科尔沁沙地风沙沉积物磁学特征及其古环境意义初探

选取位于科尔沁沙地东北缘的六户屯剖面风沙沉积物为研究对象,进行系统的磁学特征和粒度分析.结果表明:六户屯剖面磁性矿物含量较少,磁学性质主要受亚铁磁性磁铁矿控制,并含有少量赤铁矿和针铁矿,磁性矿物粒度较细,以稳定单畴和超顺磁颗粒为主.沉积物中磁性矿物的粒度分布受风力大小与成壤强度的影响,单畴颗粒相对含量随风力的增强而增加,随土壤发育程度的增强而减少,xARM/xlf和xARM/SIRM可以指示冬夏季风的相对强弱.六户屯剖面磁性矿物粒度主要受冬季风强度及其动力分选作用的控制,磁性矿物粒度与沉积物总体粒度呈反相关；但在某些层位,夏季风影响下的成土过程对其改造作用不容忽视.成壤过程中形成的超顺磁颗粒是磁化率增强的主要因素,单畴颗粒对土壤发育适宜期磁化率的增加贡献相对较弱.

Magnetic Characteristics of Aeolian Sand Sediments in Horqin Sandy Land, Northeastern China, and Its Paleoenvironmental Significance: A preliminary exploration

In the Chinese Loess Plateau, magenetic susceptibility has been widely used as a proxy for the intensity of East Asian summer monsoon. It was generally accepted that pedogenic formation of ultrafine-grained magnetic minerals was the major contributor to the high magenetic susceptibility of the paleosols. However, few works have been done to investigate the mechanisms for the enhancement of magnetic susceptibility in the case of aeolian sand sediments in Horqin Sandy Land, northeastern China. Here detailed environmental magnetism and grain size studies of aeolian sand sediments taken from LHT section, which is located in the northeastern margin of the Horqin Sandy Land, are presented. Results show that the overall magnetic minerals content is low; the main magnetic minerals in the aeolian sand sediments are magnetite, with some haematite and goethite; the main magnetic grain sizes are SSD and SP. χARM/χlf and χARM/SIRM can indicate the relative strength of winter monsoon and summer monsoon. In terms of the whole section, magnetic grain size reflects the intensity of winter monsoon well, but in some strata, it was affected by summer monsson. Pedogenic superparamagnetic particles are the main cause of the magnetic susceptibility enhancement, and single domain particles play a subordinate role in the magnetic susceptibility enhancement during the optimum period of soil development.