关于黄河形成时代的一些认识

摘要

The main contents of this paper is the formation of the Yellow River.To explain that,geomorphological,geochronological,paleomagnetical and geochemistrical methods are used.The major study area is the Hetao basinShanxi-Shaanxi Gorge-Sanmenxia basin-Sanmenxia Gorge at the middle reach of the Yellow River,and the miner area is the Xinghai basin at the upper reach of the Yellow River.There are 9 terraces found in Xinghai basin,and the age of the highest T9,T8 and T7 is 200ka,100ka,80ka based on the OSL and ESR dating,respectively.A set of Later Quaternary fluvial-lacustrine stratum is widely distributed in the Hetao basin,Inner Mongolia at the middle reach of the Yellow River.The Haojiayao section in the Togtoh mesa is located in the easternmost part of the Hetao basin,at the gateway of the Shanxi-Shaanxi Gorge,and it formed the second geomorphological platform of the Yellow River.The curves of the lightness of chrominance and the loss of ignition (LOI 950) show the unanimously change bends:from low to high from bottom to top in Haojiayao section.This tendency shows the continued increase of carbonate content in the sediment,and the rise of mineral concentration of lake water which also indicate the closed environment of the lake.The OSL dating indicates that the lacustrine deposition stopped about 100ka.The age of the highest terrace of the Yellow River in the easternmost part of the Sanmenxia basin is 150ka,while the terminating age of the white sand deposition is 200ka which indicated the water leakage.According with the research results of predecessors,the Gonghe Movement is the main cause of the formation of the Yellow River.However,the formation age of the Yellow River at the upper reaches of the Xinghai-Gonghe area (the age is 200ka) and at the middle reaches of the Sanmen Gorge area(the age is 200 ～150ka)is earlier than that of the Hetao basin (the age is 100ka),and the time of the Yellow River run-through the Shanxi-Shaanxi Gorge is the latest.That is to say that the age of the formation of the Yellow River is 100ka.%以黄河中游河套盆地-晋陕峡谷-三门峡盆地-三门峡峡谷-郑州邙山段黄河形成时代为主要研究内容,辅以黄河上游兴海盆地-共和盆地段黄河出现的时代来探讨统一黄河形成的时代.黄河上游兴海盆地共发育9级黄河阶地,ESR和OSL年代结果表明,最高三级阶地分别形成于200ka,100ka和80ka；中游河套盆地普遍发育一套湖相沉积,其中盆地东南端托克托台地郝家窑剖面湖相沉积的亮度和烧失量数据呈现一致的由下向上波动上升变化趋势,反映沉积物碳酸盐含量在不断增高,湖水盐度在增大,可能指示了湖泊处于封闭的环境,OSL结果显示湖相沉积结束的年代在100ka前后；三门峡盆地东端发育的最高黄河阶地年代为150ka,而指示古三门湖湖水外泄的河湖相白砂层结束时间是200ka.文章总结对比前人的研究成果,认为共和运动才是形成统一黄河的主因,尽管如此,上游兴海-共和河段及中游三门峡河段黄河(分别形成于200ka和200～ 150ka)出现要早于河套地区(100ka),而晋陕峡谷最晚贯通.也就是说,现今统一的黄河形成于100ka前后.