Palynological evidence for the Late Cretaceous lake transgression event in the Songliao Basin, NE China

The lake transgression event (LTE) associated with a lake anoxic event (LAE) has been reported previously from the Cretaceous Nenjiang Formation in the Songliao Basin, NE China. Detailed studies based on sedimentology, dinoflagellates, ostracods, and biomarkers have provided important evidence for this LTE in Member 1 of the Nenjiang Formation (K₂n¹). However, the related floristic record has not received enough attention. In this paper, palynological data of borehole Ji Tao Di-1 (JTD-1) from the western slope of the Songliao Basin were analyzed to investigate vegetation and climate changes associated with this Cretaceous LTE. Three palynological sub-assemblages reflect significant paleovegetation and paleoclimate changes through this LTE and reveal ecosystem fluctuations related to the global Cretaceous oceanic anoxic event (OAE3). A significant increase in the relative abundance of Schizaeoisporites and Cyathidites spores may represent the LTE in the Nenjiang Formation. Principal Components Analysis (PCA) and Sporomorph EcoGroup (SEG) model indicate that climate changed from cool and humid subtropical before the LTE, to relatively warm temperate during the LTE and temperate after the LTE in this area. The relatively warmer and drier climate during the later period of the LTE may be influenced by the contemporaneous OAE3. After the LTE, the highland mixed forests were dominant, and a large number of angiosperms (i.e., members of the Proteaceae) occupied the ecological niches of the middle canopy, indicating that the flourishing of angiosperms in the late Santonian may be closely related to environmental disturbances resulted from the LTE and OAE.