Magnetite Oxidation and Matrix Lithology Affect Sedimentary Recording of Geomagnetic Field Intensity: Evidence From Synthetic Sediment Deposition Experiments

Abstract

Magnetite and maghemite are the most common carrier minerals of paleomagnetic information in marine and terrestrial sediments. Previous research has shown that environmental factors such as salinity, flocculation, bioturbation, and sediment lithology affect depositional remanent magnetization (DRM) intensity. Whether and how much pre‐depositional low‐temperature oxidation of magnetite, known as maghemitization, influences sedimentary recording efficiency and relative paleointensity (RPI) remains controversial. To address this question, we conducted synthetic sediment deposition experiments where pure stoichiometric and partially oxidized magnetite powders dispersed in carbonate and kaolin slurries were deposited and dried in Earth‐like laboratory magnetic fields. The maghemitization levels reached by heating magnetite in air to 200 and 250°C were confirmed by changes in low‐temperature magnetic properties. Saturation magnetization and RPI decreased systematically with increasing oxidation state. Approximately 50% maghemitization reduced RPI by about 50%. A comparison of the experimental results with a simple DRM acquisition model indicates that this decrease cannot be explained by the reduction in spontaneous magnetization alone, but is mainly controlled by oxidation‐induced changes in particle aggregation. Lower RPI of unoxidized magnetite deposited in carbonate compared to kaolin slurry likely reflects matrix‐dependent differences in aggregation and associated intergranular and magnetostatic interactions.