Paleomagnetic analyses on red chert-like rocks and partly silicified paleosols within the Lower Devonian Ikniouen level of the Tadrart Formation

In order to improve the poor Gondwana paleomagnetic database for Devonian times, detailed paleomagnetic analyses were performed on red chert-like rocks and partly silicified paleosols within the Lower Devonian Ikniouen level of the Tadrart Formation. Silicification, limited to this level that is only a few meters thick, was probably due to tropical warm climatic conditions during and shortly after the rock deposition. In two sections 40 km away each other, paleomagnetic data point out a high temperature Characteristic Remanent Magnetization (ChRM) with a very well-defined mean direction and a positive reversal test. Rockmagnetism data evidence minerals of the hematite family, but the presence of a minor amount of other mineral phases remains possible. These paleomagnetic results could have major geodynamical implications for the Gondwana supercontinent. In fact, ChRM acquired in this level during or shortly after deposition should imply a very unexpected fast latitudinal continental drift of the Gondwana during the Lower Devonian. That should correspond, for the APWP, to a large loop with a reversal of the drift direction from a much more southern extreme location than previously assumed. A "more realistic" interpretation should be related to a significant True Polar Wander during this period. Though much more difficult to match with the ChRM and geological characteristics, the only possible alternative interpretation for the Ikniouen data should be a chemical remagnetization acquired during the Late Cretaceous - Early Paleocene times.