摘要
Through the studies on low temperature susceptibility, frequency dependent susceptibility, isothermal remanent magnetization, low temperature magnetization and demagnetization for loess and palaeosols one can easily reveal some significant characters of rock magnetism for the magnetic minerals of ultrafine grain sizes, those are very difficult to identify by general geological methods. It is shown in the present study that both loess and palaeosols cover magnetic grain size from superparamagnetism, single domain to multidomain. Loess samples with relative high peramagnetic minerals are dominantly of thermally stable characteristics while palaeosols have relatively high percentage of superparamagnetic grain (0.01—0.03μm). The relative grain size of magnetite is always finer in palaeosol with higher susceptibility than in loess, indicating that many tiny ferri-ferromagnetic minerals formed during the process of soll formation, which has caused a higher susceptibility in palaeosols than in loess. The climatic history of Quaternary can therefore be understood in terms of the susceptibility based on Chinese loess/palaeosol sequences.
Through the studies on low temperature susceptibility, frequency dependent susceptibility, isothermal remanent magnetization, low temperature magnetization and demagnetization for loess and palaeosols one can easily reveal some significant characters of rock magnetism for the magnetic minerals of ultrafine grain sizes, those are very difficult to identify by general geological methods. It is shown in the present study that both loess and palaeosols cover magnetic grain size from superparamagnetism, single domain to multidomain. Loess samples with relative high peramagnetic minerals are dominantly of thermally stable characteristics while palaeosols have relatively high percentage of superparamagnetic grain (0.01—0.03μm). The relative grain size of magnetite is always finer in palaeosol with higher susceptibility than in loess, indicating that many tiny ferri-ferromagnetic minerals formed during the process of soll formation, which has caused a higher susceptibility in palaeosols than in loess. The
基金
Project supported by the National Natural Science Foundation of China and by ETH Zurich, Switzerland.
