泥河湾盆地典型剖面沉积物磁化率特征及其意义

THE SUSCEPTIBILITY CHARACTERISTICS OF THE TYPICAL SECTIONS OF THE NIHEWAN BASIN AND ITS IMPLICATION

在对泥河湾盆地郝家台、小长梁、东谷坨三个典型剖面野外沉积特征初步研究的基础上，将剖面划分为四个沉积相：顶部马兰黄土堆积，上、下湖泊相和中部河流相。以１５ｃｍ为间距，系统采集了１６７４块样品，进行质量磁化率的测定与分析。结果表明：沉积物磁化率值的大小与沉积相，尤其是与沉积物的粒度相关。一般规律是滨浅湖相粉砂、粘土质粉砂的磁化率值大，而深湖相、半深湖相粘土和粉砂质粘土的磁化率值较低。磁化率值的变化在一定程度上反映了古气候的变化，磁化率高峰可能反映了干燥的气候环境，而低谷则可能反映了温湿的气候。沉积相和磁化率变化曲线相结合，将剖面分为７个对比层，初步讨论了１ＭａＢ．Ｐ．以来，盆地大概可以分为三个大的演化阶段：早期扩张期，中期收缩期，晚期扩张到收缩期。并通过剖面间的对比，初步认为剖面所含石器层的年龄大约在１Ｍａ．Ｂ．Ｐ．左右。

On the basis of the study of the three typical sections the Haojiatai section,the Xiaochangliang section and the Donggutuo section in the Nihewan Basin,the sections have been divided into four large sedimentary facies layers:loess,upper lacustrine facies,middle fluvial facies and lower lacustrine facies.The results of the susceptibility measurement,by the sample intervals of 15cm,of the three typical profiles show that the value of sediment susceptibility is related to the sedimentary facies,especially the grain size of the sediments.Generally,the susceptibility value of the fine sand and the silty sand of the shallow lacustrine facies and coastal lacustrine facies is relatively high,and that of the deep lacustrine facies is relatively low.The changes of the susceptibility in the profiles,to some extent,reflect the changes of the paleoclimate during early Quaternary in this area.The high value of the susceptibility responds to relatively dry climate period,and the low value to relatively humid climate period.Meanwhile,by the characteristics of susceptibility changes in the profiles,the 7 comparable layers in the three profiles have been decided,and the Nihewan Basin undertook three evolutional processes:early extension,middle shrinkage and late change from the extension to shrinkage.By comparing the characteristic layers in the three profiles,we get the age of the stone implement layer in the profiles to be about 1Ma.