沉积物源判别的地球化学方法

Geochemical methods for identification of sedimentary provenance

对沉积物源判别的地球化学方法进行了分类总结,并分析了各类方法中存在的问题,进一步给出了应用建议,以期更加实用。综合分析表明,常量元素(组分)主要用于表征化学风化程度和判断源岩类型;微量元素组成不仅可以示踪物源区,还可以判别构造环境,其中蛛网图和三角图是最有效的判别图解,Ce异常是判断古海洋氧化还原环境的常用指标,Eu异常常用于区分基性岩和热液流体与酸性岩和陆源物质;直接指示物源的同位素指标以Sr、Nd、Pb同位素组成及其特征值最为有效,不仅可用于追踪沉积物源,还可用于确定沉积物的年龄、划分沉积地层和反映区域性或全球性的地质事件。古气候变化是影响生物碎屑碳酸盐中C、O同位素组成变化的重要因素,而古气候直接影响物源供给。因此,生物碎屑碳酸盐中C、O同位素组成可以间接反映物源供给情况。此外,石英δ18O对于河流、沙漠、黄土和风尘等沉积物的物源分析以及陆海源汇效应的研究具有重要意义。在利用地球化学方法进行物源分析时,运用单一方法往往存在一定的局限性,应当充分利用各类方法的优势,考虑各种造成误判的因素,利用多种方法综合分析,必要时还应考虑沉积环境的其他要素。

The geochemical methods for the discrimination of sedimentary provenance are summarized,the problems existing in various methods are analysed and the application suggestions are further given.Comprehensive analysis shows that major elements(components)are mainly used to characterize chemical weathering degree and determine types of source rock.Trace elements composition can trace source area and distinguish tectonic setting by cobweb map and triangle map effectively.Ce anomaly is a common indicator to judge the redox environment of paleo seawater.Eu anomaly is often used to distinguish basic rock and acidic rock.Sr,Nd and Pb isotopic compositions and their characteristic values are the most effective indicators of provenance.They can not only be used to trace the sedimentary provenance,but also to determine the age of sediment,classify sedimentary strata and reflect regionally or globally geological events.Paleoclimate change is an important factor affecting the C and O isotopic composition of bio-clastic carbonates,while paleoclimate directly affects the source supply.Therefore,the C and O isotopic compositions of bio-clastic carbonates can indirectly reflect the supply of provenance.In addition,theδ18O value of quartz is of great significance for the provenance analysis of river sediments,desert,loess and wind dust as well as the study of source-sink effect of land and sea.There are some limitations in using a single method.Thus it is significant to make full use of the advantages of various methods,consider various factors that may cause miscalculation and other factors of sedimentary environment when necessary.