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	西藏纳木错沉积物单水方解石出现前后的环境变化
其他题名	LATE-HOLOCENE LAKE ENVIRONMENT REFLECTED BY THE OCCURRENCE OF MONOHYDROCALCITE IN NAM CO,CENTRAL TIBET
	李明慧; 康世昌; 朱立平; 王君波; 张强弓; 谢曼平; 游庆龙
发表日期	2008
ISSN	1001-7410
卷号	28 期号:4 页码:601-609
中文摘要	2005年在西藏纳木错水下60m处钻取一支332cm的湖芯,沉积物皆为灰黑-黑色碳酸盐粘土.对湖芯1cm间隔取样并进行X射线、扫描电镜、Sr/Ca和碳酸盐含量的分析.研究发现,纳木错湖底0～258cm沉积物中出现了单水方解石,扫描电镜下该矿物晶形完好,这是个亚稳定矿物,具有重要环境意义.利用碳酸盐含量(24.12%～54.52%)、Sr/Ca比值(<0.006)、方解石中Mg含量(MgCO_3,mol%<3.325%)、石膏、粘土矿物(伊利石和镁绿泥石)、单水方解石成因和沉积速率讨论了单水方解石形成前后湖泊环境的变化.2.1cal.kaB.P.单水方解石开始出现,此时纳木错湖水性质推断为pH>8.6,mol Mg/Ca>6.5,Ca~(2+)和SO~(2-)_4离子浓度足以沉淀少量石膏,演化至现代,表层湖水性质为pH=9.4,mol Mg,/Ca=10.03～15.03,SO~(2-)_4浓度较高,Ca~(2+)含量低,不足以沉淀石膏.单水方解石出现之前的3.0～2.1cal.kaB.P.时期,沉积速率低(0.134mm/a),蒸发作用强度不稳定,湖水温度低,矿化度呈上升趋势.该矿物出现后的2.1～1.7/cal.kaB.P.时期,沉积速率快(1.639mm/a),矿化度稳定,气温低.1.8cal.kaB.P.温度达到最低值,为气候冷事件的表现.较快的沉积速率(>1.168mm/a)是纳木错单水方解石形成的重要原因之一,碳酸盐沉积加快和入湖碎屑物质增加是沉积速率加快的主要原因.
英文摘要	A 332cm-long core was obtained in 2005 at a water depth of 60m from the Nam Co,Central Tibet.The core reveals continuous lacustrine accumulation of grey-black grey carbonate-clays.Samples were collected at 1cm interval and examined to identify the types of minerals by an X-ray diffractometer and scanning electron microscope.Sr/Ca and CaCO_3 content in sediments were analyzed by chemical methods.Monohydrocalcite(MHC),a rare and meta-stable carbonate mineral with important environmental significance,was found at 0～258cm(0～2.1cal.kaB.P.)in the core.This paper is aimed to elucidate the environment changes with the occurrence of MHC in this area.The mineralogy of MHC,gypsum and clays(illite and Mg-chlorite),MgCO_3 mol% in low-Mg calcite(<3.325%),carbonate content(24.12%～54.52%),Sr/Ca(<0.006)in lacustrine sediments,and sedimentation rate in the core provide important information and can be used to reconstruct ancient chemical and physical conditions in the area.MHC with distinct crystals was first observed at the depth of 258cm(2.1cal.kaB.P.),indicating a condition of pH>8.6 and mol Mg/Ca>6.5,and with activities of microorganisms such as algae and bacteria in the lake water.The concentrations of Ca~(2+) and SO~(2-)_4 were high enough to precipitate gypsum at about 2.1cal.kaB.P.As a meta-stable mineral,MHC is developed chemically in modern waters(1.7g/L)with high Mg/Ca molar ratio(10.03～15.03),high pH(9.4),sedimentation rate of more than 1.168mm/a,and the presence of bacteria,algae,and diatom.The concentrations of Ca~(2+) and SO~(2-)_4 are too low to precipitate gypsum in modern lake water.During 3.0～2.1cal.kaB.P.,there was no MHC,and the sedimentation rate was 0.134mm/a with variable evaporation,low temperature of lake water,and increasing alkalinity.During 2.1～1.7cal.kaB.P.the sedimentation rate was 1.639mm/a along with stable evaporation,low temperature of lake water,and a cold event occurred at 1.8cal.kaB.P.As an important reason of the occurrence of MHC,the possible high sedimentation rate were likely caused by the high precipitation of carbonate and inflow of detrital materials.
关键词	环境矿物碳酸盐矿物单水方解石气候与环境湖泊青藏高原
英文关键词	environmental mineral;carbonate mineral;monohydrocalcite;climate and environment;lake;Tibet
语种	中文
来源期刊	第四纪研究
来源机构	中国科学院西北资源环境生态研究院
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/89704
推荐引用方式 GB/T 7714	李明慧,康世昌,朱立平,等. 西藏纳木错沉积物单水方解石出现前后的环境变化[J]. 中国科学院西北资源环境生态研究院,2008,28(4):601-609.
APA	李明慧.,康世昌.,朱立平.,王君波.,张强弓.,...&游庆龙.(2008).西藏纳木错沉积物单水方解石出现前后的环境变化.第四纪研究,28(4),601-609.
MLA	李明慧,et al."西藏纳木错沉积物单水方解石出现前后的环境变化".第四纪研究 28.4(2008):601-609.