罗布泊耳轮区现代盐壳单元特征及其环境意义

通过对罗布泊"大耳朵"干盐湖区5个区的盐壳单元土的地球化学特征、粒度及磁学特性的研究,结果表明:(1)罗布泊"大耳朵"干盐湖区盐壳易溶性盐组分含量变化较大,总盐含量从高到低依次为LBVI >LBVⅡ >LBVⅢ >LBIX >LBV,新盐壳单元含盐量略高于老盐壳单元含盐量(除LBV外),且易溶性盐主要为Na⁺和K⁺-Cl^- -SO₄^2-型;pH值均 >7,表明均处于偏碱性环境中;TOC含量在1.19%~1.21%之间,且各盐壳单元之间差异不显著。(2)新老盐壳单元样品粒度组分均以粉砂(2~63μm)含量为主,平均含量达到80.52%,且老盐壳单元中粗砂和中砂含量明显高于新盐壳单元。(3)各样品间磁化率值差异不显著,平均值为3.7×10^-6 m³·kg^-1,呈现出由耳轮区中心依次向外逐渐升高的趋势,且样品中的磁性矿物主要以低矫顽力的亚铁磁性矿物为主。(4)总盐含量与pH、TOC呈正相关,与磁化率、粉砂呈负相关。综合表明,此时期罗布泊气候已趋向干旱化发展。

Features of modern salt crusts in the "Great Ear" playa of Lop Nor Basin and its environmental significance

Lop Nur is the typical closed inland playa in Xinjiang,its occurrence,development and demise had recorded the miniature of the climate change and environmental evolution in entire sedimentary of the Tarim Basin and Central Asia. Through surveying sample in field,and comparing the features of new and old salt in different "helix" in Lop Nur "big ears",this paper proposed that the different "helix" Ring in "big ears" had five or six sides or polygonal cracking which is its minimum or basic unit,called salt shell unit in salt crust edge,and further analyzed the soil geochemical characteristics,grain size and the magnetic susceptibility of the new and old salt crust element in the dry salt lake of "Great Ear" in Lop Nor to investigate the features of salt shell unit in different developmental stages. Results showed as follows:(1)the soluble salt content varies greatly in the salt crust samples,from high to low the total salt contents were,in ordered:LBⅥ >LBⅦ >LBⅧ >LBⅨ >LBⅤ,and the new salt shell element was higher than the old one except for LB V. The main types of soluble salt were Na⁺ and K⁺-Cl--SO₄^2-. The pH were all over 7,revealing that both the new and old salt shell element were in partially alkaline environment. TOC content varies between 1.19% and 1.21% with smaller difference in each salt shell element.(2)The particle size of sample components were dominated by silty sand(2-63μm)both in the new and old salt shell element,and the mean content was up to 80.52%. The coarse and medium sand contents in the old salt shell element were obviously higher than those in the new one.(3)Difference of magnetic susceptibility among each samples were not significant,and overall shows a gradually increase trend from the middle of the helix to the outward with the average value being 3.7×10^-6 m³·kg^-1,the maximum value being in LBⅨ and the minimum value in LBⅦ. The frequency dependent susceptibility varies between 5.77% and 21.74%,and the mean SIRM value was 314.75×10^-5 Am²·kg^-1,showing that the ferrimagnetic minerals were the main magnetic carriers. (4)The correlation analysis to each parameter showed that the total salt content was positive correlated with pH and TOC,and was negative correlated with magnetic susceptibility and silty sand. In general,the results above indicated that the area of climate has shifted to the drought trend.