Lai Z.P.,CAS Qinghai Institute of Salt Lakes |
Lai Z.P.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute |
Mischke S.,University of Potsdam |
Mischke S.,Free University of Berlin |
Madsen D.,University of Texas at Austin
Journal of Paleolimnology | Year: 2014
A geological feature in the Qaidam Basin known as the "Shell Bar" contains millions of freshwater clam shells buried in situ. Since the 1980s, this feature in the now hyper-arid basin has been interpreted to be lake deposits that provide evidence for a warmer and more humid climate than present during late marine isotope stage 3 (MIS 3). Global climate during late MIS 3 and the last glacial maximum, however, was cold and dry, with much lower sea levels. We re-investigated the feature geomorphologically and sedimentologically, and employed optically stimulated luminescence (OSL) dating to verify the chronology of the sediments. We interpret the Shell Bar to be a remnant of a river channel formed by a stream that ran across an exposed lake bed during a regressive lake phase. Deflation of the surrounding older, fine-grained lacustrine deposits has left the fluvial channel sediments topographically inverted, indicating the erosive nature of the landscape. Luminescence ages place the formation of the Shell Bar in MIS 5 (~113-99 ka), much older than previous radiocarbon ages of <40 ka BP, but place the paleoclimatic inferences more in accord with other regional and global climate proxy records. We present a brief review of the age differences derived from 14C and OSL dating of some critical sections that were thought to represent a warmer and more humid climate than present during late MIS 3. We attribute the differences to underestimation of 14C ages. We suggest that 14C ages older than ~25 ka BP may require re-investigation, especially dates on samples from arid regions. © 2013 Springer Science+Business Media Dordrecht.
Huang G.,Wenzhou University |
Huang G.,CAS Qinghai Institute of Salt Lakes |
Cheng B.,Wenzhou University |
Xu L.,Wenzhou University |
And 2 more authors.
Chemistry - A European Journal | Year: 2012
A comprehensive mechanistic study of the InCl 3-, AuCl-, and PtCl 2-catalyzed cycloisomerization of the 2-(haloethynyl)biphenyl derivatives of Fürstner et al. was carried out by DFT/M06 calculations to uncover the catalyst-dependent selectivity of the reactions. The results revealed that the 6-endo-dig cyclization is the most favorable pathway in both InCl 3- and AuCl-catalyzed reactions. When AuCl is used, the 9-bromophenanthrene product could be formed by consecutive 1,2-H/1,2-Br migrations from the Wheland-type intermediate of the 6-endo-dig cyclization. However, in the InCl 3-catalyzed reactions, the chloride-assisted intermolecular H-migrations between two Wheland-type intermediates are more favorable. These Cl-assisted H-migrations would eventually lead to 10-bromophenanthrene through proto-demetalation of the aryl indium intermediate with HCl. The cause of the poor selectivity of the PtCl 2 catalyst in the experiments by the Fürstner group was predicted. It was found that both the PtCl 2-catalyzed alkyne-vinylidene rearrangement and the 5-exo-dig cyclization pathways have very close activation energies. Further calculations found the former pathway would lead eventually to both 9- and 10-bromophenanthrene products, as a result of the Cl-assisted H-migrations after the cyclization of the Pt-vinylidene intermediate. Alternatively, the intermediate from the 5-exo-dig cyclization would be transformed into a relatively stable Pt-carbene intermediate irreversibly, which could give rise to the 9-alkylidene fluorene product through a 1,2-H shift with a 28.1 kcal mol -1 activation barrier. These findings shed new light on the complex product mixtures of the PtCl 2-catalyzed reaction. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Xia Y.,Wenzhou University |
Huang G.,Wenzhou University |
Huang G.,CAS Qinghai Institute of Salt Lakes
Journal of Organic Chemistry | Year: 2010
The reaction mechanisms of the PtCl4- and Au(I)-catalyzed intramolecular acetylenic Schmidt reactions were analyzed by means of hybrid density functional calculations at the B3LYP/6-31G*(LANL2DZ) level of theory for better understanding of the acceleration effect of ethanol solvent in PtCl4-catalyzed reaction and the different catalytic activities of Au and Pt catalysts. Calculations indicate the rate of the PtCl 4-catalyzed reaction in noncoordinative solvent of 1,2-dichloroethane is limited by isomerization of the relatively stable chelate complex to the reactive π-complex of PtCl4 with the acetylenic moiety of homopropargyl azide substrate, which requires an activation energy of 29.6 kcal/mol. All nucleophilic cyclization, dinitrogen elimination, and 1,2-H shift of metal-carbene steps are quite facile. The generation of 2H-pyrrole intermediate in PtCl4-catalyzed reaction is completed by a ligand substitution reaction, and the final 2H-pyrrole to 1H-pyrrole isomerization is an intermolecular process with another 2H-pyrrole as a proton shuttle. When in ethanol solution, the favorable coordination of solvent molecules with PtCl 4 could inhibit the chelation of PtCl4 with the homopropargyl azide. Besides, the alcohol coordination also facilitates the generation of 2H-pyrrole intermediate and the intermolecular isomerization of 2H-pyrrole to 1H-pyrrole. Consequently, the overall activation barrier of PtCl4-catalyzed reaction in ethanol solution is lowered to 21.5 kcal/mol, determined by the H-abstraction step of the intermolecular 2H-pyrrole to 1H-pyrrole isomerization. The basic steps in the Au(I)-catalyzed reaction are similar to those in the PtCl4-catalyzed one. However, no chelate complex could be formed from PR3AuSbF6 and homopropargyl azide, and the 2H-pyrrole generation step is much more favorable, indicating weaker interactions of Au(I) catalyst with the homopropargyl azide and the C-C double bond of 2H-pyrrole. © 2010 American Chemical Society.
Li X.,CAS Institute of Earth Environment |
Liu W.,CAS Institute of Earth Environment |
Liu W.,Xi'an Jiaotong University |
Xu L.,CAS Qinghai Institute of Salt Lakes
Chemical Geology | Year: 2012
To further investigate the significance of carbon isotopes of lake carbonates in arid areas, we examined the carbon isotopic composition of ostracods, bulk carbonate, fine-grained carbonates, and associated water DIC (dissolved inorganic carbon) from Lake Qinghai and several small lakes and ponds surrounding Lake Qinghai. We obtained three major results. 1) The carbon isotopic compositions of ostracods, bulk carbonate, and fine-grained carbonates in the lakes and ponds are clearly correlated with water δ 13C DIC values, which vary with water salinity in the Lake Qinghai area. 2) The variation in the δ 13C DIC values of lake water is mainly controlled by CO 2 exchanges between the atmosphere and lake waters in the Lake Qinghai area. 3) Ostracods, bulk carbonate and fine-grained carbonates show consistent trends of isotopic composition in the study area, and the differences in carbon isotopic composition between authigenic carbonates and ostracods may be explained by the differences in carbon isotopic composition between the DIC of surface water and that of the water near to the sediment-water interface as well as the 'vital offsets' of ostracods.Our results suggest that variations in the δ 13C values of carbonates in Lake Qinghai and other lakes in this arid, high-altitude area are primarily controlled by the carbon-isotope ratios of the lake water DIC, which in turn are related to water salinity. Therefore, changes in carbonate δ 13C values may be used to indirectly indicate changes in water salinity in the Lake Qinghai area. © 2012 Elsevier B.V..
Dudnik A.S.,University of Illinois at Chicago |
Xia Y.,Suzhou University |
Xia Y.,CAS Qinghai Institute of Salt Lakes |
Li Y.,Suzhou University |
And 2 more authors.
Journal of the American Chemical Society | Year: 2010
A novel highly efficient regiodivergent Au-catalyzed cycloisomerization of allenyl and homopropargylic ketones into synthetically valuable 2- and 3-silylfurans has been designed with the aid of DFT calculations. This cascade transformation features 1,2-Si or 1,2-H migrations in a common Au-carbene intermediate. Both experimental and computational results clearly indicate that the 1,2-Si migration is kinetically favored over the 1,2-shifts of H, alkyl, and aryl groups in the β-Si-substituted Au-carbenes. In addition, experimental results on the Au(I)-catalyzed cycloisomerization of homopropargylic ketones demonstrated that counterion and solvent effects could reverse the above migratory preference. The DFT calculations provided a rationale for this 1,2-migration regiodivergency. Thus, in the case of Ph3PAuSbF 6, DFT-simulated reaction proceeds through the initial propargyl-allenyl isomerization followed by the cyclization into the Au-carbene intermediate with the exclusive formation of 1,2-Si migration products and solvent effects cannot affect this regioselectivity. However, in the case of a TfO- counterion, reaction occurs via the initial 5-endo-dig cyclization to give a cyclic furyl-Au intermediate. In the case of nonpolar solvents, subsequent ipso-protiodeauration of the latter is kinetically more favorable than the generation of the common Au-carbene intermediate and leads to the formation of formal 1,2-H migration products. In contrast, when polar solvent is employed in this DFT-simulated reaction, β-to-Au protonation of the furyl-Au species to give a Au-carbene intermediate competes with the ipso-protiodeauration. Subsequent dissociation of the triflate ligand in this carbene in polar media due to efficient solvation of charged intermediates facilitates formation of the 1,2-Si shift products. The above results of the DFT calculations were validated by the experimental data. The present study demonstrates that DFT calculations could efficiently support experimental results, providing guidance for rational design of new catalytic transformations. © 2010 American Chemical Society.
Yue D.,CAS Qinghai Institute of Salt Lakes |
Yue D.,University of Chinese Academy of Sciences |
Jia Y.,CAS Qinghai Institute of Salt Lakes |
Yao Y.,CAS Qinghai Institute of Salt Lakes |
And 2 more authors.
Electrochimica Acta | Year: 2012
In this paper the structure and electrochemical stability of ionic liquid analogue based on choline chloride and urea is reported. The microscopic structure of the ionic liquid analogue is preliminary investigated by Fourier transform infrared spectroscopy (FTIR). The cyclic voltammetry behavior of ionic liquid analogue is studied. The decomposition products of chlorine gas and triethylamine are observed. Possible mechanisms for the formation of these products are given. The effects of temperature and cycle index on electrochemical behavior are discussed. The electrochemical impedance spectroscopy behavior on pt electrode is investigated at temperature of 60 °C, 80°C and 100°C ranging from 0.001 to 10 5 Hz. The equivalent circuit diagram and the electrochemical element values are given. © 2012 Elsevier Ltd. All rights reserved.
Yu L.,CAS Qinghai Institute of Salt Lakes |
Yu L.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute |
Yu L.,University of Chinese Academy of Sciences |
Lai Z.,CAS Qinghai Institute of Salt Lakes |
Lai Z.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2012
Aeolian sediments are widely distributed in the hyper-arid Qaidam Basin and are good palaeoclimatic records. Due to limited age control, aeolian processes and their relevance to palaeoclimatic change are poorly understood. In this study, we present 28 optically stimulated luminescence (OSL) ages for both loess (14 samples) and aeolian sand (14 samples) from 8 profiles in eastern Qaidam Basin (EQB) in order to provide a detailed chronology for understanding the timing of aeolian processes and associated environmental conditions. We reconstructed the history of aeolian activity in the EQB since deglaciation by combining OSL chronologies, lithologic stratigraphy and grain-size analysis. The results indicate that (1) aeolian sand underlying the loess accumulated at ca. 12.4-11.5. ka and 10-8. ka, but not during the Last Glacial Maximum, (2) loess accumulation started at 10. ka and lasted to 0.45. ka at least, while most of the loess was deposited during 8-4.5. ka, (3) palaeoclimates in the EQB are inferred to be arid during 12.4-11.5. ka, (relatively) humid during 10-8. ka, humid during 8-4.5. ka and relatively arid during 4.5-0.45. ka, and (4) evolution of aeolian sediments were mainly controlled by effective moisture, and also affected by local topography. © 2012 Elsevier B.V.
Lai Z.,CAS Qinghai Institute of Salt Lakes |
Lai Z.,University of Oxford
Journal of Asian Earth Sciences | Year: 2010
Luminescence dating of loess older than 100 ka has long been a challenge. It has been recently reported that, using optically stimulated luminescence (OSL) of fine-grained quartz (4-11 μm) extracted from loess, the range of luminescence dating could be pushed to ∼0.6 Ma with OSL ages being in agreement with independent ages [Watanuki, T., Murray, A.S., Tsukamoto, S., 2005. Quartz and polymineral luminescence dating of Japanese loess over the last 0.6 Ma: comparison with an independent chronology. Earth and Planetary Science Letters 240, 774-789]. The aim of this study is to provide a luminescence chronology (20 samples) for the standard Luochuan loess section, and to further examine the upper limit of quartz OSL dating for Chinese loess. The growth curve does not saturate at 700 Gy, and should allow reliable equivalent dose (De) determination up to at least 400 Gy. However, when compared with independent chronological control, the De that could be treated as reliable is less than ∼230 Gy (corresponding to ∼70 ka in age for Chinese loess), and the De larger than ∼230 Gy should be underestimated. Ages for samples from the lower part of palaeosol S1 are severely underestimated, with the maximum age of 95 ka for a sample from the bottom of this palaeosol, much younger than the expected age of ∼128 ka. The maximum De obtained for sample L9/M, collected from loess layer L9 which is below the Matuyama-Brunhes (B/M) boundary whose age is ∼780 ka, is only 403 Gy which corresponds to an age of 107 ka. The cause of underestimation is not yet clear. The previous results by Watunuki et al. (2005) on the extension of OSL dating of loess to 0.6 Ma is not confirmed. When evaluating the validity of OSL ages in S1, another possibility is to question the already established chronological frame for Luochuan section, which is based on the hypothesis of continuous dust deposition. The assumption of an erosion hiatus between L2 and S1 could make the OSL ages look reasonable. However, if this is the case, then it is difficult to explain why the age of sample L9/M is only 107 ka which could be treated as a saturation age, while the OSL can provide a correct age for loess as old as 94.9 ka for sample LC22 collected from the bottom of S1. Much work is required to clarify these confusions. © 2009 Elsevier Ltd. All rights reserved.
Hu B.,CAS Qinghai Institute of Salt Lakes
Russian Journal of Physical Chemistry A | Year: 2013
The Pitzer ion-interaction extended by Harvic and Weare was applied to predict the solubility isotherms of reciprocal quaternary systems in which mixed crystals are formed. On the basis of data concerning the binary and ternary subsystems, the four components systems Rb+, Cs+/Cl -, SO4 2- -H2O, and K+, Cs+/Cl-, SO4 2- -H2O were investigated at 25 C.The results of calculation can be used to model salt crystallization during the concentration of brines. © 2013 Pleiades Publishing, Ltd.
Zeng F.,CAS Qinghai Institute of Salt Lakes
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2016
Late Quaternary loess deposit is widely distributed in the Qinghai Lake region and adjacent area. The loess deposit independently recorded the environmental and climatic changes during the late Quaternary in the Qinghai Lake region, northeastern Qinghai-Tibetan Plateau. Nearly all studies are focused on reconstructing the environmental and climatic changes recorded by loess deposit in the Qinghai Lake region. However, up to now, the provenance of the loess deposit in the Qinghai Lake region is still poorly understood. Here we present the elemental concentration of the silicate fraction of the eolian deposit (<75 μm) from the ZYC section in the Qinghai Lake region and LT section at Lintao County on the western Chinese Loess Plateau, loess deposits at Guanjiaoshan Mountain, Chaka town and Wulan County, eolian sands at western and eastern shore of the Qinghai Lake, and fluvial deposits from the Buhahe river and lacustrine deposits at Erlangjian site in the Qinghai Lake region. The results show that: (1) K2O/Al2O3 (molar ratio) and Zr/Ti, Zr/Nb ratios indicate that the eolian deposits in the Qinghai Lake region and adjacent area can be distinguished clearly from the local deposits represented by river deposits at Buhahe river and lacustrine deposits at Erlangjian in the drainage basin of Qinghai Lake; (2) There is similarity of the elemental ratios (K2O/Al2O3 and Zr/Ti, Zr/Nb) between the eolian deposits in the Qinghai Lake region and loess deposits at Lintao County. Thus, the eolian deposits in the Qinghai Lake region and Lintao County may have the same source region; (3) Late Quaternary loess deposit in the Qinghai Lake region is probably sourced from the Qaidam basin. © 2016, Editorial Department of Earth Science. All right reserved.