Re: More Extinction (with refs!!!)

[Peter Sheehan <sheehan@csd4.csd.uwm.edu>]

On Wed, 26 Apr 1995, Phillip Bigelow wrote:

> Peter Sheehan <sheehan@csd4.csd.uwm.edu> wrote: 
> Peter said:
> >The other facies in Fig. 4--flood plain muds and silts-- show dinosaur bones 
> >decreasing in abundance near the top of the Hell Creek.   Again, 
> >the exact position of the iridium layer is not known--even though 
> >its' position can be guessed within a few meters.  How can you tell what 
> >happens to abundance just below a layer which you can not identify in the 
> >outcrop?
> 
> I'll buy this.   However, this doesn't bode well for your catastrophic
> hypothesis, just as it doesn't bode well for the gradualists.  Frankly, I am
> still unconvinced, but remain open-minded. 

I do not see a problem.  Microstratigraphy at the boundary is not going 
to work.  We can not address the problem by trying to study changes 
in the last 2-3 m of Cretaceous rock.  But that does not mean we can not 
examine the question.  For example, our 1991 study tried to find changes  
in dinosaur communities over the last two million years.  We satisfied 
ourselves that at that scale dinosaur communities were very stable.  We 
saw no evidence that communities were degrading.  We can not address what 
happened in say the last 70,000 years of the Cretaceous.  But for me that 
is not an issue.  If the dinosaurs were doing fine through most of the 
Hell Creek the impact scenario makes sense.  Suggesting, with no 
evidence, that dinosaurs may have begun to decline for some unknown 
reason in the 70,000 years just before a huge impact event seems 
unwarranted to me.

> 
> 
> In closing (finally), I have visited the Brownie Butte site on a couple
> occasions.  As you push away the weathered sediment of the hill to look at
> the coal/clay layer, you really get a shiver up your spine, knowing that an
> event so powerful occurred 65 million years ago that it left a mark ("scar")
> in the earth: a strip of dust that marks "one really bad day" in earth's
> history.
>  
I agree.  For me it was a moving experience to actually see the layer. It was
right in there with finding my first T. rex tooth.  (And this comming 
from a brachiopod worker.)