The characteristic and evolution of sedimentary microfacies in the middle Ordovician assemblages in the Ordos Basin

A set of typical dolomite reservoir developed in the middle Ordovician assemblages in the Ordos Basin.The authors have done some researches on evolution characteristics and types of sedimentary microfacies,which are based on core analysis,identifying under the microscope and comprehensive analysis indoors.There are two kinds of sedimentary facies four intrafacies and several microfacies in the eastern margin of central paleo-uplift in the middle Ordovician assemblages.During the deposition of the fifth Majiagou period under the background of marine regression there existed Ma5₅-Ma5₆,Ma5₇-Ma5₈,Ma5₉-Ma5₁₀three concussive transgression-regression process.The authors established a mode of sedimentary facies on the basis of petrological combination.The sedimentary facies are as follows:supratidal doloflat face,intertidal limestone-doloflat and gypsum rock depression (lagoon).