| 引用本文: | 刘梦慧，李徐生，韩志勇，陈英勇，汪雨辰，苑晓康，任翌成.2021.下蜀黄土参数化粒度端元分析及其物源示踪[J].地球环境学报,12(5):510-525 |
| LIU Menghui, LI Xusheng, HAN Zhiyong, CHEN Yingyong, WANG Yuchen, YUAN Xiaokang, REN Yicheng.2021.Parametric end-member analysis of the grain size distribution of the Xiashu loess and its provenance tracing[J].Journal of Earth Environment,12(5):510-525 |
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| 摘要: |
| 下蜀黄土的物源问题对于理解亚热带东亚季风区干旱化过程至关重要。目前采用的物源示踪方法存在一定的局限性，对下蜀黄土物源的认识也存在争议。粒度端元分析可定量分解出沉积物中不同动力过程和来源的粒度组分，具有解析风尘沉积物源的较好潜力。本文应用参数化粒度端元分析方法，对镇江大港和九江马垱两个下蜀黄土剖面的物源组分进行了研究。结果发现：下蜀黄土可分离为超细粒（EM1）、细粒（EM2）、中粒（EM3）和粗粒（EM4）4个粒度端元，其中EM1（众数分别为0.7 μm和0.9 μm）源于粉尘沉积后风化成壤作用形成的次生组分，EM2（众数均为6 μm）为长距离搬运的远源组分，EM3（众数分别为25 μm和28 μm）是区域近地面冬季风搬运的近源粉尘，EM4（分别为44 μm和45 μm）则来自于沉积区附近的局地源组分。相似的区域风化成壤背景导致两地的EM1含量及变化均十分相似；近源和局地源组分（EM3+EM4）则构成了两地下蜀黄土的主要来源；西北气流将干旱-半干旱地区的粉尘输送至长江下游地区形成远源组分，而在区域近地面东北风的作用下，两剖面间粒度端元的变化序列存在“异元相似”的现象（即大港剖面EM3与马垱剖面的EM2变化曲线相似，大港剖面EM4与马垱剖面EM3变化曲线相似）。因此，下蜀黄土是不同物源组分混合而形成的沉积物，不同区域下蜀黄土的物源既有差异，又存在一定的空间联系。 |
| 关键词: 粒度端元 物源示踪 下蜀黄土 冬季风 粉尘沉积 |
| DOI：10.7515/JEE212015 |
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| 基金项目:国家自然科学基金项目（40971004，41571188，41671191） |
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| Parametric end-member analysis of the grain size distribution of the Xiashu loess and its provenance tracing |
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LIU Menghui, LI Xusheng, HAN Zhiyong, CHEN Yingyong, WANG Yuchen, YUAN Xiaokang, REN Yicheng
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1. School of Geography and Ocean Science, Nanjing University, Nanjing 210023, China
2. College of Environment and Planning, Henan University, Kaifeng 475001, China
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| Abstract: |
| Background, aim, and scope Determining the provenance of the Xiashu loess deposition located in the middle and lower reaches of the Yangtze River is very important for understanding the evolution of the East Asian monsoon circulation in the subtropical region of China. This issue has induced widespread concern and controversy in previous studies. At present, the provenance tracing methods used (such as elemental geochemistry, detrital zircon U-Pb age spectra, etc.) have certain limitations. The grain size composition is closely related to dynamic sedimentary conditions. Parametric end-member analysis (EMA) based on grain size distribution data can quantitatively decompose components representing different sedimentary dynamic processes and sources and has great potential in extracting information regarding the transportation and provenance of the Xiashu loess. In this paper, parametric EMA is applied to study the provenance tracing of the Xiashu loess. By separating and extracting the grain size end-members of the Xiashu loess from two profiles (approximately 400 ka) in the Dagang (DG) profile, Zhenjiang City, and Madang (MD) profile, Jiujiang City, we identified the source of dust material. Materials and methods A total of 325 samples in the DG profile and 332 samples in the MD profile were collected for grain size testing. After pretreatment, the grain size distribution was measured by a Mastersizer 2000 laser particle size analyser produced by Malvern, UK, with a detection range of 0.02—2000 μm. The results were analysed by the AnalySize programme based on MATLAB software provided by Paterson et al. Ninety-six Xiashu loess samples were selected from top to bottom in the MD profile, and X-ray fluorescence spectrometry was used to analyse major element compositions. We calculated the chemical index of alteration (CIA) of the above samples and quoted 34 CIA values of the DG profile to assist in the determination of the source components. Results The results show that the grain size composition of the Xiashu loess in both profiles can be decomposed into four main end members. The modal grain sizes of the four end members in the DG profile are EM1=0.7 μm, EM2=6 μm, EM3=25 μm and EM4=44 μm; in the MD profile, they are EM1=0.9 μm, EM2=6 μm, EM3=28 μm and EM4=45 μm. Discussion EM1 (modal grain size ＜1 μm in both profiles) is the secondary weathering and pedogenic component, and the proportions in the two profiles are close (9%—10%). EM2 (modal grain sizes are 6 μm in both profiles) consists of a distant-source aeolian deposition, and the content of the DG profile (38.33%) is higher than that of the MD profile (27.99%). EM3 (modal grain size is 25 μm in the DG profile and 28 μm in the MD profile) consists of nearby-source deposition, and EM4 (modal grain size is 44 μm in the DG profile and 45 μm in the MD profile) is a local-source deposit. The proportion of nearby sources + local sources was higher in the MD profile (63.55%) than in the DG profile (51.79%). The fine-grained end members (EM1) of the two profiles are relatively similar to the time series. The coarse-grained end members are different while still being interrelated. The variation curve of the nearby-source component (EM3) in the DG profile is similar to that of the distant-source component (EM2) in the MD profile, and the variation curve of the local-source component (EM4) in the DG profile is similar to that of the nearby-source component (EM3) in the MD profile. Conclusions The above results and discussion indicated that the Xiashu loess is composed of secondary weathering and pedogenic components, as well as distant-source deposition, nearby-source deposition and local-source deposition. Although the proximal dust materials (including nearby-source and local-source dust material derived from the beaches of rivers and lakes in the Changjiang and Huaihe areas) are mainly components of the Xiashu loess, there is a certain source connection between different locations, rather than each having an independent source area. Recommendations and perspectives The Xiashu loess in the lower reaches of the Yangtze River is a complex mixed sediment formed by different material sources under variable sedimentary dynamics. Neither can the Xiashu loess simply be interpreted as the result of the southward invasion of aeolian materials from the northern desert-loess region, nor is its provenance completely derived from nearby-source materials in southern China. The Xiashu loess is composed of not only regional nearby-source and local-source components by the winter monsoon but also distant-source dust transported by long-distance suspension from the northern desert-loess region. |
| Key words: parametric end-member analysis provenance tracing Xiashu loess winter monsoon dust deposition |
