关中盆地上新世地层形成时代、层序划分及沉积相特征研究

Study on the formation time,stratigraphic sequence division and sedimentary facies characteristics of the upper Miocene strata in the Guangzhong Basin

关中盆地位于华北板块西南缘,为一新生代断陷盆地,具典型地堑形态,沉积巨厚的新生代地层。针对盆地新近纪上新世地层形成时代有争议、地层层序划分不明确、沉积相界定较笼统等问题,利用钻测井资料及野外调研,结合前人研究成果,对盆地新生代地层进行了重新划分,明确了上新世各地层形成时代及其地层层序划分和沉积相类型。研究结果表明,上新统可划分为蓝田组(11Ma—7 Ma)、灞河组(7.3 Ma—2.6 Ma)、张家坡组(3.4 Ma—2.6 Ma);新生代层序地层可划分为古近系构造层序、中新统构造层序、上新统构造层序和第四系构造层序等4个一级层序,存在6个构造层序界面。蓝田组以"三趾马红黏土"的风成沉积为特征。灞河组沉积时期,关中盆地的西安凹陷为一套冲(洪)积相、河流、三角洲相沉积,固市凹陷为一套冲(洪)积、河流、三角洲及滨浅湖相沉积;盆地边部开始出现小范围的风成黏土沉积。张家坡组以河湖相沉积为主,沉积中心向南移;盆地南北两侧或边部为冲(洪)积扇相、河流相及三角洲相沉积,边部也有小范围的风成黏土沉积。

The Guangzhong basin,located in the southwest margin of the North China plate,is a Cenozoic fault basin characterized by typical graben morphology and thick Cenozoic strata.In view of the controversy over the formation age of the Pliocene strata,the unclear stratigraphic sequence division and the definition of the sedimentary facies in the basin and so on the Cenozoic strata in the basin are redivided and the stratigraphic age,stratigraphic sequence characteristics and sedimentary facies types of Pliocene are identified based on data from drilling and logging,field research and previous research results.The Pliocene series can be divided into Lantian Formation(7 Ma-11 Ma),Bahe Formation(7.3 Ma-2.6 Ma)and Zhangjiapo Formation(3.4 Ma-2.6 Ma);Sequence stratigraphy can be divided into 4 first order sequences,including Paleogene tectonic sequence,Miocene structural sequence,Pliocene structural sequence and Quaternary tectonic sequence.There are 6 tectonic sequence interfaces.Lantian Formation is characteristic of the eolian sedimentary"Hipparion red clay".In the deposition period of Bahe Formation,Xi'an sag is of the alluvia(proluvium),fluvial,delta facies,the Gushi sag alluvia(proluvium),fluvial,delta and shore-shallow lacustri facies and aeolian clay deposits began to appear small areas at the edge.Zhangjiapo Formation is dominated by fluvial-lacustrine facies with sedimentary center moving to south and are alluvial fan facies,fluvial delta facies deposit,and aeolian clay deposits began to appear small areas at the edge.