, Chauvin Annick & Lanos Philippe, 2011
Variations of the Earth’s magnetic field during the first millennium BC in western Europe remain ... more Variations of the Earth’s magnetic field during the first millennium BC in western Europe remain poorly constrained, especially archaeointensity changes. Three salt-kilns (MOA, MOB and MOC) sampled in Moyenvic (Lorraine, eastern France) have been studied to provide new reference data. Each kiln has been dated by radiocarbon to originate from the Early Iron Age or Hallstatt period (between VIII and Vth Century BC). Rock magnetic experiments and hys- teresis results suggest the predominance of pseudo-single domain (PSD) Ti-poor magnetite. Archaeomagnetic directions obtained by thermal and alternating field demagnetizations have high mean inclination (close to 70◦) and declination (between 19 and 31◦). A first set of classical Thellier–Thellier experiments was conducted on 46 samples with a laboratory field almost parallel to the direction of the characteristic remanent magnetization (ChRM). Only 24 of these specimens present a linear NRM–TRM plot. For other specimens, NRM–TRM plots are concave-up with positive pTRM checks. The very large dispersion observed between the determined palaeointensity values suggests some artefacts have not been fully recognized. A second set of Thellier experiments was conducted on 34 sister specimens with the laboratory field applied quasi-perpendicular to the ChRM. In these cases, mineralogical evolutions during heating and chemical remanent magnetization acquisitions have been clearly recognized, de- spite positive pTRM checks. The concave-up shapes of NRM–TRM plots appear mainly due to mineralogical alteration rather than to the presence of PSD–MD grains. For the entire set of samples the success rate of the palaeointensity determinations is very low with 80 per cent of the samples rejected. Nevertheless, reliable mean archaeointensities have been obtained for two of the three kilns (MOA, 80.1 ± 14.5 μT and MOB, 86.6 ± 6.9 μT at the latitude of Paris). The high field strength and the archaeomagnetic directions determined, combined with previous published data, provide further evidence for important changes of the Earth magnetic field in Europe during the first half of the first millennium BC. These large variations of the geomagnetic field during the Iron Ages indicate that archaeomagnetism is highly suitable for dating of structures from this period.
Landreau Guilhem, Guitton David & Hervé Gwenaël, 2012
Bouchet Marion, Hervé Gwenaël & Surgent Marianne, 2009
Drafts by Gwenael Herve
Current value Archaeomagnetic dating is usually based only on directional parameters (inclination... more Current value Archaeomagnetic dating is usually based only on directional parameters (inclination and declination) of the geomagnetic eld. The intensity is not commonly used because the data, and thus the reference secular variation curve are more diicult to recover. Worldwide archaeointensities suggest that the period from 1400 to 400 BC, and especially from 1000 to 800 BC, is charecterized by the greatest variability in geomagnetic eld strength over the entire Holocene epoch. In West-Central Europe, the potential to use archaeomagnetic dating remains limited by the few available reference data during the Late Bronze and Early Iron Ages. Here, we present 21 new mean archaeointensities from pottery sherds collected from eight sites in southern Bavaria.
Excavation reports by Gwenael Herve
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Papers by Gwenael Herve
The archaeomagnetic study focuses on two kilns, unearthed in the lower city of Cumae, a tile kiln in the necropolis of the Median Gate and a pottery kiln at the Cava greca. The two kilns are dated between the Vth and the VIIth century AD by the stratigraphy and the typochronology. Archaeomagnetic samples, cored in the bricks of the kiln walls, were analyzed by thermal demagnetization and by the Thellier-Thellier protocol. The two kilns provide very good archaeointensity results and the directions of the thermoremanent magnetization are well grouped. The significant difference between the two mean archaeointensities indicates that the last use of the two kilns were not contemporaneous. Archaeomagnetic dating is performed with the predictions at Cumae of the European model of the geomagnetic field SCHA.DIF.3k. The kiln from the Cava greca is dated between 590 and 640 AD at 95 per cent of confidence. At the same confidence level, the kiln FR59006 from the necropolis of the “Median Gate” is dated between 540 and 645 AD. The second half of the VIth century appears the most probable dating. These two archaeomagnetic datings concur and precise the archaeological dating. Our results date the use of the workshops in the Byzantine period and document the medieval changes of the antique city.
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.
Drafts by Gwenael Herve
Excavation reports by Gwenael Herve
The archaeomagnetic study focuses on two kilns, unearthed in the lower city of Cumae, a tile kiln in the necropolis of the Median Gate and a pottery kiln at the Cava greca. The two kilns are dated between the Vth and the VIIth century AD by the stratigraphy and the typochronology. Archaeomagnetic samples, cored in the bricks of the kiln walls, were analyzed by thermal demagnetization and by the Thellier-Thellier protocol. The two kilns provide very good archaeointensity results and the directions of the thermoremanent magnetization are well grouped. The significant difference between the two mean archaeointensities indicates that the last use of the two kilns were not contemporaneous. Archaeomagnetic dating is performed with the predictions at Cumae of the European model of the geomagnetic field SCHA.DIF.3k. The kiln from the Cava greca is dated between 590 and 640 AD at 95 per cent of confidence. At the same confidence level, the kiln FR59006 from the necropolis of the “Median Gate” is dated between 540 and 645 AD. The second half of the VIth century appears the most probable dating. These two archaeomagnetic datings concur and precise the archaeological dating. Our results date the use of the workshops in the Byzantine period and document the medieval changes of the antique city.
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.