- 责任者：Lei Guoliang (State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology ; Institate of Geography ; Fujian Normal University ; Fuzhou 350007 ; China) ; Zhang Hucai
- 刊名：Quaternary Sciences
- 出版年：2013
- 卷期：33(5)
- 关键词：钙积层 ; caliche ; 青藏高原 ; Qinghai-Tibetan Plateau
- 页码：p.839-847
- 图表：3 illus., 3 tables, 52 refs.
- 分类号：1400
- issnNo：ISSN1001-7410
- isbnNo：CN11-2708/P
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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±104km^2 ,and the lake area is about 498km^2. 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/em）, and lake water hydro-chemical was dominated by C1-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 o~3CpDB had a range from 1.9%0 to 6.2%o,and o~SOpDB ranged from -8.6%0 to -2.9%0, they were consistent with lacustrine authigenic carbonate. Compared with inflow river water, lake water is less Ca^2＋ 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 Ca2^2＋ and CO3^2- 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 N%O 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 10kin 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 N2O 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.