Re: Hell Creek (long)

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

It is very doubtful if even global wildfires could really cause "darkness
at noon" for any length of time. The reason is that the smoke would stay in
the troposphere and be washed out quickly by rain. On the other hand many
pyrochemicals are toxic, so very large scale fires would be very unhealthy
even for animals that were not directly affected by the fire.

As for the Deccan traps, as others have already noted, there is a rich
dinosaur fauna in the intertrappan beds, so at least the earlier eruptions
didn't even eliminate dinosaurs from the indian continent. In a way this is
surprising since we know from the only (fairly small) fissure eruption in
historical times (Lakagígar 1783) that plateau basalt eruptions have very
bad environmental effects. This eruption which covered 565 square kilometer
killed 75% of all cattle on Iceland, mostly through fluorine poisoning and
by stunted grass growth because of sulfur dioxide. As a consequence 20% of
Iceland's human population died of starvation in what is known as
"móduhardhindin" (the haze famine), after of the bluish haze that lay over
Iceland during the summer of 1783. 
Note that India was isolated out in the middle of the Indiam Ocean at the
time of the reuptions, so the dinosaur couldn't have recolonized from
elsewhere during quiet intervals.

I don't think that any credible decrease in atmospheric oxygen would have a
very significant effect on animals. Extant animals certainly have a fairly
high tolerance in this respect. Elephants live well above 10,000 feet on
Mount Kenya and at least some humans can live indefinitely at altitudes up
to ca 17-18,000 feet. Birds are _incredibly_ tolerant. Many species
regularly migrate at altitudes up to 25-30,000 feet which means that they
can not only survive but also sustain intense and prolonged physical
activity at oxygen pressures that will kill most mammals within a few
minutes. 
This is usually explained as being due to their "stream through" breathing
system in contrast to the "dead-end" mammalian breathing apparatus. I'm not
quite sure how high e. g. crocodiles occur, but I remember seeing them at
ca 6,000 feet in East Africa.

Another aspect that I think hasn't been mentioned in this thread is that
the Chixculub bolide impacted on partly dolomitic rock. This means that
large amounts of sulphur were injected into the stratosphere. This may have
had a very significant effect on climate. Microscopic sulfuric acid
droplets in the stratosphere are the most important component in the "dust
veil" from volcanic eruptions and since they are so small it takes two or
three years before they settle out. Unfortunately there is no consensus on
how much dolomite there really was in the Chixculub target rock. 

Also the Chixculub bolide hit in (admittedly shallow) salt water. This
means that large amounts of water vapour and _salt_ must have gone into the
stratosphere. The salt may have been very significant since chlorine is
very bad for the Ozone Layer.

Another extinction mechanism that I don't think has been mentioned in this
thread is the tremendous earthquake (about 12(!) on the Richter scale).
This caused collapse of carbonate platforms and continental slopes on a
vast scale at least in the Caribbean and the Atlantic. The huge turbidity
currents must have caused some marine extinctions. Since there were also
tremendous tsunamis, at least the Atlantic must have been very turbid for a
while. Furthermore very large amounts of methane would have been liberated
from methane hydrates and gone into the atmosphere and reinforced the
hothouse effect from carbon dioxide.

As for early Paleocene marine faunas I can cite the Danian of Scania here
in Sweden which has been fairly intensively studied. It contains a lot of
shark teeth, a few crocodylians and a neornithine bird (Scaniornis). No
mosasaurs.

Tommy Tyrberg