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Re: K-T mammals



----- Original Message -----
From: "David Marjanovic" <david.marjanovic@gmx.at>
To: "The Dinosaur Mailing List" <dinosaur@usc.edu>
Sent: Sunday, May 12, 2002 11:18 AM
Subject: Re: K-T mammals


> ----- Original Message -----
> From: "Andrew A. Farke" <andyfarke@hotmail.com>
> Sent: Sunday, May 12, 2002 3:59 PM
>
> > ABSTRACT
> > New data from 17 Cretaceous-Tertiary (K-T) boundary sections and 53
> > vertebrate sites in the Hell Creek and Fort Union Formations in
> southwestern
> > North Dakota document a 1.76 m barren interval between the highest
> > Cretaceous vertebrate fossils and the palynologically recognized K-T
> > boundary.
>
> What kind of rock are these formations, actually? I'm asking because there
> has been that suggestion, 5 or 10 years ago, that the barren interval
> (assuming this is what the "3-m-gap" has shrunk to) was caused by the acid
> rain that dissolved the fossils but not the rock; others said that's
> impossible because the rock would have dissolved, too.

The Hell Creek is made of siliclastic rocks--mudstones, sandstones and
siltstones. Unless it was raining hydrofluoric acid, these would not have
dissolved.

In talking with Dean Pearson at the PTRM, the three-meter gap is shrinking
bit by bit, and it may just be a statistical effect. I'm not sure how valid
this is or not, as I usually avoid the whole K/T problem. The field is too
crowded for my tastes!

>         "Palynologically recognized" -- does this mean the famous boundary
> layer is not preserved?

Yes, the boundary layer is preserved in North Dakota. There was a shift in
pollen taxa across this boundary, so palynology is the cheapest and easiest
way to recognize it and pinpoint it.

There is a great deal of work going on in the Hell Creek of North Dakota
(I've been on a project dealing with microvertebrate sites). It will be
interesting to see how things change in the next couple years as more
publications come out.

Best,

Andy
__________________
Andrew A. Farke
South Dakota School of Mines and Technology, Box P404
501 E. St. Joseph St.
Rapid City, SD  57701

Phone: 605-394-2816

E-mail: andyfarke@hotmail.com