Geochemical fractionation of rare earth elements in lacustrine deposits from Qaidam Basin |
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Authors: | HuCai Zhang WenXiang Zhang FengQin Chang LunQing Yang GuoLiang Lei MingSheng Yang Yang Pu YangBin Lei |
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Institution: | (1) Key Laboratory of Salt Lake Resources and Chemistry, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008, China;(2) School of Life and Geographic Science, Qinghai Normal University, Xining, 810008, China |
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Abstract: | Based on the concentration and distribution pattern analysis of the rare earth elements (REEs) at the Shell Bar section from
Qaidam Basin, we studied the geochemical fractionations of REE in paleolake deposits and their paleo-environmental significance.
Our results show that the REE concentration in AS (acid soluble) and AR (acid residual) fractions are 20.9 μg/g and 95.4 μg/g
(except element Y) individually, showing a strong REE differentiation between AS and AR fractions. However, the two types
of fractions (AS & AR) have similar REE distribution patterns, which are slightly rich in light earth rare elements (LREEs),
with slightly right-tilting and negative Eu anomaly. The LREE of AR is richer than that of AS. There were no significant correlations
between the REE in AS, AR and other proxies. It indicated that the lacustrine deposition had different material sources and
experienced varying geochemical procedures. Correlation analysis between the REE and the content of fine grain-size (<4 μm)
of the sediments, Rb/Sr ratio and Mn concentration showed high correlation coefficients. Our results demonstrated that the
REE in acid soluble and residual fractions bear different environmental significances, which are strongly dependent on local
environment. The REE of acid soluble fraction is closely related to the paleoclimatic changes in the lake catchment and the
evolutionary processes of lake itself. Our results suggest that δCe and (La/Yb)n could be used as proxies of the reduction-oxidation conditions and furthermore the temperature change and the lake level
fluctuations. Using these proxies, we reconstructed the paleoclimate and water level fluctuation history during the high lake
level period lasting between 43.5 and 22.4 cal. ka BP. |
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