中国东部表层土壤磁化率特征及其指示意义

Magnetic Susceptibility Characteristics of Weathering-Pedogenic Topsoil along East Part of China and Its Significance

磁化率是环境磁学研究中较常用、较易获得的指标之一,但其解释和意义又最为复杂.对采自中国东部从北到南涵盖中国主要气候带的风化-成壤成因的79个表层土壤样品进行高、低频磁化率和非磁滞剩磁测试并分析其与降水量、年均温等气候参数的关系.结果表明:(1)发育于不同类型母岩的风化-成壤成因表层土壤磁学性质之间存在显著差异,各磁化率参数与气候条件参数之间的关系大不一样,在大空间尺度进行磁学与气候条件的关系研究时,必须充分考虑地质背景与母岩类型的差异.(2)发育于花岗岩的表层土壤非磁滞剩磁磁化率与年降水量和年均温间呈显著负相关关系;而发育于玄武岩的表层土壤非磁滞剩磁磁化率与年降水量呈显著正相关关系.被广泛认可的黄土-古土壤序列磁化率与成壤的关系不一定适用于大空间尺度的其他气候区域.(3)在风化-成壤过程中,磁性颗粒有变细的趋势,但降水强度增大时,一些超细颗粒较易被搬运离开原地,单一磁学参数结果难以反映气候条件及环境变化.(4)风化-成壤成因表层土壤非磁滞剩磁磁化率能较好地反映风化成因土壤的风化程度,但风化-成壤表层土壤磁学性质变化的机制特别是对相应土壤剖面的磁性矿物迁移转化有待深入研究.

Magnetic susceptibility is one of the most widely used and most easily to be obtained parameters of environmental magnetism.However,the meaning and interpretation of magnetic susceptibility is the most complicate.High,low frequency magnetic susceptibility and non-hysteresis remanence were measured for seventy-nine weathering-pedogenic topsoil samples collected from the east part of China,from north to south,covering the main climatic zones within China.Moreover,relationship between these magnetic parameters and climate indexes such as precipitation and annual average temperature was analyzed.The results indicate that：（1）Significant difference of magnetic properties is existed among weathering-pedogenesis topsoil that derived from different parent rocks.The relationship between all magnetic susceptibility parameters and climate indexes is much different.Difference of geological conditions and parent rocks must be taken full consideration when the relationship between magnetism and climate conditions is discussed in large spatial scale.（2）The non-hysteresis remanence magnetic susceptibility is negatively related to precipitation and annual average temperature for topsoil derived from granite.However,it is positively related to precipitation for topsoil derived from balsalt.The widely recognized relationship between magnetic strength of paleosol and pedogenesis of loess-paleosol sequence from the Chinese Loess Plateau isnt always proper to apply in other climate area.（3）Magnetic particles tend to be finer during weathering and soil-forming process.However,single magnetic parameter cant reflect the climate and environmental change because some ultrafine particles are easy to be carried out in situ due to increasingrainfall intensity.（4）Magnetic susceptibility of non-hysteresis remanence of weathering-pedogenic topsoil can reflect the weathering degree of weathering soil.The magnetic variation mechanism of weathering-pedogenic topsoil,especially magnetic mineral transformation of corresponding soil profile,is still needed further study.