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GRANULARITY EFFECTS OF RARE EARTH ELEMENTS (REE) OF THE HUANGHE RIVER SEDIMENTS

Dai Huimin① Bao Qingzhong① Yang Zuosheng② Wang Shuili③Gong Chuandong③ Zhang Quan① Sun Zhongren①(①Shenyang Institute of Geology and Mineral Resources, Shenyang 110033; ②College of Marine Geoscience,Ocean University of China, Qingdao 266003; ③Xi′an University of Science and Technology, Xi′an 710054)  
The East China Sea distal mud area is a modern material sink center, and the large amount of granule material (the topsoil sediments and suspended material of less than 63μm) from the Huanghe River is one of the main material sources. In this paper, according to the law of Stoke's granule sedimentation, the topsoil sediments of the Huanghe River from the Lijin hydrostation and the eighth Chaheqing station were separated into six fractions: Less than 2μm, 2μm to 4μm, 4μm to 8μm, 8μm to 16μm, 16μm to 32μm, and 32μm to 63μm. All 15 REEs were tested by ICP-MS. The results show that the contents of REE with increasing grain size of sediments have little difference between two samples. At the same grain size, the contents of REE (ΣREE) in two samples have the following characteristics: First, the contents of REE from the Lijin hydrostatuion are higher than those from the eighth Chaheqing station at the grain size of less than 2μm, 8μm to 16μm, 16μm to 32μm, and 32μm to 63μm. Secondly, the contents of REE from the Lijin hydrostation are lower than those from the eighth Chaheqing station at the grain size of 2μm to 4μm and 4μm to 8μm. The contents of ΣREE present a "high-low-high" unsymmetrical saddleshaped pattern, with increasing grain size of sediment from the Lijin hydrostation. The pattern of the eighth Chaheqing station is similar except that the lowest value of ΣREE in the "high-low-high" unsymmetrical saddleshaped pattern is 8μm to 16μm, rather than 4μm to 8μm as of the Lijin hydrostation. In clay sediments, the contents of REE are relative higher, from 4μm to 16μm, while the contents of REE are relative lower. North American shale-normalized patterns show that the fractionation patterns are similar in different grain-sized sediments, and the fractionation patterns are all right-declined. The fractionation patterns are thus similar to the all-rock samples' and loess' in the Loess Plateau. The LREE are slightly enriched, with Ce having an obvious negative abnormality but Eu presenting an obvious positive abnormality in the North American shale-normalized patterns. Through X-ray analysis and dissecting microscope observation on samples of each granularity, the authors recognized that the contents of quartz increased along with the grain size increasing, the content of feldspar is the highest in the fraction of 8μm to 16μm, the content of carbonate is the highest in the fraction of 32μm to 63μm, and the heavy minerals present an increased trend along with grain size increasing. The granularity effects of REE of the Huanghe River sediments are closely related to the sorption of clay mineralsand the mineral (especially carbonates and heavy minerals) contents and compositions in different grain-sized sediments. Comparing with the value of δEu the result shows that the loess from the loess highland is one of the main material sources of the sediments in the Huanghe River.
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