北京市浅层沉积物沉积特征分析

The characteristics analysis of shallow sediments

北京市平原区地下水系统划分为3个相对独立的区域地下水系统,选取其中典型的永定河及潮白河水系进行分析,通过17个取样点不同深度的83组样品的矿物成份、粘土矿物成份、常量元素及微量元素分析其沉积环境及沉积特征。通过聚类分析、矿物组合和风化程度计算,确定了两大水系沉积特征既有相同点,又有差异性。首先用聚类分析半定量分析出两大系统的相同点和差异性,通过风化程度计算出潮白河系统松散沉积物风化程度大于永定河系统。其次通过矿物成分衍射实验证明两条剖面主要沉积物矿物成分及其中粘土矿物类型均相同,两条剖面均处于河流沉积环境且水分条件优越,其中永定河剖面方解石及白云石百分含量和高于潮白河,潮白河剖面角闪石百分含量高于永定河。再次通过岩石化学成分分析两条剖面常量元素、微量元素主要类型相同,根据不同元素组合定量分析永定河及潮白河浅层松散沉积物差异性沉积特征。最后使用半定量、定量方法综合分析了Y6、Y14取样点沉积环境的典型性特征。这些方法的应用为河流沉积时序、古河道变迁提供了最直接的量化证明,为地下水系统划分、地下水系统边界确定提供了最有利最直接的证据,也将为未来水化学场研究、水资源合理开发利用等提出新的思路和方法。

The beijing plain groundwater system is divided into three relatively independent groundwater subsystem,this study analyzes the sedimentary environment and sedimentary characteristics of the typical profile in the Yongding river and the Chaobai river by the mineral composition,clay mineral composition,major elements and the trace elements of the 83 different depth samples in 17 sampling points.In this paper,the similarities and difference of two systems was determined by clustering analysis,typical mineral assemblage method and weathering degree method.Firstly semi-quantitative analysis the similarities and difference of the typical systems,the weathering degree of Chaobai river was calculated much more bigger than the Yongding river.Then it was found by XRD that the the mineral composition and the clay mineral component are same in the two systems,also they are blong to the fluvial deposit environment and they have a sufficient hydrodynamic condition.The sum of calcspar and dolomite in Yongding river is more than Chaobai river,but the hornblende is less than the Chaobai river.The two systems have the same major elements and trace elements,then quantitative analyzes the sedimentary characteristics differences between the systems by the different element associations.Finally determines the typical sedimentary characteristics in sampling points Y6 and Y14.The result of study is significant for the study of evolution,vicissitudes and identification of ancient river source,and the application of these methods provide the most direct quantitative proof on division and boundary confirmationof groundwater systems,at the same time this article puts forward a new method of hydrogeochemical environment analysis and the reasonable exploitation of water resource.