末次冰期以来黄土高原粉尘沉积的岩石磁学空间特征

Mineral magnetism and the spatial comparison of the loess sediments in Loess Plateau since the last glacial period

为了查明末次冰期以来黄土高原粉尘沉积的岩石磁学空间特征,对取自黄土高原由西北向东南方向的4个末次冰期以来黄土剖面的全新世古土壤(S_0)和马兰黄土(L_1)样品进行岩石磁学研究。结果显示,各剖面样品中磁性矿物均以磁铁矿为主,不同程度的含有磁赤铁矿和赤铁矿。S_0中磁铁矿和磁赤铁矿含量高,磁晶粒度相对更细,高矫顽力矿物比例少;L_1中磁铁矿和磁赤铁矿含量减少,高矫顽力磁性矿物(如赤铁矿)含量相对增多,磁晶粒度更接近于多畴(MD)。空间上,黄土高原磁赤铁矿的含量由西北向东南增加,高矫顽力磁性矿物由西北向东南减少,磁性矿物的平均粒径由西北向东南减小。磁化率增强受气候因素和源区输入物质的双重控制,磁化率的增强程度有西北向东南增加。

Based on magnetic analyses of samples from 4 profiles containing black loam （ dark loessial soil or Hei-lu-tu, So ） and Malan loess（ L1 ） on Loess Plateau from northwest to southeast. The results show similarities and differences of four profiles. At first, in all the four profiles, the primary magnetic mineral in paleosol and loess is magnetite, where there are maghemite and hematite as well but in different proportions ; in So, ferromagnetite （ magnetite and magnetic minerals is smaller and the high coercive maghemite） content is higher, the mean diameter of magnetic minerals content is low. On the contrary, in L~, ferromagnetite （ magnetite and maghemite） content is lower, the mean diameter of magnetic minerals is slightly larger and the high coercive magnetic minerals content is higher. Furthermore, we find that from northwest to southeast on Loess Plateau the content of maghemite increased, high coercive magnetic minerals content decreased, and the mean diameter of magnetic minerals is going smaller. Then, we conclude that both climate and input materials from provenance control the magnetic characteristic change of loess-paleosol sequences.