Archaeomagnetic Data Research Articles

A Rejoinder on the Value of Archaeomagnetic Dating: Integrative Methodology Is the Key to Addressing Levantine Iron Age Chronology

Archaeomagnetic dating is a firmly established dating technique applicable to a wide variety of heat-treated anthropological materials and is advantageous for sites that lack materials suitable for radiocarbon dating. To correct recent misinterpretations of the method, we provide examples of how archaeomagnetic dating curves are calibrated and show how, in some instances, the technique can provide superior results. We emphasize that no single dating technique is capable of resolving the challenging chronology controversies in the Levant, and instead argue that multiple dating methods must be integrated in order to achieve the highest possible temporal resolution.

New Directional Archaeomagnetic Data from Seven Baked Clay Structures Excavated at the Archaeometallurgical Site of Agia Varvara-Almyras, Cyprus

New Directional Archaeomagnetic Data from Seven Baked Clay Structures Excavated at the Archaeometallurgical Site of Agia Varvara-Almyras, Cyprus

Short-Term Magnetic Field Variations From the Post-depositional Remanence of Lake Sediments

Palaeomagnetic records obtained from lake sediments provide important constraints on geomagnetic field behaviour. Secular variation recorded in sediments is used in global geomagnetic field models, particularly over longer timescales when archaeomagnetic data are sparse. In addition, by matching distinctive secular variation features, lake sediment palaeomagnetic records have proven useful for dating sediments on various time scales. If there is a delay between deposition of the sediment and acquisition of magnetic remanence (usually described as a post-depositional remanent magnetisation, pDRM) the magnetic signal is smoothed and offset in time. This so-called lock-in masks short-term field variations that are of key importance both for geomagnetic field reconstructions and in dating applications. Understanding the nature of lock-in is crucial if such models are to describe correctly the evolution of the field and for making meaningful correlations among records. An accurate age-depth model, accounting for changes in sedimentation rate, is a further prerequisite if high fidelity palaeomagnetic records are to be recovered. Here we present a new method, which takes advantage of the stratigraphic information of sedimentary data and existing geomagnetic field models, to account for both of these unknowns. We apply the new method to two sedimentary records from lakes Kalksjon and Gyltigesjon where 14C wiggle-match dating floating varve chronologies provide an independent test of the method. By using a reference magnetic field model built from thermoremanent magnetisation data, we are able to demonstrate clearly the effect of post-depositional lock-in and obtain an age-depth model consistent with other dating methods. The method has the potential to improve the resolution of sedimentary records of environmental proxies and to increase the fidelity of geomagnetic field models. Furthermore, it is an important step toward fully explaining the acquisition of post-depositional remanence, which is presently poorly understood.

Using archaeomagnetism to improve the dating of three sites in Catalonia (NE Spain)

Abstract Archaeomagnetic dating was performed on four archaeological structures in Catalonia (NE Spain) using magnetic inclination and declination values from three reference curves: the Iberian SVC and two curves computed using the regional SCHA.DIF.3k model and the global SHA.DIF.14k. The results provide new data for discussions regarding the dating of three archaeological sites from three very different periods: Roman, Medieval and Modern. In addition, some considerations were made regarding the usefulness of the three reference curves and the corresponding geomagnetic models. The Iberian SVC suggests that a Roman limekiln near Tarragona was last fired during the 1st century BC, but the archaeomagnetic models suggest it was last fired during the 1st century AD, i.e. closer to the date of the kiln infillings (2nd–3rd centuries AD). All three-reference curves date two structures from an archaeological site to the north of Barcelona to the 10th or 11th century AD. These ages match those determined using radiocarbon ages. Dating a modern limekiln near Girona with a presumed age of more than 200 years produced an inconsistent age when using the Iberian SVC, but plausible ages in the 17th or 18th centuries AD using the archaeomagnetic models. This suggests that the Iberian SVC has been superseded by the regional SCHA.DIF.3k model and the global SHA.DIF.14k model, both of which exhibit excellent dating capabilities. Older archaeological sites, including prehistoric sites, should be investigated to fully exploit and verify the potential of the new SHA.DIF.14k archaeomagnetic model.

Archaeomagnetic dating of Copper Age furnaces at Croce di Papa village and relations on Vesuvius and Phlegraean Fields volcanic activity

Metallurgic furnaces, discovered in the archaeological site of Croce di Papa, Nola, at 15km NE from the Vesuvius summit, were dated here by using archaeomagnetic technique. They are positioned between the deposits of the Vesuvius eruption of Pomici di Avellino and of the Phlegraean eruption of Agnano-Monte Spina. A revision of available age data and associated uncertainties for these two eruptions was carried out in order to provide constraints on the Croce di Papa furnaces age determination. The adopted archaeomagnetic technique provides an accurate age of 3136–3027BCE corresponding to 5085 to 4976 a BP that represents the upper age limit of the Agnano-Monte Spina eruption. This study provides evidences for the existence of human settlements in the Campanian Plain in the first century of the forth millennium BC and allow to assess the limited impact of the Agnano-Monte Spina eruption on climate and human settlement.

Improvements in Archaeomagnetic Dating in Western Europe from the Late Bronze to the Late Iron Ages: An Alternative to the Problem of the Hallstattian Radiocarbon Plateau

We present a new curve of the directional secular variation of the geomagnetic field in Western Europe between 1500 bce and 200 ce. Its computation relies on a Bayesian framework. The fast secular variation during the Late Bronze and Early Iron Ages makes archaeomagnetic dating efficient with a respective precision of 150–200 and 60–100 years during these periods. The Bayesian method also provides posterior date distributions that refine the dating of reference data, especially during the period of the Hallstattian radiocarbon plateau. Archaeomagnetism becomes a valuable alternative to radiocarbon and will help to improve the archaeological chronologies.

Advances in archaeomagnetic dating in Britain: New data, new approaches and a new calibration curve

Archaeomagnetic dating offers a valuable chronological tool for archaeological investigations, particularly for dating fired material. The method depends on the establishment of a dated record of secular variation of the Earth's magnetic field and this paper presents new and updated archaeomagnetic directional data from the UK and geomagnetic secular variation curves arising from them. The data are taken from publications from the 1950's to the present day; 422 dated entries derived from existing archaeo and geomagnetic databases are re-evaluated and 487 new directions added, resulting in 909 entries with corresponding dates, the largest collection of dated archaeomagnetic directions from a single country. An approach to improving the largest source of uncertainty, the independent dating, is proposed and applied to the British Iron Age, resulting in 145 directions from currently available databases being updated with revised ages and/or uncertainties, and a large scale reassessment of age assignments prior to inclusion into the Magnetic Moments of the Past and GEOMAGIA50 databases. From the significantly improved dataset a new archaeomagnetic dating curve for the UK is derived through the development of a temporally continuous geomagnetic field model, and is compared with previous UK archaeomagnetic dating curves and global field models. The new model, ARCH-UK.1 allows model predictions for any location in the UK with associated uncertainties. It is shown to improve precision and accuracy in archaeomagnetic dating, and to provide new insight into past geomagnetic field changes.

Re-evaluating the Mimbres Region Prehispanic Chronometric Record

Many decades of archaeological research in the Mimbres region have resulted in hundreds of chronometric dates obtained from contexts dating prior to A.D. 1450, but until now these data have not been compiled into a single database. Using dendrochronological, radiocarbon, and archaeomagnetic dates, we analyze each of the chronometric data sets to identify patterns and biases that help us better understand the tempo and duration of fundamental transitions in the Mimbres archaeological record. We also identify critical gaps in our knowledge of the chronometric record that provide new research opportunities.

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.

Reconstructing the Geomagnetic Field in West Africa: First Absolute Intensity Results from Burkina Faso

We present absolute geomagnetic intensities from iron smelting furnaces discovered at the metallurgical site of Korsimoro, Burkina Faso. Up to now, archaeologists recognized four different types of furnaces based on different construction methods, which were related to four subsequent time periods. Additionally, radiocarbon ages obtained from charcoal confine the studied furnaces to ages ranging from 700–1700 AD, in good agreement with the archaeologically determined time periods for each type of furnace. Archaeointensity results reveal three main groups of Arai diagrams. The first two groups contain specimens with either linear Arai diagrams, or slightly curved diagrams or two phases of magnetization. The third group encompasses specimens with strong zigzag or curvature in their Arai diagrams. Specimens of the first two groups were accepted after applying selection criteria to guarantee the high quality of the results. Our data compared to palaeosecular variation curves show a similar decreasing trend between 900–1500 AD. However, they reveal larger amplitudes at around 800 AD and 1650 AD than the reference curves and geomagnetic field models. Furthermore, they agree well with archaeomagnetic data from Mali and Senegal around 800 AD and with volcanic data around 1700 AD.

Further evidence of the Levantine Iron Age geomagnetic anomaly from Georgian pottery

AbstractRecent archaeomagnetic data from ancient Israel revealed the existence of a so‐called “Levantine Iron Age geomagnetic anomaly” (LIAA) which spanned the first 350 years of the first millennium before the Common Era (B.C.E.) and was characterized by a high averaged geomagnetic field (virtual axial dipole moments, VADM > 140 Z Am2, nearly twice of today's field), short decadal‐scale geomagnetic spikes (VADM of 160–185 Z Am2), fast field variations, and substantial deviation from dipole field direction. The geographic constraints of the LIAA have remained elusive due to limited high‐quality paleointensity data in surrounding locations. Here we report archaeointensity data from Georgia showing high field values (VADM > 150 Z Am2) in the tenth or ninth century B.C.E., low field values (VADM < 60 Z Am2) in the twelfth century B.C.E., and fast field variation in the fifth and fourth centuries B.C.E. High field values in the time frame of LIAA have been observed so far only in three localities near the Levant: Eastern Anatolia, Turkmenistan, and now Georgia, all located east of longitude 30°E. West of this, in the Balkans, field values in the same time are moderate to low. These constraints put geographic limits on the extent of the LIAA and support the hypothesis of an unusually intense regional geomagnetic anomaly during the beginning of the first half of the first millennium B.C.E., comparable in area and magnitude (but of opposite sign) to the presently active South Atlantic anomaly.

Multi-method dating of Grimaldi castle foundations in Antibes, France

The foundations of Grimaldi castle in Antibes belonged originally to a vast monumental edifice of an unknown origin. No historical records that would allow establishing precise chronological framework of this building exist. Therefore, four approaches were combined in order to date its construction: Relative chronology from archaeology with physical dating methods applied on building materials, e.g. archaeomagnetic dating of bricks and dating of mortars by optically stimulated luminescence using both the single grain and the multigrain technique. Whereas archaeomagnetic dating followed a well-established, reliable measurement protocol, dating of archaeological mortar by optically stimulated luminescence using the single grain technique represents quite new, exploratory approach that allows direct dating of the moment of edification. Luminescence dating showed that mortars were well bleached. Variations of the dose rate due to the heterogeneous distribution of radioelements in the matrix were observed. In the given context, none of the four approaches used would succeed to date the construction of the remains with certainty if they were used separately. Nevertheless, thanks to the mutual comparison of dating results, a reliable chronology have been established. The obtained results are in agreement and suggest the Grimaldi castle foundations were built between the second half of the first century and the second century A.D. Our interdisciplinary approach thus proves ancientness of the standing masonry and attests cultural and historical significance of the monument.

Detailed archaeomagnetic study of a ceramic workshop at Kato Achaia: New directional data and archaeomagnetic dating in Greece.

New archaeomagnetic results from two ancient kilns excavated at Kato Achaia, southern Greece, are presented. According to archaeological evidence, both kilns were part of a bigger ceramic workshop, probably used for the production of bricks or ceramics. Systematic archaeomagnetic sampling was carried out collecting 9 brick samples from the first kiln (KL3) and 12 brick samples from the second kiln (KL5). Magnetic mineralogy measurements have been carried out in order to determine the main magnetic carrier of the samples and to check their thermal stability. Standard thermal demagnetization procedures have been used to determine the archaeomagnetic direction registered by the bricks during their last firing. The direction of the Characteristic Remanent Magnetization (ChRM) has been obtained from principal component analysis and the kilns mean directions were calculated using Fisher statistics. The archaeomagnetic ages of both kilns were determined using the most recent developments in data elaboration and were calculated after comparison of the kilns declination and inclination with the reference curves produced by the SCHA.DIF.3K European regional geomagnetic field model. Dating results are in good agreement with archaeological evidence of the site and suggest that both kilns were in use during Hellenistic times.

Archaeointensity results spanning the past 6 kiloyears from eastern China and implications for extreme behaviors of the geomagnetic field

Variations of the Earth's geomagnetic field during the Holocene are important for understanding centennial to millennial-scale processes of the Earth's deep interior and have enormous potential implications for chronological correlations (e.g., comparisons between different sedimentary recording sequences, archaeomagnetic dating). Here, we present 21 robust archaeointensity data points from eastern China spanning the past ∼6 kyr. These results add significantly to the published data both regionally and globally. Taking together, we establish an archaeointensity reference curve for Eastern Asia, which can be used for archaeomagnetic dating in this region. Virtual axial dipole moments (VADMs) of the data range from a Holocene-wide low of ∼27 to "spike" values of ∼166 ZAm2 (Z: 1021). The results, in conjunction with our recently published data, confirm the existence of a decrease in paleointensity (DIP) in China around ∼2200 BCE. These low intensities are the lowest ever found for the Holocene and have not been reported outside of China. We also report a spike intensity of 165.8 ± 6.0 ZAm2 at ∼1300 BCE (±300 y), which is either a prelude to or the same event (within age uncertainties) as spikes first reported in the Levant.

Maya Lime Mortars—Relationship between Archaeomagnetic Dating, Manufacturing Technique, and Architectural Function—The Dzibanché Case

Researchers have related the manufacturing technique of plasters and stucco in the Maya area with their period of production but not with their architectural function. In this paper, we establish a relationship between those three features (manufacturing technique, age, and architectural function) in the plasters of the Maya site of Dzibanché in southern Quintana Roo. Dzibanché has abundant remains of stuccos and plasters found mainly in three buildings (Plaza Pom, Pequeña Acrópolis, and Structure 2). We used thin sections, SEM and XRD, and archaeomagnetic dating processes. The pictorial layer of Structure 2 was the earliest (AD 274–316 and the stuccoes and plasters of the other two buildings were dated to the Middle Classic (AD 422–531), but we obtained different archaeomagnetic dates for the red pigment layers found in the buildings of the Pequeña Acrópolis and thus we were able to determine their chronological order of construction. The raw materials and proportions were carefully chosen to fulfil the mechanical necessities of the architectonic function: different proportions were found in plasters of floors, in the external walls, and inside the buildings; differences between earlier and later plasters were also detected.

New archaeomagnetic data recovered from the study of celtiberic remains from central Spain (Numantia and Ciadueña, 3rd-1st centuries BC). Implications on the fidelity of the Iberian paleointensity database

Variations of geomagnetic field in the Iberian Peninsula prior to roman times are poorly constrained. Here we report new archaeomagnetic results from four ceramic collections and two combustion structures recovered in two pre-roman (celtiberic) archaeological sites in central Spain. The studied materials have been dated by archaeological evidences and supported by five radiocarbon dates. Rock magnetic experiments indicate that the characteristic remanent manetization (ChRM) is carried by a low coercivity magnetic phase with Curie temperatures of 530–575°C, most likely Ti-poor titanomagnetite/titanomaghemite. Archaeointensity determinations were carried out by using the classical Thellier-Thellier protocol including tests and corrections for magnetic anisotropy and cooling rate dependency. Two magnetic behaviours were depicted during the laboratory treatment. Black potsherds and poor heated samples from the kilns, presented two magnetization components, alterations or curved Arai plots and were therefore rejected. In contrast, well heated specimens (red ceramic fragments and well heated samples from the kilns) show one single well defined component of magnetization going through the origin and linear Arai plots providing successful archaeointensity determinations. The effect of anisotropy of the thermoremanent magnetization (ATRM) on paleointensity analysis was systematically investigated obtaining very high ATRM corrections on fine pottery specimens. In some cases, differences between the uncorrected and ATRM corrected paleointensity values reached up to 86 %. The mean intensity values obtained from three selected set of samples were 64.3±5.8μT; 56.8±3.8 and 56.7±4.6μT (NUS2, CI2andCIA, respectively), which contribute to better understand the evolution of the palaeofield intensity in central Iberia during the 3rd-1st centuries BC. The direction of the field at first century BC has also been determined from oriented samples from CIA kilns (D=357.2°; I=62.2°; N=10, α95=2.7°).The new archaeointensity data disagrees with previous results from Iberian ceramics which were not corrected for the ATRM effect. On the contrary, they are in agreement with the most recent French paleointensity curve and the latest European intensity model; both based on a selection of high quality paleointensity data. This result reinforces the idea that the puzzling scatter often observed in the global paleointensity database is likely due to differences in the laboratory protocols. Further data from well-established laboratory protocols are still necessary to delineate confidently the evolution of the geomagnetic palaeofield during the first millennium BC.

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.

New Archaeomagnetic Data from Tunisia: Dating of Two Kilns and New Archaeointensities from Three Ceramic Artifacts

Two isolated kilns of unknown age and three well‐dated artifacts from Tunisia have been investigated using archaeomagnetic techniques. Dating has been attempted for the kilns and archaeomagnetic intensities have been obtained for the artifacts. The kilns lack datable artifacts although one of them (Sidi Zahruni) could be related to a nearby late Roman site. Comparison with the SCHA.DIF.3K regional geomagnetic model suggests for both kilns two possible periods of last use, either Roman or Medieval. Three archaeomagnetic intensities were obtained for the well‐dated ceramic artifacts adding to scarce archaeomagnetic data from Africa. The new data along with recently published archaeointensities from other Tunisian sites have been compared with the regional model SCHA.DIF.3K, its updated version, and the global ARCH3k.1 geomagnetic model. The models show relatively good agreement with the new archaeointensities and with previously published intensities. The uncertainty of the experimental data tends to increase for older artifacts, and their agreement with the geomagnetic models diminishes. The observed trend of the intensity models to underestimate values in the Tunisian area for the Roman period could be overcome by adding new data from well‐dated artifacts from North African, particularly from pre‐Roman and Roman sites.

Archaeomagnetic Dating of the Eruption of Xitle Volcano, Basin of Mexico: Implications for the Mesoamerican Centers of Cuicuilco and Teotihuacan

espanolLa zona arqueologica de Cuicuilco, en el sur de la cuenca de Mexico, esta cubierta por flujos de lava del volcan Xitle. Se ha intentado la datacion de la erupcion y el abandono del centro de Cuicuilco aplicando diferentes metodos. Se han propuesto fechas contrastantes alrededor de 2000 y 1670 anos AP, con implicaciones para el desarrollo de los centros urbanos mesoamericanos Cuicuilco y Teotihuacan. A continuacion, analizamos las fechas de radiocarbono y los datos paleomagneticos para los flujos de Xitle. Se presentan nuevas estimaciones de la edad de la erupcion usando datos del vector completo con el modelo geomagnetico de referencia. Los datos paleomagneticos revisados dan edades con una media de 2086 anos AP e intervalo de confianza del 95 % entre 1995–2177 anos AP. El analisis bootstrap de las edades radiocarbonicas y arqueomagneticas proporciona edades medias e intervalos de confianza de 2041 y 1968–2041 anos AP y 2035 y 1968–2073 anos cal AP, respectivamente. El intervalo estimado de ~ 90 a.C. a 20 d.C. es compatible con una posible relacion entre el abandono de Cuicuilco y el desarrollo de Teotihuacan. EnglishThe Cuicuilco archaeological site in southern Basin of Mexico is covered by lava flows from the Xitle volcano. Dating the Xitle eruption and Cuicuilco abandonment has long been attempted. Contrasting results with radiocarbon dates around 2000 and 1670 yr BP have been reported, with implications for the development of the Mesoamerican centers of Cuicuilco and Teotihuacan. Here, we analyze radiocarbon dates and paleomagnetic data for the Xitle lava flows. New age estimates for the eruption are determined from correlating full vector data with the geomagnetic secular variation reference model. The revised archaeomagnetic data give ages correlating with the radiocarbon chronology, with a mean of 2086 cal yr BP and 95% confidence interval from 1995 to 2177 cal yr BP. Bootstrap analysis of the calibrated radiocarbon and archaeomagnetic dates gives mean dates and confidence intervals of 2041 and 1968–2041 cal yr BP and 2035 and 1968–2073 cal yr BP, respectively. The interval estimated of ~90 BC to ~AD 20 supports a possible link between the abandonment of Cuicuilco and the early development of Teotihuacan.

The Earth's magnetic field in Italy during the Neolithic period: New data from the Early Neolithic site of Portonovo (Marche, Italy)

We present new, full geomagnetic field vector results from three Neolithic ovens discovered at the archaeological site of Portonovo (Marche, Italy). The discovered structures are a rare example of very well preserved underground ovens from the Early Neolithic period. Standard thermal demagnetization procedures were used to isolate the direction of the Characteristic Remanent Magnetization acquired by the baked clay during the ovens' last firing. The corresponding archaeointensities were determined by the multi-specimen procedure (MSP-DSC) and show a clear intensity low during the Neolithic period. Both directional and intensity results are of high quality, offering the first contribution of full geomagnetic field vector data for this period in Italy. The new data are compared with other contemporaneous data from Europe and with global geomagnetic field models. Independent archaeomagnetic dating of the three ovens was also performed by means of the SCHA.DIF.14k model. The obtained results are in excellent agreement with available radiocarbon dates and confirm that all ovens belong to the Neolithic. These new data importantly enrich our knowledge of the geomagnetic field during the Neolithic period that is poorly documented by data, not only in Italy but also in the whole of Europe and show that archaeomagnetic dating can provide precise results even for prehistoric periods.