内蒙古呼伦湖表层沉积物的矿物组成和沉积速率

呼伦湖表层沉积物的取样和分析表明,沉积物主要由碎屑矿物和自生碳酸盐矿物组成。碳酸盐含量为10％—18％。碳酸盐沉积作用与湖水的较高含盐量和碳酸盐过饱和度有关。湖泊中心HL8号柱样的~(210)Pb测定结果是,10cm以上平均沉积速率0.25cm/a,10—12cm为0.05cm/a。60年代开始随湖泊水位上涨沉积物输入量迅速加大。

Mineral composition and sedimentation rate of surficial sediments in Hulun Lake, inner mongolia

Hulun Lake, the fifth largest lake in China, is located in the west side of Hulun Buir Prairie. It was seldom studied and understood before due to the remote border district. The observation and sampling of the modern sediment in Hulun Lake has been carried out and the mineral composition and the sedimentation rate analysed recently. The surficial sediments of Hulun Lake are distributed unevenly, for the lake is linked to the influxes of the Herlen River, the Orxon River and the ancient Harlar River. Grainsize analysis of 7 sediment samples in the northwest demonstrates that the median size of most sample is 7. 0-9. 2(?) , falling in the size fraction of clay-very fine silts. Mineral identification by microscope and XRD analysis for the sediment shows that the sediments are such allogenic minerals as quartz, feldspar, mica and heavy minerals and authigenic minerals, mainly calcite. Carbonate content of the sediment samples ranges from 10. 1 % to 17. 6% indicated by chemical analysis, which is linked to higher salinity and supersaturation to carbonate of the lake water. 210Pb dating was tested for a short core in the central part (site HL8) of the lake and the sedimentation rate was calculated using CIC model. The average sedimentation rate is 0. 25 cm/a above lOcm-depth of the core and 0. 05 cm/a in 10 ?12cm, implying higher sedimentation rate since 1959 A. D. Based on the hydrologyical data, the lake level rose gradually beg in ing from the 1950s and up to its historical highest in the 1960s. It is inferred that the influx sediment amount increased as the lake level rose.