Abstract:

The Quaternary sequence of the source area of the Yellow River is set up on the basis of research on the natural exposures and cores, and it consists of the Lower Pleistocene, Middle Pleistocene, Upper Pleistocene and Holocene. The Lower Pleistocene is alluvial and lacustrine sediments; the Middle Pleistocene is composed of lacustrine, glacial and fluvioglacial sediments; the Upper Pleistocene consists of lacustrine, glacial, fluvioglacial, pluvial and alluvial sediments; and the Holocene is made of alluvial, pluvial and lacustrine sediments.Three glacial periods in the source area since the Middle Pleistocene are recognized, which are the last glacial period, the reciprocal second glacial period (late Middle Pleistocene) and the reciprocal third glacial period (early Middle Pleistocene). During the reciprocal third glacial period an ice sheet in the source area may be formed.The last glacial period is divided into two stadial stages with an interstadial stage. Evolution of lakes of the source area during the Quaternary went through three stages.The first stage is the Early Pleistocene, in which numbers and areas of lakes largely decreased compared to those of the Pliocene and lakes developed only along the south foreland of the Buqing Shan.The second stage, lake-expending stage, is the Middle Pleistocene.Lake cover at that time was ten times in area more than that of the Early Pleistocene. The last stage is the Late Pleistocene and the Holocene and is recognized two lake-expanding periods with two lake-shrinking periods.The Yellow River in the source area occurred from the last Late Pleistocene to the earliest Holocene, and meanwhile the Yellow River captured the current of the upper reaches of the Yangtze River.

Key words: the source area of the Yellow River, Quaternary sequence, glacial period, ice sheet, lake evolution, drainage evolution