Interesting. The relation between the Siberian flood basalts and the extinction has been known for a long time, but this is the first time I've heard about the coal ash.

But, some things to think about: there was also a massive flood basalt in India at the time of dinosaurs extinction (Deccan traps). But there is also wide agreement that there was an asteroid impact in Yucatan, Mexico at that time. A couple of people, lead by Luann Becker, proposed they had found a crater north of Australia for Permo-Triassic boundary (the time of the extinction in the article). This was controversial and I am under the impression that the majority of people who work on this boundary don't believe it.

But 2 or 3 km from where my parents in law lived in southern France is a mine that became a museum, that according to the geologic maps is on the same boundary. We talked to a geologist who worked on this, and it is a world class mineral deposit including what he said was an extra-terrestrial mineral (Mine of Cape Garrone (spelling?). The sedimentary rocks there are fluvial, and I kind of doubt they can date the boundary very precisely. But still odd. We took some samples and Becker looked at them and did not find any evidence for impact (but it was a clay layer above the mineral layer, and not the minerals).

So, why not giant impacts triggering flood basalts? Lowell Whiteside, who used to post here, likely had ideas along those lines.

Chris