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 ( δ 26 Mg and 87 Sr/ 86 Sr) from lacustrine dolostones in the Upper Cretaceous Qingshankou Formation, Songliao Basin, Northeast China. The δ 26 Mg and 87 Sr/ 86 Sr 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 (millimeters per year), 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.