Rock magnetism and geomagnetic field strength of the rare Iron Age (300–500 BC) artifacts from Tamilnadu: The first Virtual Axial Dipole Moment determination from India

Abstract

Archaeological artifacts are abundant in India to undertake archaeointensity (AI) research. High quality AI data from this region are essential to improve global geomagnetic field (GGF) model secular variation curve for the past few millennia for its applicability to the Indian region. Rock magnetic and AI investigations are carried out on 15 rare Megalithic/Iron Age (300–500 BC) pottery samples from the Sengalur site, Tamilnadu, India. Rock magnetic results indicate that either SD/PSD type of ferrimagnetic mineral (magnetite/titanomagnetite) is responsible for magnetic remanence. Temperature versus susceptibility experiments for most of the samples yield reversible heating and cooling curves with Curie temperatures of 565–585 °C. AI values are determined by the Thellier–Thellier method as modified by Coe 1967 (Zero-field/In-field method). The AI data of the present study meets the reliability and quality criteria adopted for the AI determinations worldwide. The mean AI of 47.48 ± 1.72 µT and a mean Virtual Axial Dipole Moment of 11.7 ± 0.4 × 10²² Am² are estimated. This new AI data are in good agreement with the predictions of ARCH3K.1 GGF model for the period of 300–500 BC for India derived from the GEOMAGIA. V₃ updated database. Other models incorporating sediment data are not consistent with the actual values of direct determination.