Diagenesis In Sequence Stratigraphic Framework Of Ordovician Yingshan Formation In Tahe Area

By making full use of outcrop,drilling,logging,seismic,experimental analysis and other data,sequence stratigraphy and diagenesis of Ordovician Yingshan Formation in Tahe area are studied in detail.Based on these detailed works,the diagenesis characteristics in sequence stratigraphic framework and relationship between diagenesis development and sequence stratigraphy of Ordovician Yingshan Formation carbonate rocks in Tahe area have been studied.Eventually,diagenesis model in sequence stratigraphic framework of Ordovician Yingshan Formation carbonate rocks in Tahe area have been established.Based on the outcrops data and through the observation of core and thin sections under microscope,the study identified sequence boundaries of Yingshan Formation carbonate rocks.On a boundary of this,the paper divided the Yingshan Formation into two third-order sequences,named SQ1 and SQ2,and four forth-order,named Ysq1,Ysq2,Ysq3 and Ysq4 segment.Each third-order sequence is mainly composed of transgressive systems tract(TST)and highstand system tract(HST).Through the macroscopic and microscopic observation of Ordovician Yingshan Formation carbonate rocks,the main diagenetic events in Yingshan Formation carbonate strata are identified as: dissolution,cementation,micritization,burial dolomitization,compaction,pressure solution,fracturing,etc.Diagenesis developed in various diagenetic environments exhibit different characteristics.Dissolution can be divided into three types according to the diagenetic environment,including syndepositional corrosion,burial dissolution and supergene karst dissolution.Cementation also can be divided into marine cementation,meteoric cementation and burial cementation.On the basis of these works,combining with regional tectonic background and depositional environment evolution of the Tarim basin,the study has established the diagenetic evolution sequence Ordovician Yingshan Formation carbonate rocks in Tahe area: marine diagenetic environment?shallow burial diagenetic environment meteoric water diagenetic environment?shallow-middle burial diagenetic environment?meteoric water diagenetic environment?midlle-deep burial diagenetic environment.Based on these studies,the diagenesis in sequence stratigraphic framework of Ordovician Yingshan Formation carbonate rocks in Tahe area have been finely analyzed.According to the research,diagenesis characteristics are distinct in different system tracts and levels of sequence boundaries.Supergene karst dissolution is more likely to distribute in the HST near sequence boundary.Syn-sedimentary corrosion always occours near the early stage of TST and the late stage of HST.Marine cementation is commonly present near the maximum flooding surface of third-order sequence,but in the maximum flooding surface,marine cementation are rarely developed.Burial dolomitization is generally developed in the lower part of the high frequency sequences.