The Toarcian anoxic event
The oceans lose their oxygen again, and black shale is laid down across the world.
- When
- Known to
- ± 1 million years
- Era
- Jurassic, Mesozoic
The early Toarcian oceanic anoxic event, about 183 million years ago, brings high carbon dioxide, intense continental weathering, rising sea level and widespread deoxygenation, lasting somewhere between 300,000 years and a million. Organic-rich black shales deposited during it across Europe and beyond became major petroleum source rocks. Boron isotopes show the oceans acidified at the same time — the same coupling of warming, anoxia and acidification seen in the great extinctions.