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, the timing and mechanism of its global initiation remain elusive. Here we report a high-resolution initial osmium isotope (Os-187/Os-188(i), Os-i) and delta C-13(org) record from an expanded OAE2 interval in southern Tibet, China that was deposited in the Southern Hemisphere. The Os-i record documents episodic, intensifying volcanism with the highest intensity episode marked by a large Os-i excursion at similar to 94.5 Ma and a subsequent similar to 200 kyr Os-i minimum concomitant with a cooling interval, which is broadly synchronous with the Plenus Cold Event (PCE) recorded in the Northern Hemisphere. Also, the large Os-i excursion lags the onset of OAE2 by similar to 50 kyr and occurred during a near synchronous global transgression based on high-resolution correlation with other major OAE2 records. These results are interpreted as indicating that enhanced ocean connectivity played a critical role in helping trigger the global onset of OAE2 at similar to 94.5 Ma. (c) 2021 Elsevier B.V. All rights reserved.