Oceanic Anoxic Event 2 Triggers the Cretaceous Thermal Maximum

At the Cenomanian-Turonian boundary approximately 93.9 million years ago, massive volcanic CO₂ emissions from multiple large igneous provinces — including the Caribbean, Madagascar, and Kerguelen — overwhelmed the ocean's buffering capacity. Global temperatures rose 4-5°C in shelf seas, atmospheric CO₂ reached 1,000-4,000 ppm, and reduced ocean circulation created widespread oxygen-depleted zones that deposited organic-rich black shales across ocean basins worldwide. The event eliminated approximately 26% of marine genera and triggered the Cretaceous Thermal Maximum, a period of sustained hothouse conditions with ice-free poles, broadleaf forests in the Arctic, and sea levels 100-200 meters above present.