通过对柴达木察尔汗盐湖贝壳堤剖面沉积物粒度、碳酸盐和磁化率的对比,结合沉积物粒度频率曲线与多种粒度参数分析,详细讨论了研究剖面形成过程中物质搬运和沉积作用以及所反映的环境变化。结果表明沉积物粒度特征指示了湖泊水位的相对变化。在距今约38.2 ka BP(14-C年代,未校正。下同)左右,沉积记录指示古湖泊的范围和水位已达到剖面位置,之后湖泊继续扩张、水位波动上升;在距今约35.5 ka BP,粒径有一突然变细又变粗的过程,可能为一次较快速的湖面波动;在距今约35.5 ~ 33.3 ka BP之间,沉积物颗粒较粗,碳酸盐含量和磁化率值低,揭示湖泊水位较低。距今约33.3 ~ 27.1 ka BP之间,沉积物颗粒较细,碳酸盐含量较前一阶段高,表明此阶段湖泊水位相对较深,但粒度、碳酸盐和磁化率等指标也记录了三次较明显的湖泊快速但短暂的退缩过程;在距今约29.7~28.3 ka BP,沉积物颗粒最细,指示了此时期可能为湖泊水位最高期。从距今约27.1 ka BP开始,沉积积物颗粒明显变粗,揭示湖泊进入到退缩期,距今约18.1 ka BP,粒度指标的变化和上层的盐壳指示湖泊进入快速盐化阶段,之后湖泊退出剖面所在的位置,此后研究区湖泊水位再也没有达到这个高度。 相似文献
On the basis of the analyses of TOC, CaCO3, δ13Corg, δ18O, and δ13C of the shell bar section in the Qaidam basin, and compared with grain size data, the environmental change history of the high water level of paleolake Qarhan was reconstructed and it could be divided into five stages. From 39.7 to 35.8 kaBP was the development period of high paleolake level. From 35.8 to 33.6 kaBP and 33.6 to 27.2 kaBP, TOC and CaCO3 contents and δ18O values were high, whereas, δ13Corg values and median size content were low, reflecting a warm-humid climate and high lake level. During 27.2-22.3 kaBP and 22.3-17.5 kaBP, both temperature and the lake level were lower than those in the previous stages, but the climate was still warmer and more humid than that of today. The lake level decreased between 32.4 and 32.2 kaBP, 30.4 and 29.8 kaBP, and 28.4 and 27.2 kaBP. Generally, the climate was warm and humid in Qaidam basin and the high lake level sustained between 39.7 and 17.5 kaBP. The lake retreated abruptly at 17.5 kaBP, with a very strong increase in evaporation, which resulted in salt formation and the extinction of Corbicula. 相似文献