The Jurassic started around 200 Mya, after Hettangian volcanic pulses. Earlier this week Reynolds linked the Toarcian Oceanic Anoxic Event, which may even define "Toarcian": 183 Mya.
The claim is that a South African volcano roared to life for 300 millennia. Which is... a lot. That's about what we're looking forward to as our tectonic plates grind to a halt. 20,500 GT of CO2 were emitted. Apparently that depleted oxygen in the oceans. Anoxic waters don't rust metals, meanwhile. The article talks uranium: uranium rust dissolves, pure uranium sinks.
CO2 diminishing O2 would be the step I don't grok. CO2 and oxygen are mutually inert. If anything, the existence of plants should cause excess CO2 to lead to more oxygen.
Unlike 17 My earlier, these volcanoes seem unpoisonous. It may be that atmospheric carbon - and phosphorous! - fed plants... too well. And 17 My into the Triassic, maybe there weren't the landplants to soak it up. That leaves algae. The atmosphere is nicely oxygenated; but the shores and lakes get stuck with the rotting greenery.
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