Development And Distribution Character Of Reef And Bank And Microfacies Research Of Middle-Late Ordovician, Jingyang-Liquan

This major object of this study is the reef and bank of the middle-late Ordovician in Jingyang-liquan.On the basis of scouting field sections and collecting data of relevant wells,combining the outcomes of predecessors.The depositional environment of reef and bank are studied,the distribution range of reef and bank,the major reef building and attaching organisms,the rock types are defined,the microfacies and evolution of the reef and bank are analysed.The trace element and isotope of C and O are applied to analyse the reef and bank.After this,the control conditions about the reef and bank in Jingyang-liquan are discussed and summarise its formation mode.In study area,middle-late Ordovician,sedimentary facies can be divided into restricted platform,open marine platform,platform edge reef and bank facies,platform frontclinothem facies,deep water clinothem facies.The reef and bank are developed in platform edge reef and bank facies.Research shows that the reef building organisms are made up of coral,algae and stromatopora and the reef attaching organisms are brachiopod,trilobite,condoontophoridia,et al,the biogenic rock types are framestone,bafflestone,bindstone,intralimestone,algal limestone and dolomite,microfaceies are reef base,reef core,reef cover,reef flank,et al.The process of evolution is discontinuous,the reefs have many layers,and bank is the basis of reef.The organisms absorb the vast12 C,then the water contain abundant13 C,so that the carbonatite which form within late Ordovician have high ?13C,the ?13C of reef carbonatite is lower than the usual carbonatite.The salinity is not one of the factors which influence the development of reef as there is not a significant change when reef appear.The ?18O in late Ordovician has a little rise,it shows that the temperature has a little rise,and warm water is appropriate for organism.Sr has a closed relationship to organism,the more mass organisms,the higher Sr level there is.There are many factors affect the development of reef and bank such as structure,paleoclimate,reef building and attaching organisms,foundation conditions,sea-level change and sea water nature.According to the research,we summarize the formative pattern of the reef of the late Ordovician in Jingyang-Liquan district.