Early Cretaceous palynological assemblages from the Dabeigou Formation at Yushuxia in the Luanping Basin, northern Hebei Province, China and their stratigraphic significances

Late Jurassic–Early Cretaceous strata in western Liaoning and northern Hebei provinces are famous for yielding the Yanliao and Jehol biotas. However, there are great disputes over the stratigraphic division and correlation and chronology between the two regions, which will surely affect our understanding of the origin and evolution of the Jehol Biota. The Dabeigou Formation in the Luanping Basin is among the most argued. Palynostratigraphy, as an effective approach to stratigraphic correlation within or between basins, has been studied relatively preliminary on the formation. Our new material recovered from a well excavated section at Yushuxia, Luanping County, provides a fairly good, continuous, and complete succession for the pollen and spore study of this formation. Plenty of pollen and spores are obtained from the section, encompassing a palynological succession of three assemblage zones. These fossils provide a solid Early Cretaceous or middle Valanginian–early Hauterivian age for the Dabeigou Formation. This material found at Yushuxia, Luanping County allows us to build up a correlation between the northern Hebei and western Liaoning for the Upper Jurassic–Lower Cretaceous strata. A combined palynostratigraphic sequence is established, namely the Classopollis, Classopollis-Densoisporites-Cicatricosisporites, Perinopollenites-Crybelosporites and Bisaccates assemblages in ascending order. Our research implies that the Dabeigou Formation in northern Hebei is very likely to correlate with the Third Member of the Tuchengzi Formation and the lowermost part of the Yixian Formation in western Liaoning and the palaeoenvironment was diversified between the two sites during the early Early Cretaceous.