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astroblemes and extinctions



>>       - No vertebrates larger than a breadbox proliferated from the
>>         late Cretaceous through to the Tertiary. In other words, 
>>         "the meek inherited the earth". 
>
>Not entirely true, probably for the reasons you describe below.  Among the
>"larger than a breadbox" sized animals which persisted were several genera
>of crocodillians, river turtles, and champsosaurs (crocodile-like diapsids
>of uncertain affinity).

I stand corrected. I should have said "few" vertebrates larger than
a breadbox...
Any reactions to the point I was trying to make, i.e. that big animals 
have a tough time surviving large impacts? I think that has important
implications for models as to what actually happens when a big one hits.

>Actually, there has been no supported evidence of an astrobleme at the
>Permian/Triassic extinction, which is by far the most severe in the
>post-Cambrian world.

Are you familiar with Rampino's P/T impact hypothesis? It does not have
anywhere near the supporting evidence that the K/T impact does, but 
when you add the Chinese P/T stratigraphic evidence, it becomes a pretty 
strong case for a massive impact(actually 2 huge impacts) at that boundary.
If you haven't seen the data, there are two boundary clays very reminiscent
of the Gubbio, Italy K/T section, _with_ large Ir/siderophile spikes.

>It is important to note that the Deccan Traps begin millions of years prior
>to any iridium spike, so anyone who wants them to be generated by the K/T
>impact has to believe in time-travel as well...
 
I assume you refer to another Rampino hypothesis concerning antipodal
volcanism. I don't know what to make of the K/T impact-Deccan traps
correlation or the P/T impact-Siberian traps correlation, but there
is evidence on planet Mercury for astroblemes having antipodal crustal
effects. Perhaps a very large impact can have antipodal or other associated
volcanic effects if the underlying mantle/crust are favorable towards it. 
For example, a medium flood basalt province(e.g. Columbia River) becomes 
a Siberian trap level event, or a mantle plume volcano such as Hawaii
gets elevated to a Deccan trap level eruption sequence. It is important to 
note that the Deccan traps span the K/T interval, the lava poured out
some before, some during and some after the Iridium spike. It might be
erroneous to insist on volcanic activity as solely caused by the impact,
or conversely that the impact had no effect on the volcanism.