THE ANALYSIS ON THE DEVELOPMENT OF ALLUVIAL AND LAKE LANDFORM IN FEN RIVER DRAINAGE BASINS

It has been unclear how the landform in Fen River drainage developed in Quaternary until now.This paper reveals that there exist three alluvial or lake terraces in the edges of Fen River drainage basins since the middle-late Pleistocene.There are a succession of loess-paleosol unites accumulated on these terraces.The ages of these terraces can be inferred by studying the stratigraphy of the overlying loess/paleosol,particularly the superjacent loess/paleosol on it.The facts acquired in the fieldwork show that three terraces formed when paleosols began to develop,whereas the paleoclimate became warm and wet.Using paleomagnetism,loess/paleosol series,thermoluminescene to date the terraces,we find that these terraces emerged in consistent with the formation of S₈,S₅ and S₁ in time,while the basins were experiencing three low-stands of lake-level.The ages of three terraces in Fen River drainage basins are about 0.76MaB.P.,0.55MaB.P.and 0.13MaB.P.respectively.Taking all the facts into account,we draw the conclusions:1) It is three teconic uplifts that results in the formation of three alluvial of lake terraces,or three low-stands of lake-level in the drainage.2) It seems reasonable that the thee uplifts of Tibet plateau caused the changes of Fe River drainage basins.