准噶尔盆地玛湖凹陷百口泉组岩石相划分

Litho-Facies Classification of Baikouquan Formation in Mahu Sag,Junggar Basin

准噶尔盆地玛湖凹陷下三叠统百口泉组发育一套以砾岩为主的粗粒沉积复杂地层,前人对其岩石相类型进行了深入研究,但依然存在岩石相分类过于粗化、岩石相与沉积微相联系不够密切等问题。主要原因在于,运用少量的岩石相类型,难以表达不同微相中岩石相的组合规律,也难以区分相似沉积微相的岩石相特征及其组合的差异性。在系统描述玛湖凹陷77口取心井的岩性、颜色、沉积构造、分选性、磨圆度、定向性、支撑方式、胶结类型、胶结物成分、最大粒径、平均粒径、含油性和砾石成分等13种属性的基础上,提出一个新的岩石相分类方案,以岩石的沉积构造、颜色、粒度和支撑方式等4种属性为主,进行岩石相分类命名。运用新的岩石相分类方案,在玛湖凹陷百口泉组岩心中识别出了227种岩石相类型,其中砾质岩岩相153种,砂质岩岩相58种,泥质岩岩相16种,这一方法较好地反映了玛湖凹陷百口泉组岩石相的多样性,为准确描述不同沉积微相的沉积学特征奠定了基础,为精细判别沉积相提供了依据。

A set of multi-lithological coarse-grained sediments dominated by conglomerate are developed in the Lower Triassic Baikouquan formation in Mahu sag, Junggar basin. Researchers conducted in-depth studies on litho-facies types, but some problems still exist in lithofacies classification and relationship between lithofacies and sedimentary microfacies. The reason is that it is difficult to express the lithofacies associations in different microfacies and to differentiate the characteristics and association differences among similar microfacies by means of small amount of lithofacies types. Based on the systematic descriptions of lithology, color, sedimentary structure, sorting, roundness, orientation, fabric support, cementation type, cement composition, the max. grain size, average grain size, oil-bearing property and gravel component from 77 cored wells in Mahu sag, the paper proposes a new lithofacies classification method, which can be used to classify and denominate lithofacies mainly according to 4 properties such as sedimentary structure, color, grain size and fabric support. 227 lithofacies types have been identified from the cores of Baikouquan formation in Mahu sag, including 153 for conglomerate, 58 for sandstone and 16 for mudstone. The results well reflect the diversity of lithofacies of Baikouquan formation in Mahu sag, lay a foundation for accurate description of sedimentary characteristics of different sedimentary microfacies and provide basis for detailed sedimentary facies identification .