晚第四纪科尔沁黄土堆积的Rb-Sr地球化学特征及古气候变化

在科尔沁沙地南缘选取了两个典型的风成黄土-古土壤序列,对其记录的Rb-Sr地球化学特征进行了分析。结果表明,Rb-Sr含量变化与黄土高原黄土-古土壤序列相似,但Rb含量小于黄土高原,Sr含量则相反,可能是因为研究区距源区较近,粒径较粗,加之气候干冷,化学风化强度较弱造成的。总体而言,我国东北地区黄土Rb/Sr值作为反映东亚夏季风强弱变化的替代性指标是可行的。综合分析认为,晚第四纪科尔沁地区古气候存在多次明显的干湿变化,特别是在108~144、233±21和86±7 ka前后,气候较为暖湿;在261±32 ka前后,极为干冷,甚至出现沙漠化过程。晚第四纪科尔沁沙地的古气候变化,是东亚季风强弱变化的反映,也可能是全球气候变化在我国东北地区的体现。

Rb/Sr GEOCHEMISTRY OF LOESS DEPOSITS IN THE HORQIN DUNEFIELD,NORTHEASTERN CHINA,AND ITS IMPLICATIONS FOR CLIMATE CHANGE DURING LATE QUATERNARY

The aeolian silt deposit is a good record of palaeoclimatic and paleoenvironmental changes in Late Quaternary. However, Loess deposition and Palaeoclimatic changes in the Horqin dunefield, Northeastern China, during the late Quaternary remains poorly understood. In this paper, the Rubidium (Rb) and Strontium (Sr) geochemical characteristics of the typical loess sequence in the southern margin of the Horqin dunefield are analyzed. Results show that the variation pattern of Rb-Sr in the Horqin loess are similar to those of the Chinese Loess Plateau, excepted for that the Rb content is lower and the Sr content is higher, probably resulted from the colder and drier climate in this study area, which led to very weak chemical weathering. It further indicates that the variations in Rb/Sr ratio in the Northeastern China loess sequence may represent the alternation of East Asian summer and winter monsoon climates. Based on the Rb-Sr geochemical data, it is suggested that Horqin dunefield had experienced a warmer and wetter climate in the periods of 108-144 ka 86±7 ka, and 233±21 ka, while it was very cold and dry, even worse than the desertification environment in the period of 262±32 ka. The climate changes in this study area are consistent with variations of the East Asian monsoon during Late Quaternary. It could be a footprint of the global glacial-interglacial climatic variations in northeastern China.