Combined archaeomagnetic and thermoluminescence study of a brick kiln excavated at Fontanetto Po (Vercelli,Northern Italy)

A combined archaeomagnetic and thermoluminescence study was carried out as part of a rescue archaeological excavation on a kiln discovered during the installation of methane gas pipelines beneath a rice field, along the southern border of Fontanetto Po village (Vercelli province, Italy). A total of 23 independent brick samples have been collected, oriented in situ with an inclinometer; the use of magnetic and sun compass was not possible due to the existence of metallic tubes beneath the kiln and a plastic cover above it. Standard archaeomagnetic procedures have been used for the determination of the archaeomagnetic inclination and absolute geomagnetic intensity. Stepwise thermal demagnetization shows a very stable characteristic remanent magnetization and the calculated mean inclination of the 23 samples is I = 65.3° with α₉₅ = 2.4° and k = 156. Archaeointensity experiments have been performed using the classical Thellier method as modified by Coe, with regular partial thermoremanent magnetization (pTRM) checks. The cooling rate and remanence anisotropy effects upon thermoremanent magnetization (TRM) have been investigated in all the specimens. A total of 19 archaeointensity determinations (at specimen level) that correspond to linear NRM–TRM plots were used for the calculation of the site mean archaeointensity that is 46.4 ± 2.9 μT. Archaeomagnetic dating results show two possible dating intervals for the last 1000 years, calculated at 95% confidence interval: a first one from 1511 to 1614 AD, and a second one from 1768 to 1872 AD. Thermoluminescence (TL) study has been also performed on two brick samples from the kiln's internal wall, using conventional laboratory procedures. According to the thermoluminescence results the kiln's last usage lies between 1796 and 1914 AD. This age is in good agreement with the second dating interval obtained by the archaeomagnetic analysis. The combined archaeomagnetic and thermoluminescence results suggest that the last firing of the kiln could have occurred between the end of the 18th century and the beginning of 20th century.     

RESEARCH REPORT: MAGNETIC INVESTIGATIONS AND THE AGE OF A MEDIEVAL KILN AT KUNGAHÄLLA (SOUTH‐WEST SWEDEN)*

The results from a magnetic survey and archaeomagnetic investigation of a medieval brick kiln at Kungahälla in Bohuslän (south‐west Sweden) are reported. Detailed magnetic total field and magnetic gradient measurements over known traces of the kiln showed marked local magnetic anomalies of up to 200 nT, revealing the rectangular shape of the kiln remains. Palaeomagnetic investigations of the remanent magnetization of 12 bricks from the kiln floor gave precise definitions of both the direction of the archaeomagnetic field [(D_m, I_m) = (66.7°, 8.8°), k = 655, α₉₅= 1.7°] and the palaeointensity [B_m= 69.0 ± 3.6 µT]. An archaeomagnetic date is obtained by comparing the direction of the archaeomagnetic field found in the kiln with a geocentral dipole‐transformation of the British master‐curve for secular variation. Of two possible archaeomagnetic dates (ad 1280 ± 50 or ad 1480 ± 50), the ad 1280 ± 50 age is in good accordance with the C‐14 ages and archaeological dates as well as with direct historical evidence, whereas a c. 100 years younger TL date appears to be too young.     

Archaeomagnetic data from three Punic sites in Tunisia

Archaeomagnetic analyses on bricks and slag fragments from kilns have been undertaken. Four new archaeomagnetic directions and two new archaeomagnetic intensities have been reported for three Punic sites in Tunisia. The SCHA.DIF.3K archaeomagnetic model gives the most consistent age estimates, in agreement with the archaeological ages for three of the four analyzed kilns. The archaeomagnetic models appeared to be surprisingly proficient both using archaeodirections and intensities for El Maklouba. The existence of kilns from different chronological archaeological phases (4th–3th century BC and 2nd–3rd century AD) has been confirmed for this site. The archaeological hypothesis that associates the kiln in El Gaala with the neighboring Punic necropolis is compatible with the archaeomagnetic data obtained from the kiln, though a modern use or remagnetisation of the kiln cannot be excluded.     

Archaeomagnetic versus luminescence methods: the case of an Early Byzantine ceramic workshop in Thessaloniki,Greece

In this contribution, we present a combined archaeomagnetic and luminescence study of archaeologically dated structures. The investigated area is a ceramic workshop comprising several Early Byzantine kilns. Based on (a) the archaeological–anthropogenic stratigraphy of the site, (b) the structural characteristics of the kilns and (c) the few ceramic findings revealed within their context, the operation of this brick and tile factory is approximately dated between the middle of the fifth century until the first decades of the sixth century AD. Three of the well-preserved workshop kilns have been studied archaeomagnetically. The full vector of the geomagnetic field, accompanied by rock magnetic analyses of the studied material, has been defined. The archaeomagnetic study revealed similar directions among the three kilns indicating and confirming their contemporary use. Additionally, several luminescence measurements were obtained on material from the same kilns. The dating of the site was performed with both methods. The archaeomagnetic dating is convergent with the archaeological estimation only when its upper limit is considered. Concerning the luminescence dating, the calculated ages (corrected for anomalous fading and for the ⁴⁰K content) with their standard deviations are convergent with the archaeological estimations for the first kiln, while for the other two, the results seem to be incompatible. The possible factors that provoked this divergence are thoroughly discussed.     

Archaeological and archaeomagnetic dating at a site from the ager Tarraconensis (Tarragona,Spain): El Vila-sec Roman pottery

A very accurate archaeological dating of a Roman site in NE Spain (El Vila-sec) was made based on the typology of pottery artifacts. Three different phases were identified with activity ranging from the mid-1st century BC to the early-3rd century AD. Analyses of bricks from kilns at El Vila-sec produced data on their stored archaeomagnetic vector. These data were compared with the secular variation curve for the Iberian Peninsula and the SCHA.DIF.3K regional archaeomagnetic model. Both, the reference curve and the model, produced probability distributions for the final period of use for two kilns from the second archaeological phase that were not used during the third phase. At a 95% confidence level, both time distributions cover a wide chronological range including the presumed archaeological age. Both the Iberian secular variation curve and the SCHA.DIF.3K regional model proved to be suitable models for dating the site, although on their own they do not produce a single unambiguous solution. This archaeomagnetic approach could also be applied to neighbouring archaeological sites that have an imprecise archaeological age.     

Archaeomagnetic data from four Roman sites in Tunisia

Archaeomagnetic analyses on bricks and slag fragments from kilns have been undertaken. The initial aim of the paper was to constraint the age of four Roman sites in Tunisia (Neapolis, Pheradi Majus, Leptiminus and Sullecthum) using either archaeodirections or archaeointensities. However, the archaeomagnetic models appeared to be only proficient using directions. It has been established that the Neapolis' studied kiln was probably active until the early 6th century AD, whereas the kilns investigated in Pheradi Majus were probably active until the middle 5th century AD. Measured archaeointensities point to higher values than those predicted by the models during the whole range of possible ages for the studied sites.     

Archaeomagnetic research in the Andean highlands

Eleven archaeomagnetic samples were collected from several sites near Porco, Bolivia as part of the Proyecto Arqueológico Porco-Potosí. These samples were collected in order to 1) explore the availability of appropriate sample materials in the Bolivian Andes, and 2) assess the feasibility of pursuing reference curve research for this region. In addition, this research explored the archaeomagnetic dating application of reference curves constructed from the global geomagnetic field model gufm1 (Jackson et al., 2000), which covers the period from AD 1590–1990. This model is particularly applicable to our project, since many of the project sites are late prehispanic (pre-AD 1532) and early historic (ca. AD 1532–1825) in age. Of the 11 samples, three appeared to contain an insufficient amount of ferromagnetic minerals to provide reliable results, while eight samples produced acceptable-to-good results. The data from the eight good samples were compared to a reference curve for the period of AD 1600–2000 that was calculated for this project from the global field model, gufm1. The archaeomagnetic dates obtained for two of the samples agreed with archaeological expectations, while those for four other samples marginally or greatly postdated the archaeological age expectations. Two additional samples produced significantly different directions and could not be dated against the reference curve. It is likely that the age discrepancies for four of the samples stem from inaccuracies in the archaeomagnetic data, the archaeological age expectations, the calculated reference curve, or some combination of these factors.     

A Stamford Ware Pottery Kiln in Pontefract: A Geographical Enigma and a Dating Dilemma

Abstract

THIS REPORT PRESENTS the results of analyses carried out following the discovery and excavation of a medieval pottery kiln in Pontefract, a discovery which featured in the ‘Fieldwork Highlights’ section of Medieval Archaeology 53 (2009). The kiln is remarkable for having produced vessels previously only associated with the Stamford ware industry of the late 11th and 12th centuries and demonstrates the existence of at least one northern production site, the likely existence of which was first mooted in the 1950s. As both radiocarbon and archaeomagnetic dating methods indicate a last firing of the Pontefract kiln in the late pre-Conquest period, the discovery also poses questions about the chronology of Stamford ware production.     

Full‐Vector Archaeomagnetic Dating of a Medieval Limekiln at Pinilla Del Valle Site (Madrid,Spain)

Archaeomagnetic dating based on the full geomagnetic field vector was carried out on a limekiln excavated at Pinilla del Valle archaeological site (Madrid, Spain). The limekiln tradition in this area is largely documented by historical sources for recent centuries but the date of the studied kiln's last use was unknown. The combination of mean archaeomagnetic directional and absolute archaeointensity results shows that the kiln was last used between ad 1296 and 1413, in good agreement with two independent radiocarbon dates. This study provides the first archaeomagnetic evidence that the local limekiln tradition dates back to at least late medieval times. Furthermore, the inclusion of these data in the Iberian secular variation curve and geomagnetic field models will help to improve the archaeomagnetic dating technique.     

Archaeomagnetic dating of archaeological sites from Switzerland and Bulgaria

Baked materials from three archaeological sites in Switzerland and one in Bulgaria have been examined and dated archaeomagnetically. The detailed rock-magnetic properties of the burnt clay collected have already been studied therefore and have been published elsewhere (Geophysical Journal International 153 (2003) 146). The main aim of this paper is to determine the terminus ante quem for the last firing of the clay collected from pottery kilns or burnt layers. The directional and intensity results of the ancient geomagnetic field corresponding to the time of the structure's last firing are given for each site. These geomagnetic parameters are then compared with reference curves to provide archaeomagnetic dates for the last use of the kilns. Application of archaeomagnetism as a dating tool is only possible for those regions that already have reference curves. Bulgaria is fortunate in having established reference curves covering almost the last 8000 years. Two Swiss sites were dated using only directional results on the basis of existing palaeodirectional results for Switzerland as well as the French directional reference curves. The archaeomagnetic dates of three of the sites were then compared to archaeological evidence and available radiocarbon dates. The palaeointensity data obtained from this study will enrich the existing archaeomagnetic database for western Europe.     

Combining an archaeomagnetic and radiocarbon study: dating of medieval fireplaces at the Mühlegasse,Zürich

During the restoration of the Radium cinema located in the old Town of Zürich, a stratigraphic sequence of medieval fireplaces came to light. Based on ceramic finds, a preliminary age of about 1000 AD was assigned. In this paper we show the results from archaeomagnetic and radiocarbon dating, which combined with the stratigraphic information yield a better constrain of the period of use of these fireplaces. Whilst the radiocarbon technique continues to be the most widespread methodology for dating young archeological artifacts, archaeomagnetic dating is becoming increasingly more established in Europe thanks to the increased number of available measurements. A Bayesian model on the period of use of these fireplaces was produced with OxCal, by a combination of magnetic and radiocarbon ages, together with the stratigraphic information. The results show that the fireplaces were probably used during 1 to 2 generations (e.g. 20–40 years each), and are in good agreement with the archaeological context of this site. To make use of the magnetic measurements for future reconstructions of the field, we carried out an additional age model using only the radiocarbon and the stratigraphic information. Although some of the structures show large directional scatter due to poor baking in antiquity, the results confirm the trend of the geomagnetic field around 1000 AD.     

Dating environmental change using magnetic bacteria in archaeological soils from the upper Thames Valley,UK

An archaeomagnetic date has been recovered from an organic rich sediment at the base of an alluviated ditch section found during archaeological excavations near the village of Yarnton, Oxford, UK. The magnetic minerals carrying this remanence include greigite and biogenic magnetite, derived from magnetotactic bacteria, that both indicate the presence of a micro-aerobic environment. It is proposed that the archaeomagnetic date from this material indicates the onset of floodplain conditions at the site due to increased population pressure and intensification of land clearance in the late British Iron Age.     

Development of Probabilistic Framework for Performance-Based Seismic Assessment of Structures Considering Residual Deformations

Recently, the importance of considering residual (permanent) deformations in the performance assessment of structures has been recognized. Advanced structural systems with re-centering properties as those based on unbonded post-tensioning tendons are capable of controlling or completely eliminating residual deformations. However, for more traditional systems, which count for the vast majority of buildings, residual deformations are currently considered an unavoidable result of structural inelastic response under severe seismic shaking.

In this article, a probabilistic framework for a performance-based seismic assessment of structures considering residual deformations is proposed. The development of a probabilistic formulation of a combined three-dimensional performance matrix, where maximum and residual deformations are combined to define the performance level corresponding to various damage states for a given seismic intensity levels, is first presented. Combined fragility curves expressing the probability of exceedence of performance levels defined by pairs of maximum-residual deformations are then derived using bivariate probability distributions. The significance of evaluating and accounting for residual deformations within a Performance-based Earthquake Engineering (PBEE) approach is further confirmed via numerical examples on the response of Single Degree of Freedom (SDOF) systems, with different hysteretic behavior, under a selected suite of earthquake records. Joined fragility curves corresponding to various performance levels, defined as a combination of maximum and residual response parameters, are derived while investigating the effects of hysteretic systems and strength ratios. It is observed that stiffness degrading Takeda systems result in lower residual deformations than elasto-plastic systems and show lower probability of exceeding a jointed maximum-residual performance level. For a chosen performance level, Takeda systems with higher strength ratios show better performance, particularly with lower intensity of excitations.     

ARCHAEOMAGNETIC FIELD INTENSITY DURING THE ROMAN PERIOD AT SIWA AND BAHRYN OASIS,EGYPT: IMPLICATIONS FOR THE FIDELITY OF EGYPTIAN ARCHAEOMAGNETIC DATA

A preliminary survey was conducted in Siwa and Bahryn Oasis to test the possible influence of various rock magnetic and experimental constraints on the fidelity of the Egyptian archaeomagnetic field record. Five potsherds from the Roman era, which lasted from 1981 bp to 1555 bp , have been investigated. Archaeologists dated the localities to ～1620 bp . Ten ceramic specimens, two of each potsherd, were subjected to archaeointensity determination, including tests for domain state effects, magnetic anisotropy and magnetic cooling rate dependency. Six successful archaeointensity determinations are obtained from three individual cooling units, revealing an average field value of 37.7 μT for the late Roman period in Siwa and Bahryn oasis, which is comparable to the present‐day field strength. The error propagation of the individual uncertainties related to all applied experimental techniques results in a maximum uncertainty estimate of 4.4 μT. The obtained field value is significantly smaller than early results and slightly smaller than some more recent determinations of the field intensity in Egypt. The difference is attributed to a combined effect of alteration, magnetic anisotropy and magnetic cooling rate dependencies. Along with other high‐quality data from the south‐east Mediterranean, our data suggest a field intensity minimum during the Egyptian Roman era.     

Archaeomagnetic Dating of Pyrotechnological Contexts: a Case Study for Copper Smelting Sites in the Central Timna Valley,Israel

This study is focused on establishing age constraints for several copper slag deposits at the centre of the Timna Valley (Israel) via reconstruction of their ancient geomagnetic intensities as recorded by the individual slag samples at the time of their formation. The results show a correlation between the location of the slag deposits (labelled as individual ‘mounds’ in our survey) and their inferred ages, reflecting varying socio‐economic and political dynamics in the region. While the slag mounds found at the unprotected foothills represent a variety of dates (mostly Early Islamic), the slag mounds on the hilltops are chronologically constrained to the early Iron Age (late 11th to 10th centuries bce ), supporting the idea for a need for protection during this period. Furthermore, in comparing the new data with previous archaeomagnetic studies from Timna, we can assert the existence of simultaneous copper production at the archaeological Sites 30, 30a and 34. This gives further support to the claim of intense smelting in the central Timna Valley during the early Iron Age. Finally, this project demonstrates the potential of archaeomagnetic experiments to provide chronological insights, and their particular advantage in addressing pyrotechnology‐related cases.     

Raw or Pre-Fired: Kiln Construction at Sawankhalok,North Central Thailand,as a Guide to Ceramic History

Sawankhalok, located in north central Thailand, was an early stoneware ceramic production site where the first kilns were dug cave-like into the natural ground, a method used in China for thousands of years. After a century or so, kilns at Sawankhalok began to be constructed of brick. It is suggested that if the bricks were pre-fired then an external influence may have been responsible. To the contrary, if raw unfired clay was used in the construction of the kilns the evolution was more likely a consequence of conceptual continuity.With the aid of chemical and mineralogical analyses it is shown that the kiln bricks were unfired at the time of kiln construction thereby suggesting that traditional conservatism, apparent in many aspects of the industry, caused processes to remain unaltered in the absence of a persuasive reason for change. These conclusions reflect on the degree of indigenous technology and artistic development associated with Sawankhalok ceramics as opposed to external influence.     

What do muscle marker ruggedness scores actually tell us?

Musculoskeletal stress markers (MSM) have been used to reconstruct activity patterns and labour intensity of past populations. Age and size have been found to correlate with MSM, and these aspects should be considered in activity reconstructions. The aim of this study was to find out the nature and the effects of labour intensity, age and size on MSM. Study material were skeletons (N = 108) of individuals of known age, sex and occupation housed at the Natural History Museum, Finland. MSM were scored for Pectoralis major, Deltoid, Teres major and Biceps brachii. These scores were combined to reflect total activity of an individual. Geometric mean of humeral measurements was used as a size indicator and radial tuberosity size was used as a muscle size indicator. Factors explaining MSM were studied using ANCOVA. This included age, size, muscle size, sex, labour intensity, and their interactions. Age and muscle size were the most significant factors explaining MSM, where muscle attachment areas and MSM grow with advancing age. Muscle attachment areas and skeletal frame size were also found to correlate. Least squares regression parameter estimates were used to study the effects of labour intensity, sex and side on MSM. It was found that in early life scores are higher in heavy labour group, but there is less age‐related increase in these scores. This could mean that bone is unable to respond to heavy and continuous loading with surface structure. Therefore labour intensity cannot be reliably recorded in old individuals. Also age and size (as reflected in muscle attachment area) affect MSM and these aspects should be considered before making assumptions on labour intensity. Copyright © 2009 John Wiley & Sons, Ltd.     

微波技术在砖石质文物含水率检测中的应用

水是造成砖石质文物劣化的主要因素之一,因此探明其在文物内部的分布、运移规律是开展保护研究的重要基础。微波技术在检测材料内部的水分含量方面表现出较好前景,但在文物保护领域还未普遍应用。基于此,本研究首先介绍了微波技术的理论基础和相关仪器,并选取山西省的长春玉皇庙为对象,针对砖石材料的内部含水率开展了室内样块检测和现场墙体检测。结果表明,微波技术能够较为准确地揭示出文物内部的空间含水率分布规律,这对于研究其病害成因等具有重要作用。此外,与其他多种无损检测技术相比,微波技术检测材料含水率的优点更多,值得文物工作者进一步研究与应用。