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Re: Gastroliths



Roger wrote:

> We see out-of-context stones in the Hell Creek, and I have suspected
and
> suggested that these were gastroliths. They are smooth and rounded,
> quatzite-ish, maybe granite. These don't look like stream polished
stones
> in that they are TOO smooth. These stones are sometimes within a few
feet
> of each other. It isn't like I see piles of them, but I have seen a
few.

I also have seen a few isolated piles of highly rounded and highly
polished ("waxy textured") pebbles in the H. Cr. Fm.  The piles are
almost always laying on the surface of a massive mudstone substrate.
But in the case of Montana, there is a complication.  Throughout the
eastern half of the state, the highest widespread pre-Quaternary
formation is usually the Flaxville Gravel (Pliocene).  (I think it is a
formally-designated formation, but will have to re-check).  Anywayyy...
the Flaxville Gravel often caps the flat-topped buttes.  It's clasts are
very smooth and rounded, too.

A few years ago, I had this wacky theory that some of the piles of
polished pebbles laying on the ground in the Hell Creek Fm. were simply
reworked Flaxville Gravel clasts.  As the buttes eroded, instead of
getting washed away, the Flaxville clasts may have simply stayed in
place.  Eventually, the clasts would wind up at the bottom of a coulee
(at the same geographic locality where they began, but a hundred feet
lower).
Imagine an ice-cream sundae with a cherry on top.  Put the sundae out in
the sun.  As the icecream melts, the cherry simply rides the top of the
icecream down.

But that still doesn't explain the occurrence of isolated *clusters* of
clasts laying on H. Cr. mudstone...

                                           <pb>