A 500-kyr Pluvial Interval Triggered Lacustrine Carbon Burial in Late Cretaceous East Asia

The early Late Cretaceous hothouse was featured by intense storms and a prevailing monsoon climate, yet direct evidence for regional extreme precipitation events is rare. Here, we reconstruct local weathering and hydrological processes using magnesium and strontium isotopes from lacustrine dolostones in the Upper Cretaceous Qingshankou Formation, Songliao Basin, Northeast China. The δ26Mg and 87Sr/86Sr records exhibit coherent bimodal variations. Surficial Mg cycling reveals two hydroclimatic regimes: during 91.9∼91.2 Ma, high precipitation intensified weathering, especially a 500‐kyr pluvial interval with rainfall exceeding 2,000 mm/yr, which triggered lake flooding and organic carbon burial; during 91.2∼90.7 Ma, declined weathering and precipitation indicated monsoon retreat. The Hadley circulation shrinkage, orbital‐paced aquifer‐eustasy, and coastal mountains induced by Okhotomorsk‐East Asia collision, were triple amplifiers in elevating the Songliao Basin into a unique mid‐ latitude humidity hotspot with carbon burial, while contemporaneous inland and low‐latitude areas experienced aridification or exhumation.