Anomalous directions of the natural remanent magnetization in Late Pleistocene marine sediments from the coast of Mauritania (West Africa)

Abstract

Two closely located deep-sea cores taken along the coast of Mauritania contain zones of anomalous directions of the natural remanent magnetization (NRM) which fall mainly within the potential time-spans of the published excursions/events (e/e) of the Earth magnetic field for the last 220 kyr. In two cases even reversed polarity is seen. In all cases in which anomalous directions are detected the sediments show a strong change in magnetic properties, such as natural and anhysteretic remanent magnetization and low field susceptibility. Changes of the magnetic parameters and anomalous remanence directions coincide with rapid changes of stable oxygen isotope ratios, i.e., correspond to isotope stage or substage boundaries, and thus correspond to glacial/interglacial transitions. The good accordance of ages of the observed anomalous directions with previously identified e/e may be partially caused by the large uncertainty in dating of many of these previously determined short e/e. Therefore, it is concluded that climatically controlled changes of the ferromagnetic mineralogy with related remagnetization and mineral interactions cause the anomalous NRM directions. On the other hand, if one considers the correlation between anomalous directions, climatic changes and published e/e to be significant, one is led to postulate either that both Earth field related directional changes of the NRM and climatically induced mineralogical changes are caused by a common mechanism or that changes in climate with changing sea level and changing ocean circulation triggered the e/e of the geomagnetic field.