Palaeomagnetic dating of the "Borne de Fer" ferricrete (NE France): Lower Cretaceous continental weathering
Résumé
A palaeomagnetic study was carried out on the Borne de Fer ferricrete in north-eastern France, close to the Luxembourg border. This ferricrete is overlain by kaolinitic red clay and caps a silto-argilaceous saprolite 15 to 40 m thick showing weathering features, evolution of the clay minerals from the base to the top and karstic solution pipes beneath. This weathering profile lies above Jurassic marl and limestone from around 425 to 450 m a.s.l. and may correspond to a scarce remnant of an old weathering palaeosurface. Palaeomagnetic, rockmagnetic and petrographic analyses reveal presence of a dominant hydroxide contribution with a magnetic remanence carried by goethite. A small contribution of maghemite or hematite carries a more scattered but similar direction. The virtual geomagnetic pole derived from the goethite component lies at lat 73.4°N, lon. 205.9°E, dp 4.3, dm 6.2. This location close to the 120-140 Ma reference poles and presence of normal and reversed polarities are consistent with a Lower Cretaceous age close to the Long Normal Cretaceous Superchron. Our results are consistent with the ones obtained recently in Germany, Belgium and France and prepare the ground for reconstructing the Lower Cretaceous continental palaeosurface geometry and palaeogeography.