DavidMcC wrote:... I realise that there is the view that it was a pure coincidence that the Deccan traps ocurred at about the same time as the KT impact, but that does require a chance coincidence, which makes it seem less likely to be true.

There are quite a few LIPs, and while cases have been made for a connection of the Siberian traps and P/Tr as well as the CAMP and Tr-J you have NAIP, which exceeded the SIberian traps by a factor of 3 in the volume of magma produced and no associated mass extionction, Paraná which exceeded the Deccan traps at least and Ontong-Java (the biggest of them all and no association with any biological change).
In the past 250Ma, 12 LIPs have been active, each for 5-10Ma. That gives you a ~0.25-0.5 chance for a coincidental cooccurence.

Rumraket wrote:

DavidMcC wrote:

Rumraket wrote:

DavidMcC wrote:I don't see any evidence that all three events - the Chixulub impact, the Deccan traps and the dinosaur extintion couldn't have been causally related, in the order listed above.

Nobody is claiming, afaik, that they couldn't. But you've got the burden of proof backwards.
It needs to be established that they did in fact causally relate in your listed order, with evidence.

I don't know why you are so sure that I have the order wrong.

I'm not sure of that, I didn't even insinuate it. In fact I might even agree that the order you lay out is totally reasonable, but I was talking about whether that has actually been established. We cannot just take it for granted that they happened in that order, it needs to be established first before we start demanding evidence to change our minds.

DavidMcC wrote: Indeed, we may never know, because they are too close in time, and there has been too much smearing, as susu.exp said. However, my proposed causal order is sensible, AFAIAC and that is all am concerned about. Like I say, probably, no-one will ever be sure, because it all happened too long ago.
If you can justify a different causal chain, please let us know.

You've misunderstood the purpose of my comment. I'm not claiming that the order you suggest is wrong, I was commenting on the fact that you want to see evidence to refute your proposed order. In the absense of any evidence to decide, we should not hold any particular order of events as superior to another. That was all I was trying to say.

The bit I've bolded is what made me think you had some major issue with my earlier post, suggesting a likely order of events. I was not trying to claim that it was all "established".
In short, this looks like a "storm in a teacup" to me.

susu.exp wrote:

DavidMcC wrote:... I realise that there is the view that it was a pure coincidence that the Deccan traps ocurred at about the same time as the KT impact, but that does require a chance coincidence, which makes it seem less likely to be true.

There are quite a few LIPs, and while cases have been made for a connection of the Siberian traps and P/Tr as well as the CAMP and Tr-J you have NAIP, which exceeded the SIberian traps by a factor of 3 in the volume of magma produced and no associated mass extionction, Paraná which exceeded the Deccan traps at least and Ontong-Java (the biggest of them all and no association with any biological change).
In the past 250Ma, 12 LIPs have been active, each for 5-10Ma. That gives you a ~0.25-0.5 chance for a coincidental cooccurence.

What are "CAMP", LIPs and NAIP, please?

DavidMcC wrote:

susu.exp wrote:

DavidMcC wrote:... I realise that there is the view that it was a pure coincidence that the Deccan traps ocurred at about the same time as the KT impact, but that does require a chance coincidence, which makes it seem less likely to be true.

There are quite a few LIPs, and while cases have been made for a connection of the Siberian traps and P/Tr as well as the CAMP and Tr-J you have NAIP, which exceeded the SIberian traps by a factor of 3 in the volume of magma produced and no associated mass extionction, Paraná which exceeded the Deccan traps at least and Ontong-Java (the biggest of them all and no association with any biological change).
In the past 250Ma, 12 LIPs have been active, each for 5-10Ma. That gives you a ~0.25-0.5 chance for a coincidental cooccurence.

What are "CAMP", LIPs and NAIP, please?

CAMP: Central Atlantic magmatic province
LIP: large igneous province
NAIP: North Atlantic igneous province

Susu, could it be, therefore, that the geographical distribution, duration and CO2 & SO2 content of a traps event is at least as important as the total magma volume involved (in terms of its impact on extinctions)?

... For example, a gradual, widely distributed traps eruption will not produce the high local concentrations of dangerous gases that a short, but intense one with much SO2 in it would. Eg, they could be harmlessly diffused, over time, never building up to lethal concentrations.

EDIT: In short, the total magma volume is not the only important parameter.

DavidMcC wrote:... For example, a gradual, widely distributed traps eruption will not produce the high local concentrations of dangerous gases that a short, but intense one with much SO2 in it would. Eg, they could be harmlessly diffused, over time, never building up to lethal concentrations.

EDIT: In short, the total magma volume is not the only important parameter.

Well, there's not a huge amount of variation in SO2 and CO2 content of basaltic magmas AFAIK - the concentrations in the places of origin for the magmas is relatively constant across the globe. As noted in an earlier post in this thread, the total CO2 output of the deccan traps was less than anthropogenic output over 2 years and the SO2 output less than anthropogenic output per decade. While our emissions are a cause for concern, the deccan traps were spread out over longer time periods and did not continue.

For P/Tr there's a far more relevant source of CO2 - exposure and oxidization of some large coal fields in Gondwana. And for KT there's a very relevant source of aerosols in the impact, which lead to a global spread of the Ir containing dust and massive forest fires, mainly contained to the Americas (and hence close to the impact site), which produced massive amounts of soot. Tr/J has seen somewhat less research (and I don't have my literature collection on me). But I don't think the gas release from magmatic provinces provides a plausible scenario for extinction, at least so far.

susu.exp wrote:

DavidMcC wrote:... But I don't think the gas release from magmatic provinces provides a plausible scenario for extinction, at least so far.

Maybe not, but when there is a bolide impact, the combination of the that and the gas release from the "magmatic province" might make the difference between mass extinctions and merely population reduction, especially as the bolide impact could exacerbate the traps eruption, even if it didn't initiate it.
Having said that, I am not claiming that the KT impact wasn't sufficient alone to cause the mass extinction, especially as there happened to be a large sulphur deposit in the Chixulub area.