Provenance and controlling factors of major elements in graded components of sediments from the Yalu River

Terrigenous surface sediments taken from the Yalu River estuary were separated into grades in order to reduce the control of grain size on sediment geochemistry. With the statistical method for multivariate, major elements content, controlling factors and provenance characteristics of samples were discussed grade by grade in this paper, compared with the original testing data for bulk samples. The results show that the chemical weathering intensity in the provenance is the major factor controlling the distribution patterns of major elements. Grain size and authigenesis also play certain roles in control over the distribution patterns of elements in the samples smaller than 8μm. The provenance is now suffering from moderate chemical weathering characterized by the weathering of plagioclase and never affected by potassium replacement. The differences in Al₂O₃、Fe₂O₃、MgO、MnO、TiO₂、P₂O₅ contents in the fractions >63μm、32~63μm and 8~32μm are rather small, but increased significantly in the fraction smaller than 8μm. The contents of CaO and Na₂O in each fraction are opposite to those of the above six elements, suggesting the consistency of lithology of provenance rocks. The K₂O, which can be used as an indicative element, remains high in each grain fraction. According to the lithologic characteristics of provenance, the components >2μm are mainly coming from metamorphic basement and granitic intrusive rocks at the middle and lower reaches, while the components < 2μm are mainly from the weathering products of basic intrusive rocks from the upper reach. Comparative analysis also suggests that the original bulk sample test results are close to the average of graded samples. As the result, the differences and change trend of geochemical characteristics between grades are hard to be observed. Therefore, integrated consideration is required in case the original geochemical data of bulk samples are used to trace the provenance.