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In this study, nineteen brine samples from the Qarhan Salt Lake (QSL) in western China were collected and analyzed for boron (B) and chlorine (Cl) concentrations, total dissolved solids (TDS), pH values and stable B isotopic compositions. The B concentrations and δ11B values of brines in the QSL range from 51.6 mg/L to 138.4 mg/L, and from +9.32‰ to +13.08‰, respectively. By comparison of B concentrations and TDS of brines in QSL with evaporation paths of brackish water, we found that B enrichment of brines primarily results from strong evaporation and concentration of Qarhan lake water. Combining with comparisons of B concentrations, TDS, pH values and δ11B values of brines, previously elemental ratios (K/Cl, Mg/Cl, Ca/Cl, B/Cl) and δ11B values of halite from a sediment core (ISL1A), we observe good correlations between B concentrations and TDS, TDS and pH values, pH and δ11B values of brines, which demonstrate that higher B concentrations and more positive δ11B values of halite indicate higher salinity of the Qarhan paleolake water as well as drier paleoclimatic conditions. Based on this interpretation of the δ11B values of halite in core ISL1A, higher salinity of the Qarhan paleolake occurred during two intervals, around 46–34 ka and 26–9 ka, which are almost coincident with the upper and lower halite-dominated salt layers in core ISL1A, drier climate phases documented from the δ18O record of carbonate in core ISL1A and the paleomoisture record in monsoonal central Asia, and a higher solar insolation at 30°N. These results demonstrate that the δ11B values of halite in the arid Qaidam Basin could be regarded as a new proxy for reconstructing the salinity record of paleolake water as well as paleoclimate conditions. Keywords: B isotope compositions, Brine, Chemical concentrations, Qarhan salt lake, Western China, Salinity of paleolake water

The aim of this study is to evaluate the local impact of human activities on surface pollen assemblages and identify pollen indicators associated with grazing and cultivation in the Qinghai-Tibetan Plateau. We analyzed 80 surface and 10 dung pollen samples from five communities of vegetation in the Qinghai Lake Basin. Each vegetation zone was identifiable based on surface pollen assemblages. Principal component analysis of 33 pollen taxa and two supplementary variables of human influences was used to assess the impact of anthropogenic activities on surface pollen assemblages in the Qinghai Lake Basin. Surface pollen assemblages were moderately influenced by cultivation, as indicated by the content of the cultivation-associated Hordeum-type and Brassiaceae pollen. Severe grazing led to changes in pollen assemblages, including increases in Chenopodiaceae, Plantago, Potentilla-type, Thymelaeaceae and Aster-type pollen. Pollen assemblages are similar among dung samples and are dominated by Artemisia, Poaceae, Fabaceae and Asteraceae. Hordeum-type pollen content is relatively higher in dung samples, indicating herbivores are important in the dispersion of Cerealia Poaceae pollen into pastures. Characterizing modern pollen assemblages will provide a more precise reference for reconstructing prehistoric human activities during the Holocene based on fossil pollen assemblages in the Qinghai Lake Basin. Copyright (C) 2018 John Wiley & Sons, Ltd.

Central Asia experienced a number of significant elevational and climatic changes during the Cenozoic, but much remains to be understood regarding the timing and driving mechanisms of these changes, as well as their influence on ancient ecosystems. Here we describe the palaeoecology and palaeoclimate of a new section from the Nangqian Basin in Tibet, northwestern China, here dated as late Lutetian–Bartonian (late middle–late Eocene) based on our palynological analyses. Located on the east-central part of the Tibetan Plateau, this section is excellently placed for better understanding the palaeoecological history of Tibet following the India-Asia collision. Our new pollen record reveals that a strongly seasonal steppe-desert ecosystem characterised by drought-tolerant shrubs, diverse ferns and an underlying component of broad-leaved forests existed in east-central Tibet during the Eocene, influenced by a southern monsoon. Warming during the Middle Eocene Climatic Optimum only prompted a temporary vegetation response, while a drying signature in our pollen record after 40 Ma demonstrates that proto-Paratethys sea retreat caused widespread long-term aridification across the plateau. To better distinguish between local climatic variation and farther-reaching drivers of Central Asian palaeoclimate and elevation, we correlated key palynological sections across the Tibetan Plateau by means of established radioisotopic ages and biostratigraphy. This new palynozonation illustrates both intra- and inter-basinal floral response to plateau uplift and global climate change during the Paleogene, and provides a framework for the age assignment of future palynological studies in Central Asia. Our work highlights the ongoing challenge of integrating various deep time records for the purpose of reconstructing palaeoelevation, indicating that a multiproxy approach is vital for unravelling the complex uplift history of the Tibetan Plateau and its resulting influence on Asian climate.

Potash plays an important role in agricultural production. The Qaidam Basin (QB) in western China is a typical inland evaporite basin, which contains an abundance of K-rich brines, including shallow brines (i.e., surface brines and intercrystalline brines) in salt lakes and deep brines (i.e., pore brines and oilfield brines) in the strata. Significant studies on these brines have been reported, however, the integrated studies on sources of K, its distribution, and the sedimentary pattern of the two brine types are still inadequate. In this study, the K+ concentrations of sixty-four intercrystalline brines from the Qarhan Salt Lake (QSL), the largest playa in the QB, are presented. After combining those results with the major ionic compositions of river waters and deep K-rich brines, and the K+ concentrations of shallow brines in the QB, we concluded that: (1) The K of brines in the QSL is mainly from the high&ndash, flux K input by rivers which gain K from silicate weathering, while the &ldquo, ancient Qaidam Lake&rdquo, contributed little K to the QSL, (2) the large K flux supplied by rivers, the appropriate concentration degree, and the mixing of river waters and spring waters, cooperatively account for the highest K concentrations of brines in the QSL in the QB. The different river K recharges in different sections and isolated depressions are responsible for uneven K+ concentrations of brines in the QSL. (3) The deep brines are mainly distributed in the western QB. The K source of pore brines is from the interaction of pore water with the overlying evaporite layer. While the K in oilfield brines may be meteoric water, salt dissolution, the mixing of hydrothermal fluids, and the conversion of clay minerals to K-feldspar may consume K in the oilfield brines.

Salt lakes on the Qinghai-Tibetan Plateau (QTP) are remarkable for Li-rich brines. Along with the surging demand of Li, the Li-rich brines in salt lakes on the QTP are of great importance for China’s Li supply. Previous studies reported the geological, geographical, geochemical signatures of numerous salt lakes on the QTP; however, conclusive work and the internal relationships among the hydrochemistry, distribution and geological setting of Li-rich salt lakes are still inadequate. In this study, major and trace (Li, B) ionic compositions of 74 Li-rich salt lakes on the QTP were reviewed. The Li-rich brines cover various hydrochemical types (carbonate, sodium sulfate, magnesium sulfate, and chloride types) and present horizontal zoning from the southwest to the northeast along with the stronger aridity. The Li concentrations and Mg/Li ratios in these salt lakes range from 23 to 2895 mg/L, 0.0 to 1549.4, respectively. The distribution of these salt lakes is close to the major suture zones. Geothermal water is proposed to be the dominant source of Li in the investigated salt lakes, while weathering of Li-bearing sediments and igneous rocks, and brine migration provide a minor part of Li. Four factors (sufficient Li sources, arid climate, endorheic basin and time) should be considered for the formation of Li-rich brines in salt lakes on the QTP.

With the uplifting, large-scale thrusting and striking of the Tibetan Plateau, several Paleogene intracontinental basins formed within the northernTibetan Plateau (TP). Stratigraphical and paleoenvironmental studies of the sedimentary successions within these basins are critical for understandingPaleogene climatological changes in Eurasia. The Nangqian Basin, one of such basins, formed in the Yushu area of the northeastern Tibetan Plateau.A set of lacustrine sediments, dominated by red clasolite, marlite, and gypsum, developed in the Yang Ala section in this basin. Paleontologicalrecords from the Nangqian Basin remain poorly known. Here, we investigate the palynological assemblages of one sedimentary succession at theYang Ala section that belongs to the Gongjue Formation, and their implications regarding the geological age and paleoclimate are discussed. Theresults reveal that the assemblages are dominated mainly by angiosperm pollen (tricolpates and tricolporate), including Nitrariadites (Pokrovskaja), Quercoidites, and Labitricolpites, followed by gymnosperm pollen taxa, such as Ephedripites and Taxodiaceaepollenites, and sparse pteridophytespores produced by ferns. A late Eocene age is inferred based on palynostratigraphy and comparison with other pollen assemblages in the TP. Arelatively dry climate with brief humid periods is indicated by the high abundance of xerophytic pollen taxa, such as Ephedripites and Nitrariadites,which are associated with broadleaved deciduous and evergreen plants. The characteristics of the pollen assemblages from the studied Yang Alasection are consistent with other Cenozoic palynofloras from the Mahalagou Formation in the Xining Basin and with those of the Yaxicuo Groupin the Hoh Xil Basin. These results provide an improved stratigraphical scheme for parts of the Cenozoic and enrich the current knowledge of thevegetation history of the northeastern Tibetan Plateau. This work was financially supported by grants from the National Natural Science Foundation of China (Grant No. 41302024) and The Youth Guiding Fund of Qinghai Institute of Salt Lakes, CAS (Grant No. Y360391053)