>I have seen quite a few dropstones of all sorts, including examples I
have
>interpreted as glacial, volcanic projective, impact projectile, and
vegetational rafting.
I understand that dropstones are fairly common in eastern US
Carboniferous coals. Of the options you offer above, I would think the
only reasonable one in a coal seam would be vegetational rafting.
>Schutz's study is largely discredited these days and has been superseded
by
>many studies which do show weathering in paleosols. Not only that, they
show
>many different weathering styles which reflect modern variations in
>weathering and which are consonant with other palaeoclimatic indicators
in
>the sediments. A good place to start is Greg Retallack's book
"Paleosols" (I
>think).
I was aware of Schultz's study being discredited as you say. But, being
open-minded as we are :-), would it be possible that the "paleosol
weathering" were the result of secondary weathering after deposition?
Coal seams generally carry more water than the sandstones/shales/clays
they are associated with, so we would expect the clay aquitard beneath
the coal aquifer to develop minor chemical degradation after deposition,
due to the flow of water through the overlying coal. This expected
chemical profile in the underclay beneath a coal seam might well mimic a
soil-weathering profile.
This is one of probably several possible alternate interpretations that
might explain the observations. Everyone seems to forget that Schultz's
macroscopic field observations confirmed his belief that these coals were
allochthonous.
I've very much enjoyed our discussion. I made a copy of Gastaldo's paper
today, and will try to get to the Post Office with it tomorrow. If
anyone else would like a copy, send me your name and address offline and
I'll send one to you (as long as the demand isn't too great).
Bill
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