淮河上游全新世黄土-古土壤序列元素地球化学特性研究

在野外考察研究的基础上,对河南禹州全新世风成黄土-古土壤剖面系统采样,利用X-荧光光谱仪测定了常量元素和微量元素的含量及其变化,并与磁化率曲线、粒度变化曲线对比分析发现:常量元素氧化物比值钾钠比、残积系数和以Rb为代表的微量元素含量等随剖面层次呈规律性变化,即在古土壤层(S0)中含量最高,表土层(MS)中次之,在黄土层(L1、Lt、L0)中最低。硅铝率和Sr的含量表现出相反的变化规律。表明在全新世古土壤层和表土层形成时期,气候温暖湿润,成壤作用和次生粘化作用较强;在黄土堆积时期,气候比较干旱,沙尘暴频繁,成壤作用微弱。这些化学参数与磁化率曲线可以进行对比,表明成土过程中元素的迁移变化受全新世以来气候变化和成壤环境变化的控制。与黄土高原腹地的洛川剖面相比,淮河上游禹州剖面中绝大多数常量元素的含量较高,而绝大多数微量元素的含量偏低,磁化率也显著偏低,绝对值差别很大,粒度组成当中细沙成分含量很高,这说明淮河上游黄土物质来源与黄土高原地区明显不同。联系全新世时期黄河频繁泛滥、改道、沉积与黄淮平原盛行东北风形成流沙地的事实,认为淮河上游的黄土是黄河泛滥沉积物质经过风沙活动改造,由东北风力系统搬运而来的近源粉尘堆积,再经过就地风化或者成土改造而形成。

GEOCHEMICAL CHARACTERISTICS OF ELEMENTS IN HOLOCENE LOESS-PALEOSOL PROFILE IN THE UPPER-REACHES OF THE HUAIHE RIVER BASIN

Based on field surveys,soil samples were collected systematically at the YPC loess-paleosol site,Yuzhou County,Henan Province for analysis of contents of macro-and micro-elements and their variations with XRF and comparison with the curves of magnetic susceptibility and particle-size distribution.It was found that K2O/Na2O ratio, eluvial coefficient and contents of micro-elements with Rb as an indicator varied regularly with the layers of the Holocene aeolian loess-paleosol profile,i.e. they peaked in the paleosol(S0),and were lower in the modern topsoil(MS) and the lowest in the loess(L0,Lt,L1),Whereas SiO2/Al2O3 ratio and content of Sr went the other way in the profile,showing that during the stage of S0 and MS formation,the climate was warm and humid,and pedogenesis and secondary clayification were stronger;and during the stage of loess accumulation,the climate turned very dry and with frequent dust storms and pedogenesis was weakened.Comparison of these chemical parameters with magnetic susceptibility showed that transference of these elements was mainly controlled by the Holocene climate.The contents of most macro-elements were much higher,the contents of most micro-elements were much lower,and the magnetic susceptibility was much lower too,and the content of most fine sands in the particle-size composition was much higher in the YPC loess-paleosol profile than in the Luochuan profile which is located in the hinterland of the Loess Plateau,which suggested that the sources of Holocene loess-paleosol in the upper-reaches of the Huaihe River Basin evidently differed from that of the Loess Plateau.Considering the fact that the Yellow River overflowed and changed route frequently,leading to deposition during the Holocene and the prevailing North-East wind in the Huang-Huai plains caused formation of flowing sands,it can be concluded that the loess in the Huaihe River Basin was deposition of Aeolian sands from nearby sources,i.e.the Yellow River alluvial deposition,which was weathered and conveyed by North-East wind.Then aeolian sand deposited,accumulated and weathered on the spot to form loess-paleosol.