Geomagnetic moment instability between 0,6 and 1,3 Ma from cosmonuclide evidence.

International audienceThe reliability of paleomagnetic records as proxies of the geomagnetic field intensity is still a matter of controversy since volcanic materials hardly provide continuous records, and marine sediments are suspected to carry a remanence biased by post‐depositional realignments and/or by overprints. Such long standing debate emphasizes the need for the development of methods independent from paleomagnetism to decipher geomagnetic intensity variations. High resolution measurements of authigenic 10Be/9Be along with a detailed sedimentary record of directional and relative paleointensity variations evidence, over the 0.6–1.3 Ma time interval, frequent and recurrent excursions or short events in the late Matuyama and the early Brunhes epochs, among which two Brunhes‐Matuyama reversal precursors and an intra‐Jaramillo excursion. The results of this study confirm the idea of a highly unstable geomagnetic field as suggested by paleomagnetic evidences