青藏高原东北缘地区晚第四纪水系沉积物年代标尺的初步研究

STUDY ON THE TIME SCALE OF LATE QUATERNARY HYDROGENIC SEDIMENTS ALONG THE NORTHEASTERN MARGIN OF QINGHAI XIZANG PLATEAU

对青藏高原东北缘地区河流阶地资料的对比研究表明，阶地的高度与阶地的形成年代之间具一定相关性，同时，阶地的形成年代与黄土剖面中古土壤年代完全可以对比，因此，以阶地的高度代替阶地级数，并借用兰州地区黄土标准剖面的古土壤年代，建立了青藏高原东北缘地区晚第四纪水系沉积物的年代标尺。阶地抬升速率研究表明，大约自１５０万ａ以来，青藏高原东北缘地区正在进行着持续的构造抬升，并且呈越来越快的趋势。

The comparative research of the river terraces along the northeastern margin of Qinghai Xizang plateau indicates that the heights and ages of terraces of different grade rivers are quite different. But there is correlation between the heights and the ages. A statistical relationship formula is proposed. The terrace ages of river and the drainage system are compared with the ages of paleosoil in the loess profile. The results indicate that the development of terrace is controlled by tectonics and climate. We can use the paleosoil ages of Lanzhou area loess profiles (one of the standard loess profiles) to establish an initial late Quaternary microgeomorphogy time scale. The vertical rising rates reflected by the terraces show that since 1.5Ma the northeastern margin of Qinghai Xizang plateau are continuelly rising with a tendency of becoming quicker. During mid Pleistocene the rise rate is about 0.1～0.25mm/a. Since late Pleistocene to Holocene, the rise rate is about 0.5～1.5mm/a. The relationship between the rise rates and ages has been changed with time.