Abstract：The dolostone, as the dominant rock type in carbonate rocks of the Ordovician Majiagou Formation in Ordos Basin, is the main reservoir for natural gas. This paper discussed the lithofacise, geochemical characteristics and detecting methods of dolostone diagenetic facies of the Ordovician Majiagou Formation in Ordos Basin. Based on core and outcrop observation,thin section identification,X-ray diffraction test,elemental analysis,the stable carbon and oxygen isotope test and strontium isotope test,eight kinds of dolostone diagenetic facies were recognized,which formed in the evaporation,poikilohaline,and normal seawater,as well as early and epigenic freshwater,formation water diagenesis environment respectively, and belong to near-surface,weathering crust and deep-buried diagenetic system. The new templates of Fe-Mn,Cs-Sc,(K×Tl)/Na-(Sc×Ni)/Sr,δ13C-87Sr/86Sr are created to recognize dolostone diagenetic facies effectively. The evaporated seawater diagenetic facies is rich in immobile elements like Sc,Ni,as well as13C and18O. The poikilohaline and normal seawater diagenetic facies is rich in mobile elements like Cs. The reductive environment diagenetic facies is rich in K and Tl,and the oxidation environment diagenetic facies is rich in Fe and Mn. The epigenic diagenetic facies is characterized by a great deal of adsorbed disperse elements and 87Sr. The above results show that the near-surface and weathering crust diagenetic system are key factors to decide lithofacies and geochemical characteristics of dolostone diagenetic facies of the Majiagou Formation in study area,and the microscopic petrography and geochemistry experiment are effective means of research on diagenetic mechanism of dolostone.
Wang Qicong,Wei Wei,Zhao Jing et al. Geochemical characteristics of dolostone diagenetic facies of the Ordovician in Ordos Basin[J]. JOPC, 2017, 19(5): 849-864.
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