柴达木盆地西部大浪滩140ka以来沉积特征与古环境

Sedimentary Characteristics and Paleoenvironmental of Dalangtan Salt Lake in Western Qaidam Basin,Since 140 ka BP

文章选取柴达木盆地西部大浪滩盐湖沉积中心的钻孔岩芯为研究对象,通过U系年代学研究,建立了该地区140kaBP以来的湖相地层沉积序列。从沉积特征来看,期间共经历了8次成盐期和6次淡化期,成盐期沉积的主要矿物为石盐、石膏、芒硝和白钠镁矾。淡化阶段主要矿物为粘土(伊利石占绝大多数,次为绿泥石和高岭石)、碳酸盐(方解石和白云石为主)和石英长石。对该时段碳氧同位素分析显示,140～113kaBP(92～84m),同末次间冰期的演化阶段(5e)有着很好的对应关系;113～93kaBP(84～78m)(5d),从碳同位素组成特征看,该阶段也有多次气候的颤动发生,在78～80m层段,有近2m厚的中粗粒芒硝,其为冷相矿物,这说明该阶段水体温度变化频繁;此外,93～87kaBP(78～74.6m)、87～79.5kaBP(74.6～67.5m)、79.5～76kaBP(67.5～63.5m)也都分别对应着末次间冰期后的5c、5b、5a三个阶段。76～72kaBP(60～64m)(MIS4),氧同位素组成快速偏重(-4‰～-8‰(PDB)),温度下降,水体明显咸化;72～30kaBP(60～16m)(MIS3),总体碳氧同位素组成偏重,代表干凉的古气候环境,期间有两次成盐期,代表了冷干时段;30～14kaBP(16～0m)(MIS2),氧同位素组成明显偏重,代表了末次盛冰期的到来,进而结束了湖泊水体沉积。

The essay researches the drill core samples from the center of Dalangtang salt lake in the western of Qaidam basin.By the study of U series chronology,we get the sediment sequence of lake strata since 140ka BP in this area.The sedimentary characters indicate that this area suffered 8 times salifying periods and 6 times freshening periods.The main minerals include the halite,gypsum,mirabilite and bloedite during the salitying periods,and the main minerals include the clay minerals（the illite mainly,the chlorite and kaolinite secondly）,carbonate（the calcite and dolomite mainly）,quartz and feldspar during the freshening periods.Correspondingly,the carbon and oxygen isotope analysis in this period indicate that the changes from 140 to 113 ka BP（92~ 84m）of drilling core was corresponding well with the evolution stages（5e）during the last interglacial.From 113 to 93 ka BP（84~78m）（5d）,the component of oxygen isotope indicate the it existed several climate fluctuations during this time.The medium-coarse grain mirabilite as the index minerals of low temperature gets 2 meters thick from 78~80m of drill core,reflecting the temperature of water changes frequently.Besides,the three periods including 93~87 kaBP（78~74.6m）,87~79.5 ka BP（74.6~67.5m）,79.5~76 ka BP（67.5~63.5）are corresponding with the periods stages of 5c,5b,5a after the last interglacial period respectively.From 76 to 72ka BP（60~64m）,the oxygen isotope becomes heavy quickly（-4‰^-8‰（PDB））,indicating the temperate goes down and the water becomes salty obviously;from 72 to 30 ka BP（60 ~16 m）,the components of carbon isotope and oxygen isotope become heavy,reflecting the character of dry and cool climate,and the two salty periods appearing in this period,representing the stage of cool and dry climate;from 30 to 14 ka BP（16~0 m）,the component of oxygen isotope become heavy obviously,representing the coming of the last glacial and the end of lake water sediment.