Late Cretaceous (Santonian to Campanian) Palynological Records and Paleoclimatic Significance from Borehole ZKY2-1, Songliao Basin

The global temperature gradually decreased from the Cretaceous Santonian to Campanian, while angiosperms evolved rapidly and gradually became dominant. The Songliao Basin, NE China, contains abundant fossil palynomorphs from the Santonian to Campanian age. A thorough investigation of fossil palynomorphs in borehole ZKY2-1 of the SW Songliao Basin was performed, reconstructing the vegetation and paleoclimate transition from the Santonian-earliest Campanian (lower Nenjiang Formation) to the late Campanian (Sifangtai Formation). Eighty form-genera from borehole ZKY2-1 have been identified. Three palynomorph assemblages were identified: the Schizaeoisporites-Cyathidites-Inaperturopollenites assemblage, Schizaeoisporites-Classopollis-Retitricolporites assemblage, and Schizaeoisporites-Aquilapollenites-Tricolporopollenits assemblage, from bottom to top. Based on palynological analysis from ZKY2-1 and other boreholes in the Songliao Basin, angiosperm pollen proportion in the Sifangtai Formation is significantly higher than in the lower Nenjiang Formation, indicating rapid angiosperm spread from late Santonian to Campanian. Palynological records indicate relatively humid climate during this period; the content of cool palynological types increased from the lower Nenjiang Formation to the Sifangtai Formation, suggesting a transition from warm to cool climate during the late Santonian-earliest Campanian to the late Campanian. The new palynological evidence from the Songliao Basin reveals a global cooling on land and sea during the late Santonian-Campanian period. This climate change may further promote angiosperm spread during the Late Cretaceous period.