Study On The Weathering Indicators Of Sediments Of The Huanghe (Yellow River), Changjiang (Yangtze River) And Zhujiang (Pearl River) To The Sea, The Comparison Of The Weathering Intensities Among The River Drainage Basins And Their Influential Factors

Semi-quantitative analysis of the quartz, feldspars and carbonate minerals contents of the bulk and size-fractionated sediment samples form the Huanghe, Changjiang and Zhujiang to the sea were conducted by X-ray diffraction method. The feldspar/quartz ratio F/Q, K-feldspar/quartz ratio Fk/Q and P-feldspar/quartz ratio Fp/Q as weathering indicators were used together with the percentage contents of carbonate minerals to evaluate and compare the weathering intensities of the above three rivers. Their influential factors were discussed.The results show that the ratios of the quartz percentage contents of the Changjiang , Huanghe and Zhujiang are 1/1.2/2.6/2,The ratios of feldspar contents from the Huanghe, Changjiang, Zhujiang bulk sediments and the loess are 1/0.7/0.3/0.5.The sequence of the F/Q ratios of the Huanghe, Changjiang and Zhujiang sediments are consistent with the sequence of their chemical weathering intensity levels.The difference of the F/Q ratios of the Huanghe, Changjiang and Zhujiang sediment vary significantly with the sediment grain size. It increases with the decreasing of the grain size in general. The F/Q ratio of the 2μm-4μm fraction of the Huanghe sediment is 3.4 times of that of the Changjiang. The F/Q ratios of the 2μm-4μm and 16μm-32μm fractions of the Huanghe sediment are 6.2 and 6.8 times of that of the Zhujiang, respectively. The F/Q ratios of the 16μm-32μm32μm-63μm fractions of the Changjiang sediment are 3.7 and 4 times of that of the Zhujiang. These differences in the ratios of above-indicated fractions reveal clearly that the weathering intensity of the three rivers is followed by a sequence of Zhujiang > Changjiang> Huanghe. The above grain size fractions are the weathering sensitive grain fractions, and the F/Q ratios of which can be used to distinguish the weathering intensity of three rivers basins as proxy indicators.The percentage contents of the calcite in the bulk sediments of the loess and the Huanghe are higher than that of the Changjiang by 2-3 times, but the dolomite contents are just in reverse. The calcite/dolomite ratio in fine fractions of the loess and the Huanghe are high, and gets to the lowest in the 16μm-32μm fraction. The calcite/dolomite ratio is low in the coarser fractions of the Changjiang sediment, just in reverse to that of the Huanghe, and gets to the lowest in the finest fraction. The carbonate minerals in the Zhujiang sediment show only a trace content on the X-ray diffractograms. The differences in contents of the carbonate minerals of the three river sediments indicate that the Zhujiang basin is the first and the Changjiang is the second and the Huanghe is the third in terms of the weathering intensity.The SEM photos of the Huanghe calcite and dolomite grains illustrate that the eroding features occur mostly on the grain surface. A saddle-shaped dolomite grain was found in good shape. The calcite and dolomite grains in the Changjiang sediment suffer from strong erosion with dissolving-eroding structures intruded into the grains. The eroding morphology of the carbonate mineral grains of the Changjiang and Huanghe sediments are quite complicated and varied due to their different sediment source, basin weathering intensity and mineral structures.The study on the weathering indicators of sediments of the Huanghe (Yellow river), Changjiang (Yangtze River) and Zhujiang (Pearl River) to the sea, and the weathering intensities among the river drainage basins reveal the causes of the difference in the sediment compositions of the three rivers. The weathering indicators of the three rivers can be used to the evolution of the weathering intensity of the river basins in the past and identification of the sediment sources on the shelves.