First archeomagnetic data from Kenya and Chad: Analysis of iron furnaces from Mount Kenya and Guéra Massif

Abstract

The variation of the Earth's magnetic field over the last millennia is poorly known in Africa, especially in Sub-Saharan Africa that represents less than 1% of the global archeomagnetic dataset. Fourteen iron furnaces from Kenya and Chad have been studied here for archeomagnetic purposes. These structures were dated by 14C from the 14th century in Kenya and from the 18-19th centuries in Chad. Samples, oriented with the plaster cap technique, have been subjected to thermal and alternating field demagnetization, rock magnetic analysis and paleointensity experiment, with the classical Thellier-Thellier technique corrected for anisotropy and cooling rate effects. New directional data (4 from Kenya and 10 from Chad) and one new paleointensity estimate from Kenya (43.5 ± 1.8 μT) were obtained. The Kenyan declinations are in good agreement with the geomagnetic global models, but the inclinations are lower and the intensity higher than predicted. For Chad, the new results prove the efficiency of the archeomagnetic dating, with a precision that is better than radiocarbon for the 18–19th centuries.