Geomagnetic field in the Near East at the beginning of the 6th millennium BC: Evidence for alternating weak and strong intensity variations

This study presents new archeointensity results from the multilayered settlement Yarim Tepe I located today in Northern Iraq. Archeological evidences and new radiocarbon dates indicate that this site was occupied for about four centuries, between the end of the 7th and the beginning of the 6th millennium BC, leading to a 6.5 m-thick sequence of archeological deposits. A series of 16 groups of potsherds, with a total of 76 fragments, were collected from superimposed stratigraphic layers, with thicknesses of ∼30 cm on average. Archeointensity measurements were carried out using the Triaxe procedure, which takes into account both anisotropy and cooling rate effects on thermoremanent magnetization acquisition. In this study, 114 specimens from 40 fragments have fulfilled our selection criteria and mean archeointensity results were derived from nine different groups of fragments, with a minimum of three fragments per group. According to an age model constructed using a bootstrap approach, the new archeomagnetic record spans a time interval of ∼220 years between ∼6070 BCE and ∼5850 BCE. No significant intensity variations were observed during this time interval, with an overall mean intensity value of 42.0 ± 1.6 μT. A comparison of the Yarim Tepe I data with other archeointensity results spanning the 7th and 6th millennia BC previously obtained from the Near East, as well as from Eastern and Western Europe was conducted. The Yarim Tepe I results enabled to constrain the short duration, one century at most, of an intensity peak evidenced around 5750 BCE from the Bulgarian database. Intensity variation rates associated with the ascending branch of the peak reached values as high as ∼0.12-0.15 μT/year. Summarizing the geomagnetic field intensity variations in the Near East and Eastern Europe during the entire 6th millennium BC, it appears that they were likely characterized by the occurrence of two short-lasting intensity peaks at ∼5750 BCE and ∼5500 BCE, with intensity variation rates similar or slightly higher than the maximum rates prevailing in the modern field. Finally, it is worth mentioning that the four radiocarbon dates reported in our study provide new constraints for deciphering the temporal correlation between the cultural/historical phases (Halaf and Hassuna) that were independently defined from excavations carried out in Iraq and Syria.