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

Abstract

We present absolute geomagnetic intensities from iron smelting furnaces discovered at the metallurgical site of Korsimoro, Burkina Faso. Up to now, archaeologists recognized four different types of furnaces based on different construction methods, which were related to four subsequent time periods. Additionally, radiocarbon ages obtained from charcoal confine the studied furnaces to ages ranging from 700–1700 AD, in good agreement with the archaeologically determined time periods for each type of furnace. 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 selection criteria to guarantee the high quality of the results. Our data compared to 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.

New Archeomagnetic Directional Records From Iron Age Southern Africa (ca. 425–1550 CE) and Implications for the South Atlantic Anomaly

“…Although several recent studies have improved coverage over the African continent, for example, archeointensities (Kapper et al, ; Mitra et al, ) and directions (Donadini et al, ) from west African archeological sites, these locations remain at least 40° north of the CMB reversed flux patch (i.e., extrapolated to a surface location) linked to the present‐day SAA. We recently presented the first archeomagnetic data from Iron Age sites of southern Africa (∼1000–1550 CE) (Neukirch et al, ; Tarduno et al, ).…”

“…Here we present a new magnetic record from sites of southern Africa. The new record supports our prior inferences that the SAA is just the most recent manifestation of a recurring phenomenon in the core beneath Africa-called flux expulsion-that is having a profound impact on the expression of the geomagnetic field.Although several recent studies have improved coverage over the African continent, for example, archeointensities (Kapper et al, 2017;Mitra et al, 2013) and directions (Donadini et al, 2015) from west African archeological sites, these locations remain at least 40 ∘ north of the CMB reversed flux patch (i.e., extrapolated to a surface location) linked to the present-day SAA. We recently presented the first archeomagnetic data from Iron…”

Novel insights on the geomagnetic field in West Africa from a new intensity reference curve (0-2000 AD)

“…The low standard deviations indicate a low anisotropy effect, because the anisotropy correction is not only affected by characteristics of the magnetic grains, but also by the orientation of the NRM respectively to the applied laboratory field (e.g., Veitch et al 42 ). Anisotropy corrections of specimens from KRS obtained by Kapper et al 43 as well are low for the majority of the specimens.…”

“…The low success rate of 29% for all sites combined of the pseudo-Thellier method may be caused by the presence of a hard magnetic phase, which is not eliminated by a 300 mT alternating magnetic field. We did not apply an anisotropy correction on these specimens based on previous low determinations 43 . In total, we obtained ten new data with the TH-C protocol, eight new data with the P-TH protocol, and seven reanalysed data from the TH-I method.…”

Recent Advances in Chinese Archeomagnetism

“…Recent archeomagnetic studies are mostly concentrated in Europe Gómez-Paccard et al, 2012;Tema et al, 2012;Genevey et al, 2013;Hervé et al, 2013a,b;Kovacheva et al, 2014) and the Middle East (Ertepinar et al, 2012(Ertepinar et al, , 2016Gallet et al, 2015;Shaar et al, 2016;, with a few publications from other areas such as Mexico (Guerrero et al, 2016), Africa (Mitra et al, 2013;Tarduno et al, 2015;Kapper et al, 2017) and Asia (Yu et al, 2010;Hong et al, 2013;Venkatachalapathy et al, 2013). China constitutes a huge part of Eastern Asia and has a civilization that spans thousands of years leaving abundant archeological artifacts.…”