Self-reversal of natural remanent magnetisation in the Olby-Laschamp lavas

Abstract

In 1967 Bonhommet and Babkine1 reported reversed magnetisation directions in two lavas at Laschamp and Olby (Chaine des Puys, Auvergne, France). They argued that the remanent magnetisation might have originated either from an episode of reversed polarity of the geomagnetic field within the Brunhes normal epoch or from a process of self-reversal2 occurring in these lavas. I report here experimental evidence that the natural remanent magnetisation (NRM) of certain samples of the Olby flow undergoes complete self-reversal during thermal demagnetisation. Other Olby samples show partial self-reversal of NRM at room temperature.