Garin writes: The late Permian saw the greatest mass extinction event of all-time. The causes for this extinction are hotly debated, but one key piece of the puzzle has recently been revealed: while the deep-water environments were anoxic, shallower waters showed clear signs of being oxygenated. This rules out global anoxia, and strongly suggests that other factors, such as the Siberian Traps vulcanism, must have played a dominant role.
From the article: "Rather than the direct cause of global extinction, anoxia may be more a contributing factor along with numerous other impacts associated with Siberian Traps eruption and other perturbations to the Earth system.”
See the full research article (behind a paywall) here.