MAGNETOSTRATIGRAPHICAL RESEARCH OF LUOCHUAN LOESS SEDIMENTS
Ge Tongming (South China Sea Headquaters Geological Invertigation,Ministry of Geology and Mineral Resources)
About 350 loess samples collected from a bore hole near Luochuan, Shaanxi province, were studied with palaeomagnetic method. The samples were oriented relatively vertically, and the Information of inclination and the intensity of NRM were got. A part of samples were demagnetized by alternating field demagnetizer or by thermal-demagnetizer. The results of NRM got by thermalclean method are better than others. Then, all the samples were cleaned by thermal-demagnetizer. The remanence of the samples were measured by C-110 Cryogenic magnetometer with HP-1000 computer in ETH palaeomagnetism laboratory. The susceptibility was measured by susceptibility bridge which is made in Czechoslovakia. The results show that the polarity of the geomagnetic field changed regularly. The geo-magnetic polareties of the strata can be grouped into three epoches, i. e. Brunhes, Matuyama and Gauss, and the measurements suggested that the loess has been deposited since early-Pleistocene. This is the first time the Gilsa and the Olduvai events found in Luochuan Loess and the boundaries of Brunhes-Matuyama, Matu-yama-Gauss and Jaramillo events in Loess sequence have been determined. The results provided reliable data of polarities for classificatioa and comparison of the strata. The susceptibility measurement values of Loess sediments are obviously different from those of soil intercalations, suggesting that the susceptibility method is very useful in researching the ancient climate.