四川盆地回龙地区下侏罗统自流井组大安寨段混积岩特征及模式

Features and Model of Mixed Sediments of Da'anzhai Member in Lower Jurassic Ziliujing Formation,Huilong Area,Sichuan Basin

川西回龙地区自流井组大安寨段发育湖相碳酸盐岩和碎屑岩的混合沉积,结合野外露头、钻井岩芯、测井和显微组构等资料的综合分析,对该研究区混积岩沉积微相特征进行了精细刻画。研究认为,回龙地区大安寨段属湖泊混合沉积相,分为滨浅湖混合沉积和半深湖混合沉积两个亚相,并划分了五个沉积微相,分别为高能介壳滩混合沉积微相,低能介壳滩混合沉积微相,砂质浅滩混合沉积微相,浅湖混合沉积微相以及半深湖混合沉积微相。基于所划分的混合沉积相的特征和四川盆地以及研究区回龙大安寨段在侏罗纪的沉积相演变过程,分析了该区混积岩的成因及混合沉积演化模式。得出结论:研究区湖相混合沉积主要受物源供给和水动力条件的控制,在五种不同混合沉积微相控制作用下形成了不同类型的混积岩。

Mixed sediments of lacustrine carbonate rocks and clastic rocks are developed in the Da＇anzhai Member of Ziliujing Formation in Huilong area,western Sichuan. Based on the comprehensive analysis on field outcrops,drilling cores,well logging and microfabric,the sedimentary microfacies of mixed sediments of the study area was finely depicted. The results revealed that the Da＇anzhai Member in Huilong area belonged to the lacustrine mixed sedimentary facies consisting of shore-shallow lake and semi-deep lake subfacies,which was further divided into five mixed sedimentary microfacies,including high-energy shelly beach,low-energy shelly beach,sandy shoal,shallow lake and semi-deep lake. Further more,based on the features of mixed sedimentary facies and the evolution process of the Da＇anzhai Member in Huilong area in Jurassic Period,the origin and evolution pattern of mixed sediments in the study area was analyzed. It was concluded that the lacustrine mixed sediments in the study area were predominantly controlled by provenance supply and hydrodynamic condition and various type of mixed sediments were formed under the control of five mixed sedimentary microfacies.