地下水补给型湖泊表层沉积物矿物组成及其形成机制——以巴丹吉林沙漠湖泊群为例

盐湖中的矿物沉积记录着丰富的环境气候变化信息,是古环境研究的重要对象.在无地表径流补给的盐湖中,其矿物组成及沉积特征与有地表径流补给的湖泊相比是否有一定的特殊性,是值得探讨的问题.采集巴丹吉林沙漠33个不同矿化度地下水补给型湖泊的表层沉积物和10个地表风积砂样品,通过X衍射的方法,分析样品的矿物组成.结果显示:湖泊表层沉积物主要为石英、长石、辉石、云母等碎屑矿物,部分湖泊含有少量的碳酸盐和氯化物盐类矿物.湖泊沉积物的矿物组成与湖水矿化度的关系较为密切,淡水湖仅分布碎屑矿物,微咸水湖含有碎屑矿物和碳酸盐类矿物,盐湖含有碎屑矿物、碳酸盐类矿物和氯化物.风积砂样品中主要为碎屑矿物,占总矿物含量的90%,对湖泊沉积物的矿物组成影响较大,但对湖泊沉积物中的盐类矿物没有贡献,表明湖泊表层沉积物中盐类矿物主要是自生作用形成的.虽然本地区湖泊边缘的沉积物中盐类矿物种类相对较少并且含量较低,但其盐类矿物组成与分布能够响应湖水矿化度的变化,其环境指示意义与有径流补给的盐湖相同,可以指示其湖水的盐度.因此,可以从巴丹吉林沙漠地下水补给型湖泊沉积的盐类矿物中提取相应的古环境信息,用于恢复古气候和古环境的研究.

Mineralogical assemblages in surface sediments and its formation mechanism in the groundwater recharged lakes: A case study of lakes in the Badain Jaran Desert

The mineral deposit of salt lakes was widely used to reconstruct paleoenvironment. However, whether mineral composition and deposition characteristic in no runoff recharged lakes is different from that in runoff recharged lakes remains uncertain. In this paper, we collected 33 lake surface sediment samples from groundwater recharged lakes with different salinity and 10 surface aeolian sand samples in the Badain Jaran Desert. Mineralogical assemblages of all the samples were measured by X-ray diffraction. Results indicated that lake surface sediments were mainly composed of detrital minerals such as quartz, feldspar, pyroxene and mica. Moreover, some lakes included small amounts of carbonate and chlorine. Saline mineralogical assemblages in lake sediment varied with the lake water salinity:freshwater lake contains only detrital mineral, brackish one contain both detrital mineral and carbonate, and saline ones contain detrital mineral, carbonate and chloride simultaneously. The content of detrital minerals in aeolian sand samples was 90%, which indicated that the aeolian sand had a great contribution to the lake surface sediments mineralogical assemblages, while the saline minerals in lake surface sediments were authigenic minerals. Hence, the composition and distribution of saline minerals could respond to the changes of water salinity, and have same environmental significance compared with that in runoff supply salt lakes. Moreover, lake mineralogical assemblages in the surface sediments of groundwater recharged lakes can be a proxy for paleoclimate and palaeoenivronment reconstructions.