中更新世中晚期以来汾河流域地貌阶段性发育及成因分析

汾河流域中系列断陷盆地在第四纪期间的阶段性演化历史一直不甚清楚。最近作者在野外调查中发现:在流域中的太原、临汾等几个构造盆地的周边地带,普遍发育了三级冲湖积台地。根据三级台地的沉积结构特征和利用黄土古土壤序列定年法、古地磁定年法及TL测年法对三级台地的年代研究结果,发现自中更新世中晚期以来,汾河流域系列盆地中都曾同时发生过三次大幅度的湖退和三次湖进过程;其中三次湖退开始的时间分别为0.76MaB.P.、0.55MaB.P.、0.13MaB.P.;由湖退而产生的三个低湖面阶段分别对应着S₈、S₅、S₁古土壤发育时期。从引起湖盆大幅度收缩的原因看,构造运动是根本因素,三级冲湖积台地的形成是对区域三次构造抬升的地貌响应。 

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.