大柴旦盐湖化学沉积特征及其控制因素

Chemical Sedimentary Sequence from Subbottom Sediment Profiles of Da Qaidam Salt Lake in Qaidam Basin and Its Controlling Factors 

中文关键词:  大柴旦盐湖  湖底沉积剖面  沉积序列  柱硼镁石矿层  柴达木盆地

英文关键词::Da Qaidam salt lake  Subbottom sediment profile  Sedimentary sequence  Pinnoite deposit  Qaidam Basin

中文摘要:

      大柴旦盐湖岩性地层层序依据湖底沉积剖面DCD-2和DCD03自上而下可划分为蒸发盐类盐层与灰黑色淤泥层混合层(Ⅰ层)、灰白色柱硼镁石矿层(Ⅱ层)和土黄色泥质沉积层(Ⅲ层)。湖底化学沉积以石膏为主,并见有石盐和碳酸盐等盐类矿物,这些蒸发盐类矿物几乎贯穿整个化学沉积过程,碎屑矿物夹杂其中,化学沉积分异很不充分。在柱硼镁石矿层形成前的较长时期内,大柴旦盐湖是以碎屑沉积为主的非盐湖相沉积环境,此后快速进入硫酸盐型盐湖阶段和湖底柱硼镁石矿层形成阶段。个别层位见有大柴旦盐湖这种独特化学沉积序列,与其它陆相和海相蒸发沉积序列有明显的差异,这可能主要受该地区的构造环境、物源背景以及气候变化等因素的控制。新构造运动、气候的持续干旱化、湖底柱硼镁石矿层形成前后截然不同的湖区气温、水量平衡和水化学条件(包括化学动力学因素)以及盐湖硼酸盐矿物形成的内外耦合条件,促使全球分布有限的柱硼镁石矿层在大柴旦湖底形成。构造运动、气候干湿变化以及不同水体(包括入湖淡水、盐湖卤水和周边出露泉水)的掺杂兑卤作用的耦合机制控制了大柴旦盐湖如此特殊的化学沉积序列。

英文摘要:

      :Based on subbottom sediment profiles DCD-2 and DCD03 from Da Qaidam salt lake, the lithostratigraphic sequence can be divided into evaporite and silt mixed layer (unit Ⅰ), pinnoite deposit (unit Ⅱ) and argillaceous sediment layer (unit Ⅲ). Gypsum-halite-carbonate evaporite minerals dominated in chemical sedimentary sequence in subbottom sediment of Da Qaidam salt lake, which almost throughout the whole chemical sedimentation process. Detrital minerals are mixed up with evaporite minerals that result in chemical sedimentary differentiation is insufficient. The results show that Da Qaidam salt lake had been a non-salt lake facies sedimentary environment that dominated by detrital deposit for a long period of time before subbottom pinnoite deposited.Then it rapidly changed into sulfate-type salt lake sedimentary stage and subbottom pinnoite sedimentary stage.Consequent changes in temperature, water balance and water chemistry of the lake, and as well as other control conditions may in a way associate with the sedimentary conditions favorable for the deposition of pinnoite deposit. The coupling mechanism of quaternary neotectonics, continuous arid climate and dilution and mixing from the different water bodies might have been responsible for the formation of this peculiar chemical sedimentary sequence in Da Qaidam salt lake.