Roots in coal?

On Sat, 6 Dec 2003 09:55:11 -0600 "Glenn Morton"
<glennmorton@entouch.net> writes:

> Kevin Sharman, the coal geologist who sent me the photos has given me
> permission to post this. I have put some more photos of the canadian
coal
> which show radiating root patterns from the former bases of bushes
which
> grew in place. You can see them at
http://home.entouch.net/dmd/cancoal.htm

I agree that these are radiating roots, possibly from a former base of a
bush. However, to say that they "grew in place" is an interpretation
which may or may not be correct.

> The seam was 1.5 meters thick, and most of what you see as coal has
been
> disturbed. This is a banded coal. Vitrinite layers in this coal do
not
> represent individual layers of bark, but woody tissue including bark
that
> has been coalified. At this rank (med volatile bituminous) there has
been a
> lot of compaction. The original textures that remain are only visible
under
> the microscope. The J seam ranges from 1.5 m to 8 m thick.

This past week I visited an outcrop of coal recently exposed by road
construction near my office. Beneath the coal are the best examples of
stigmarian axial roots and rootlets I have ever seen. These
roots/rootlets look somewhat like a bottle brush with the axial root
being an inch or two in diameter and flat rootlets radiating out from the
axial root as much as a foot from the axial root. I saw maybe a dozen or
so axial roots, and all appeared to be laying parallel to bedding except
one, which was at about a 10 degree angle with bedding. Rootlets are
visible throughout the strata beneath the coal (at least in certain
areas), which consist of a sandstone grading up into a shale. Rootlets
in some areas were an average of 1/4 to 1/2 inch apart. In this rooted
outcrop area of maybe 2,000 to 3,000 square feet, I did not notice any
tree stumps (which we might expect if the roots were in situ).

The overlying coal is fairly irregular, especially the top contact with
the sandstone roof rock. It appears that the top of the coal may have
been eroded during deposition of the overlying sandstone. Because of the
shallow depth of this coal, the outcrop is somewhat weathered, but I have
a sample of coal which clearly exhibits the banded structure of this coal
seam near my office.

> Check out new photos 124 and 125 - these clearly show a shrubby root
system
> radiating from a common point. 125 is to the right side of 124.This
was one
> comment from Payne - why shrubs not trees. The answer is the
ecological
> succession of the pioneering vegetation - [edited by grm] shrubs, then
when
> enough of a mat is built up, trees. This is why big tree roots are
uncommon.
> ****end of Kevin's part****

We agree that there are roots below the J seam of coal. I contend that
the roots are transported, as evidenced by the upside-down roots, even
dispersal of intermittent roots, and the common plane of termination of
several roots. Kevin maintains that the "dozens if not hundreds of fine
roots" override my evidence. We agree that the fine roots go in and out
of the plane of the rock face, but if these roots were in situ I would
like to see more of a pattern, similar to the "radiating" roots. We
should also see more of the parent plants to which the fine roots were
attached. The radiating roots seem to be thicker than the fine roots we
had been discussing, and therefore may be from a different type of plant.
  The photo with "Big root" appears to have several "shrub" roots that are
upside down (branching upward).

The main objection I have to these intervals (Kevin's J seam and the seam
near my office) being in situ is the small number of preserved roots. At
the rate of 1 to 2 mm per year for the accumulation of peat in a swamp
(swamps include trees, marshes are grass and shrubs only - no trees), I
can't imagine that only a few roots would be preserved in the uppermost
soil horizon. The radiating roots in the photo with the finger pointing
to the root mass are well over a foot long. For the peat mat to get over
a foot thick (too thick for the roots to penetrate into the underlying
soil) at the rate of 1 to 2 mm/yr would take 30 to 60 years. With even
as little as 30 years of grass and shrub growth we should see a solid
mass of roots, not individual roots separated by sandy zones with no
roots. Therefore the evidence suggests that these roots were
transported.

The radiating pattern can certainly be maintained during transportation;
this only requires that the plant be uprooted with the roots still
attached, which can easily happen in wet soil. Since the root end is
heavier, the plant settles out of suspension with the roots down and gets
buried in growth position.

The main question I would like to ask Kevin is about tree roots in the
coal itself. Kevin says trees didn't begin to grow until the mat built
up. If Kevin has studied the microscopic structure of this coal, I would
like to know if he commonly saw tree roots cross-cutting the banded
structure of the coal. Indeed, I would like to know how banded coal
could form at all if this was an intensely-rooted peat mat. Compaction
will not transform crossscutting tree roots into horizontally-banded
coal.

I ran across what may be the only reference I have seen to crosscutting
roots in coal: "However, the upper lithotype sample contains a small
collotelinite fragment oriented perpendicular to the bedding, which may
represent a rootlet, and as such might signify pedogenesis. However, no
further evidence exists to support this." (Glasspool, Ian J. 2003.
Hypautochthonous-allochthonous coal deposition in the Permian, South
African, Witbank Basin No. 2 seam; a combined approach using
sedimentology, coal petrology and palaentology. International Journal of
Coal Geology, v 53, Issue 2, pp 81-135, p 22 of 36)

Glasspool is grasping at straws to describe a single crosscutting
fragment "which may represent a rootlet", in an effort to retain some
indication that this coal seam might be somewhat in situ. IMO, roots
crosscutting sand or shale bedding planes may or may not be in situ since
the sediment could settle down around the roots. However, roots
crosscutting or penetrating sheets of bark would (I think) have to be in
situ since a sheet of bark could not settle down around rootlets that
penetrate the bark.

If Kevin's J seam coal formed from trees growing on the peat mat, I would
like to know if crosscutting tree roots were found in the banded coal.
If so, can he furnish photos? I will predict that no such crosscutting
relationship of roots and banded coal exist, which will be strong
evidence that the coal was transported.

Bill

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Received on Mon Dec 15 23:21:17 2003