Microwave palaeointensity results from the Matuyama-Brunhes geomagnetic field reversal

We present new palaeointensity and palaeodirectional results from the Matuyama-Brunhes geomagnetic field reversal. Volcanic sequences from La Palma and Guadeloupe record the Matuyama-Brunhes boundary, possible precursors, and fluctuations in the magnetic field prior to the main polarity reversal. Absolute palaeointensity was determined using the microwave technique and palaeodirectional results were obtained from thermal demagnetisation. Ten flows from the 29 flows studied gave reliable mean palaeointensities; however, only 1 of the 10 flows records a transitional direction. The VDM determined from this flow is 1.9±0.6(±σ)×1022 A m2. Analysis of all Matuyama-Brunhes data suggests that the main directional changes occurred once the VDM was reduced below 3×1022 A m2(∼35% of the present field value).