New palynological data and U–Pb dating from the Jiufotang Formation: Implications for the late Jehol Biota

Abstract

The Lower Cretaceous terrestrial strata of northeast China are predominantly located in northern Hebei, western Liaoning, Jilin, and eastern Inner Mongolia Provinces. Among these, the Jiufotang Formation in western Liaoning has garnered significant global attention due to its rich fossil record, particularly in relation to Jehol Biota. The age of the Jiufotang Formation has long been debated primarily due to the absence of biostratigraphic fossil evidence. In this study, we analyzed the palynological content collected from the Jiufotang Formation in the Pijiagou section of the Fuxin Basin. A total of 41 species in 24 palynomorph genera were recognized as belonging to the Appendicisporites-Pinuspollenites-Jiaohepollis assemblage. We documented the new occurrence of Appendicisporites imperfectus in the Jiufotang Formation, which has been recognized as a valid biostratigraphic indicator for Aptian palynological assemblages, thereby providing crucial new palynological evidence for dating this formation. Furthermore, LA-ICP-MS zircon U–Pb dating for a rhyolitic tuff yielded a new age of 118.07 ± 0.98 Ma, suggesting that the Pijiagou section was dated to the middle Aptian. Based on the palynological data, the Lower Cretaceous Jiufotang flora was represented by coniferous forests. Considering the associated biota, the palaeoenvironment during the middle Aptian was characterized by a sub-humid warm temperate climate with seasonal changes.