Bartington MS2和Kappabridge MFK1-FA不同频率的磁化率在黄土、红粘土和湖相沉积物中的应用

Characteristics of frequency-dependent magnetic susceptibility in Bartington MS2 and Kappabridge MFK1-FA,and its application in loess-paleosol,red clay and lacustrine sediments

通过Bartington MS2和Kappabridge MFK1-FA两种仪器对黄土-古土壤、红粘土和湖相沉积物样品进行了5个频率的磁化率测试,并计算得到了4个频率磁化率.通过对比分析不同类型样品磁化率-频率变化曲线可知,当样品中细颗粒磁性矿物含量较高时,磁化率在较低频率即可达到峰值,而当样品中细颗粒磁性矿物含量较低时,磁化率在较高频率时才能达到峰值.因此,在黄土-古土壤等样品的应用中,成壤作用较强,细颗粒亚铁磁性矿物含量较高,Bartington MS2的低频(465Hz)与Kappabridge MFK1-FA的F1(976Hz)和F2(3905Hz)频率均处于磁化率峰值区域,可以检测到SP/SD阀值区域颗粒的信息,但是对于红粘土和湖相沉积物等细颗粒亚铁磁性矿物含量较低的样品,磁化率峰值对应的频率较高,MS2型磁化率仪无法有效地检测其中细颗粒的含量,而MFK1-FA中F2(3905 Hz)和F3(15616 Hz)两个频率间的频率磁化率则可以较好地完成这一任务.

Magnetic susceptibility （MS） of typical samples from Luochun loess-paleosol sequence, Zhuanglang core red clay, and Heqing core lacustrine sediments had been measured by Bartington MS2 and Kappabridge MFK1-FA meters. These two devices have five frequencies （two in MS2 and three in MFK1-FA） in all, and could get four frequency-dependent susceptibilities. MS achieve its peak value in low and high frequency when samples contain more and less fine grained particles respectively. Because of strong pedogenesis, loess-paleosol samples contain more fine grained particles, and could be detected by frequency-dependent susceptibility in both devices. However, for application in red clay and lacustrine sediments which lack fine grained ferrimagnetic particles, the low-frequency （465 Hz） in Bartington MS2 can not achieve peak value of magnetic susceptibility, and frequency-dependent susceptibility can not indicate the concentration of fine grained particles well. But Kappabridge MFK1-FA can do it well for its higher low-frequency （F1 is 976 Hz, and F2 is 3905 Hz）.