Hi Bill
Bill Payne wrote:
> Hi Jonathan,
>
> I should be able to get to Tuscaloosa next week to copy the articles you
> referenced. I will be very busy for the next six weeks or so, but will
> try to pick up again later where we left off.
Don't over do it.
>
>
> One comment to your post:
>
> On Mon, 09 Jul 2001 20:09:22 +1000 Jonathan Clarke
> <jdac@alphalink.com.au> writes:
>
> > Seeing that most mires are defined by the water table their surfaces
> can be very flat, especially when occurring in a low relief depositional
> setting. Why is this a problem? On the scale of an outcrop or mine
> exposure why would not
> these appear "as flat as a table top"? It may be my fault, but I seem to
> have lost
> your point. I can't see the global significance you are trying to draw out
>
> of this.
>
> Picture a swamp. Make it as flat as you like for as far as you like. My
> point in this is that swamps have trees growing in them. A "flood event"
> (local) that deposits impurities which are preserved as a parting in the
> coal seam would necessarily be interrupted by the trunks of the standing
> trees.
>
I agree. Now we need to add in some variables. Not all mires are forested,
not all are buried in the forested state, some are drowned and others are
eroded prior to burial. So we went up with a situation where some coal
deposits have their upper surfaces interrupted by trees and some do not. it
will depend on individual cases.
>
> We don't normally see any interruptions in the partings. Nor do we
> normally see any interruptions in the fine banded structure of the coal
> seams. Where are all the vertical trees? The ones that we do see are
> usually some distance above a coal seam.
Examples are known, but they are rarely seen. I suspect this is a
preservational artifact. My recollection of coal seams (and most are
lignites rather than your highly compacted Pennsylvanian ones) is that the
banding is discontinuous on a larger scale. With compaction in black coals
of the order of 10 or 20 to 1 it would be very hard to see an original
stumps. Compaction in sandstones is much less (less than 2 to 1), which is
why we see these erect trees well preserved in sandstones. This difference
in compaction may also explains some cases where the bases of upright trees
and their appendages are fractured. No always though, there is a nice photo
(Figure 7) in the Fielding and Alexander paper that Joel referenced the
other day (Palaeogeography, palaeoclimatology, palaeoecology 170:59-80) that
shows an erect tree in the Permian of the Sydney Basin (Australia, not Nova
Scotia) that is rooted in coal and terminates in sandstone.
>
>
> The photos I had hoped to post showing this are too big for the ASA
> e-mail, but the list manager has offered to post them on a temporary
> site. I'll get back to this when I have time. Meanwhile, I'll try to
> read up on some articles.
>
> Oh, one more thing. I visited an old strip mine a couple of weeks ago.
> The underclay had been exposed and weathered in a wash. There were some
> very nice round roots up to maybe an inch in diameter and exposed for
> about a foot of length. The roots were reddish in color and contained
> very little carbon - maybe a little in places on the surface. If I had
> seen them in fresh outcrop, I don't know that they would have been
> apparent. When I get back up there, I'll take a pick and see what I can
> find when I dig down.
>
Good observation. Clearly weathering brings out the best in rocks!
>
> Thought you might want to know. :-(
Thanks for sharing it with us :-)
>
> Later :-),
>
> Bill
>
God Bless
Jonathan
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