海拉尔盆地贝尔凹陷下白垩统层序地层与沉积体系分析

应用层序地层学原理对贝尔凹陷下白垩统地层进行划分和对比,建立了等时的层序地层格架,分析了不同级别层序界面的特征。对沉积体系的研究表明,不同沉积期沉积体系的空间展布和配置关系有明显区别。SQt-SQn_2层序为断陷湖盆型层序,发育冲积扇、扇三角洲、湖底扇、滨浅湖等沉积组合;SQd_1- SQd_2层序为断坳期半深湖-深湖盆层序,发育三角洲、滨浅湖、浅湖和半深湖等沉积组合。不同层序发育期各次级构造单元的分布决定着特定沉积相带的展布,沉积体系域的沉积相构成也有变化。贝西次凹中部洼陷带、贝西次凹西侧的反向同沉积断裂或古斜坡坡折的下斜坡带以及贝南次凹是后期勘探的有利目标区。

Research of depositional system and sequence stratigraphy in lower Cretaceous in Beier sag, Hailaer basin

Based on the concept of sequence stratigraphic meth- odologies,the cyclic sequence in Lower Cretaceous in Bei- er Sag is classified and correlated in detail,the strata con- trast framework of cyclic sequence is defined and estab- lished,and the characteristic of different grade sequence boundary is analyzed.The study of the sedimentary sys- tem shows the spatial distributions and sedimentary as- semblages of depositional system vary significantly in dif- ferent depositional stage.The sequence of SQt-SQn2 formed in faulted down lacustrine basins,which developed the sedimentary assemblage as alluvial fan,fan delta, sublacustrine fan and Shore-shallow lacustrine.The se- quence of SQd1-SQd2 formed in semi-deep lake and deep lake in depressed stage,which developed the sedi- mentary assemblage as delta,shore-shallow lacustrine, shallow lacustrine and semi-deep lake.In different sedi- mental stage,the distribution of different sub-structural units control the special distribution of sedimentary faci- es,and the architecture of sedimentary facies of system tracts vary.The central sub-sag depression of western Beier Sag,the antithetic contemporaneous fault and downdip areas of palaeoslope break in western Beier sub- sag,and southern Beier sub-sag,where are the main ob- jects of exploration.