Carbonate Sedimentation And Diagenesis Of Ordovician Formation In Fugu Region,Shaanxi

The study area of this paper is Fugu area,Ordos basin.The study section is Yeli ?Liangjiashan and Majiagou formation of Ordovician.In order to establishes a sequencestratigrphy framework of the Ordovician Formation and figure out its lithologic character and main diagenesis,then reestablishes its lithofacies paleogeography,this paper adopts many research methods and means,such as core description,thin section identification,cathodeluminescence,electron probe,major and trace elements,strontium isotope and carbon and oxygen isotope analysis.The study result shows that the Yeli,Liangjiashan formation of lower Ordovician series can be divide into 5 third-order sequence,Majiagou formation of middle Ordovician can be divide into 3 third-order sequence.According to the formation lithology and superimposed relationship,there are 4 system tract named low system tract,transgressive system tract,high system tract and forced regressionsystem tract in one 3third-order sequence.The ordovician carbonate rock types in this area include micritelimestone,grainstone,dolomitic limestone,micrite dolomite,grain dolostone,fine-crystal dolostones in relict texture,coarsecrystalline dolomite in mosaic structure,gypsodolomiteand anhydrock.theserocks experienced normal seawater,evaporated seawater,infiltration and circumfluence variable salinity seawater,early freshwater,surface freshwater,middle&deep buried environment.The diagenesis includes cementation,dissolution,recrystallization,penecontemporaneous dolomitization,infiltration and circumfluence dolomitization,blind circumfluence dolomitization,burial dolomitization.Lithofaciespalaeo geography shows that sequence stratigraphy has an important control for the lithofacies.