Is the Geodynamo Characterized by a Distinct Geomagnetic Secular Variation Regime During the Cretaceous Normal Superchron?

Lhuillier, Florian ; Lebedev, I. E.; Tikhomirov, P. L. und Pavlov, V. E. (2025): Is the Geodynamo Characterized by a Distinct Geomagnetic Secular Variation Regime During the Cretaceous Normal Superchron? In: Journal of Geophysical Research: Solid Earth, Vol. 130, No. 4, e2024JB030928

Abstract

The Earth's magnetic field stochastically reversed its polarity over geological time, yet enigmatically interrupted this process during the Cretaceous Normal Superchron (CNS; 84–121 Ma). Two scenarios have been proposed in terms of either gradual or abrupt changes to describe the transition of the geodynamo from the CNS to a period with frequent polarity reversals. To discriminate between these two scenarios, we sampled 136 volcanic flows emplaced 66–73 Ma in the eastern part of the Okhotsk-Chukotka Volcanic Belt (NE Eurasia). The 1,700 collected paleomagnetic samples provide, after correction for serial correlation, a robust data set of 112 independent paleodirections characterizing the behavior of the geomagnetic field at a paleolatitude of N shortly after the end of the CNS. Compared to paleomagnetic data from Chukotka and Northern Canada emplaced at similarly high paleolatitude, the dispersion of the virtual geomagnetic poles, used as a proxy for paleosecular variation (PSV), is 19% (resp. 55%) higher at 66–73 Ma than at the end of CNS when transitional directions are discarded (resp. retained). In contrast, our value at 66–73 Ma is, whatever the filtering strategy, statistically indistinguishable from the value at 0–10 Ma derived from the Antarctica and Spitsbergen volcanics. From the viewpoint of PSV observed at high paleolatitude (70–80 ), our new results are consistent with an abrupt change between two geodynamo regimes. Nevertheless, once the geodynamo starts reversing its polarity, the vigor of PSV does not seem to correlate with the reversal rate.

Plain Language Summary:

The geomagnetic field, produced by the convection of an electrically conducting alloy in the Earth's outer core (a process termed geodynamo), can be modelled in first approximation by a geocentric axial dipole. Over centennial to million-year timescales, it experienced directional fluctuations around it dipolar geometry as well as stochastical reversals of its polarity, although these polarity reversals unexpectedly became dormant during the 37 million year long Cretaceous Normal Superchron (CNS, 84–121 Ma). Whether the amplitude of the directional fluctuations correlates with the rate of polarity reversal remains controversial. To decipher how the geodynamo transitioned from a stable state of polarity to a state with frequent polarity reversals, we scrutinized the magnetic remanence of 136 volcanic flows from north-eastern Eurasia, emplaced at high latitude soon after the end of the CNS. These records provide independent instantaneous readings of the Earth's magnetic field and can be used to assess the amplitude of the directional fluctuations. Our paleomagnetic results are consistent with an abrupt change of the state of directional fluctuations at the end of the CNS. At the same time, the amplitude of directional fluctuations seems to be uncorrelated with the reversal rate when the geodynamo experienced frequent polarity reversals.

• Item Type: Journal article
• Faculties: Geosciences > Department of Earth and Environmental Sciences > Geophysics; Geosciences > Department of Earth and Environmental Sciences > Projects > SPP 2404 DeepDyn
• Subjects: 500 Science > 550 Earth sciences and geology
• ISSN: 2169-9313
• Language: English
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 405632737
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 500707704
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 521315821