Sedimentary Facies Of Jianfang Formation In The Ordovician Of Tarim Basin

Based on the latest research results of Yijianfang Formation in Tarim Basin and the related carbonate sedimentary facies literatures at domestic and abroad,the spatial distribution,the characteristic of sedimentary petrology,the type of sedimentary facies,the vertical and horizontal sedimentary facies development characteritics of the Ordovician Yijianfang Formation in Tarim Basin are investigated comprehensively in current study,which take the theories and methods of sedimentary petrology,logging geology and petroleum geology,etc.as guidance,combining with the macroscopic and microscopic ways.On the base of the results above,the single factor analysis and multi-factor comprehensive mapping methods are employed to investigate the comprehensive distribution characteristics of sedimentary facies of Yijianfang Formation in Tarim Basin,and the sedimentary facies distribution models of Yijianfang Formation in Tarim Basin was completed.According to the different lithofacies and simultaneous heterogeneous depositional phenomena of the Middle Ordovician,the Middle Ordovician strata in the Tarim Basin are divided into four different stratigraphic subregions,the Keping stratigraphic subregion,the Taklimakan-Tangguzibasi stratigraphic subregion,the Queerqueke-Tadong stratigraphic subregion and Louxi stratigraphic subregion.Among them,the Taklimakan-Tangguzibasi Formation and the Louxi Formation belong to platform stratigraphic subregion,and the Keping Formation and the Queerqueke-Tadong Formation belong to basin stratigraphic subregion.It is found that the thickness of the strata in the Taklamakan-Tangguzibasi and Louxi stratigraphic subregion is larger than that of the Keping and the Queerqueke-Tadong stratigraphic subregions.There are four depositional facies of platform facies,platform margin facies,the slope facies and the basin facies in Yijianfang Formation of the Ordovician in Tarim Basin.The subfacies contain intraplatform shoal,platform margin shoal,platform margin reef,and beach interact sea.Vertically,from bottom to top,the platform facies show the interactive development between the intraplatform shoal subfacies and the beach interact sea subfacies,and the intraplatform reef subfacies grow in the middle of the platform.The interactive growth of platform margin shoal,platform margin reef,and beach interact sea subfacies occur on the platform margin facies.On the plane,during the depositional period of Yijianfang Formation,three platform facies are identified in Tarim Basin,which are Tabei platform,Tazhong-Bachu platform and Luoxi platform.Besides,two basin facies of Keping basin and Tadong basin were also obtained.The most significant feature of depositional tectonic pattern about the Ordovician Yijianfang Formation in Tarim Basin is that the original Tabei-Tazhong platform is divided into Tabei platform and Tazhong-Bachu platform.On the basis of research about the stratigraphic thickness and distribution characteristics,the type and characteristics of the sedimentary rocks,the type and the spatial distribution of sedimentary facies,the sedimentary facies models of the open platform facies-platform margin facies-the slope facies-the basin facies in Yijianfang Formation of the Ordovician in Tarim Basin were established.