Research On Sedimentary Evolution In Four-Level Sequence Stratigraphic Framework Of Ordovician Yingshan Formation In Shunnan Area,Tarim Basin

Tarim Basin is the largest petroliferous basin in China.The Cambrian-Ordovician marine carbonate rocks have good prospects for exploration.The Ordovician Yingshan Formation is of great exploration value.Therefore,based on the results of many previous researches,this paper uses the Yingshan Formation in Shunnan Area as the research object,making full use of field profile data,drilling core data,and test analysis data to carry out four-level sequence and the sedimentary evolution within sequence stratigraphic framework.In order to provide basic information and discipline basis for further promoting the Yingshan Formation oil and gas exploration.Mainly achieved the following results and understanding:1.By making full use of field profile data,drilling core observation and indoor comprehensive analysis,the material manifestations of the four-level sequence boundary of the Yingshan Formation are including eight types,karst breccia,bird eye structure,weak erosion surface,top-bottom structure,freshwater cement,penecontemporaneous selective dissolution,exposed oxidation and various lithological conversion surfaces.They can be further summarized four genetic types:local exposed unconformity,shoal exposure unconformity,weak erosion eroded surface,lithology or lithofacies transformation planes.2.Using Fischer diagram and wavelet analysis combined with the feature of sedimentary geochemistry carried out the four-level sequence of the Yingshan Formation division.From the bottom up,it can be divided into 4 four-level sequences(FSQ1-FSQ4),and describing each of the development characteristics of the sequence stratigraphy in detail.throughing comparison,a four-level sequence stratigraphic framework was constructed.3.Based on the identification of sedimentary facies,such as petroelectric characteristics,paleontology,logging data,and seismic data,the Ordovician Yingshan Formation in Shunnan Area was divided into 3 sedimentary facies,which were the restricted platform,open platform,and platform edge,and six of them were subphase and 11 microfacies were analyzed;the vertical and horizontal variation characteristics of sedimentary microfacies in the four-level sequence stratigraphic framework were described.4.On the basis of the characteristics of the above-mentioned sedimentary facies,the sequence-facies palaeogeography of the FSQ1 to FSQ4 depositional periods was prepared for the first time in the four-level sequence.During the period of FSQ1 and FSQ2,the characteristics of the the sedimentary facies are restricted platform in the southeast and the open platform in the north,and the relatively narrowly developed platform marginal facies,marginal slope facies,and the shelf facies in the periphery of the plateau facies were narrow.These narrow facies are distributed along the edge of the open platform facies;the FSQ2 period is narrower toward the southwest than the FSQ1 period;the FSQ3 and FSQ4 periods are dominated by the development of open platform facies,with a large number of grain beds in the south of the area.Compared with the FSQ3 period,the FSQ4 increased the number of grain-bearing deposits in the open platform,mainly sand-beach-flats,and the massive development of the beach resulted in the increase of dolomite in the southwest of the study area.Based on the evolution of lithofacies and palaeogeography,a four-level sequence-sedimentary filling model was developed that met the actual conditions in the study area.