Mineralogy Petrology And Ore Deposit Geology Majiagou Formation Sedimentary And Diagenetic Features Of The South Central Part Of The North Shaanxi Slope,Ordos Basin

The study area of this paper is the south central part of the northern Shaanxi Slope in Ordos basin.And the study section is Ordovician Majiagou Formation.By the core decription,thin section identification,cathode luminescence,scanning electron microscopy,electron probe,trace element and carbon and oxygen isotope analysis to figure out its lithologic character and main diagenesis.Combined with the Well logging interpretation to study lithofacies and diagenetic facies and lithofacies palaeogeography.The results show that the main rock types of Majiagou Formation in study area include dolomicrite,karst breccia dolomite,dolarenaceous,Secondary limestone and micritic limestone etc.And the study area of Majiagou carbonate rocks experienced near surface diagenesis environment,epidiagenetic environment,middle and deep burial diagenetic environment.The diagenesis includes penecontemporaneous dolomitization,seepage reflux dolomitization,karstification,dedolomitization,cementation and pressolution etc.According to the stratigraphic characteristics,Majiagou formation is divided in into six stratums(Ma 1 section,Ma 2 section,Ma 3 section,Ma 4 section,Ma 5 section,Ma 6 section).Ma 5 section is the main stratum of natural gas production in Ordos basin,so it is divided in ten parts detail(Ma 5 1-10 section).This paper dicusses the basic characteristics of strata and points out that the change of sea level has a controlling effect on the formation and development.Finally draw the lithofacies palaeogeography maps of Majiagou Formation in the study area.It shows the distribution characteristics of lithofacies palaeogeography in different periods.