Enhanced ocean connectivity and volcanism instigated global onset of Cretaceous Oceanic Anoxic Event 2 (OAE2) ∼94.5 million years ago

Oceanic Anoxic Event 2 (OAE2) exemplifies an episode of global oceanographic and climatic changes in the mid-Cretaceous greenhouse. However, timing mechanism its initiation remain elusive. Here we report a high-resolution initial osmium isotope (187Os/188Osi, Osi) δ13Corg record from expanded OAE2 interval southern Tibet, China that was deposited Southern Hemisphere. The Osi documents episodic, intensifying volcanism with highest intensity marked by large excursion at ∼94.5 Ma subsequent ∼200 kyr minimum concomitant cooling interval, which is broadly synchronous Plenus Cold (PCE) recorded Northern Also, lags onset ∼50 occurred during near transgression based on correlation other major records. These results are interpreted as indicating enhanced ocean connectivity played critical role helping trigger Ma.