Geomagnetic Dipole Strength During the Cretaceous Normal Superchron Recorded by Baked Sediments From Hainan (SE Asia)

Chi, Yuchen; Lhuillier, Florian; Meng, Jun; Zhang, Chunyang; Shcherbakov, Valeriy P. (2025): Geomagnetic Dipole Strength During the Cretaceous Normal Superchron Recorded by Baked Sediments From Hainan (SE Asia). Geophysical Research Letters, 52 (17): e2025GL116. ISSN 0094-8276

Abstract

The Cretaceous Normal Superchron constitutes an enigmatic ∼37-Myr interval of stable polarity in the history of the Earth's magnetic field. The strength of the geomagnetic dipole moment during this interval is controversial, with absolute paleointensity determinations on crystallized volcanic rocks, volcanic glasses, and silicate crystals yielding statistically different averages. In this study, we present the first paleointensities in the mid of the superchron conducted on baked sediments from Hainan (SE Asia). This hitherto underexploited material, akin to baked clays used in archeomagnetism, produces unambiguous linear Arai-Nagata diagrams over 60%–90% of the fraction of natural remanent magnetization. Using strict selection criteria, we show that baked sediments, volcanic glasses, and silicate crystals are consistent with a dipole moment ∼40% higher than the present-day value. Relying on 22 independent determinations only, this combined data set leaves open the question of the dependency between geomagnetic dipole strength and reversal frequency.

Plain Language Summary:
The paleomagnetic field, produced by the convection of liquid iron in the Earth's outer core, regularly switched the polarity of its dipole over geological time and yet experienced an unusual ∼37 Myr interval of stable polarity during the Cretaceous. The strength of the paleomagnetic dipole during this so-called superchron remains contentious, with paleointensity experiments yielding values 2–3 times higher for single crystals of silicate than for crystallized volcanic rocks. In this study, we conducted the first absolute paleointensity experiments on sandstones baked by diabase dykes in the mid of the Cretaceous superchron. These baked sediments, similar in their properties to the baked clays used in archeomagnetism, are reliable paleomagnetic recorder, yielding a paleointensity of 40–50 μT at ∼105 Ma in Hainan (China). Compared to strictly selected determinations from the absolute paleointensity database, our results from baked sediments are largely consistent with those from silicate crystals and volcanic glasses, pointing to a dipole moment during the Cretaceous superchron ∼40% higher than the present-day value. In disagreement with controversial paleointensity determinations conducted on crystallized volcanic rocks, the results from baked sediments, volcanic glasses, and silicate crystals may be consistent with an inverse relationship between geomagnetic dipole strength and reversal frequency.

• Dokumententyp: Artikel (LMU)
• Organisationseinheit (Fakultäten): 20 Geowissenschaften > Department für Geo- und Umweltwissenschaften > Geophysik
• DFG-Fachsystematik der Wissenschaftsbereiche: Naturwissenschaften
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 491502892
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 521315821