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

地球磁场是由外核发电机过程产生的，是一个动态的物体，其时间变化，在百年至千年的时间尺度上，被称为古长期变化（PSV）。在数百万年的时间尺度上，这个磁场被认为是随机反转其极性的，但令人惊讶的是，它也可以产生长时间（> 2000万年）的稳定极性，称为超时。这些在地球历史上持续发生的事件，在中生代和元古代都有记载，通常以强偶极场和低方向色散为特征。然而，最近有人提出，在一个超时期内，可能存在更复杂的时间动态，其周期变化更大，需要进一步研究。 对超时期地磁场行为的了解，对理解外核动力学有直接的意义，为此，我们想对白垩纪正常超时期地球磁场的行为进行比较研究（CNS，121-83 Ma）和中新元古代玛雅超时（PMS，~ 1，000 Ma）记录在鄂霍次克-楚科奇火山带（俄罗斯东北部）和叶尼塞海脊（西伯利亚西南部）的沉积物中。该项目包括在每个地区进行两次野外活动，以收集大量的古地磁样品。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，可以在同一纬度上对CNS内部和之后几个时间间隔的火山流进行采样。另一方面，碳酸盐岩Kartochka形成的叶尼塞海脊，是一个无与伦比的位置，以仔细检查PMS期间和周围的场的时间演化，并进行相对palaeostigmentsexperiments.The项目的主要目的是产生详细的磁性地层的Kartochka形成，并确定方向PSV估计在不同的时间间隔的鄂霍次克-楚科奇火山带。我们将特别注意磁场的时间依赖性，以辨别在两个研究的超时期间地球发电机的可能振荡。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化，这被认为是一个强大的和纬度无关的PSV估计。该项目的一个次要方法相关方面将是更好地评估伪Thellier实验的鲁棒性。最终，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.