Impacts of grain size sorting and chemical weathering on the geochemistry of Jingyuan loess in the northwestern Chinese Loess Plateau |
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| Institution: | 1. Geowissenschaftliches Zentrum der Georg-August-Universität Göttingen, Abteilung Sedimentologie/Umweltgeologie, Göttingen, Germany;2. Helmholtz Institute Freiberg for Resource Technology, Freiberg, Germany;3. Chemostrat Ltd., Welshpool, UK;1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an 710061, China;2. Joint Center for Global Change Studies, Beijing 100875, China;3. State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology, School of Geographical Sciences, Fujian Normal University, Fuzhou 350007, China;4. Research Center for Ecology and Environment of Center Asia, Chinese Academy of Sciences, Urumqi 830011, China;5. Institute of Geology, Earthquake Engineering and Seismology, Academy of Sciences of Tajikistan, Dushanbe 734063, Tajikistan;1. Department of Earth and Planetary Sciences, University of California Davis, One Shields Ave., Davis, CA 95616, USA;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P. O. Box 9825, Beijing 100029, China;3. Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, P. O. Box 9825, Beijing 100029, China |
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| Abstract: | Major and trace elemental compositions of loess samples collected from the Jingyuan section in the northwestern Chinese Loess Plateau (CLP) were analyzed to investigate the potential impacts of grain size sorting and chemical weathering on the loess geochemistry and to extract appropriate geochemical indices for better evaluating the East Asian monsoon variability. Based on variations of major and trace elements in different grain size fractions, seventeen elements were classified into three types: (1) Si and Na display higher contents with the increased particle sizes; (2) Al, Fe, Mg, K, Mn, Zn, Rb, Cr, V are mainly enriched in fine size fractions; (3) Ti, Ba, Zr, P, Ca and Sr show irregular variations among different size fractions. Comparison of Al-normalized elemental ratios with Zr/Rb and Rb/Sr ratios (two commonly employed indicators for grain size sorting and pedogenic weathering) indicates that Si/Al, Zr/Al, Ti/Al variations match well with Zr/Rb and grain size results, whilst Ca/Al, Sr/Al, P/Al ratios display similar variability as that of Rb/Sr ratio. Comparison of loess based proxies (e.g., elemental ratios, magnetic susceptibility, grain size) of Jingyuan section with speleothem and ice-core records confirms that elemental ratios of high-resolution loess sequences developed in the northwestern CLP can be employed to address fluctuations of the winter monsoon-induced grain size sorting and summer monsoon-related weathering and pedogenesis at glacial–interglacial and millennial timescales. |
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