The P-T impact was probably on the ocean somewhere, as the oceanic carbon shifted from C13 toward C12, which is something that volcanic eruptions won’t do; either the C12 was in the impactor, or the impact released methane ices on the ocean floor.
These large asteroid impacts blanket the Earth with cloud cover in a couple of hours, and this takes years to clear. The hydrologic cycle slows to a crawl as solar energy can’t reach the surface. Within days large fauna start to die, and vegetation eaters begin to starve. Predator species eventually run out of food; they may even lose their marbles from the constant darkness.
Ocean temperatures of 40C may have released some of the “frozen” methane very late in the progression initiated by the traps. In fact, that is what a number of geologists believe happened. Time will tell.