Sequence Stratigraphic Division of the Devonian Liujiang Formation Dominated by Silicalites in the Northeastern Part of the Dianqiangui Basin, South China

Silicalites are extensively developed in the Liujiang Formation (Fm.) of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales. This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments, which not only gives the shales unusual spatio-temporal distribution features, but also induces the shales in the Liujiang Fm. to frequently be rich in organic matter (OM). This study summarises the special deep-water sedimentary succession of the Liujiang Fm., which is mainly distributed around synsedimentary faults, as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm. in the west–east and southwest–northeast directions. Under the sequence stratigraphic frameworks, the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm. and the regional variations of the Liujiang Fm. were investigated. In addition, the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope. The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage, developed spatially mainly on the east and west sides of the study area, as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a ‘biological pump’.