Behaviour of the Earth’s magnetic field during superchrons: comparative study of the Cretaceous and Meso-Neoproterozoic Maya events recorded in the flows of the Okhotsk- Chukotka Volcanic Belt (NE Russia) and the sediments of the Yenisey Ridge (SW Siberia

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The Earth’s magnetic field, generated by a dynamo process in the outer core, is a dynamic object, the time variability of which, on centennial-to-millenial timescales, is called palaeosecular variation (PSV). On multimillion-year timescales, this field is known to stochastically reverse its polarity, but can surprisingly also produce prolonged periods (> 20 Myr) with stable polarity termed superchrons. These persistently occurring events over the Earth’s history, documented both during the Phanerozoic and Proterozoic, are usually characterised by a strong dipolar field and low directional dispersion. Nevertheless, the possibility of more complex temporal dynamics with periods of higher variability within a superchron, has been recently proposed, and needs to be investigated further. Having a clear view of the behaviour of the geomagnetic field during superchrons, indeed has direct implications on the understanding of the outer core’s dynamics.To this end, we would like to investigate comparatively the behaviour of the Earth’s magnetic field during the Cretaceous Normal Superchron (CNS, 121–83 Ma) and the Meso-Neoproterozoic Maya superchron (PMS, ~1,000 Ma) recorded in the flows of the Okhotsk-Chukotka Volcanic Belt (NE Russia) and the sediments of the Yenisey Ridge (SW Siberia). The project includes two field campaigns in each area to collect a large amount of palaeomagnetic samples. On one hand, the almost unexplored magnetic record of the Okhotsk-Chukotka Belt offers a unique possibility to sample, at the same latitude, piles of volcanic flows from several time intervals within and after the CNS. On the other hand, the carbonate Kartochka formation of the Yenisey Ridge, is a nonpareil location to scrutinise the temporal evolution of the field during and around the PMS, and conduct relative palaeointensity experiments.The primary aim of this project is to produce detailed magnetostratigraphy for the Kartochka formation, and determine directional PSV estimates over various time intervals for the Okhotsk-Chukotka Volcanic Belt. We will pay special attention to the time dependency of the magnetic field to discern possible intermittencies of the geodynamo during the two investigated superchrons. We will also conduct relative (or where possible — absolute) palaeointensity experiments to determine the relative variability in intensity, which is assumed to be a robust and latitude-independent PSV estimator. One secondary method-related aspect of the project will be to better assess the robustness of pseudo-Thellier experiments. Ultimately, our new results will be compared with the existing palaeomagnetic dataset and the predictions from numerical dynamo simulations.