EVENT MODEL: A ROBUST BAYESIAN TOOL FOR CHRONOLOGICAL MODELING

We propose a new modeling approach for combining dates through the Event model by using hierarchical Bayesian statistics. The Event model aims to estimate the date of a context (unit of stratification) from individual dates assumed to be contemporaneous and which are affected by errors of different types: laboratory and calibration curve errors and also irreducible errors related to contaminations, taphonomic disturbances, etc, hence the possible presence of outliers. The Event model has a hierarchical structure which makes it possible to distinguish between date of an Event and dates of the artifacts involved. Prior information on the individual irreducible errors is introduced using a uniform shrinkage density with minimal assumptions about Bayesian parameters. The model is extended in the case of stratigraphic sequences which involve several Events with temporal order constraints (relative dating). Calculations are based on MCMC numerical techniques and can be performed using the ChronoModel software which is freeware, open source and cross-platform. This modeling provides a very simple way to automatically penalize outlying data without having to remove them from the dataset. This approach is compared to alternative approaches implemented in Oxcal or BCal software: we show that the Event model is more robust but generally yields less precise credibility intervals. Mathematical formulations are explained in detail and comparisons are done thanks to synthetic examples. Three application examples are shown: the radiocarbon dating of the shroud of Turin, the dating of a medieval potter's kiln in Lezoux (Auvergne, France) by using radiocarbon, archaeomagnetism and thermoluminescence, and the OSL dating of the Shi'bat Dihya 1 sequence in Wadi Surdud middle paleolithic complex (western Yemen)

Posterior archaeomagnetic dating: An example from the Early Medieval site Thunau am Kamp, Austria

International audienceThe Early Medieval valley settlement of Thunau am Kamp in Lower Austria has been under archaeological excavation for 10 years. The site was occupied during the 9th and 10th centuries AD according to potsherds, which seem to indicate two phases of activity: in the older phase ovens were placed in the corners of houses while during the younger phase they are found in the middle of the wall. The present study has been conducted in order to increase the archaeomagnetic database and fill the temporal gap around 900 AD. For this purpose 14 ovens have been sampled for their paleaomagnetic signals. Laboratory treatment generally confirmed that the baked clay has preserved stable directions. Apart from one exception, all the mean characteristic remanent magnetisation directions are concentrated on the Early Medieval part of the directional archaeomagnetic reference curve of Austria at about 900 AD. Using this curve archaeomagnetic dating provides ages between 800 and 1100 AD, which are in agreement with the archaeological dating. Together with the archaeological age estimates and stratigraphic information the new data have been included into the database of the Austrian curve and it has been recalculated using a new version of RenCurve. The new data confine the curve and its error band considerably in the time interval 800 to 1100 AD. This calibration process also provides probability density distributions for each included structure, which allows for posterior dating and refines temporal errors considerably. Because such dating includes archaeological information it is not an independent age estimate but is a combination of all available dating method

La datation archéomagnétique des matériaux de construction d’argile cuite : apports chronologiques et technologiques

International audienceThe archaeomagnetic dating is now applied to building materials of baked clay such as tiles, bricks and paving tiles. The presentation of the physical and statistical principles and the complete presentation of an experimental study concerning modern paving tiles show the great reliability and precision of the method. Thus, we can obtain, in France, dates with a precision of ± 20 years for the major part of the periods from the end of the protohistory till now. Application examples illustrate the multiple chronological contributions of the method. Finally, we show how archaeomagnetism allows to obtain archaeological and technological informations from study of the firing positions of the materials and the magnetic characteristics of the clays.Depuis peu, la datation archéomagnétique s'applique aux matériaux de construction d'argile cuite tels que les tuiles, les briques et les carreaux de pavage. L'exposé des principes physiques et statistiques de l'archéomagnétisme et la présentation complète d'une étude expérimentale portant sur des carreaux de pavage modernes montre la grande fiabilité et précision de la méthode. Ainsi, on peut obtenir, en France, des dates avec une précision de ± 20 ans pour la majeure partie des périodes allant de la fin de la protohistoire à nos jours. Des exemples d'application viennent illustrer les nombreux apports chronologiques de la méthode. Enfin, on montre comment l'archéomagnétisme permet d'obtenir des renseignements archéologiques et technologiques à partir de l'étude des positions de cuisson des matériaux et des caractéristiques magnétiques des argiles

Hierarchical Bayesian modeling for combining Dates in archaeological context

A Bayesian approach is proposed for combiningdates from different dating methods used in archaeology.This modeling provides an automatic way to penalize outlying data. Examples are provided from different archaeological contexts involving radiocarbon,luminescence and archaeomagnetic results. This new combinationprocedure is also applied to the wiggle-matching process indendrochronological dating. Calculations are based on MCMC numericaltechniques and can be performed using the cross-platform ChronoModelapplication which is free, open source software (FOSS)

Archaeomagnetism in Italy: a compilation of data including new results and a preliminary Italian secular variation curve

Published Italian archaeomagnetic data are combined with new data from the Genève and Torino laboratories. A total of 74 directional data is presented with age estimates falling between 1300 BC to 1600 AD, including results from volcanic deposits of unquestionable age. The data set has been analysed using the Bayesian stochastic approach for curve building to produce a preliminary Italian secular variation (SV) curve. Comparison with the French SV curve shows a general agreement but some significant differences are also observed. The new Italian SV curve can be used for archaeomagnetic dating of Italian artefacts, even though caution must be paid for the period 9th-12th century AD and times older than 8th century BC, when only few data are available and error envelopes are larg

PROGRAMME DE DATATIONS DES FONDATIONS DU CHATEAU GRIMALDI, MUSEE PICASSO, ANTIBES. Rapport scientifique final auprès de la mairie d'Antibes, janvier 2016

Dans le cadre d’un programme archéologique dirigé par Eric Delaval sur les fondations du Château Grimaldi, l'IRAMAT-CRP2A est intervenu afin de dater les structures architecturales correspondantes par des méthodes physiques. Une intervention des membres de l'IRAMAT-CRP2A a eu lieu en décembre 2012. Elle a permis d'échantillonner des terres cuites (briques) et 5 échantillons de mortier de blocage et de jointoiement pour la datation par luminescence, ainsi que 92 échantillons de briques pour la datation par archéomagnétisme.Les objectofs de ce travail sont à la fois archéologiques et méthodologiques :- Dater la construction du mur de fondation grâce aux terres cuites architecturales dont on a envisagé de déterminer la datation de la production à partir des données d’archéomagnétisme et de luminescence.- Mettre en place la datation des mortiers par OSL monograin, en comparant les datations obtenues avec celles de terres cuites architecturales.Les résultats obtenus par le couplage entre l'archéomagnétisme des terres cuites et l'OSL des mortiers montrent que les fondations gallo-romaines du château Grimaldi (actuel Musée Picasso) ont été construites dans l'intervalle 30-220 AD (à 95% de probabilité) avec une médiane située vers 100 AD. Sur le plan méthodologique, il s'agit de la première datation de mortiers par OSL single grain véritablement aboutie

Archaeomagnetic results on three Early Iron Age salt-kilns from Moyenvic (France)

International audienceVariations of the Earthfs 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 ƒÊT and MOB, 86.6 } 6.9 ƒÊT 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

Extended and revised archaeomagnetic database and secular variation curves from Bulgaria for the last eight millennia

International audienceThe efforts of geophysicists to describe geomagnetic field behaviour in the past lead to creation of different geomagnetic field models. On the other hand, the established regional palaeosecular variations of geomagnetic elements are increasingly used for dating purposes in archaeology. Both of these goals can be achieved if sufficient amounts of long archaeomagnetic data sets exist for different geographical regions. The accumulation of archaeomagnetic determinations began at the middle of the last century, parallel with the progressive development of experimental methodology and acceptance criteria. The presence of great number of old determinations requires their critical assessment. The important question about the reliability of the associated dating intervals should be also re-assessed. All this requires the continuous refinement and extension of the accumulated databases. This paper presents the last synthesis of Bulgarian archaeomagnetic database and the local palaeosecular variation curves obtained using a statistical treatment based on Bayesian approach (RenCurve software). The rock-magnetic characteristics of the newly included, non-published results are summarized

Les transformations de la végétation du bassin parisien par la modélisation des données polliniques holocènes

International audienceLa synthèse palynologique du Bassin parisien repose sur un corpus de 91 séquences de fonds de vallées qui résume l’histoire de la végétation holocène régionale. Parmi elles, 22 ont été utilisées pour reconstruire quantitativement le couvert végétal, en utilisant un nouveau modèle de reconstitution des paysages, REVEALS. Il corrige la relation non linéaire entre pollen et végétation et permet ainsi de convertir les assemblages polliniques en surfaces de couverture relatives aux différents taxons végétaux. Les dynamiques de ces plantes, ou groupes de plantes, reconstituent alors l’évolution de la structure des paysages du Bassin parisien durant l’Holocène