A detailed record of the Matuyama-Brunhes (M-B) transition has been obtained from the loess unit 8 (L8) at Duanjiapo (34.2° N, 109.2° E), Shannxi Province of China. An investigation of the rock magnetic properties using hysteresis loops, thermomagnetic analyses identifies pseudo-single domain magnetite as the main carrier of the rema-nence, with a small contribution from maghemite and hema-tite. The paleo-direction records obtained reveal: ( i ) The M-B transition was recorded in the middle and lower part of L8, and comprises of five fast reversals. (ii) The duration of the M-B polarity transition related to the directional change is about 4800 a. (iii) The virtual geomagnetic pole (VGP) path during the transition is confined over Africa, peaked 90° away from the sampling site, in contrast with the results obtained from the Weinan loess section. The different VGPs are probably attributed to the pedogenesis.
QUO BinZHU RixiangFlorindo FabioPAN YongxinYUE Leping
A detailed record of the Matuyama-Brimhes (M-B) transition has been obtained from the loess unit 8(L8) at Duan...
GUO Bin~1,ZHU Rixiang~1,Florindo Fabio~2, PAN Yongxin~1 & YUE Leping~3 1.Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing 100101,China
We have conducted detailed rock magnetic experiments on samples from loess unit 8 (L8) and paleosol unit 8 (S8) in Jingbian, Yichuan and Duanjiapo loess sections along an N-S transect in the Chinese Loess Plateau. Major rock magnetic results are as follows: (i) An increase of high field susceptibility (χh) in the same level of loess or paleosol from north to south is observed, suggesting an enhancement of pedogenesis. (ii) The low field susceptibility(χL) in loess unit L8 is almost the same in three sections. In contrast, the χL of paleosol unit S8 in Yichuan is highest, and the χL of Duanjiapo is lower than that in Yichuan section, suggesting that there is not correlation between the χL and the degree of pedogenesis in loess-paleosols. (iii) With the increasing of χL, both the contents of the superparamagnetic (SP) and the ferrimagnetic grains in loess-paleosol increase, however, the enhancement of magnetic susceptibility is probably dependent more on the increase of the ferrimagnetic concentration than on a change in the grain size. (iv) The content of the maghemite in loess unit 8 increases from the northern to the southern part of the Chinese Loess Plateau, and is positively correlated with the pedogenesis of the loess.
