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长江沉积物从源到汇过程研究的关键是揭示长江沉积物的组成特征,准确识别其时空组成变化规律,这也是东部边缘海海陆相互作用研究和长江水系构造演化研究的关键。本文研究一些常用的元素地球化学参数在现代长江水系的河漫滩和悬浮沉积物中组成的时空变化特点。在稀土元素(REE)组成上,下游近河口段干流悬浮沉积物在季节性时间尺度上比较稳定,可以代表现代长江入海沉积物的平均组成,而长江主要支流和干流间REE组成变化较大,化学相态分析可以更好地揭示特定物源区的REE组成特征以及由矿物分异引起的REE参数变化。相比REE而言,悬浮物中Al/Ti与Zr/Rb比值更能敏感地指示不同物源区的源岩组成信息,且减弱水动力分选引起的粒级和矿物分异影响。长江入河口的干流悬浮物作为整个流域风化剥蚀细颗粒物质的平均混合,具有更好的源区平均组成的示踪特性;但在不同季节也存在不同的主导性源区,主要受控于流域内季风降雨区的迁移。在河流沉积物源汇过程重建中,要特别关注流域物质风化和输运的自然过程可能引起的这些地球化学参数变化。
The key to the research on the process of sediment from source to sink in the Yangtze River is to reveal the compositional features of sediments in the Yangtze River and accurately identify the variation of its temporal and spatial composition. This is also the key point of the study on the sea-land-land interaction in the eastern margin and the tectonic evolution of the Yangtze River. In this paper, the temporal and spatial variations of the compositions of some commonly used elemental geochemical parameters in the floodplain and suspended sediments of the modern Yangtze River system are studied. On the REE composition, the suspended sediments in the lower reaches near the estuary are relatively stable on seasonal time scales, which can represent the average composition of the sediments from the Yangtze River into the sea, while the REE composition varies greatly between the main tributaries and the mainstream of the Yangtze River. Chemical phase analysis can better reveal the REE compositional characteristics of a specific provenance area and the variation of REE parameters caused by mineral segregation. Compared with REE, the ratio of Al / Ti to Zr / Rb in suspended solids is more sensitive to the information of source rock composition in different provenance areas, and weakened the grain size and mineral differentiation induced by hydrodynamic separation. As the average mixture of weathered and denuded fine particulate matter in the whole Yangtze River estuary, the suspended sediment of the Yangtze River estuary has better tracing characteristics of the average composition of the source area; however, there are also different dominant source areas in different seasons and are mainly controlled by the catchment Internal monsoon rainfall area migration. In the process of reconstructing the source and sink of river sediments, it is necessary to pay special attention to the changes of these geochemical parameters that may be caused by the natural processes of riverbed weathering and transport.