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

地球磁场是由外核的发电机过程产生的，是一个动态的物体，其时间变化在百年到千年的时间尺度上被称为古长期变化（PSV）。在数百万年的时间尺度上，我们知道这个磁场会随机地反转其极性，但令人惊讶的是，它也会产生长时间的（bb0 - 20myr）稳定极性，被称为超时。这些在显生宙和元古代记录的地球历史上持续发生的事件通常以强偶极场和低定向色散为特征。然而，最近提出了在超时线内具有较高变率周期的更复杂时间动力学的可能性，需要进一步研究。对超时期间地磁场的行为有一个清晰的认识，确实对理解外核的动力学有直接的影响。为此，我们将比较研究俄东北部鄂霍次克-楚科奇火山带流动和西伯利亚西南部叶尼塞脊沉积物中记录的白垩纪正常超时（CNS, 121-83 Ma）和中-新元古代玛雅超时（PMS, ~ 1000 Ma）的地球磁场行为。该项目包括在每个地区进行两次实地考察，以收集大量的古地磁样本。一方面，鄂霍次克-楚科奇带几乎未被探索的磁记录提供了一种独特的可能性，可以在同一纬度取样，从几个时间间隔内和之后的火山流堆。另一方面，叶尼塞脊的碳酸盐岩Kartochka组是研究PMS期间及其周围的场的时间演化和进行相对古强度实验的绝佳地点。该项目的主要目的是为Kartochka地层生成详细的磁地层学，并确定鄂霍次克-楚科奇火山带在不同时间间隔内的定向PSV估计。我们将特别注意磁场的时间依赖性，以辨别在两个所研究的超时期间地球发电机可能的间歇性。我们还将进行相对（或在可能的情况下-绝对）古强度实验，以确定强度的相对变异性，这被认为是一种鲁棒且与纬度无关的PSV估计器。该项目的第二个与方法相关的方面将是更好地评估伪泰勒实验的稳健性。最后，我们的新结果将与现有的古地磁数据集和数值发电机模拟的预测结果进行比较。

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.