Both effects would have lasted something at the order of at most hundred years, far below our capabilities to detect timescale of events, so the unfortunate answer (for the public, at least; I think most scientists can live with it) is that we will probably never know whether it was the heat or the cold, of a combination of these, or an even more complex combination. All we can see is that many of these species were wiped out rapidly – but you have to consider that this is geologically speaking ‘rapidly’, which can mean anything at the order of hundreds of thousands to about 1 million of years, as it is impossible to have a better accuracy time-wise.