Abstract
The reversed natural remanent magnetisation (NRM) of the volcanic features at Laschamp and Olby (Chaîne des Puys, Auvergne, France) is commonly believed to document the youngest excursion of the geomagnetic field during the present Brunhes epoch. Recent radiometric dating determines the age of these lavas to be 35000–45000 y. Continuous thermal demagnetisation indicates that under laboratory conditions the NRM of many Olby samples undergoes complete or partial self-reversal; to a lesser extent this is also true for the Laschamp material. Thus self-reversal may be another possible explanation of the reversed NRM directions. Magnetic, optical and microprobe analyses suggest that the self-reversal mechanism is based upon magnetostatic interaction between differently oxidised titanomagnetite phases.
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