若尔盖风成砂-古土壤序列的古气候与古环境记录研究

通过对若尔盖盆地中部辖曼地区风成砂-古土壤沉积序列的粒度分析、孢粉鉴定、磁化率测定以及AMS 14C年代测定，探讨了该地区末次冰消期以来古气候与古环境的演化过程。研究结果表明，若尔盖地区的土地沙化现象至少在距今16 ka余年的末次冰消期就已经出现。地层结构、粒度、磁化率皆指示该区古气候在末次冰消期以来经历了多次冷暖交替变化，沙地也经历了多次的固定与活化过程，其中16130~6460 aB.P.、3445 aB.P.前后以及700 aB.P.前后气候较为温暖湿润，在8170~6460 aB.P.期间有一次极暖事件。自11.3 kaB.P.开始，古土壤中的喜暖型乔木花粉含量明显降低，草本植物、尤其是狐尾藻属和莎草科等沼泽植物孢粉含量明显增多，指示该区古环境发生明显变化，开始发育沼泽泥炭。 

Paleoclimatic and paleoenvironmental evolution recorded by the aeolian sand-paleosol sequence in the Zoigê basin

The aeolian sand-paleosol sequence in the Zoigê basin is a sensitive record of paleoclimate change and paleoenvironmental evolution for the northeastern region in the Tibet Plateau. A typical aeolian sand-paleosol section, called Xiaman, was tested for its AMS C age, grain size, magnetic susceptibility and sporo-pollen. Then the paleoclimate and paleoenvironment evolution since the last deglacial period in this area was discussed. The results show that the land desertification in the Zoigê basin occurred at least in the last deglacial period of more than 16 ka years ago. Variations of the formation structure, grain size and magnetic susceptibility indicate that the paleoclimate has undergone many alternations of cold and warm, and the sandy land has also experienced many processes of fixation and activation. The climate tended to be relatively warm and wet during 16130~6460 aB.P., around 3445 aB.P. and 700 aB.P.. There was a very warm period during 8170~6460 aB.P.. Since 11.3 kaB.P., the sporo-pollen contents of warm-fitted trees in paleosol have decreased considerably, while that of herbaceous plants, especially swampy plants, such as Myriophyllum and Syperaceae, have increased obviously, indicating that the paleoenvironment has significantly changed and the swampy peats have begun to develop.