Chemical weathering of monsoonal eastern China: implications from major elements of topsoil |
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| Institution: | 1. Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA;2. South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 Xingang Road, Guangzhou, China;3. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;4. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, USA;1. Laboratory for Provenance Studies, Department of Earth and Environmental Sciences, Università di Milano-Bicocca, Piazza della Scienza 4, 20216 Milano, Italy;2. Dipartimento di Scienze della Terra e dell''Ambiente, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy;3. Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain;4. Institut für Geologie, Universität Bern, Baltzerstrasse 3, 3012 Bern, Switzerland |
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| Abstract: | Major element compositions of 36 bulk samples and 41 clay samples, which were obtained from 47 topsoils collected in monsoonal eastern China, were investigated with conventional wet chemistry and X-ray fluorescence (XRF) spectrometry, respectively. Based on major element analyses, the mobility of major elements and latitudinal distributions of SiO2/Al2O3 ratio, chemical index of alteration (CIA), chemical index of weathering (CIW) and weathering index of Parker (WIP) were analyzed. Meanwhile, the suitability of these chemical weathering indices to topsoils in monsoonal eastern China and its controls were discussed.These investigations indicate that Na, K, Ca, Mg, and Si are relatively depleted, while Mn, P, Fe and Ti are relatively enriched in topsoils of the study area by comparison with their contents in the upper continent crust (UCC), and that alkali metal (Na, K) and alkaline earth metal (Ca, Mg) elements are generally easier to be depleted from their parent materials than other major elements during chemical weathering. The latitudinal distributions of CIA, CIW and WIP show that they are suitable to both bulk and clay samples, but SiO2/Al2O3 is only suitable to clay samples, not suitable in bulk ones. All these investigations indicate a significant dependence of grain-size in major element abundance and latitudinal distributions of SiO2/Al2O3, CIA, CIW and WIP, but parent rock type has little effect on them, except its impact on the latitudinal distribution of WIP in clay samples. The significant grain-size dependence probably indicates the presence of unaltered minerals in bulk samples, thus we suggest that clay samples are more suitable to investigating chemical weathering of sediments on continents than bulk samples. The trivial effect of parent rock type probably indicates a relatively uniform chemical weathering on various parent rocks. Correlation analyses indicate that climate is the dominant control of chemical weathering of topsoils in the study area, and the significant latitude effect indicated by the spatial distributions of chemical weathering indices actually reflect the climate control on chemical weathering of topsoils.Chemical weathering indices actually reflect the integrated weathering history in the study area. Besides the dominant control of climate, other factors like tectonics, parent rock, biology, landform and soil depth and age might also have some effect on the chemical weathering of topsoils in the study area, which needs further research. |
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| Keywords: | Chemical weathering Monsoonal eastern China Topsoil Major elements |
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