陕西商丹盆地一级阶地上黄土的微量元素分布特征及其气候意义

Distribution of Trace-Elements in Loess-Paleosol on the First Terrace of the Shangdan Basin in Shaanxi Province and Its Climate Significance

以陕西丹凤县茶房村黄土剖面为研究对象,对其微量元素含量进行了系统的元素测定分析。选取Rb/Sr、磁化率作为参比,探讨了微量元素分布和其所反映的气候演化特征及其与成壤强度的关系。结果表明:微量元素(Mn、Pb、Ga、Cr、Cu、Ni、As、V、Zn、Ti)的含量变化与磁化率曲线、Rb/Sr曲线变化相同,呈极显著相关关系,即微量元素含量变化与气候关系密切,表明元素动态变化受气候变化和成壤环境的影响;微量元素(Mn、Ga、Cr、Cu、Ni、As、V、Zn)的含量在古土壤层最高,指示全新世中期主要受夏季风影响,气候温暖湿润,黄土风化成壤作用强,黄土层(L_0、L_t、L_1)气候相对冷干,受冬季风活动影响较大。

Loess-paleosol sequences were recognized as one of the most complete terrestrial records of environmental changes in the past. The research on geochemical properties of loess sediments is meaningful to reveal the chemical weathering intensity of Aeolian loess and its recorded climate change. Field investigations were carried out along the first river terrace of the Danjiang River valley in Shaanxi Province. The Chafangcun profile with loess-soil sequences in the Shangdan Basin was measured for detailed study and the systematical sampling. The stratigraphic and sedimentological features,pedogenic intensity and the profile structure were observed in the field. The contents of trace elements,i. e. Mn,Pb,Ga,Cr,Cu,Ni,As,V,Zn and Ti in soil were measured and analyzed by X-Ray fluorescence as the main climate change indicators. Magnetic susceptibility and Rb/Sr ratio were selected as the supplement indicators. The results are as follows： 1 The curves of Mn,Pb,Ga,Cr,Cu,Ni,As,V,Zn and Ti elements were similar with the curves of the Rb/Sr ratio and magnetic susceptibility. There were the highly significant correlations among them,which revealed that the dynamic changes of trace elements were closely related to the climate change and pedogenesis environment; 2 The Paleosol layer（ S0） was well defined by very high contents of Mn,Ga,Cr,Cu,Ni,As,V and Zn,suggesting the intensified pedogenic modification to the accumulated dust during a more humid paleoenvironment. It further indicated that the climate was warm and humid during the midHolocene optimum. The loess levels（ L1,Lt,L0） were well defined by lower content of Mn,Ga,Cr,Cu,Ni,As,V and Zn when compared with the paleosol layer（ S0）,which suggested that the pedogenic modification to the accumulated dust was weak. It further indicated that the paleoenvironment was cold and dry with frequent dust storms during the periods of loess formation.