Redefinition of the original Neogene strata in the south-central Jiayin basin, northern Heilongjiang, China

The Yuliangzi Formation on the southern bank of the Heilongjiang RAver at the northern end of the Jiayin basin, Heilongjiang Province, is the horizon where reptile fossils were found in China earliest and there occur abundant dinosaur fossils. The strata in the south-central basin has long been assigned to the Neogene Sunwu Formation. Study of sporopollen in Wulaga Township and the Qinglin forest farm shows that the strata are late Late Cretaceous in age, corresponding to the early Maastrichtian, which may be correlated with the Yuliangzi Formation in the Jiayin area on the southern bank of the Heilongjiang RAver. In the sporopollen assemblage there are abundant drought-, salt- and alkali-enduring Classopollis and Ephedripites, but no once reported Aquilapollenites or Ariadnaesporites which reflects the warm-wet climatic environment has been found. This reveals that there occurred a great transient climatic change from the warm-humid one to dry-hot one then. This climatic change might be one of the causes for mass extinction of dinosaurs.