Lithostratigraphy and biostratigraphy features of Zhangjiakou Formation and Dabeigou Formation and its significance for stratigraphic subdivision and correlation in the Northeast Asia

Comprehensive studies of the Zhangjiakou Formation and Dabeigou Formation in North Hebei and their corresponding strata in Inner Mongolia in terms of lithostratigraphy and biostratigraphy show that the Dabeigou Formation is equivalent with the upper part of typical Zhangjiakou Formation in Zhangjiakou Basin. Conchostracans in Dabeigou Formation can be divided into the Nistoria pissovi assemblage and Ambonella lepida－Jibeilimnadia ovata and Keratestheria gigantea－Abrestheria rotunda sub-assemblages. The ostracods of the Dabeigou Formation can be divided into the Luanpingella－Torinina－Eoparacypris assemblage and the Luanpingella postacuta and Torinina obesa sub-assemblages. By distinguishing these biozones and subbiozones, a standardized and valuable means of stratigraphic division and correlation in Northeast Asia is provided.