| 青藏高原西部昂拉仁错古湖岸钙华沉积的地球化学特征及环境意义 |
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| 引用本文： | 雷国良, 张虎才, 李志忠, Adam M. Hudson, 朱芸, 姜修洋, 陈秀玲, 常凤琴, 李华勇. 青藏高原西部昂拉仁错古湖岸钙华沉积的地球化学特征及环境意义[J]. 第四纪研究, 2013, 33(5): 839-847. doi: 10.3969/j.issn.1001-7410.2013.05.02 |
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| 作者姓名： | 雷国良 张虎才 李志忠 Adam M.Hudson 朱芸 姜修洋 陈秀玲 常凤琴 李华勇 |
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| 作者单位： | ① 福建师范大学地理研究所, 福建省湿润亚热带山地生态省部共建国家重点实验室培育基地, 福州 350007;; ② 云南师范大学旅游与地理科学学院, 高原湖泊生态与全球变化实验室, 昆明 650500;; ③ Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA |
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| 基金项目： | 国家自然科学基金项目，福建省自然科学基金项目，中国科学院战略性先导科技专项项目(批准号:XDA05000000)子课题 |
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| 摘 要： | 通过对青藏高原西部昂拉仁错湖古湖岸阶地钙华常量地球化学元素的分析,探讨了钙华沉积的常量元素特征及其古环境意义。结果显示:钙华中CaO含量达34.75%~58.48%,是其主要组分; 此外还含有少量的MgO,K2O和Na2O等,其含量低于3%,是湖泊自生作用形成的矿物。与湖泊古水位对比显示,元素Mg的含量及 Mg/Ca 比值等对湖泊水位的响应没有明显规律性; 在古湖面高度约 4777±5m之上,K2O和Na2O的含量低并且稳定,在古湖面 4777±5m 之下,K2O和Na2O的含量随湖泊水位下降逐渐增加。结合现代湖泊钙华的沉积特征,结果显示K2O和Na2O的含量随湖泊盐度增加而增加,表明钙华中K2O和Na2O含量与湖泊水位可能呈反相关关系,是潜在的重建湖泊水位或盐度的代用指标。同时发现,在湖泊相对淡化阶段,湖水中的元素K和Na处于富集阶段,钙华中K2O和Na2O含量低且稳定; 而当湖泊进入咸水阶段,湖水中的K+和Na+离子接近饱和,钙华中的元素K和Na逐渐富集,因此钙华中K2O和Na2O含量增加是湖泊进入咸水阶段的重要特征。基于这些事实,推断当该湖泊水位降至 4777±5m左右时,湖水的性质开始向钠-氯型转化,是昂拉仁错湖泊演化过程中的一个重要转折点。
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| 关 键 词： | 昂拉仁错 湖岸阶地 钙华 常量元素 湖泊水位 |
| 收稿时间： | 2012-12-29 |
| 修稿时间： | 2013-02-25 |
GEOCHEMICAL FEATURES AND SIGNIFICANCE OF SHORELINE TUFA FROM A CLOSED-BASIN LAKE NGANGLA RING TSO IN THE WESTERN TIBETAN PLATEAU |
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| Lei Guoliang, Zhang Hucai, Li Zhizhong, Adam M.Hudson, Zhu Yun, Jiang Xiuyang, Chen Xiuling, Chang Fengqin, Li Huayong. GEOCHEMICAL FEATURES AND SIGNIFICANCE OF SHORELINE TUFA FROM A CLOSED-BASIN LAKE NGANGLA RING TSO IN THE WESTERN TIBETAN PLATEAU[J]. Quaternary Sciences, 2013, 33(5): 839-847. doi: 10.3969/j.issn.1001-7410.2013.05.02 |
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| Authors: | Lei Guoliang Zhang Hucai Li Zhizhong Adam M.Hudson Zhu Yun Jiang Xiuyang Chen Xiuling Chang Fengqin Li Huayong |
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| Affiliation: | ① Institute of Geography, State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology, Fujian Normal University, Fuzhou 350007;; ② Laboratory of Plateau Lake Ecology and Global Change, College of Tourism & Geography Science, Yunnan Normal University, Kuming 650500;; ③ Department of Geosciences, University of Arizona, Tucson, Arizona USA 85721 |
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| Abstract: | Ngangla Ring Tso,situated in Lung Kruger County,is a closed-basin lake in the western Tibetan Plateau.The drainage area of Ngangla Ring Tso(30.71°~31.91°N,81.49°~83.74°E) is about 1.0983×104km2,and the lake area is about 498km2.Shorelines and shoreline tufa are well developed around the lake,forming typical shoreline series.During the field work,11 shoreline with tufa,ranging from 4745m to 4862m above the sea level were examined in detail and were sampled,and also,2 modern tufa samples from the shallow water near beach were collected.Based on the analysis of major elements in shoreline tufa by XRF method,elemental geochemistry and paleo-environment significance was discussed in this paper.Ngangla Ring Tso was a salt lake(with pH=9.4,conductivity=21.2ms/cm),and lake water hydro-chemical was dominated by Cl-and Na+.The analyses results show that CaO was the major composition of tufa and had a value ranged from 34.75% to 58.48%,and content a little MgO,K2O and Na2O,which were less than 3%.The stable isotopic analysis showed that δ13C PDB had a range from 1.9‰ to 6.2‰,and δ18OPDB ranged from -8.6‰ to -2.9‰,they were consistent with lacustrine authigenic carbonate.Compared with inflow river water,lake water is less Ca2+ but rich inand Na+ and K+,with a value of 370~440 times higher than the value of inflow water.It showed the combination of Ca2+ and CO32- in the lake was the mainly process for tufa formation.Comparison of geochemistry data with elevation of paleo-lake level,the content of element Mg and Mg/Ca ration value were insensitively response to the lake level,and contents of K2O and Na2O were consistent well with the change of lake level change below 4777±5m above the sea level but they had a stable content value above 4777±5m.For the tufa at 4777±5m above the sea level,it has similar values of K2O and Na2O with the modern shoreline tufa collected from Rinqen Shubtso,that was a closed-basin lake with little salinity water and sited 10km away at the southeast of Ngangla Ring Tso. Based on modern and paleoshoreline evidences,the follow processes can be deduced,in the early stages of lake evolution,the lake was relative desalination,and elements K and Na in lake were enrichment in water body,K2O and Na2O were low and stable in tufa.When the lake became salty,K+and Na+ were close to saturation in lake water and K2O and Na2O became enriched in tufa deposition.Along with the process of lakes retreat,the contents of K2O and Na2O were increased in tufa,implying that the increase of K2O and Na2O in tufa were an important proxies to salt lake.When the lake water changed to salty enough,the contents of K2O and Na2O in tufa became consistent to lake level,suggesting that they could be potential geochemistry index for salt lake level or water salinity.So the lake level of 4777±5m was a crucial altitude for the evolution of Ngangla Ring Tso. |
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| Keywords: | Ngangla Ring Tso shoreline tufa major elements lake level |
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