Rock magnetic and geomagnetic field intensity studies on Megalithic archaeological pottery samples from Tamilnadu, India

Abstract

Archeointensity (AI) data from India are necessary in order to constraint the global models of the Earth's magnetic field. Unfortunately, no attempts have been made in India for archeointensity determinations using reliable modern scientific methods. In the present study, the rock magnetic and archeointensity investigations were carried out for 40 pottery samples collected from two different archaeological sites of southern India, Marungur (Megalithic burial: 200–300 BC) and Vadaharirajapuram (Megalithic habitation: 200–100 BC). Rock magnetic analyses confirm the suitability of samples for reliable AI measurements. Thermo-magnetic (χ–T) curves for most of the samples indicate the presence of stable magnetite as the main magnetic mineral. AI values were estimated using Zero field/infield (ZI) method, which is a modified Thellier–Thellier technique. All samples were corrected for cooling rate effects. After cooling rate correction, the mean AI values are estimated as 48.22 ± 1.50 μT and 46.08 ± 0.85 μT for the Marungur and Vadaharirajapuram sites respectively. These new AI data from southern India are a little higher compared to the values predicted for the same period from the existing global geomagnetic field models, and would help to improve the global models of the Earth's magnetic field for the past few millennia.