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Abstract: Rare Earth elements (REEs) from a 332 cm-long core, surface sediments and soils of the lake shores were examined with the aim of evaluating their suitability as a paleo-environmental proxy. REEs were transported into the Nam Co Lake not only by runoff but also by wind. Concentrations of REE in the core range from 97.57 to 162.98 ppm with an average of 126.5 ppm, from 171.3 to 475.7 ppm in the soils of shores, and from 65.03 to 354.03 ppm in the surface sediments with an average of 130.64 ppm. The REE average of soils is 158.9 ppm for the northern shore, 214.72 ppm for the southern shore, 244 ppm for the eastern shore, and 289.69 ppm for the western shore. The REE average of surface sediments is 114.45 ppm for the northern lake, 115.73 ppm for the eastern lake, 129.69 ppm for the western lake, 144.38 ppm for the southern lake, and 150.95 ppm in the center of the lake, suggesting an accumulation of REEs in the center of the lake. The ratios of LREE/HREE range from 8 to 11.85 for the core, from 7.8 to 11.8 for the surface sediments and from 6.5 to 14.5 for the soils, which suggesting that LREE are richer than HREE. The REE distribution patterns of all samples are characterized by “V-shape” curves with slightly negative Ce anomalies (from 0.83 to 0.99) and obviously negative Eu anomalies (from 0.28 to 0.72). Mn played an active role on the Ce anomaly. The values of δCe showed almost no variance, suggesting a stable post depositional environment in the core. The REEs peaks of >140 ppm occurred at 6.9 ka (307 cm), 5.9–5.5 ka (292–287 cm), 2.2–2.0 ka (262–252 cm) and 1.78 ka (212 cm) corresponding to the beginning of environmental shifts and/or events, while the REEs peak at 0.91–0.87 ka (107–102 cm) and the REEs valley of <100 ppm at 7.8–7.5 ka (317–322 cm) corresponded to the end of Zepu Glacier advance and a cold event, respectively. Lagging behind climate changes, this suggests a careful use of REEs can be used as a proxy of paleo-environment in the Nam Co area. [Copyright &y& Elsevier]

Abstract: Qaidam Basin is a tectonically controlled depression on the northern margin of the Tibetan Plateau. In 2008, a long core was drilled in the Qahansilatu sub-basin in the western Qaidam basin. The sediment layers in the upper 400m alternate between evaporite mineral layers and carbonaceous clay layers. The detailed mineralogical investigation focused on evaporite minerals including halite, gypsum, mirabilite, thenardite, glauberite, eugsterite, and bloedite. Gypsum and halite make up the majority of the evaporate minerals. Environmentally induced variations in the mineralogy and crystal habit of the sulfates have been extensively investigated. Gypsum has prismatic and pyramid habits, such as disc pyramid, stubby prismatic, slender prismatic. Visible isolated gypsum and aggregates (rosette/radial and twins) are mostly scattered in carbonaceous clay layers, suggesting that secondary gypsum is well developed. Gypsum may be a precursor mineral of glauberite, and thenardite is the precursor of bloedite. As a metastable and rare mineral, eugsterite does not appear in other Tibetan areas. It forms at the expense of pre-existing gypsum or thenardite in the core at an experimental temperature of higher than room temperature. The presence of eugsterite indicates a warm and/or hot climate at its deposition time. Mineralogical variations have been explained by the brine evolution of Na–Cl, Na–Ca–SO4, Na–SO4, Na–SO4–Cl, Na–Ca–SO4–Cl, Ca–SO4, and Na–Mg–SO4. For instance, Na–Mg–SO4 corresponds to bloedite, while Na–Ca–SO4–Cl to the assemblage of halite, gypsum and glauberite. The evaporite minerals and carbonaceous clay layers'' alternation indicates the shift between dry and wet climate. According to the thickness, 18 evaporite stages and/or dry climate stages were identified from 0.97Ma to about 0.03Ma. The two early dry climate stages are identified at 0.96–0.97Ma and 0.87Ma. The other 16 evaporite stages occurred from 0.78Ma to about 0.03Ma. The evaporate-rich stages suggested that evaporation was high and groundwater inflow was sufficient at the sub-basin. [Copyright &y& Elsevier]