汾渭地堑系列湖盆第四纪中晚期地貌与沉积阶段性演化的时间序次差异及其构造指示意义

依据汾渭地堑系列湖盆地貌与沉积特征对其阶段性演化历史进行了研究。野外调查发现,在第四纪中晚期,各湖盆内曾发生过3次大幅快速的湖退或河流强烈下切事件; 从渭河盆地至临汾太原盆地,再至大同阳原盆地,每一次事件的出现在各盆地中都有时间序次上的差异。以黄土-古土壤序列作为时间坐标系,渭河盆地中的3次湖退或河流下切分别发生在L9,L6和L2黄土堆积期; 临汾太原盆地分别发生在S8,S5和S1古土壤发育时期; 大同阳原盆地分别发生在L8,L5和L1黄土堆积期。也即是,第一次事件在几个盆地中出现的时间序次是L9-S8-L8,第二次事件是L6-S5-L5,第三次为L2-S1-L1。事件出现的时间序次差异显示: 距青藏高原越远的盆地,事件出现的时间越晚。根据早期对区域湖退-湖侵发生机制的研究成果并结合上述这些发现,本文认为正是受到青藏高原挤压隆升的影响,而非西太平洋板块俯冲的影响,才产生了区域系列湖盆第四纪中晚期地貌与沉积阶段性演化的这种时间序次差异。

THE SEQUENCE DIFFERENCE IN THE TIMES IN THE GEOMORPHIC-SEDIMENTARY EVOLUTION IN THE FENWEI GRABEN BASINS DURING THE MIDDLE-LATE QUATERNARY AND ITS TECTONIC SIGNIFICANCE

The paper analyzed the periodical evolution of the Fenwei Graben Basins based on their geomorphic-sedimentary characteristics.Field works found all the basins in the graben had experienced three fast paleolake regressions or intensive down-incisions of the rivers,and there exist a sequence difference in the occurrences from the Wenhe Basin,the Linfen-Taiyuan Basin to the Datong-Yangyuan Basin.The loess-paleosol layers are taken as time series,and the paleolake regressions or down-incisions of the Weihe River in the Weihe Basin took place in the times when Loess L9,L6 and L2 accumulated,respectively.In the Linfen-Taiyuan Basin,three paleolake regressions occurred in the times when paleosol S8,S5 and S1 developed,respectively.In the Datong-Yangyuan Basin,three paleolake regressions emerged in the times when Loess L8,L5 and L2 deposited,respectively.The facts show that the far the basin is from the Tibet Plateau,the later the paleolake regression or the down-incisions of the rivers took place.Taking these facts and the former research results in term of the mechanism of the local paleolake regression-transgressions,the paper put forwards that it is under the influence of the compressive uplift of the Tibet Plateau,not the subduction of West Pacific tectonic plate under the Eurasian plate,which causes such geomorphic-sedimentary phenomena in the graben basins.