cm 0cm 0pt" class=MsoNormal>Layer Ma5B>1³ developed in the top of Ordovician weathering crust is one of the main pay zones in the eastern ce prefix = ns0 ns = "urn:schemas-microsoft-com:office:smarttags" />ce>ceName>ce prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />ce w:st="on">ceName w:st="on">OrdosceName>ceName>ce> ceType>ceType w:st="on">BasinceType>ceType>ce>, and the coccoid anhydrite concretion dolomite is the important reservoir bed of it. Research on the lithologic characteristics and microfacies signs of layer Ma5₁³ demonstrates that the coccoid anhydrite concretion dolomite and its interbedded dolomites with or without anhydrite are tidal flat deposits. Anhydrite concretion dolomite flat is the optimum sedimentary microfacies of layer Ma5₁³, secondarily the dolomite flat with anhydrite concretion. The Jingbian large gas field is distributed in the anhydrite concretion dolomite flat. Sedimentary microfacies is the fundamental factor controlling the distribution of favorable reservoirs in the Jingbian gas field and Yulin-Mizhi area.ce prefix = o ns = "urn:schemas-microsoft-com:office:office" />