Reconstructing the Geomagnetic Field in West Africa: First Absolute Intensity Results from Burkina Faso

We present new absolute geomagnetic intensity determinations from iron smelting kilns discovered at the metallurgical site of Korsimoro in Burkina Faso. A large number of furnaces were found at this site, which extends over an area up to 50 km2 . Up to now, archaeologists recognized four different types of kilns based on different construction methods. The types of kilns are related to four distinct subsequent time periods. Additionally, radiocarbon ages obtained from charcoal confine the studied kilns to ages ranging from about 700 – 1700 AD, in good agreement with the archaeologically determined time periods for each type of kiln. Archaeointensity results reveal three main groups of Arai diagrams. The first two groups contain specimens with either linear Arai diagrams, or slightly curved diagrams or two phases of magnetization. The third group encompasses specimens with strong zigzag or curvature in their Arai diagrams. Specimens of the first two groups were accepted after applying several selection criteria to guarantee the high quality of the results. Our data compared to the palaeosecular variation curves show a similar decreasing trend between 900-1500 AD. However, they reveal larger amplitudes at around 800 AD and 1650 AD than the reference curves and geomagnetic field models. Furthermore, they agree well with archaeomagnetic data from Mali and Senegal around 800 AD and with volcanic data around 1700 AD.