Terrestrial Hydroclimatic Variations During the Turonian Greenhouse Period: Evidence from Palynological Records of the Qingshankou Formation, Songliao Basin, Ne China

While the Cretaceous greenhouse climate and associated geological events are well-documented in marine environments, the scarcity of continuous terrestrial sedimentary records has hindered our understanding of continental climate-biosphere coupling during peak greenhouse conditions. The Songliao Basin, a massive continental basin in mid-latitude East Asia, preserves extensive mid-Cretaceous lacustrine deposits, notably the Qingshankou Formation. Based on a continuous core from Borehole ZKH34, this study presents new palynological records from the Qingshankou Formation to reconstruct the paleoclimate during its initial transgression phase. The floral assemblage is dominated by gymnosperms with abundant angiosperms and fern spores. Crucially, thermophilous (warm/hot) palynomorphs constitute 71.11% of the assemblage, reflecting a predominantly hot Turonian terrestrial climate. However, the records also reveal dynamic hydroclimatic fluctuations superimposed on this extreme greenhouse background. We identified distinct episodic cooling anomalies alongside significant dry-wet hydrologic cycles, progressing from a relatively cool and arid initial stage to a stable, hot, and humid condition. These climatic transitions closely correlate with lake basin expansion and anoxic events. Our findings fill a critical gap in mid-latitude terrestrial Cretaceous datasets, highlighting the instability of the continental climate system under extreme greenhouse conditions and providing empirical evidence for terrestrial-marine paleoclimate correlations.