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Re: extinctions and personality
On Tue, 25 Apr 1995, Mickey Rowe wrote:
> case in point. Peter Sheehan came the closest to supporting you, but
> he most certainly did not address all of my concerns. What Peter did
> write about them was:
> The problem is that William's statement about the decline has no
> evidence to back it up. Personally, I have seen no evidence
> presented that there was a gradual decline of dinosaurs at any scale
> in the Hell Creek. In fact, the only field study of the Hell Creek
> designed to test the hypothesis rejected a gradual decline.
> I've asked Peter about this via personal e-mail, but he has not yet
> responded. Since the topic isn't dying here, I'll ask him again
> publicly. Peter, do you think that Williams misrepresents the data
> from the Hell Creek Formation in his Figure 1c? Also, do you have any
> quarrels with his analysis of your work in the section beginning on
> page 186: "Significance of the Barren Zone"?
((Sorry, I did write back to you, Mickey, but I just noticed the e-mail was
returned to me--something strange in my mailer.))
Williams' Fig. 1c (fig 1, part 3). He shows many dots randomly
distributed, then 2-3 meters below the top of the Hell Creek the dots
are scarce. I see no evidence for this.
To begin with the iridium layer is not spread all over N.D. and Montana.
It is well developed in two places--one in MT and one in ND. Over most
of the region the iridium layer is not present or at least has not been
recognized! So how can you tell when you are 2-3 meters below the iridium
Dinosaur bones are rare in the Hell Creek. If I remember correctly in the
two places where the iridium layer has been found the nearest dinosaur
bones are many meters below the horizon--don't quote me on this.
In Williams' Fig. 4 the facies are broken up into stream channel and flood
plain facies. No stream channels that were clearly active at the time of
the impact have been identified,
because any iridium falling in an active stream was eroded away. If the
channel is caped by an iridium layer, the channel was much older. Fig. 4
shows many stream channels. Of those that cut through the iridium layer,
the deeper they cut into the Hell Creek the more dino bones they have.
Which to me suggest that the Tertiary channels that cut through the most
dino-bearing sediment contain the most reworked dinosaur bone. Tertiary
channels that do not cut deeply into the Hell Creek have few dinosaur bones.
Since the dino-bones are big, and the Hell Creek is mud
and sand, the fine particles eroded from the Hell Creek moved down stream,
the dino bones become concentrated, and number of bones reflects how
deeply the channel cut into the Hell Creek and how much sediment was eroded.
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
As to my reaction to Williams' comments about our work (his p. 186) where
he states: "Intensive fieldwork by Sheehan et al. (1991) has added a
considerable number of remains to the total known from the formation, but
the "gap" remains nearly as barren as before."
I do not remember addressing the "gap" in our paper--and from my field
experience I did not notice anything that suggested a "gap".