Re: Devonian?
Most of the output of the Deccan Traps is under the Iridium layer, so comet causing the eruptions can be safely be ruled out.
Current hypothesis is that the Traps were erupting for quite some time before the Chicxulub strike, with fossil evidence supporting the idea - there was a dieoff underway for some period before the iridium layer appeared.
Under normal circumstances, Chicxulub should not have been a global extinction level event, even with the added input of the Deccan Traps. The final straw is that at the time it was a shallow sea with a _huge_ layer of limestone underneath and most of that got vaporised, putting an enormous CO2 pulse into the atmosphere along with billions of tons of water vapour.
This underscores that it's just as important where a rock hits as to the size of it (Modelling large ones shows that land strike = bad, open ocean strike = worse, shallow sea/continental shelf = even worse still)
For local extinction levels, there may not even be an observable crater. There at least one hypothesis that the younger dryas dieoff in north america was caused by a fragmenting comet skimming the atmosphere, generating a shitload of airbursts that effectively sterilised the surface - https://craterhunter.wordpress.com/ - I can't fault the idea and there does seem to be a fair bit of supporting evidence including melted rock formations in Mexico which appear to have been windblown into their current shapes whilst molten.
As others have said, the australian crater was known, but not the multiple large lumps. It's probably not large enough to have caused a global extinction level event though, especially given that life at the time was extremely simple.
The Deccan traps aren't the only ones associated with a dieoff - the much older Siberian traps are also about the same age as a dieback.
Personally I wouldn't be surprised if most of the larger craters caused by fragmented impacts rather than a single solid one - Shoemaker-Levi9 serves as a good observed example - but they're generally so badly eroded that it's impossible to tell.
From a human point of view, extinction level events aren't needed to wipe out civilisation. There are plenty of rocks whizzing around the inner solar system which are large enough to do the job and enough of them come worryingly close each decade that as a species, we really should be making plans to get off this planet.
Biting the hand that feeds IT
