According to the previous research,there was a highland/underwater uplift developed in western Hubei and Hunan area,because of the absence of shell layer of Ordovician Guanyinqiao section or at least two graptolitic biozones between Ordovician Wufeng Formation and Silurian Longmaxi Formation.Based on the detailed study of sedimentary characteristics and the evolution of sedimentary environment,it can be figured out that there was nondepositional hiatus between Ordovician Wufeng Formation and Silurian Longmaxi Formation,and the existence of Hrinantian deposition.In the depositional process of Wufeng- Longmaxi Formations,the depth of sedimentary water was from gradually deep to shallow,and the paleoclimate experienced the significant cooling period.It was shallow shelf facies of Hrinantian under the background of global ice age,which was deposited on the Wufeng deep shelf facies,most as carbonaceous pelitic siltstone with the minerals of highest content of quartz,fewest of clay minerals,and higher of organic carbon content,and with the elemental constituent of the highest SiO_2 and the least Al_2O_3.The shallow shelf facies was the most developed of Wufeng-Longmaxi Formations in southwestern Hubei,with rapid changes in lithology.Compared to others in Middle-Upper Yangtze area,the shallower sedimentary water was not conducive to the shale gas enrichment.