Widespread occurrence of a novel high coercivity, thermally stable, low unblocking temperature magnetic phase in heated archeological material

McIntosh, G.; Kovacheva, Mary; Catanzariti, Gianluca; Osete, M. L.; Casas, Lluı̀s

doi:10.1029/2007gl031168

Cited by 37 publications

(41 citation statements)

References 20 publications

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“…The high thermal stability observed on the thermomagnetic curve ( Fig. 1(b)) is suggestive of a substituted hematite phase as recently reported by McIntosh et al (2007). Other two samples (SC1 and SC2) show a mixed behavior indicating the coexistence of (titano)magnetite and (titano)hematite.…”

Section: Magnetic Mineralogysupporting

confidence: 59%

First archeointensity results from Portuguese potteries (1550-1750 AD)

et al. 2009

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Geomagnetic field variations at archeomagnetic timescales can be obtained from well-dated heated structures and archeological potsherds. Here, we present the first archeointensity results obtained on Portuguese ceramics (1550 to 1750 AD) collected at Brazilian archeological sites. The results are compared to those obtained from Western Europe and currently available geomagnetic field models. Continuous thermomagnetic and IRM acquisitions curves indicate that Ti-poor titanomagnetite is responsible for the remanence in these ceramic fragments. Five fragments (24 samples) out of twelve analyzed yielded reliable intensity estimates. The row archeointensity data were corrected for TRM anisotropy and cooling rate effect. The mean dipole moments are obtained for three different age intervals: 1550±30 AD, 1600±30 AD and 1750±50 AD. Mean intensities vary from 37.9±4.2 μT to 54.8±7.6 μT in agreement with the previously reported data for 1550 AD and 1750 AD. Relatively weaker, but still highly dispersed, values were obtained for 1600 AD ceramics.

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Section: Magnetic Mineralogysupporting

confidence: 59%

First archeointensity results from Portuguese potteries (1550-1750 AD)

et al. 2009

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“…Summary of archaeomagnetic directions obtained from AF demagnetization. This phase shares the same characteristics as those exhibited by a thermally stable, high coercivity and low unblocking temperature phase described by McIntosh et al (2007McIntosh et al ( , 2011. NRM unblocking temperatures around 150-300 • C and AF coercivities in excess of 100 mT suggest that the same phase contributes to the stable remanence of the material.…”

Section: A G N E T I C M I N E R a L O G Ysupporting

confidence: 53%

Archaeomagnetic and rock magnetic study of six kilns from North Africa (Tunisia and Morocco)

Gómez‐Paccard¹,

McIntosh²,

Chauvin³

et al. 2012

Geophysical Journal International

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International audienceNew full-vector archaeomagnetic data for North Africa recovered from the study of six kilns, five from Tunisia and one from Morocco, are presented. Archaeological and historical considerations, along with three radiocarbon dates, indicate that the age of the kilns ranges between the 9th and 15th centuries AD. Rock magnetic analyses showed that the principal magnetic carriers are magnetite and low Ti titanomagnetite, along with variable contributions of thermally stable maghemite and a high coercivity phase with low unblocking temperatures. The magnetic mineralogy of the studied material is thermally stable and behaves ideally during archaeointensity experiments. Stepwise alternating field demagnetization isolated a single, stable, characteristic remanence component with very well defined directions at both specimen and structure levels. Mean archaeointensities have been obtained from successful classical Thellier experiments conducted on between five and eight independent samples per kiln. Thermoremanent magnetization (TRM) anisotropy and cooling rate effects upon TRM intensity have been investigated. The results showed that these effects are low for four of the six studied kilns, with differences between the uncorrected and corrected means of less than 3 per cent. For the other two structures differences between the uncorrected and corrected mean site intensities are 4.4 per cent and 5.8 per cent. These results highlight the necessity for TRM anisotropy and cooling rate corrections in archaeomagnetic studies if accurate archaeointensities are to be obtained. The new results suggest that high intensities occurred in Northwest Africa during the 9th century. Although more data are clearly needed to define this period of high intensity, the results are in agreement with the available European archaeointensity data. Acomparison between the newdata, other available archaeomagnetic determinations in nearby locations, and palaeosecular variation (PSV) curves derived from the regional SCHA.DIF.3k and global ARCH3K.1 geomagnetic field models shows good agreement between the new data and directional results derived from the models. However, some differences are observed between geomagnetic field models intensity results and available archaeointensity data for the studied regions. This highlights the need for new data for unexplored regions such as North Africa. The new data presented here better constrains the evolution of the geomagnetic field during historical times in this region. They represent a new step towards the construction of a reference PSV curve for Northwest Africa. Once established, this curve will represent a new dating method for this region

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“…4a-f). We note that this mineral, whose precise identification is still debated (Mcintosh et al, 2007(Mcintosh et al, , 2011, is quite frequent in archeological baked clay fragments, whatever their age and their geographic origin (e.g. Chauvin et al, 2000;Genevey and Gallet, 2002;Hartmann et al, 2011).…”

Section: Magnetic Mineralogymentioning

confidence: 99%

New archeointensity data from French Early Medieval pottery production (6th–10th century AD). Tracing 1500 years of geomagnetic field intensity variations in Western Europe

Genevey

Gallet

Jesset

et al. 2016

Physics of the Earth and Planetary Interiors

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a b s t r a c tNineteen new archeointensity results were obtained from the analysis of groups of French pottery fragments dated to the Early Middle Ages (6th to 10th centuries AD). They are from several medieval ceramic production sites, excavated mainly in Saran (Central France), and their precise dating was established based on typo-chronological characteristics. Intensity measurements were performed using the Triaxe protocol, which takes into account the effects on the intensity determinations of both thermoremanent magnetization anisotropy and cooling rate. Intensity analyses were also carried out on modern pottery produced at Saran during an experimental firing. The results show very good agreement with the geomagnetic field intensity directly measured inside and around the kiln, thus reasserting the reliability of the Triaxe protocol and the relevance of the quality criteria used. They further demonstrate the potential of the Saran pottery production for archeomagnetism. The new archeointensity results allow a precise and coherent description of the geomagnetic field intensity variations in Western Europe during the Early Medieval period, which was until now poorly documented. They show a significant increase in intensity during the 6th century AD, high intensity values from the 7th to the 9th century, with a minimum of small amplitude at the transition between the 7th and the 8th centuries and finally an important decrease until the beginning of the 11th century. Together with published intensity results available within a radius of 700 km around Paris, the new data were used to compute a master curve of the Western European geomagnetic intensity variations over the past 1500 years. This curve clearly exhibits five intensity maxima: at the transition between the 6th and 7th century AD, at the middle of the 9th century, during the 12th century, in the second part of the 14th century and at the very beginning of the 17th century AD. Some of these peaks are smoothed, or nearly absent when the selection of the data is extended to a 1250 km radius around Paris. The apparent regularity in the occurrence of intensity maxima, with a recurrence of $250 years, is particularly intriguing and might reflect a new characteristic of the secular variation, at least in Western Europe. It clearly requires further investigation and in particular the acquisition of new data from older periods.

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Widespread occurrence of a novel high coercivity, thermally stable, low unblocking temperature magnetic phase in heated archeological material

Cited by 37 publications

References 20 publications

First archeointensity results from Portuguese potteries (1550-1750 AD)

First archeointensity results from Portuguese potteries (1550-1750 AD)

Archaeomagnetic and rock magnetic study of six kilns from North Africa (Tunisia and Morocco)

New archeointensity data from French Early Medieval pottery production (6th–10th century AD). Tracing 1500 years of geomagnetic field intensity variations in Western Europe

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