宁夏银川盆地灵武地区古近纪—新近纪沉积岩地球化学特征及对古环境演化的启示

Geochemistry characteristics of Paleogene-Neogene sedimentary rocks in the Lingwu area of Yinchuan Basin,Ningxia and its enlightenment for paleoenvironmental evolution

沉积岩元素地球化学特征是研究古沉积环境的一种有效方法,特别适用于露头局限分布的地区。银川盆地第四系覆盖广、沉积厚度大,古近纪—新近纪沉积仅分布于盆地周边局部地区,且露头不连续,沉积环境研究较薄弱。通过对银川盆地灵武地区古近系—新近系碎屑岩主量、微量和稀土元素的系统采样分析,探讨该时期沉积物源特征、沉积环境与古气候变化。研究结果认为:①银川盆地灵武地区古近系—新近系物源以长英质火山岩为主;②古近纪—新近纪的沉积环境总体上为氧化环境,含盐度较高,气候特征以干旱炎热为主;③新近系彰恩堡组与古近系清水营组相比,氧含量相对增加,含盐度相对较低,水体相对变迁,湖盆由封闭体系逐步向开放体系过渡。该研究成果为银川盆地和宁南盆地渐新世—中新世晚期统一湖盆系统的建立提供了基础地质资料。

Elemental geochemistry of sedimentary rocks is an effective method to study the ancient sedimentary environment,which is especially suitable for areas with restricted outcrops.Yinchuan Basin has wide Quaternary coverage with great sedimentary thickness.The Paleogene-Neogene is only distributed in some areas around the basin,with discontinuous outcrops and relatively weak research on the sedimentary environment.Through systematic sampling and analysis of the major,trace and rare earth elements of the Paleogene-Neogene clastic rocks in the Lingwu area of the Yinchuan Basin,the characteristics of sediment sources,sedimentary environment and paleoclimate changes were discussed.The results show that the Paleogene-Neogene source in the Lingwu area of the Yinchuan Basin is dominated by felsic volcanic rocks;the sedimentary environment of the Paleogene-Neogene period was generally an oxidizing environment with high salinity,and the climate was mainly dry and hot;compared with the Qingshuiying Formation,the Zhang’enpu Formation had relatively increasing oxygen content,relatively low salinity,relatively changeable water bodies,and the lake basin gradually transitioned from a closed system to an open system.The research results provide basic geological data for the establishment of an unified lake basin system in Yinchuan Basin and Ningnan Basin from Oligocene to Late Miocene.