Three lava flows (Buenavista, Xalitzintla and Nealtican) and pyroclastic density currents (Lorenzo and Pink Pumice) from two Popocatepetl Plinian eruptions were sampled for paleomagnetic dating. A detailed rock-magnetic characterization of the lavas, scoria clasts and pottery shards intercalated between the volcanic deposits was also carried out. Reliable results, both in direction and in intensity, were obtained for the Nealtican lava flow, which enabled its full-vector paleomagnetic dating using the archaeo_dating tool together with the global paleosecular variation model SHA.DIF.14 k, obtaining an age interval between 1040 AD and 1140 AD (95% probability confidence level), in good agreement with its associated 14C age. The well-grouped paleomagnetic direction of the seven specimens from two different scoria clasts of the Lorenzo Pumice pyroclastic density current suggests that clasts were emplaced hot, at a temperature that seems to have almost completely erased the original remanent magnetization of the clasts. This fact is supported by the reheating of the underlying pottery shards, evidenced as a clear secondary low-temperature range (room temperature to 350 °C) component at the orthogonal vector plots. Similarly, the three mean clusters directions obtained for site PO-2 (Pink Pumice)—roughly concentrated around the present geomagnetic field—suggest also a high emplacement temperature. Also, the first archeointensity dating of a pottery shard within the pyroclastic density current is reported. Finally, results of the rock-magnetic and paleomagnetic dating of the last Plinian eruptions from the Popocatepetl volcano, applied to different volcanic materials (lava and pyroclastic density currents), show the usefulness of these nonconventional and alternative techniques in the study of the eruptive activity of volcanoes. .
31 October 2013 in Studia Geophysica et Geodaetica
We report an archeomagnetic study from the Early Iron Age archeological site of Cerro de San Vicente (Salamanca, Spain). The studied materials were sampled from one roundhouse and its central fireplace, a surrounding burnt floor, and slags with a twofold objective. First, to archeomagnetically determine the last use of the central fireplace, because dating with other methods was imprecise. Second, to retrieve information about the Earth's magnetic field in Western Europe from a period when the Levantine Iron Age Anomaly (LIAA) has been occasionally reported. This study includes mineralogical, archeomagnetic directional analyses, and multimethod archeointensity determinations. Paleomagnetic analyses of the central fireplace yield a mean direction: declination D = 15.1°, inclination I = 52.5°; k = 477.1, and α95 = 5.6°. Archeointensity determinations yield a mean anisotropy‐corrected archeointensity of 72.4 ± 2.0 μT (74.7 ± 4.3 μT if a pTRM‐check correction is applied) on the central fireplace and 48.2 ± 2.0 μT on slags. A full‐vector archeomagnetic dating was performed with the SHA.DIF.4k geomagnetic field model which yielded an age interval of last use of the central fireplace between 644 and 575 BCE (654–575 BCE with the pTRM‐check corrected data) at 95% confidence level. This date agrees with the archeological context. Results allows to place the high paleointensity obtained near the maximum observed in Iberia at this age, confirming the existence of this peak related to the LIAA in Western Europe where records of this feature are still scarce.