等温剩磁获得曲线揭示的西伯利亚黄土磁化率变化机制

Isothermal Remanent Magnetization Acquisition Curves Reveal the Magnetic Susceptibility Variations Mechanism of the Siberian Loess

探索古土壤层磁化率低值的原因,选取Kurtak剖面的20个典型黄土-古土壤样品测量等温剩磁(IRM)获得曲线.基于样品的IRM获得曲线符合累积对数高斯模型,所有样品拟合出3个矫顽力组分.组分1 (<30 m T)是成壤组分,组分2 (60~100 m T)是碎屑组分,组分3 (>100 m T)是赤铁矿或针铁矿;组分2是Kurtak黄土的主要磁性矿物,其含量变化受控于风速变化. CBD处理后所有样品只拟合出组分2,且CBD处理前后样品的磁化率值呈正相关性,指示碎屑组分是影响剖面磁化率的主要因素.黄土-古土壤层中都存在针铁矿,但针铁矿的含量不足以影响整个剖面磁化率的变化;而Kurtak黄土中的赤铁矿与针铁矿也可能是在源区生成,表明组分3也能指示源区信号.

In order to explore the reason of low magnetic susceptibility of the paleosol layer,20 typical loess-paleosol samples of the Kurtak section were selected and their isothermal remanent(IRM) magnetization acquisition curves were measured. The IRM acquisition curves from the samples accords with the cumulative log Gaussian model,and all samples are fitted with three coercivity components. Component 1(30 m T) is pedogenesis component,component 2( 60 ~ 100 m T) is detrital component,and component 3(100 m T) is hematite or goethite;component 2 is the main magnetic minerals of Kurtak loess,and its content is controlled by changes in wind speed. After CBD treatment,all the samples were only fitted out component 2,and the magnetic susceptibility of the samples before and after CBD treatment was positive correlation,indicating that the main factors affecting the magnetic susceptibility of the section are detrital components. Goethite is found in both the loess-paleosol layers,but the content of goethite is not enough to affect the change of the magnetic susceptibility in the whole section;while the hematite and goethite in the Kurtak loess may alsobe generated in the source region,indicating that the component 3 can also indicate the source region signal.