巴基斯坦Bahawalpur黄土岩石磁学特征及磁化率变化机制研究

Aeolian loess is one of the most widespread deposits on the land and records many kinds of information of paleoclimate changes. Currently, the studies of loess in Pakistan are rare, and the studies on the mechanism of magnetic susceptibility variation are still unavailable. In this study, the the rock magnetic parameters of the newly discovered loess-paleosol section (29 degrees 19'56 '' N, 71 degrees 42'65 '' E) in the Bahawalpur area of the Indus Plain of Pakistan were systematiclly measured. Combined with the grain size characteristics and the diffuse reflectance spectrum (DRS) , the mechanism of magnetic susceptibility variation was discussed. The results show that the main magnetic minerals in loess are magnetite, coupled with goethite and maghemite. And the magnetic domain particles in the magnetic minerals are Pseudo-single domain (PSD) and multi-domain (MD). Compared with the loess, the main magnetic minerals in paleosol are goethite, coupled with magnetite and paramagnetic minerals. This changing mechanism of the susceptibility is different from that of Chinese Loess Plateau (CLP). There is a possible threshold of magnetic susceptibility 12. 8 x 10(8) m(3) . kg(-1) in the study area, above which the main magnetic minerals are strongly magnetic minerals (magnetite and maghemite) ; below this value, the main magnetic minerals are weakly magnetic minerals (such as goethite). This transition of magnetic minerals may lead to a decrease in magnetic susceptibility. This study provides a new clue for further paleoclimatic research in Pakistan based on magnetic susceptibility in the future.