Etude paléomagnétique des formations du Plio-Pléistocène de la région de la Peninj (Ouest du lac Natron, Tanzanie). Limites de l'interprétation magnétostratigraphique. Paleomagnetic study of Plio-Pleistocene formations in the Peninj area (west of Lake Natron, Tanzania ). Limits of the magnetostratigraphic interpretation

Abstract

Complementary experiments have been performed on the sedimentary and volcanosedimentary fossiliferous deposits of the western margin of the Lake Natron basin in order to check the previous interpretations. The dominant reverse polarity was thought to be interrupted by five normal polarity zones possibly correlated with events in the Matuyama epoch. However, uncertainties remained on the depositional origin of the stable normal magnetization. According to the new results (Saturation Isothermal Remanent Magnetization and new thermal analysis), the normal polarity zones cannot be further considered as geomagnetic polarity events but resulting from complete or nearly complete remagnetizations probably due to chemical alteration. The only reliable polarity is the reverse one, attributed to the Matuyama epoch.