中国东部红土的磁性及其环境意义

MAGNETIC MEASUREMENT CHARACTERISATION OF RED EARTH PROFILE IN EASTERN CHINA AND ITS ENVIRONMENTAL IMPLICATIONS

通过中国东部红土剖面的环境磁学参数（磁化率、频率磁化率、非磁滞剩磁、饱和等温剩磁等）测量，获得了红土剖面磁性矿物浓度、粒度和类型等特性随深度的变化曲线以及红土经连二亚硫酸钠一柠檬酸钠一重碳酸钠溶液（ＤＣＢ）处理后的磁性参数变化．根据红土剖面环境磁学参数及其磁参数比值的变化可将红土分为３个层段，各层段的磁性矿物特征存在明显的差异．证实了红土剖面中的磁性载体主要是磁赤铁矿、赤铁矿和针铁矿，并分离出了球粒状磁颗粒．认为红土磁性矿物的数量、粒度、类型等的变异指示了其形成时的环境特征，其频率磁化率和ＤＣＢ处理的磁化率损失量指示了红土成壤化作用的强弱，可作为在红壤区研究过去全球变化的一种新途径．

Environmental magnetism parameters, including magnetic susceptibility (X),anhysteretic remanent magnehzation (ARM), saturation isothermal remanentmagnetization (SIRM), Frequency dependent susceptibility (Xfd), magnetization parameters (F+xmT and demagnetization parameters (F-xmT), have been measured on a redearth profile from eastern China. The variation curves of ferrimagnetic mineralconcentration, mineralogy assemblages and grain size of red earth profile with depthbefore and after iron oxides were removed by dithionite-citrons system buffered withsodium bicarbonate (DCB) were illustrated. On the basis of the magnetic properties ofred earth, three distinctive stratigraphic horizons have been identified. The spheruliticmagnetic particles were separated by magnetic separation method, indicating that thecontribution of magnetism in red earth is maghemite, hematite and goethite. Resultssuggested that enhancement of magnetism and shift in magnetic domain andmineralogy assemblage are correlated with pedogenic environments. Frequencydependent susceptibility and the fraction of magnetic susceptibility that is removed byDCB treatment are attributed to the pedogenic ferrimagnetic component suggestingthat they are index of soil development degree. Thus, magnetism of red earth, aneasily measured soil attribute, can be used to evaluate the environmental change ofQuaternary in southern China.