Chitinozoan biostratigraphy of the Silurian Shamao Formation in Yichang of Hubei Province

One hundred and fifty-six samples from the Silurian Shamao Formation of the Gongjiachong, Yi chang were investigated. Ninety-five samples collected from gray-greenish mudstone and siltstone contain well-preserved and very abundant Early Silurian chitinozoans. Five chitinozoan biozones, which in ascending order are Conochitina malleus, Plectochitina pseudoagglutinanss, Eisenackitina dolioliformis, Eisenachitia causiata and some other biozones, were recognized. Each chitinozoan biozone is diverse and contains new species occurring with well-known species. They can be correlated with chitinozoan biozones established from the contemporary strata of Latvia, Estonia and north Central Saudi Arabia. The correlation between the chitinozoan biozones and the graptolite and conodont biozones indicates that the geological range of the Shamao Formation in the Yichang area can be roughly correlated with the interval ranging from the upper part of Stimulograptus sedgwickii to Oktavites spiralis graptolite biozones. The basal boundary of the Telychian stage is located on the bottom of 2^nd member of the Shamao Formation, which is close to the basal boundary of the Plectochitina pseudoagglutinans chitinozoa biozone.At the same time, the stratum in Jiaoshiba, Fuling of Chongqing and other places is organic rich shale that contains large amounts of graptolite, which is an important reservoir of shale gas.