Re: Roots in coal?

Hi Bill,

As promised, some contributions on sulphur and partings.

>
> > Are you proposing a marine setting for these coals?
>
> In some cases, yes, based upon the association of marine fossils,
> carbonates and high sulfur (which I assume from my reading is from marine
> influence). In other cases the coal may have settled in predominately
> fresh water. This flood model would require that all of the waters were
> not uniformily mixed.

It is generally accepted that coals with the original peat or roof strata
formed in marine influenced environments have a higher sulphide sulphur
content than those with fresh water influence (Holuszko et al, 1993, Stach
et al, 1982). The mechanism involved is bacterial reduction of sulphate
(supplied by seawater) to sulphide.

"Low ash and low sulphur coals were deposited as fresh water peats which
were underlain and overlain by fresh-water clastic sediments in which
limestones were absent." (Stach et al, 1982, Cecil et al, 1979a).

The Gates Fm. coals are low in sulphide sulphur with the exception of D
seam, the highest mineable seam. This is overlain by a conglomerate
interpreted to be of marine estuary channel origin (Carmichael, 1983), based
on sedimentary features noted above, Macaronichnus segregatus burrows, and
its position below a marine lag facies.

Using the above as criteria, the low sulphur coals of the Gates Fm. could
not have been deposited in a marine floating mat model. A fresh water
floating mat model would have to account for the lateral extent of these
coals (230 km X 90 km = 20,700 km2), deposition of the interbedded sediments
(65 m to 90 meters thick), and the multiple seams (8 seams, 0.5 meters to 10
meters thick). Proposing a zone of fresh water in contact with marine water
leaves one with explaining why this would not be mixed. Even brackish water
peats have high sulphur content.

Carmichael, S. M. M. (1983): Sedimentology of the Lower Cretaceous Gates and
Moosebar Formations, Northeast Coalfields, British Columbia. Unpublished
Ph. D thesis, Department of Geological Sciences, University of British
Columbia, 1983.

Holuszko, M., Matheson, A., and Grieve, D. (1993): Pyrite Occurrences in
Telkwa and Quinsam Coal Seams. Ministry of Energy, Mines, and Petroleum
Res., Geological Fieldwork 1992, Paper 1993-1, p. 527-536

>
> One thing I would add is partings within coals which seem invaribly to
> have few or no plant macerals. I was going to ask you if you have
> partings in your Canadian coals, and if so, do they preserve the stems of
> the trees that were growing in the swamp when the parting was deposited,
> and do they show roots from the trees that would have grown on top of the
> parting when the swamp was re-established? You said everything got
> metamorphosed in the coal seams, but I assume the structures would be
> preserved in the partings as they are in the sandstone beneath the coal
> in your photos. Can you describe the partings?

Partings in these coals range from small 1 cm bands within the coal to
layers 1 to 2 meters thick. Parting composition can be mudstone,
carbonaceous mudstone, and/or coaly mudstone, reflecting varying amounts of
plant material in the original sediment. Contacts with the underlying and
overlying coal range from sharp to gradational; generally they are
reasonably sharp. In two dimensions, the contacts are flat, but when the
contact is exposed in 3D, undulations can be seen (up to 0.5 meters of
relief).

I have never observed tree trunks or stems extending from a seam, through a
parting, into overlying coal (It has only been in the last year that I have
specifically hunted for details in the field relevant to the origin of these
coals; in my 16 years as a geologist at the operating mine, my priority was
usually more "practical" matters). Roots are sometimes observed in the top
of the parting in these coals, evidently originating from the coal above
(Glenn has one of my photos on his coal page showing this, the one with the
label "shale with roots" in the lower right corner).

I agree that one would expect at least some trees to be sticking through the
parting if it were deposited by an influx of water and sediment into the
swamp (unless the influx of water knocks down the trees). I also agree that
it is surprising that the lower contacts of the partings can be so sharp and
planar if the mud is draped over an irregular surface like the top of a peat
swamp.

I submit that sharp planar contacts of the bottom of the parting are a
problem for the shedding mat model as well. The pile of shed veg material
would have relief on the top of it, especially if it has larger trees and
stumps in it. Then, when sediment is laid on top of it, the layer should
conform to the relief. But, as we can see, partings with relatively planar
bottom contacts occur. In answer to this, I would say that compaction of
the veg material flattens out the top surface of it (this applies to the
floating mat model as well as the in-situ model).

So, partings are another inconclusive feature in the coals with respect to
our debate. If all partings had sharp contacts, no roots, and no trees
sticking up through them, it would be hard to explain with an in situ
model. But some have these features, and some don't.

It is the nature of geology that information is often incomplete,
contradictory, and downright confusing. What we must do is sort through it,
consider the range of possibilities, and pick the possibility that fits the
evidence best.
>
> Aonther criterion is fecal pellets which are abundant in in situ peat
> deposits but rare in transported peat mats. It's my impression that
> fecal pellets are not common in coals.

I found a reference to coprolites in a German brown coal in Stach (p.
281-282). I haven't found any info on coprolites in Cretaceous coal. While
looking for this, I found a reference to forams in marine peats: Cohen and
Spackman (1977) quoted in (you guessed it!) Stach "(in Florida peats)
foraminifers were present in all marine and brackish peats". So in your
floating mat model, we would expect forams in the coal, since you are saying
some were deposited in a marine environment. Are there forams in any coals
that you know of?

Kevin
>

>
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Received on Mon Dec 22 12:28:10 2003