This study systematically investigates changes in both compositions and grain-sizes of magnetic minerals in the Chinese loess/paleosol samples (Yichuan, China) during thermal demagnetization processes. Between 100 and 200°C, (1) Hc and Hcr significantly decrease while Mrs and Ms remain stable; (2) concentration of the multi-domain (MD) grains increases while that of superparamagnetic (SP) grains decreases; and (3) there exists the abnormal behavior of the thermal demagnetization in the natural remanent magnetization (NRM). In addition, the corresponding changes in all these parameters are gradually muted with the increase of the pedogenesis degree. The results indicate that the observed alteration probably relates to reducing processes caused by the burning of the organic matter in samples. Before the thermal treatment, the MD grains in loess samples had been partially altered in nature by low-temperature oxidization (LTO). This CRM can be sufficiently attenuated or even removed by the reducing process between 100 and 200°C during the thermal treatment and has no apparent harmful effects on the characteristic remanent magnetization (ChRM) between 300 and 500°C.
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Acknowledgements We thank Guo Bin for helping to collect samples. This work was supported by NSF (Grant Nos. EAR 0003421 and EAR/IF 9818704) and the National Natural Science Foundation of China (Grant No. 49834001). All the measurements were performed at the Institute for Rock Magnetism, which is funded by the Keck Foundation, the US National Science Foundation, and the University of Minnesota. References 1. Liu, T. S. et al., Loess and the Environment, Beijing: China Ocean
- Chemical remanent magnetization
- Chinese loess
- Low-temperature oxidation
- Natural remanent magnetization
- Verwey transition