Magnetic Properties and Magnetic Mineralogy of Subtropical Ferrisols

Abstract

AbstractMineral magnetism parameters, including magnetic susceptibility (χ), frequency dependent susceptibility (χfd), anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM), had been measured on 55 Ferrisols formed on Quaternary red clay in subtropical regions of China. Magnetic measurement data, combining with chemical selective dissolution technique of iron oxide and X‐ray diffraction analysis, provided insight into the magnetic characteristics and magnetic mineralogy of Ferrisols. Results showed that the strongly magnetic minerals were found in most of the Ferrisols. The χ values of Ferrisols had a highly significantly exponential positive relation with free iron oxide (Fed) contents of soils (R2=0.5971), and the χfd values of Ferrisols were highly significantly linearly correlated with Fed contents of soils (R2=0.4289). The χfd and ARM susceptibility (χARM) values of Ferrisols showed that the magnetic minerals in the soils existed mainly in superparamagnetic (SP)/stable single domain (SSD) grain sizes. The χ values of Ferrisols were highly significantly positive proportional to χARM of soils (R2 = 0.9429), indicated that the magnetism of Ferrisols mainly came from the contribution of pedogenic SP and SSD magnetic grains. Mineral magnetic measurements and X‐ray diffraction patterns indicated that iron oxide mineralogy of Ferrisols was comprised of hematite (α‐Fe2O3), maghemite (γ‐Fe2O3) and goethite (α‐FeOOH), suggesting that maghemite is the main magnetic minerals in Ferrisols. The possible mechanisms of origin of maghemite in Ferrisols were also discussed.