Magnetic susceptibility of loess in China

Abstract

The low-field susceptibility of the loess deposits in the Chinese Loess Plateau is due to both paramagnetic and ferromagnetic minerals. Paramagnetism can be seen in the less- to unweathered loess horizons where superparamagnetic contributions which arise from ultrafine magnetite particles, are not as strongly developed as in the heavily weathered palaeosols. Frequency-dependent susceptibility and minimum unblocking temperatures of low-temperature thermoremanent magnetization generally indicate finer grain sizes in the palaeosols as compared to the loess beds. This grain size difference and the fact that susceptibilities of the same stratigraphic palaeosol layer vary by an order of magnitude between the western and central regions of the plateau, are considered as strong evidence that the ultrafine magnetite is not of detrital (aeolian) origin but was formed in situ. The pedogenetic processes are clearly related to palaeoclimatic changes. Therefore the various susceptibility properties may serve for a detailed reconstruction of the continental palaeoclimatic conditions for the last 2.5 Ma since the palaeomagnetically dated beginning of loess sedimentation in China.