粒度年龄模型在伊犁昭苏黄土地层中的初步应用

Application of grain-size age models on Zhaosu loess stratigraphy in Ili region

通过伊犁昭苏剖面末次冰期以来黄土和古土壤层粒度对比分析,发现昭苏地区>30μm、>40μm和>63μm等粗粒径组分在古土壤层的含量较黄土高,与粒度年龄模型原理相悖,不适于昭苏地区黄土粒度年代模型的计算,而2~10μm细粒径适宜于粒度模型年代计算。以重建年代为基础的剖面>40μm粒度序列所记录的7个冷事件和20个暖事件与格陵兰GISP2冰芯氧同位素揭示的Heinrich事件和Younger Dryas冷事件及D-O事件具有较好的对应关系,印证了重建年代的可靠性。此外,伊犁昭苏剖面S0和L1底部地层年龄、光释光外推年龄均与黄土高原具有较好一致性,意味着末次冰期以来伊犁昭苏地区黄土沉积可能与黄土高原是同步进行的。

Based on the comparative analysis on the particle size of the loess and paleosol at the Zhaosu section in lli since the last glacial, we found that the content of coarse grain size 〉 30 Ixm, 〉 40 txm and 〉 63 Ixm in paleosol are higher than those of loess, which contradict the principle of grain-size age models, therefore, all these particles are not suitable for the loess grain-size age models in Zhaosu region, while fine particle size 2 - 10 I^m is suitable for it. The curve of the content of grain size 〉 40 IJ, m based on the reconstructed ages is well consistent with the oxygen isotope records from Greenland ice core. Seven peaks correspond to Heinrich cooling events and the Younger Dryas cold event, respectively; and most of the valleys are similar to D - O warm events. The similarity between the Ill loess and GISP2 confirmed the reliability of the ages. In addition, the bottom of SO and L1 strata ages using grain-size model as well as the optically stimulated luminescence ages consistent with the strata ages of Loess Plateau, which suggests that the loess deposition in Ili Basin simultaneously started with the Loess Plateau since the last glaciation.