Reproducibility of archaeointensity determinations with a multimethod approach on archaeological material reproductions

Archaeointensity determinations on burnt archaeological material are complex and reliable data scarce, although this kind of material can be of great interest in archaeological investigations. With the goal of analysing the reliability of archaeointensity determinations, an interlaboratory comparison study has been performed combining different experimental protocols on present-day reproductions of Pre-Columbian Mesoamerican archaeological artefacts and two brick samples. Samples were baked in an original kiln from an artisan workshop in western Mexico. The ambient magnetic field at the site during the experiment was measured and continuous temperature data were recorded at four different positions in the kiln during the heating–cooling procedure. Archaeointensity determinations were carried out with four different methods at four different palaeomagnetic laboratories: Thellier–Coe (Burgos, Spain), microwave (Liverpool, UK), multispecimen (Morelia, Mexico) and multispecimen with the extended protocols for fraction and domain-state correction (Montpellier, France). 26 conventional resistive heating determinations with the Thellier–Coe protocol yielded a 100 per cent success rate, while 7 out of 8 microwave-heating determinations with the Thellier–Coe protocol also provided successful results. Also, two multispecimen determinations performed with both multispecimen methods provided statistically reliable results. In all cases, a good agreement between the determined archaeointensities and the ambient field at the production site could be observed. Highly reversible magnetization-versus-temperature curves yielded slightly Al, Mg or Ti-substituted magnetite as the main ferromagnetic (s.l.) phase. In addition, in several samples, a thermally stable low Curie-temperature phase displaying a high coercivity behaviour could be observed in thermomagnetic curves and by thermal demagnetization of saturation isothermal remanent magnetization. This phase is interpreted as ε-Fe2O3. To our knowledge, its occurrence has never been reported through the experimental recreation of burnt archaeological materials. No correlation could be observed between the proxies of domain-state behaviour and deviation of palaeointensity determinations from the expected result. Results obtained on clay samples heated in this type of ancient kiln can be considered a good source for determining the geomagnetic field strength variation in the past. Matching palaeointensity results obtained with different methods based on different principles can be taken as a quality criterion for result reliability and consistency.Projects BU0066U16 and BU235P18 (Junta de Castilla y León, Spain) and the European Regional Development Fund (ERDF). AG is grateful for financial support of CONACyT 252149 and UNAM-PAPIIT project 101717. The Géosciences Montpellier survey was supported by a grant from the CNRS-PNP. The FUReMAG rapid furnace construction was supported by the French National Agency for Research (ANR-12-BS06–0015)

Rock Magnetism of Lapilli and Lava Flows from Cumbre Vieja Volcano, 2021 Eruption (La Palma, Canary Islands): Initial Reports

We present initial rock magnetic results for both lava flows and lapilli produced by the 2021 eruption of the Cumbre Vieja, La Palma (Canary Islands). Samples were taken during the eruption to minimize early alteration and weathering of the rocks and tephra. Standard procedures included progressive alternating field and thermal demagnetization, hysteresis curves, thermomagnetic experiments, progressive acquisition of isothermal remanent magnetization (IRM), and First-Order Reversal Curves (FORCs). Overall, our observations, including low to medium unblocking temperatures, isothermal remanent magnetization to 1 Tesla, and the abundance of wasp-waist hysteresis loops, strongly suggest the presence of Ti-rich titanomagnetites as the main remanence carriers in both lava flows and lapilli, in addition to some hematite as well. Whereas the former has been directly seen (SEM), hematite is elusive with nonmagnetic-based methods. Rock magnetic data, on a Day plot, also reveal that the magnetic grain size tends to be larger in the lava flows than in the lapilli.This research was funded by Agencia Estatal de Investigación, Spain, grant no. PID2019-105796GB-00/AEI/10.13039/501100011033

Datación arqueomagnética de un horno romano excavado en el yacimiento arqueológico de Casa del Mitreo (Mérida, Extremadura, España)

Trabajo presentado en: Magiber XI, 4-7 de septiembre de 2019, Condeixa a NovaProyectoBU235P18delaJuntadeCastillayLeónyelFondoEuropeodeDesarrolloRegional(ERD

A comparison of Thellier-type and multispecimen paleointensity determinations on Pleistocene and historical lava flows from Lanzarote (Canary Islands, Spain)

Sixteen Miocene, Pleistocene, and historic lava flows have been sampled in Lanzarote (Canary Islands) for paleointensity analysis with both the Coe and multispecimen methods. Besides obtaining new data, the main goal of the study was the comparison of paleointensity results determined with two different techniques. Characteristic Remanent Magnetization (ChRM) directions were obtained in 15 flows, and 12 were chosen for paleointensity determination. In Thellier-type experiments, a selection of reliable paleointensity determinations (43 of 78 studied samples) was performed using sets of criteria of different stringency, trying to relate the quality of results to the strictness of the chosen criteria. Uncorrected and fraction and domain-state corrected multispecimen paleointensity results were obtained in all flows. Results with the Coe method on historical flows either agree with the expected values or show moderately lower ones, but multispecimen determinations display a large deviation from the expected result in one case. No relation can be detected between correct or anomalous results and paleointensity determination quality or rock-magnetic properties. However, results on historical flows suggest that agreement between both methods could be a good indicator of correct determinations. Comparison of results obtained with both methods on seven Pleistocene flows yields an excellent agreement in four and disagreements in three cases. Pleistocene determinations were only accepted if either results from both methods agreed or a result was based on a sufficiently large number (n>4) of individual Thellier-type determinations. In most Pleistocene flows, a VADM around 5 31022 Am2 was observed, although two flows displayed higher values around 931022 Am2.project CGL2012-32149 (Ministerio de Econom ıa y Competitividad, Spain), project 320/2011 (Ministerio de Medio Ambiente y Medio Rural y Marino, Spain) and the European Regional Development Fund (ERDF)

Un singular ambiente doméstico del Hierro I en el interior de la península ibérica: la casa 1 del Cerro de San Vicente (Salamanca, España)

The excavations undertaken at the Early Iron Age village of Cerro de San Vicente (Salamanca) revealed an informal aggregate of dwellings and ancillary buildings of adobe which matches the cross‑cultural spatial pattern for patrilocal practices. The paper focuses on house 1 and its adjoining middens. This dwelling was exceptional due to its long and stable biography, its clay furniture –with two benches for 20 people and a hearth in the shape of an oxhide– and ritualized abandonment using an intense conflagration dated to 650‑575 BC and its filling with adobes. The excavations revealed an unusual concentration of querns and fine local hand‑made pottery. The excavations recovered implements used for specialized and high‑quality crafts, such as potterymaking and weaving, as well as a set of finds unprecedented in the interior of Iberia stands out: exotic faience beads and tableware from the eastern Mediterranean, Phoenician red slip ceramics, and liturgical terracotta items with Tartessian and Mediterranean parallels. All these findings suggest that house 1 was the gathering hall of an extended corporate group where intense social activities –hosting banquets and transactions with guests– took place and where such startling artefacts ended up.Se presentan los resultados de las excavaciones (2006, 2017 y 2021) en un sector de la aldea del Hierro I del Cerro de San Vicente (Salamanca). Se ha exhumado un agregado informal de edificios y estructuras adjetivas de adobe cuyo patrón espacial es afín al esquema transcultural patrilocal. El artículo se centra en la casa 1 y sus cenizales. Tal vivienda fue excepcional por su larga e ininterrumpida biografía, su mobiliario de barro –con dos poyos que pudieron acoger hasta 20 personas y un hogar con forma de piel de toro extendida– y su abandono ritualizado –quemada c. 650-575 a.C. y recrecida con adobes de sus paredes–. La excavación reveló una alta concentración de molinos y vajilla fina local pintada, así como instrumental de labores especializadas y altamente cualificadas –alfarería e hilado–. Sobresale un lote de hallazgos inéditos en el interior de la península ibérica: exóticos abalorios y vajilla de fayenza del Mediterráneo oriental, cerámica de engobe rojo fenicia y objetos litúrgicos y coroplástica con paralelos tartésicos y mediterráneos. Todos estos hallazgos indican que la casa 1 acogió una asidua actividad social –banquetes y transacciones con huéspedes– como cabaña de reuniones de un grupo corporativo extenso, donde acabaron tan destacados objetos

An integrated palaeomagnetic, palaeointensity and 40Ar/39Ar investigation on a Miocene polarity transition recorded in a lava sequence in la Gomera, Canary Islands

A detailed palaeomagnetic, rock-magnetic and palaeointensity study has been carried out on a Miocene volcanic sequence which consists of 39 consecutive lava flows recording a polarity transition in La Gomera (Canary Islands, Spain). In addition, new 40Ar/39Ar ages were obtained in two flows, yielding 9.63 ± 0.06 Ma in the lower and 9.72 ± 0.08 Ma in the upper part of the sequence. Palaeomagnetic results allowed determining a ChRM direction in all studied lavas: The 25 lowermost flows of the sequence display normal polarity directions and above, a sequence of 14 flows correspond to a transitional geomagnetic regime. If considered together with palaeomagnetic results from a previous study, which were obtained on the flows immediately overlying the upper part of the sequence analysed in this work, these results indicate that the reversal recorded in the Hermigua sequence corresponds to the normal to reverse C4Ar2n to C4Ar3r polarity transition. The lower-lying 25 normal-polarity flows yield a mean direction D = 359.6°, I = 42.4° (α95 = 5.1°; k = 33) which agrees well with the expected values. Above, a sequence of 14 flows displays a more irregular directional behaviour, including several transitional directions, suggesting the occurrence of a precursor to the transition. The presence of a virtual geomagnetic pole (VGP) cluster in the western Atlantic Ocean observed in this study coincides with previous records of Miocene transitions. Interestingly, this region corresponds to a near-radial flux centre of the present-day non axial dipole field. Angular dispersion of VGPs calculated for the 25 lowermost normal polarity flows of the sequence shows a lower than expected result. Palaeointensity determinations were carried out using a Thellier type double heating method. 27 of the 48 analysed samples measured yielded successful results. Mean VDMs mean values range from 1.1 ± 0.5 to 8.8 ± 0.9 × 1022 Am2. The intensity values decrease significantly on approaching the directional transitional zone, suggesting an earlier start of the polarity transition in the intensity record, typical of a decreasing axial dipole.This work was funded by project CGL2012-32149 (Ministerio de Economía y Competitividad, Spain), projects CGL2011-23755 and CGL2010-14869 (Ministerio de Ciencia e Innovación, Spain) and the European Regional Development Fund (ERDF). AC acknowledges the support of CONACYT scholarship no. 257639 (Mexico). Technical and human support provided by SGIker (UPV/EHU, MINECO, GV/EJ, ERDF and ESF) is gratefully acknowledged.Peer Reviewe

New high precision full-vector archaeomagnetic data from a roman kiln in Mérida (Spain)

This study presents new high precision age and full-vector archaeomagnetic data from a kiln excavated in the Roman archaeological site of Mitreo's house (Mérida, Badajoz, Spain). The age of the kiln was obtained by the stratigraphic method and by the ceramological study of the italic and sigillata pottery found with a very precise age date of 55 ± 15 years AD. Rock-magnetic experiments pointed towards magnetite as the main carrier of remanence and highly reversible thermomagnetic curves suggested that the studied samples were suitable for archaeoeointensity determinations.Paleomagnetic experiments including thermal and stepwise alternating field demagnetization yielded the following mean direction for the kiln: declination D = 0.6°; inclination I = 54.0°; (k = 481; α95 = 2.5°). Archaeointensityexperiments with the Thellier – Coe protocol on 28 samples yielded successful determinations in 27 cases. Anisotropy factors between 0.90 and 1.04 were obtained from anisotropy of thermoremanent magnetization (ATRM) experiments. A mean anisotropy-corrected archaeointensity value F = 56.3 ± 5.5 μT was obtained. The geomagnetic model SHA.DIF.14 k was used for an archaeomagnetic dating yielding a chronological interval between 40 BCE and 150 CE. This low age resolution when compared with the pottery-based age data is related to the behavior of the geomagnetic field in the Iberian Peninsula during the Roman period, which does not allow to differentiate well between results corresponding to those centuries. However, it is also related to the fact that the Iberian archaeomagnetic dataset in the analysed time range is highly scattered. A high quality full-vector data with a very precise age have been obtained which contribute to improve the Iberian secular variation curve and geomagnetic databases.Project BU235P18 (Junta de Castilla y Leon, Spain) and the European Regional Development Fund (ERDF) and the PID2019-105796GB-I00 of the Agencia Estatal de Investigación (AEI / 10.13039/501100011033). N-G.R acknowledges the financial support given by the Junta de Castilla y León and the European Union (ERDF funding). MCR acknowledges funding from the Fulbright Commission and the Spanish Ministry of Science, Innovation and Universities for a research stay at Hawaii University at Manoa. Thanks to the archaeological team who worked at the site. MBA acknowledges the following project: “Corpus Vasorum Hispanorum. Analisis tipológico, cronológico y prosopográfico de los sigilla en terra sigillata hispanica a partir de los centros consumidores. Parte I: Lusitania” (PGC2018-093478-A-I00 – Convocatoria Proyectos de Excelencia – Plan Estatal de Generación de Conocimiento – Ministerio de Ciencia, Innovación y Universidades – España)

A paleomagnetic and rock-magnetic study of a neogene lava flow sequence in La Gomera (Canary Islands, Spain)

We present rock-magnetic and paleomagnetic results obtained on samples belonging to a Neogene sequence of 11 successive lava flows and a dyke from La Gomera (Canary Islands, Spain). Analysis of thermomagnetic curves allows to distinguish three types of samples: (i) Type H samples with low-Ti titanomagnetite as the only carrier of remanence; (ii) type M samples with a main intermediate Curie-temperature phase (TC = 450°C) and low-Ti titanomagnetite; (iii) type L curves with a low Curie-temperature phase (TC = 120 to 200°C) and an intermediate Curie-temperature phase (TC = 400°C). Analysis of hysteresis parameters suggests that the grain size of most studied samples corresponds to pseudo single-domain particles, which can be also interpreted as a mixture of single-domain and multi-domain particles. Paleomagnetic experiments reveal only a single paleomagnetic component. Characteristic remanence of all studied lava flows and the dyke shows reverse polarity. The mean direction of the whole sequence is D = 188.2°, I =-35.4° (k = 46.9; α95 = 6.4°) and the calculated paleomagnetic pole yields a longitude λ = 150.7° and a latitude φ = 78.8° (k = 59.4; A95 = 5.7°). Secular variation is analysed through the scatter of virtual geomagnetic poles (VGP). A VGP angular scatter SB = 5.9 with an upper confidence limit Sup = 8.0 and a lower confidence limit Slow = 4.6 are obtained. This scatter is clearly smaller than the average for this latitude obtained for the last 5 Ma. The studied lava flows were probably emitted in a relatively short time interval

A reconnaissance magnetostratigraphy of Georgian Plio- Quaternary volcanic provinces (southern Caucasus)

Se presentan resultados de un estudio paleomagnético y de magnetismo de rocas en muestras de las regiones de Djavakheti, Khrami y Kazbeki, en Georgia (Cáucaso). Se tomaron muestras de 247 coladas volcánicas subaéreas y de 3 estratos sedimentarios lacustres intercalados entre éstas, pertenecientes a 44 localidades. El objetivo del trabajo consistía en el estudio de la estabilidad magnética y paleomagnética de muestras para determinar su potencial en estudios de magnetoestratigrafía y paleointensidad. Los experimentos de magnetismo de rocas demostraron que la magnetización remanente está asociada principalmente a la presencia de magnetita de tipo PSD. 113 coladas volcánicas y un estrato sedimentario dieron como resultado una magnetización de polaridad normal, mientras que otras 130 coladas volcánicas presentaron una magnetización de polaridad inversa. 4 coladas volcánicas y 2 estratos sedimentarios se caracterizan por mostrar direcciones correspondientes a una polaridad intermedia. Se determinó una dirección paleomagnética media para todas las unidades volcánicas, salvo las de polaridad intermedia, de D=4.7°, I=58.3°, k=28 y á95=3.7° y se estableció una magnetoestratigrafía preliminar de las provincias volcánicas georgianas. doi: https://doi.org/10.22201/igeof.00167169p.2001.40.2.37