Clay balls are not coal concretions

James Mahaffy (
Fri, 8 May 1998 13:23:39 -0500 (CDT)

Apologies for those getting this twice but I am sending this back to
acg-l and asa both of whom received Steve's post. I think I will have
the secretary check and see how much overlap there is between the two
lists, since I know I don't like double posts.

Steve Dutch responded to this article.

> >
> > (Phillips, Tom L. and William A. DiMichele. 1998. A transect through a
> > clastic-swamp to peat-swamp ecotone in the Springfield Coal, Middle
> > Pennsylvanian age of Indiana, USA. Palaios 13(2):113-128.)
> >
> > coal balls formed by reworking of organic-rich mud during a marine
> > transgression.

Steve said:

> Those of us from around the Great Lakes are familiar with armored clay
> balls, balls of till clay with pebbles on their surfaces. They are formed
> by wave action. As the clay rolls around, it incorporates pebbles, and
> fine material washes away, leaving a pebbly surface. I hadn't even thought
> of clay balls in many years, but they sound much the same. I've also seen
> wave-rounded and compacted masses of peat from Pleistocene deposits as
> well.

> Steve Dutch
> UW-Green Bay


Coal balls are not clay balls but calcareous concretions. The evidence
is that they were not moved around much, but represent in situ peat.
Some recent studies have been done on their occurances in a well mapped
mine and the indications are that the carbonate came into the peat in
areas where a clay roof had been eroded. I did the palynology on the
coal in this area so I am quite familiar with this work which was
carried out by DeMaris and some others at the Illinois Survey. Bill
DiMichele and Tom Phillips did the vegetation analysis from the coal
balls and I compared these to the coal. I am in the library, and don't
have the references at my fingertips, but could get them to anyone

James  F. Mahaffy (     Biology Department