Ferrimagnetic minerals in red paleosols of Pleistocene Epoch, eastern China

Abstract

The type, grain size and origin of ferrimagnetic minerals separated from red paleosols of Pleistocene Epoch (Q2) in eastern China, were studied by using mineral magnetic measurement, X-ray powder diffraction and electron microscopy. Results showed that the iron oxides in red paleosols were composed of hematite (α-Fe2O3), maghemite (γ-Fe2O3) and goethite(α-FeOOH). Mineral magnetic parameters and X-ray diffraction patterns indicated that maghemite was the dominant remanence carrier in red paleosols, which is characterized by superparamagnetic (SP) and stable single domain (SSD) grains. The variations of magnetic susceptibility (χ), anhysteretic magnetic susceptibility (χarm) and saturation isothermal remanent magnetization (SIRM) for red paleosols following heating to various temperatures showed two peak values at 700°C and 900°C. The spherulitic magnetic particles measuring 250–1000μm in diameter in red paleosols were separated by the magnetic separation method, indicating that these magnetic particles were an assemblage of superparamagnetic and stable single domain ferrimagnetic grains. It is suggested that the ferrimagnetic minerals of red paleosols be a pedogenic ferrimagnetic component under high temperature and high humid conditions in the Pleistocene Epoch (Q2). It is concluded that the magnetism characteristics of red paleosols can be used to evaluate the environmental changes of Quaternary in eastern China.