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

Weak palaeointensity results over a Pliocene volcanic sequence from Lesser Caucasus (Georgia): transitional record or time averaged field?

A palaeointensity study has been carried out on a Pliocene sequence of 20 consecutive lava flows where previous directional results seem to reflect anomalous behaviour of the Earth’s magnetic field (EMF), which can be explained by a polarity transition record or non-averaged palaeosecular variation or both. Here, we perform a total of 55 palaeointensity determinations using the original Thellier–Thellier (TT) method and 100 with the IZZI method.We assess the performance of our selection criteria using a set of strict threshold values applied to a set of test data whose TRMs were acquired in known fields. Absolute palaeointensity determinations that passed our selection criteria were obtained on four specimens with the TT method and on 41 specimens with the IZZI method. Application of reliability criteria at a site level yielded palaeointensity results in 8 of 20 studied lava flows. We obtained median values of VADM between 28.9 and 45.6 ZAm2 for the reverse polarity lower Apnia section, while the normal polarity upper section displayed a single value of 54.6 ZAm2. The low palaeointensity values before a transitional direction lava flow and the higher value after it, suggest the common behaviour at the start of a polarity reversal and the recovery after it. However, an isolated record of a stable EMF, where the intensity is lower than the current for the same location (83.7 ZAm2), cannot be discarded. Consequently, this interpretation would support a weak time-averaged field.Project CGL2012-32149 (Ministerio de Economía y Competitividad, Spain), project BU066U16 (Junta de Castilla y León, Spain), pre-doctoral grant BES-2013-064060 (Ministerio de Economía y Competitividad, Spain) and by National Science Foundation (USA) grant EAR1345003

An Integrated Paleomagnetic, Multimethod- Paleointensity, and Radiometric Study on Cretaceous and Paleogene Lavas From the Lesser Caucasus: Geomagnetic and Tectonic Implications

Sixteen rhyolitic and dacitic Cretaceous and Paleocene-Eocene lavas from the Lesser Caucasus have been subjected to paleomagnetic and multimethod paleointensity experiments to analyze the variations of the Earth's magnetic field. Paleointensity experiments were performed with two methods. Thellier-type experiments with the IZZI method on 65 specimens (nine flows) yielded 15 successful determinations and experiments with the multispecimen method on 14 samples (seven flows) yielded two successful determinations. The joint analysis of the results obtained with both methods produced a mean FuK = (19.9 ± 3.7) µT for upper Cretaceous and FPg = (20.7 ± 3.3) µT for Paleogene sites. Low virtual axial dipole moments for the Cretaceous (3.4 × 1022 Am2) and Paleogene (3.5 × 1022 Am2) samples support the idea of a lower average dipole moment during periods of stable polarity of the Earth magnetic field. Mean flow paleomagnetic directions did not match expected upper Cretaceous to Paleogene directions calculated from the European Apparent Polar Wander Path. While inclination results roughly agreed with expected values, a group of sites showed nearly North-South paleodeclinations (D = 1.1° ± 14.2°), and another group displayed eastward deviated paleodeclinations (D = 72.9° ± 26.6°). These results suggest the occurrence of nearly vertical-axis rotations, probably as a result of continental collision since Oligocene. In addition to paleomagnetic and palaeointensity analyses, new K-Ar absolute age determinations have been performed on three of the studied sites, yielding Late Cretaceous ages (78.7 ± 1.7, 79.7 ± 1.6, and 83.4 ± 1.8 Ma (2σ)).Project PID2019-105796GB-100/AEI/10.13039/501100011033 (Agencia Estatal de Investigación, Spain). M. Calvo-Rathert acknowledges funding from the Fulbright Commission and the Spanish Ministry of Science, Innovation, and Universities for a research stay at Hawaii University at Manoa. A. Goguitchaichvili acknowledges financial support from UNAM-PAPIIT no. IN101920. N. García-Redondo acknowledges financial support from Junta de Castilla y León and the European Research Development Fund (ERDF). EHB acknowledges financial support for laboratory maintenance and measurements to SOEST-HIGP and National Science Foundation grants. These is SOEST 11143 and HIGP 2420 contribution

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)

Magnetic dating of the Holocene monogenetic Tkarsheti volcano in the Kazbeki region (Great Caucasus)

The radiocarbon technique is widely used to date Late Pleistocene and Holocene lava flows. The significant difference with palaeomagnetic methods is that the 14C dating is performed on the organic matter carbonized by the rock formation or the paleosols found within or below the lava flow. On the contrary, the archaeomagnetic dating allows to date the moment when the lava is cooling down below the Curie temperatures. In the present study, we use the paleomagnetic dating to constrain the age of the Tkarsheti monogenetic volcano located within the Kazbeki Volcanic Province (Great Caucasus). A series of rock-magnetic experiments including the measurement of hysteresis curves, isothermal remanence, back-field and continuous thermomagnetic curves were applied. These experiments indicated that Pseudo-Single-Domain Ti-poor titanomagnetite is responsible for remanence. A characteristic remanent magnetization was obtained for all twenty analyzed samples yielding a stable single magnetization component observed upon both thermal and alternating field treatments. Comparison of the mean directions obtained (Inc = 48.6º, Dec = 6.4º, A95 = 4.0° and K = 67) with the SCHA.DIF.14k model yielded two main time intervals (4740–4650 or 4427– 4188 BC) as the best age estimate of the Lesser Tkarsheti lava flow. These results suggest an earlier age (between approximately 200 and 700 years) for this monogenetic lava flow than expected from the estimated age provided by a former 14C dating obtained in 1973 on woody remains. This first attempt to use the archaeomagnetic technique in the Caucasus indicates that the SCHA.DIF.14k geomagnetic model may be successfully used for dating purposes in the region.Projects BU0066U16 and BU235P18 (Junta de Castilla y Leon, Spain) and the European Regional Development Fund (ERDF). AG is grateful for financial support of CONACyT 252149 and UNAM-PAPIIT project 101717. MC-R and AC acknowledge the financial support given by the Junta de Castilla y León (project BU235P18) and the European Regional Development Fund (ERD)

Paleointensity Results From Pliocene Lavas of the Lesser Caucasus Obtained Using the Multispecimen Parallel Differential pTRM Method: A Comparison With Thellier- Thellier and IZZI Data

We report paleointensity results obtained with the multispecimen method (MSP) over the Pliocene sequence of Apnia (Georgia) which records a polarity reversal. Paleointensity determinations with the multispecimen technique were performed on 12 flows with the original (MSP-DB) and the domain-state corrected (MSP-DSC) protocol. Eight MSP-DSC determinations passed the proposed quality criteria. To obtain highly reliable data through the agreement between intensity values from different methods, MSP results were combined with paleointensities from a previous study with Thellier-type methods and especially strict selection criteria (RCRIT) on same flows (Sánchez-Moreno et al., 2020). Application of this multimethod procedure resulted in three new paleointensities including both MSP and Thellier-type results and an additional one obtained with two different Thellier-type methods, yielding one paleointensity of 36.9 µT in the normal-polarity, and three paleointensities between 19.2 and 24.1 µT in the reverse-polarity section. Additionally, Thellier-type data have been reinterpreted in this study with more flexible criteria (TTP) and the results combined with the MSP data. As a result, four flows yield paleointensities including MSP and Thellier-type determinations and seven include paleointensities obtained with two different Thellier-type methods. Results range from 37.2 and 44.3 μT in the normal-polarity and from 12.5 to 24.6 μT in the reverse-polarity section. Comparison of results from the four flows yielding multimethod determinations applying RCRIT criteria with those from the same flows under TTP criteria yields no significant difference in paleointensity values and their experimental uncertainty. Thus, application of a multimethod approach supports the possibility of using TTP criteria.Project PID2019-105796/10.13039/501100011033 (Agencia Estatal de Investigación, Spain), project BU066U16 (Junta de Castilla y León, Spain) and pre-doctoral grant BES-2013-064060 (MINECO, Spain). 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. AG is grateful to the financial support given by DGAPA-PAPIIT IN101717. At Montpellier laboratory, the FUReMAG rapid furnace construction was supported by the French National Agency for Research (ANR-12-BS06-0015)

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