银额盆地额济纳旗伊很乌苏地区下白垩统巴音戈壁组的微体化石及沉积环境

The microfossils and depositional environment from Bayingebi Formation of Lower Cretaceous in the Ejina area of Yingen-Ejin Basin

银额盆地额济纳地区中生代地层分布广泛,近些年的研究表明,盆地内发现的油气多来源于中生代地层的烃源岩,因此研究银额盆地中生代地层具有十分重要的意义。通过对银额盆地额济纳地区微体化石进行分析研究,发现鉴定了孢粉3属3种,介形类3属6种,其共存时限为早白垩世。据此将前人原划上侏罗统重新厘定为下白垩统巴音戈壁组,并根据岩石组合特征将其划分为3个岩性段。结合化石古生态、沉积构造和区域地质背景,认为巴音戈壁组3个岩性段分别代表了近岸水下扇、滨—浅湖、扇三角洲平原的淡水—微咸水内陆河湖相沉积环境,揭示其沉积经历了湖盆从产生、发展到萎缩的演化过程。巴音戈壁组岩石组合、沉积环境和化石组合特征的研究结果,有助于区域地层研究对比,为研究油气基础地质和区域演化提供基础资料。

The Mesozoic stratigraphic distribution in the Ejina area,Yingen-Ejin Basin,has been widely studied.Recent research indicates that the discovered oil and gas in the basin mainly originates from Mesozoic hydrocarbon source rocks.Therefore,the study of the Mesozoic strata in the Yingen-Ejin Basin holds great significance.By analyzing and studying microfossils in the Ejina area of the Yingen Basin,three genera and three species of spores,as well as three genera and six species of protozoans,have been identified.Their coexistence is limited to the Early Cretaceous.Based on this,the previously designated Jurassic was redefined as the Lower Cretaceous Bayingobi Formation,and it was divided into three lithological sections based on rock composition characteristics.Considering the fossil paleoecology,sedimentary structures,and regional geological background,it is believed that the three lithological sections of the Bayingebi Formation represent depositional environments of near-shore subaqueous fans,shore-shallow lakes,and freshwater-brackish inland river-lake on the alluvial plain.This reveals the evolutionary process of the basin from its formation and development to its contraction.The results of the study on the rock composition,sedimentary environment,and fossil assemblages of the Bayingobi Formation contribute to regional stratigraphic research,providing basic data for the study of petroleum geology and regional evolution.