东秦岭地区黄土堆积的岩石磁学特征及磁化率增强机制探索

对东秦岭地区洛南盆地的上白川、刘湾和丹江上游的二龙山黄土剖面进行了岩石磁学研究。结果表明,大部分黄土和古土壤样品的磁性矿物以磁铁矿和磁赤铁矿为主，古土壤中亚铁磁性矿物的含量比黄土的多，极少数黄土样品以反铁磁性矿物为主。亚铁磁性矿物和反铁磁性矿物的含量随成土作用增强而增加，成土作用形成的细粒亚铁磁性矿物包括超顺磁性和单畴（似单畴）颗粒，但以单畴和（或）似单畴为主。古土壤磁化率增强与这些土壤成因的细粒亚铁磁性矿物含量有关，显示出受气候变化控制的特点。东秦岭地区黄土岩石磁学性质与黄土高原地区的相似，但也存在一定差异，而且三个剖面之间磁化率值整体差别较大。温湿的气候和复杂的山区地形可能是导致这种差异的原因。

Magnetic Properties of Loess Deposit in Eastern Qinling Mountains and An Investigation on the Magnetic Susceptibility Enhancement

We have carried out a relatively complete rock magnetism investigation on loess deposit in the eastern Qinling Mountains, central China. 251 and 341 samples were obtained from Shangbaichuan (SBC) and Erlongshan (ELS) loess-paleosol sections at 10 cm and 5cm intervals, respectively. Magnetic susceptibility was measured on all these samples. Isothermal Remanent Magnetization (IRM) and Anhysteretic Remanent Magnetization(ARM) were measured on 24, 26 and 6 samples selected from SBC, ELS and Liuwan (LW) sections, respectively. The thermal properties and hysteresis properties were measured on 14, 14 and 6 samples from SBC, ELS and LW sections. The results indicate that most of loess and paleosol samples are dominated by ferrimagnetic minerals (magnetite and maghemites) and the paleosols have more ferrimagnetic minerals than that in the loess, but there are still some cases that antiferromagnetic minerals (hematite) play a more important role in the magnetic properties. Both of the concentration of ferrimagnetic minerals and antiferromagnetic minerals systematically increase with the intensified degree of pedogenesis. The fine-grained ferrimagnetic minerals, which were formed in pedogenesis, are dominated by single domain and/or pseudo-single domain grains which contribute significantly to the magnetic susceptibility enhancement. The results reveal a strong linkage between the magnetic properties and the palaeoclimate. The rock magnetic properties of the three loess-paleosol sections are generally similar to that in the Loess Plateau, but with a minor difference. In addition, the rock magnetic properties among the three loess-paleosol sequences are slightly different; this may be caused by a warmer and more humid climate in this region.