Geochemical characteristics of modern river sediments in Myanmar and Thailand: Implications for provenance and weathering |
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| Institution: | 1. Department of Geology and Geophysics, Louisiana State University, Baton Rouge 70803, USA;2. Department of Earth and Environment, Boston University, Boston, MA 02215, USA;3. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, USA;4. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;5. The Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;1. Department of Earth and Planetary Sciences, Birkbeck University of London, Malet Street, London WC1E 7HX, UK;2. Hanoi University of Mining and Geology, 18 Vien Street, Duc Thang ward, Bac Tu Liem District, Hanoi, Vietnam;3. Geophysical Division of Vietnam, No1, 95, Chien Thang Street, Van Quan ward, Ha Dong District, Hanoi, Vietnam;4. Vietnam Administration of Sea and Islands, 83 Nguyen Chi Thanh Street, Dong Da District, Hanoi, Vietnam |
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| Abstract: | The elemental composition of organic matter and the major and trace element compositions of stream sediments from Myanmar (Ayeyarwady and Sittaung rivers) and Thailand (Mekong and Chao Phraya rivers, and their tributaries) were determined to examine their distributions, provenance, and chemical weathering processes. Higher total organic carbon (TOC) and total nitrogen (TN) contents in the finer grained sediments indicate hydrodynamic energy may control their distributions. TOC/TN ratios indicate inputs of both aquatic macrophyte and higher vascular plant material to the river sediments. The major element abundances of the sediments are characterized by predominance of SiO2 in coarser fractions and a marked negative correlation with Al2O3, representing primary grain size primarily control on SiO2 content. Marked depletion of most labile elements (Na2O, CaO, K2O, Ba and Sr) relative to UCC (upper continental crust), indicate destruction of feldspar during chemical weathering in the source area or during transport. However, enrichment of some high field strength elements (Zr, Th, Ce and Y) relative to UCC and higher Zr/Sc ratios indicate moderate concentration of resistant heavy minerals in finer-grained samples. Discriminant diagrams and immobile trace element characteristics indicate that the Mekong, and Chao Phraya river sediments were largely derived from felsic sources with compositions close to typical rhyolite, dacite/granodiorite, UCC, I- and S-type granites. Relative enrichment of ferromagnesian elements (e.g. MgO, Cr, Ni) and high Cr/V and low Y/Ni ratios in Ayeyarwady and Sittaung sediments indicate the presence of a mafic or ultramafic component in their sources. The ICV (Index of Compositional Variability), CIA (Chemical Index of Alteration), PIA (Plagioclase Index of Alteration), αAl, Rb/Sr and K2O/Rb ratios indicate that the Ayeyarwady and Sittaung sediments record low to moderate degrees of chemical weathering in their source, compared to moderate to intense chemical weathering in the Mekong and Chao Phraya river basins. These results are compatible with existing major ion data for river waters collected at the same locations. |
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| Keywords: | Geochemistry Weathering and provenance River sediments Myanmar and Thailand |
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