| 摘要: |
| 河流颗粒物的不同粒级组分定量分选对解析硅酸盐风化信息至关重要。利用超声分散和多级微孔过滤，建立1套简便可靠的微米级颗粒物分选流程，并对雅砻江河漫滩7个沉积物样品的4种粒径组分（<2 μm、2—41 μm、42—100 μm和>100 μm）进行分选实验和元素组成分析。结果表明：该流程能精确分选不同粒径组分，<2 μm组分含有较高的难溶元素和较低的可溶元素，更接近次生黏土矿物；该组分中Na/Al比值较低、CIA值较高，且存在明显的流域空间变化。综合分析显示：细颗粒物的元素组成受化学风化和物质来源等多种因素控制，<2 μm组分在风化示踪研究中具有更高的潜力。然而，由于沉积循环的影响，该组分可能包含古风化信息，因此在研究时需区分现代风化与古风化的叠合效应。 |
| 关键词: 分粒级 河流沉积物 定量分选 风化 硅酸盐 |
| DOI：10.7515/JEE242013 |
| CSTR：32259.14.JEE242013 |
| 分类号: |
| 基金项目:国家自然科学基金项目（42303007）；中国地质调查项目（DD20230040） |
| 英文基金项目: |
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| Quantitative separation of different grain sizes of river particles and their implications for silicate weathering |
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SONG Yilong，HOU Kejun
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Key Laboratory of Metallogeny and Mineral Assessment, Ministry of Natural Resources, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037 , China
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| Abstract: |
| Background, aim, and scope River sediments contain abundant weathering products, holding valuable information about silicate weathering. However, the prorpotions of primary rock fragments and secondary weathering minerals vary across grain size fractions, leading to differences in how they reflect the weathering process. In traditional research, a combination of methods such as sieving, sedimentation, and elutriation is often used for particle size separation of various types of samples, but methods for micron-scale river particle separation remain unstable and underdeveloped. This study aimed to establish a simple and reliable micron-scale particle separation process for use in watershed silicate weathering research. Materials and methods This study developed a simple and reliable micron-scale particle separation process using ultrasonic dispersion and multistage microporous filtration. Seven floodplain sediments (YL-3, YL-4, YL-5, YL-18, YL-23, YL-30, and YL-31) were sampled from upstream to downstream along China’s Yalong River. Separation experiments and elemental composition analysis were performed on four particle size fractions (<2 μm, 2—41 μm, 42—100 μm, >100 μm) of these sediment samples. Results The results showed that the separation process established in this study enabled high-precision separation of different particle size fractions in river sediments. Elemental composition analysis showed that the fine particles smaller than 2 μm contained a higher concentration of insoluble elements and relatively lower concentrations of soluble elements, with a composition more characteristic of secondary clay minerals. Additionally, those <2 μm fine particles had a lower Na/Al ratio and a higher chemical index of alteration (CIA) value, with significant spatial variations across the Yalong River watershed. Discussion Our research indicated that the relation between the mineral-element composition of river sediments and particle size fractions was influenced not only by chemical weathering but also by the source material. During chemical weathering, soluble elements like Na and Ca gradually leach out through water–rock interactions, whereas insoluble elements like Al and Fe are retained in secondary minerals. Because the particles smaller than 2 μm were rich in secondary weathering products such as clay minerals and Fe-Al oxides, those fine particles had lower concentrations of soluble elements. Additionally, particles of different sizes might have originated from different lithological sources. For instance, the fraction smaller than 2 μm often contained more sedimentary debris that had undergone multiple sedimentary cycles, gradually accumulating insoluble elements such as Al, resulting in higher Al concentrations. Further analysis of the Na/Al ratio and CIA values found that the fine particles smaller than 2 μm had undergone more intense chemical weathering than coarse particle fractions, and their chemical weathering intensity varied between the up- and downstream regions along the Yalong River. The higher altitudes and steeper terrain in the upstream areas lead to more pronounced mechanical erosion and relatively less chemical weathering. In contrast, the downstream regions, characterized by gentler terrain and longer sediment retention times, experience stronger water-rock interactions and, consequently, more intense chemical weathering. This spatial variation reflects the effect exerted by river topography and sediment retention time on the weathering process. Our research found that fine particles smaller than 2 μm might have recorded paleo-weathering information because they incorporated ancient weathering products in sedimentary cycles. That highlighted the importance of considering both weathering intensity and the sediment source area and deposition history when using fine particles to trace weathering. Conclusions Overall, the fine-grained fraction held extensive chemical weathering information, making it particularly valuable for silicate weathering studies. Recommendations and perspectives Because the particle fraction smaller than 2 μm also contained a considerable amount of sedimentary rock debris and was strongly influenced by sedimentary cycles, it is essential to carefully distinguish between modern and ancient weathering signals when using those particles for tracing weathering processes. |
| Key words: particle size separation river sediment quantitative separation weathering silicate |
