The Study Of Sequence Stratigraphy And Sedimentary Characteristics Of The Middle Ordovician Period In The North Slope Of Tazhong Area In Tarim Basin

The study area of this paper locate in the North slope of Central Tarim Basin which is limited to the north side of katake uplift and the footwall of No.1 structural belt of Central Tarim Basin,The purpose layer of the study is the middle series of ordovician,including upper yingshan formation and yijianfang formation.According to research content of the paper,guided by the multi-disciplinary theory,combined with oversea and domestic research status of carbonate rock and sequence stratigraphy,on the basis of careful analysis of the thin core,drilling、logging、geochemical and geophysical data,deeply research the purpose layer,including rock types,sedimentary environments,sequence stratigraphy,relationship between sequence and the karst.Tectonic movement which impacts the middle series of ordovician on North slope of Central Tarim Basin include the early caledonian movement and the middle caledonian movement,the first act of the early caledonian movement have occurred in the beginning of Cambrian,the second act of the early caledonian movement have occurred in the end of Cambrian,the first act of the middle caledonian movement have occurred in the beginning of middle Ordovician,the second act of the middle caledonian movement have occurred in the end of Ordovician.Compared with the early ordovician,climate of the North slope of Central Tarim Basin in the middle Ordovician was relatively humid,depth of water lager,platform facies zone from restricted platform transit to open platform deposits in the lower series of Ordovician,and on the edge of the platform and the interior of platform where relatively high terrain develop intra-platform beach.Base on the theories of sequence stratigraphy,combine with the sedimentary background,the rock strata,seismic stratigraphic of the study area,make a comprehensive analysis,identify a secondary order sequence interface SSB2 and two erosion unconformity third order sequence interface SB3 and SB4,and identify the maximum flooding surface mfs3 in the internal upper yingshan formation;the middle ordovician were divided into two third order sequence(SQ3 and SQ4),and identify three system tracts,including low,transgressive and high in the internal upper yingshan formation.On the basis of the research on well profile and the seismic facies,research on sedimentary facies distribution in sequence framework and its main control factors,establish sequence sedimentary evolution model in the study area.Finally compile the floor plan of sedimentary facies,and reveal the distribution rule of sedimentary facies.Main controlling factors of the formation of Ordovician sequence on North slope of Central Tarim Basin are tectonic sbsidence,sea level change and ancient climate conditions.Tectonic movement controls sequence which is mainly embodied in the its influence on sequence interface and sedimentary paleogeomorphology;The rise and fall of sea level controls the formation of third order sequence interface and succession of systems tracts within sequence;The ancient climate change affect the change of carbonate platform type and location.North slope of Central Tarim Basin have experienced multiphase tectonic movement and sea level change,formed the different levels of sequence interface,corresponding develop exposed denudation discontinuous interface which are in different time limit,under different sequence interfaces develop the dissolution of different time limit.The level of corrosion from small to large is divided into four to six levels of sequence interface(late high period)dissolution,third order sequence interface(erosion unconformity,low period)karst.High level sequence interface dissolution can overlay low level sequence interface dissolution.