兰州地区晚更新世古风成砂的发现及环境变化

The Discovery of Palaeo-eolian Sand and Environmental Changes of the Late Pleistocene in Lanzhou Area

兰州地区秦王川古风成砂具有明显的斜层理及交错层理,新月形沙丘形态,由细砂和极细砂组成,单峰型,分选好等典型的特征。它是末次冰期晚期的产物,形成于距今2.7—1.0万年之间。当时兰州属荒漠草原,气候干燥寒冷。此外,还探讨了兰州地区晚更新世环境演化过程。 兰州地区位于我国黄土高原西北边缘。年气温9—10℃,年降水量300mm左右,30年来最大年降水量超过500mm,最少不足200mm,降水量的年际变化相当大,属于暖温带半干旱气候区。现代植被主要为干草原兼有荒漠化植被,相应的土壤是以灰钙土为主,兰州市之南为淡黑垆土地带,向北逐渐由灰钙土过渡到棕钙土。第四纪气候波动对兰州地区自然环境产生深刻影响。冰期时气候干冷,蒙古高压加强,西北风盛行,沙漠向南、向东扩张,兰州则成为来自沙漠区的尘暴沉降中心,形成巨厚的黄土沉积。目前,世界上最厚的风成黄土剖面出现于兰州。间冰期时太平洋高压增强,太平洋季风直达兰州以北,沙漠收缩,兰州地区为夏季风控制,气候温暖湿润,黄土地层内发育古土壤。因此,兰州是中国气候变化剧烈,具有黄土、古土壤互层的最典型地区之一。 近年来,我们在开展第四纪黄土研究时,对于兰州地区晚更新世环境演化有了较深刻的认识,孢粉分析的资料,基本上可以了解本地区晚更新世植被类型及其变?

The palaeo-eolian sand at Qinwangchuan basin in Lanzhou Area has very clearly inclined bedding and cross bedding structures. It was deposited as crescent dunes mainly Composed of finesand andvery finesand. The sand was best sorted and has only one peak in grain-size frequency curve. Therefore, It is typical eolian sand eroded from nearby alluvial sand and Malan loess. It was the outcom of the late last glacial period and formed between 10 ka B. P. to 27 ka B. P. , when the vegetation fell into desert steppe and the climate was quite cold and dry in Lanzhou Area. This paper has also dealt with the environment changes of the late pleistocene in Lanzhou Area.