| 摘要: |
| 于1994-1996年，采用高精度正热电离质谱测定氯同位素（δ37Cl）的方法，对青海柴达木盆地昆特依盐湖区的盐湖卤水、湖底盐类矿物、油田水以及该地区的盐类沉积物钻孔剖面的δ37Cl值进行了初步研究。结果表明，该地区的δ37Cl值（卤水）变化范围在-2.05‰-1.04‰，盐湖卤水的δ37Cl值较低，这与卤水的相对密度及pH值有关；盐类沉积钻孔剖面的δ37Cl值呈现自下而上逐渐降低的趋势，这一变化与该地区的古气候变化有关。盐类沉积的δ37Cl值研究将会对高原干旱、蒸发环境条件下湖相沉积古气候演化的研究提供一种新的手段。 |
| 关键词: 柴达木盆地 盐湖 氯同位素 古气候 |
| DOI： |
| 分类号: |
| 基金项目:国家自然科学基金资助项目，49173163;号青海省自然科学基金资助项目，97-07-09号 |
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| CHARACTERISTICS OF CHLORINE ISOTOPES IN SALT LAKES OF KUNTEYI AND THEIR SIGNIFICANCE OF PALEOCLIMATE |
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LIU Wei-guo,XIAO Ying-kai,HAN Feng-qing;,PENG Zi-cheng
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1.Institute of Salt Lakes, The Chinese Academy of Sciences, Xining, 810008;2.Department of Earth and Spece, University of Sciences and Technology of China, Hefei, 230026
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| Abstract: |
| Chlorine has two stable isotopes, 37Cl and 35Cl. The isotopic fractionation of chlorine in natural environments has been identified on the basis of the procedures for high – precision measurement of chlorine isotopes. In this paper, the feature of chlorine isotopes in the salt lakes of Kunteyi area, Qinghai, has been studied. The chlorine in the samples, including brine, oil-field water and saline deposit, was separated using Ba-cation resin and H-cation resin to form CsCl by adjusting to pH 3 using a Cs2CO3 solution. The chlorine concentration of test solutions is around 5 mg/ml. The isotopic compositions of chlorine in the brine, oil-field water and saline mineral derived from drilling in the Kunteyi salt lakes have been determined by positive thermal ionization mass spectrometry, based on the measurement of Cs2Cl+ ion. The Ta filaments were treated with a 2.5 μl graphite slurry, and 2 μl of test solution containing l0p.g of chloride in the form of CsCl were loaded on the filament The isotopic measurements of chlorine were carried out by collecting data on messes 301 (133Cs235Cl+) and 303(133Cs237Cl+). The isotopic compositions of chlorine in the studied samples are expressed as δ37Cl (‰), in relation to a reference standard seawater collected at 120°26' E, 21°50' N.
The results show that δ37Cl values vary from -2.05‰ to 1.19‰ and the brines have lower δ37Cl compared to the oil-field water. The chlorine isotopic compositions of brine are associated with the density and pH value of brine. The brines with low pH values and high densities have low δ37Cl values due to evaporation of brine. When brines are evaporated to saturation, preferential incorporation of the 37Cl into the saline mineral causes depletion of 37Cl in relation to 35Cl in the brine during the precipitation of salt The brine is subjected to an isotopical fractionation during the precipitation of the salt, which causes continuous changes in the isotopic composition chlorine in the saline deposit The δ37Cl value of salt deposits from the Kunteyi bore holes decreases from the upper part towards the lower part and exhibits eight cyclical changes. Such changes in the δ37Cl value represent changes in the paleoclimate environment. Therefore, the systematic variation in δ37Cl of saline deposits is useful for the study of paleoclimate in drought and strongly evaporated areas. |
| Key words: Qaidam basin, Salt lake, Chlorine isotopic, Paleoclimate |
