Full vector archaeomagnetic dating of an Early Iron Age archaeological settlement: El Castillar site (Navarra, northern Spain)

Abstract

During the course of the excavations of the Early Iron Age site of El Castillar (northern Spain), a well-preserved burnt level was discovered. The wide time interval provided by four ¹⁴C dates (ca. 800–––416 BCE) offered a good opportunity to perform a full-vector archaeomagnetic study to date the last heating and site abandonment. These studies analyze the remanent magnetization acquired by ferromagnetic minerals after a heating event. For this purpose, eight magnetically oriented hand blocks were collected, and we performed a suite of rock-magnetic experiments and X-ray diffraction analyses along with paleomagnetic and archaeointensity determinations with the Thellier-Coe and Tsunakawa-Shaw methods. Paleomagnetic analyses yielded a mean direction of Declination = 14.9˚ and Inclination = 58.6˚ (α₉₅ = 4.1˚, k = 214, n = 7/8). Successful archaeointensity results were obtained with the Thellier-Coe method, which yielded a mean intensity value of 64.3 ± 1.8 µT (VADM = (10.8 ± 0.3)*10²² Am²). The main magnetic carrier is magnetite with Mg-cation substitutions. A full-vector archaeomagnetic dating, using the SCHA.DIF.4 k geomagnetic model and the Iberian Iron Age PSVC (at 95 % confidence), suggested different compatible age intervals. The youngest is the archaeologically most consistent one, which narrows the dating range to only a few decades according to the Iberian − Iron Age PSVC (685–––655 yr BCE). The relatively high intensity values obtained are compatible with the occurrence of the Levantine Iron Age Anomaly (LIAA) in Western Europe, although not at its highest values. The potential of archaeomagnetism over other dating techniques to accurately date Early Iron Age combustion events is demonstrated.