Paleointensity of the Geomagnetic Field in Egypt from 4000 BC to 150 AD Using the Thellier Method.

Abstract

A total of 170 ceramic specimens from 16 archaeological sites representing 16 well determined ages from 4000 BC to 150 AD were investigated using the Thellier method. These paleointensities were compared with data from countries near Egypt after reduction to a common latitude to determine a secular variation curve of the geomagnetic field for the time period from 4000 BC to 150 AD. The field intensity increases from about 30 μT around 3500 BC to a maximum of 70 μT at about 400 BC when it starts to decrease until 150 AD. The Thellier double heating method was used together with the following additional test measurements : a) during the Thellier experiments the laboratory field F Lab . pointed in the direction of stable NRM, b) magnetic susceptibility was measured after each double heating step to check for chemical alteration, c) a TRM check was made, by repeating the pTRM induction at a lower temperature, d) recent samples which were fired in a known field were used to test the reliability of our experimental setup and method. Based on rock magnetic measurements magnetite was identified as the predominant carrier of magnetization in the ceramics and bricks.