8～7Ma左右南亚气候的变干是否由青藏高原隆升到最大高度而引发现代形式季风所造成，是一个极具挑战的理论问题。对位于高原东北部临夏盆地15Ma以来地层中的石英砂扫描电子显微镜分析表明，风成砂一直存在并于8和6～5Ma时含量最高；最大风沙颗粒的平均粒径在15～3.6/2.6 Ma 达0.44m，3.6～2.6Ma之后显著下降，平均仅为0.1～0.07mm左右。前者可能反映中国西部在8～5Ma气候也十分干旱，是全球气候变化的一部分，与高原隆起并无直接联系；后者表明上新世末研究区近源风沙作用的消失，代之以远源风沙作用的盛行，可能反映了此时青藏高原的急剧隆起和大气环流的重大改变。

本文通过对临夏盆地长达30m•y•的连续沉积（临夏群） 共计779个样品的粒度特征分析, 划分出七大完整的沉积旋回。粒度曲线明显地表示出青藏高原的强烈隆升始于距今314Ma前。该文还初步确定出青藏高原地区两次夷平过程最终结束的年代。

临夏盆地东山古湖（2.35～1.65 Ma B.P.） 沉积厚达84m，是六盘山以西早更新世湖相沉积的典型代表。以2.5m的间隔对其进行系统采样，以CaCO3含量变化为指标建立高分辨率的气候变化曲线，对曲线进行周期分析表明，东山古湖所反映的气候波动具有明显的41000a主导周期；其中2.28 Ma B.P.和1.75～1.80Ma B. P.时段为两个明显的冷湿时期，表明东亚季风在建立初期具有不稳定性。

The carbonate content in the stratigraphy of Loess and inland lakes is a sensitive indicator of climatic changes. 3267 samples in total were collected at 215 cm intervals from a 80 m thick lacustrine deposits, spanning 2135 Myr, in the Dongshanding section of Linxia Basin. All the samples were analyzed by using a standard Bascomb calcimeter. The variation of carbonate contents shows that there are two obvious cold-humid events in the early Pleistocene at about 2128 Ma and 118～1175 Ma respectively. During these two periods, the climate was cold or cool. The climatic change was dominated by an obvious 41 000a periodicity. The results also indicate that in the early period of the Quaternary, the monsoon climate had been established but was not very stable.