The Laschamp excursion

Abstract

The reversely magnetized lavas at Laschamp and Olby (Chaine des Puys, Auvergne, France) are commonly believed to document the most recent geomagnetic field excursion in the present Brunhes normal epoch. However, complete or partial self-reversal of natural remanent magnetization (n.r.m.) is observed in many Olby samples and to a lesser extent in the Laschamp rocks during thermal laboratory experiments. Magnetic and optical examination suggests that the self-reversal mechanism is caused by a negative magnetostatic coupling between titanomagnetite phases of widely varying degrees of oxidation. To check independently whether field reversal or self-reversal caused the reversed n.r.m. directions, a contemporaneous loess section at Steinheim (southern Germany) has been studied magnetostratigraphically. No reversed polarities have been detected in this section or in other loess profiles from Czechoslovakia and northern China.