A palaeomagnetic study of Cambrian red beds from Cartaret, Normandy, France

Results are reported from a short stratigraphic sequence of Lower Cambrian red sediments outcropping in Dennemount Quarry, Cartaret and Pointe-de-Rozel, Normandy. After af cleaning the data show a smear from steep to shallow positive magnetic inclination. Changes in inclination appear to be related to stratigraphic position – steep inclinations are stratigraphically lower than shallow inclinations. Further thermal and chemical treatment reveal that this smear does not record polar wander, rather it is the result of the interaction of two distinct remanence phases. Fold tests, chemical cleaning and opaque petrology indicate that the sequence of remanence acquisition was first the shallow south-westerly magnetization, followed later by the steep magnetization. Pole FB (13° S, 301° E, α95= 8°) appears to date the initial depositional event. It may either be a chemical, or a detrital magnetization, or some combination of the two. Pole FA (22° N, 354° E, α95= 11°) is related to the red pigmentation of the sediments. Although no strict age constraints can be applied to this remanence, a basal Ordovician age is preferred.