Yangtze River Sediments from Source to Sink Traced with Clay Mineralogy
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Journal of Asian Earth Sciences xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Yangtze River sediments from source to sink traced with clay mineralogy ⇑ Mengying He a, Hongbo Zheng b, , Xiangtong Huang c, Juntao Jia d, Ling Li a a Institute of Surficial Geochemistry, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, PR China b School of Geography Science, Nanjing Normal University, Nanjing 210046, PR China c State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, PR China d School of Earth Science & Technology, China University of Petroleum, Qingdao 266555, PR China article info abstract Article history: River bed sediments were collected from the main stream and major tributaries of the Yangtze River for Available online xxxx clay mineralogy study. Surface sediments from the Yarlung Zangbo River on the Tibetan Plateau were also examined for comparison. The results show that the clay mineral compositions of the Yangtze River dis- Keywords: play a similar pattern through the whole truck stream, with illite being dominant, kaolinite and chlorite Clay minerals being lesser abundant, and smectite being minor component. Clay mineralogy shows distinct differences Provenance in the tributaries, which correspond to the heterogeneous source rocks and weathering intensity of the Weathering drainage. The illite crystallity and the illite chemical weathering index (5 Å/10 Å peak ratio) both increase Erosion downstream, indicating a increasing trend of hydrolysis along the river. It also indicates that the upper- The Yangtze River stream of the drainage is characterized with physical weathering while the middle- and lower reaches are controlled by chemical weathering process. In accordance with the result derived by the illite indexes, sediment input from upperstream including Yalong Jiang, Dadu He, Min Jiang and Jialing Jiang accounts for the major sediment load, whereas Wu Jiang, Xiang Jiang, Gan Jiang and Dongting Lake provide rela- tively less sediments. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction et al., 2003; Kessarkar et al., 2003; Liu et al., 2003a,b; Suresh et al., 2004; Liu et al., 2007; Long et al., 2007; Dou et al., 2010). The large river systems draining the Tibetan Plateau are the ma- As one of the rivers that originate from the eastern Tibetan Pla- jor transfer of continental masses to the ocean, playing significant teau, the Yangtze River is the third longest in the world and the roles in global geochemical cycles, and are thus the key areas in the fourth largest in terms of its water discharge. It has numerous trib- ‘‘source to sink’’ studies. Information about the bedrock lithology, utaries, entering the East China Sea with great amount of water weathering regimes, erosion and sedimentation rates are all funda- discharge, sediments and associated chemicals. The changes of mental issues in better understanding the catchment behaviors. the Yangtze River deposition area and the process of sediments Heavy minerals and geochemical fingerprints of river sediments from ‘‘source to sink’’ transport pattern have been widely dis- are most widely used for the determination of provenance, cussed. In recent years, various approaches of the sediment source tectonics and weathering in the source region (Moral-Cardona in the Yangtze River have been performed, such as Sr–Nd isotopic et al., 1996; Clift et al., 2002a,b,c; Cawood et al., 2003; Kuhlmann compositions (Yang et al., 2007), detrital mineral compositions et al., 2004; Boulay et al., 2005; Moral Cardona et al., 2005; (Wang et al., 2006; Yang et al., 2006), heavy mineral compositions Lim et al., 2006; Alt-Epping et al., 2007; Lan et al., 2007; Borges (Yang et al., 2009), carbon distribution (Wu et al., 2007) and mag- et al., 2008; Liu et al., 2008; Yang et al., 2009; Singh, 2010; Wu netic properties (Wang et al., 2007; Liu et al., 2010), whereas the et al., 2011). Clay mineral assemblages are sensitive to bedrock clay assemblages of the Yangtze River drainage, and their implica- geology and chemical weathering and therefore have long been tions, have not been fully investigated. Previous studies examined regarded as a powerful indicator of the nature of the source areas. the clay mineralogy based on scattered samples collected mainly In addition, in comparison with heavy minerals, clay minerals are from the Yangtze estuarine and the inner shelf area, and were easily transported as suspended load, and are more powerful to mostly concerned with their general comparison with other rivers, trace the provenance (Franz et al., 2001; Gingele et al., 2001; Chen such as the Yellow River and Pearl River (Yang, 1988; Fan et al., 2001; Zhou et al., 2003; Ding et al., 2004; Fang et al., 2007). In this study, we will examine the clay mineral assemblages of the river bed samples from the main stream and major tributaries ⇑ Corresponding author. Tel.: +86 25 83597512. E-mail addresses: [email protected] (M. He), [email protected] (H. of the Yangtze River, as well as the surface (soil) samples from the Zheng). drainage basin. The principal objectives are to characterize the clay 1367-9120/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2012.10.001 Please cite this article in press as: He, M., et al. Yangtze River sediments from source to sink traced with clay mineralogy. Journal of Asian Earth Sciences (2012), http://dx.doi.org/10.1016/j.jseaes.2012.10.001 2 M. He et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx mineral distribution in the Yangtze River drainage, determining (Yang et al., 2004; Wu et al., 2005). Different drainage basins in the mixing of sediments from different tributaries, and ultimately the mainstream and its major tributaries consist of distinct tecton- to understand how tectonics, basement geology and climates inter- ics and source rocks. Generally speaking, in the upper basin, the play to control the erosion and the production of clay mineral in drainage is covered by Mesozoic rocks with subordinate upper the drainage. Paleozoic and Cenozoic rocks, the eastern Tibetan Plateau is mainly the metaigneous and metasedimentary rocks, carbonate rock and 2. The Yangtze River catchment igneous rock, especially the Himalayan intermediate-acid igneous rock, which is rich in K. The middle-lower basins mostly consist The Yangtze River is one of the world’s great rivers, which is about of Paleozoic marine and the Quaternary fluviolacustrine sedimen- 6300 km long. With a catchment area of 1.8 Â 106 km2 and an an- tary rocks, together with intermediate-felsic igneous rocks, and nual average discharge of 9.6 Â 1011 m3, it is the largest river in older metamorphic rocks. Clearly, different tributaries consist of China and ranks the third in the world. The Yangtze River catchment distinct tectonic and source rock types (Fig. 2). can be divided into five broad physiographic provinces. From west to Tectonically, the upper and lower reaches are very different: the east, these include the northeast Tibet Plateau, the high mountains western catchments, dominated by the Longmen Shan, are subject of the Longmen Shan (‘‘Shan’’ is ‘‘Mountain’’ in Mandarin) and asso- to ongoing uplift, whereas eastern China is comparatively stable. ciated ranges, the Sichuan Basin, mixed mountain and basin terrains The Longmen Shan rises to over 6000 m, and the rivers receive (broadly referred to as the Three Gorges area), and eastern lowlands. large inputs of sediment from landslides cascading off steep unsta- Conventionally, the basin is divided into three reaches, the up- ble slopes that rise 1500–2500 m above the local valleys. In con- stream, midstream and the downstream (Chen et al., 2001), but geo- trast, the eastern lowlands are a complex of floodplains and graphically, the upstream can be divided into two segments, the lacustrine basins, rimmed by relatively low mountains. Jinsha Jiang segment and the Chuan Jiang segment (Fig. 1). The Jinsha Meteorologically, the Yangtze River catchment is dominated by Jiang (‘‘Jiang’’ means ‘‘River’’) descends from the plateau through the Asian monsoon system, with seasonal alternation between the mountains and is joined in the Sichuan Basin by several major trib- warm and wet summer monsoon, and the cold and dry winter utaries that pass through very deep valleys and gorges in the Long- monsoon. However, there is slight difference in the patterns of men Shan, including the Yalong Jiang, the Dadu He (‘‘He’’ is ‘‘River’’ in monsoon precipitation between the upper and lower streams, be- Mandarin), and the Min Jiang. The Chuan Jiang mainly flows through cause the upper mainly receives rainfall from the south Asian mon- the Sichuan Basin, containing the tributaries of the Jialing Jiang and soon. Annual precipitation tends to decrease westward from about the Wu Jiang, which are joined the main stream before passing 1000 mm in the eastern lowlands to about 700 mm in the Sichuan through the Three Gorges to the eastern lowlands. Further mid- Basin, but rises to over 1700 mm on the eastern flanks of the cen- stream, the Yangtze River is joined by the Han Jiang from the moun- tral Longmen Shan. West of the Longmen Shan, precipitation de- tainous northwest, and the Yuan Jiang, Xiang Jiang and Gan Jiang creases across the plateau, from about 600 mm in the middle from the south. And several large lakes such as Dongting Lake and reaches of the Yalong Jiang to about 400 mm at the head of the Jin- Poyang Lake separate the tributaries from the mainstream and trap sha Jiang. Summer temperatures tend to be warm throughout the a great deal of sediments. From Hukou downstream, the Yangtze Yangtze River catchment, particularly in the eastern lowlands River enters the lower reaches, and tributaries are much smaller in where the average for July can exceed 30 °C.