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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
> > 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

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.


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