Sulphur, Forams and Partings in Coal

OK, Kevin, I'll try to finish this one this time before I send it.

On Mon, 22 Dec 2003 10:24:37 -0700 "Kevin and Birgit Sharman"
<ksharman@pris.bc.ca> writes:

> 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.

How did the seawater get into the peat swamp? Did this happen when the
swamp was inundated by seawater, but not with clastics? I suppose the
spray from waves breaking on the beach could drift inland and provide a
constant supply of salt water, but wouldn't this negatively impact the
viability of the plants? Also, due to the lateral extent of some of
these coal seams, spray would not carry far enough to reach the full
extent of the swamp.

> "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).

> 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.

High rainfall could keep the salt water away from the peat mat. The
extensive lateral continuity of the coal and interbedded sediments of
constant thickness supports the floating mat model. Thick coal only
requires a 10x thicker mat of peat - the mats must have been hundreds of
feet thick. Multiple seams only require an influx of sediment to
separate the seams, or separate mats drifting over the area of deposition
to form stacked seams with different plant types.

> 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 would think that the bottom contact of partings overlying a coal could
be gradational or sharp in either model. Partings overlain by coal (the
top contact) could be either sharp or gradational in the floating mat
model, but should be gradational in the swamp model due to root
penetration and burrowing by critters.

> I have never observed tree trunks or stems extending from a seam,
> through a parting, into overlying coal

Unfortunately we didn't get a photo, but an engineer in a Walker Co.,
Alabama coal strip mine told me and a geologist tool pusher this year
that he and others had seen a tree trunk resting on the Nickle Plate seam
and extending up at about a 30 degree angle from vertical through 8 to 10
feet of shale or sandstone and through the overlying Pratt seam. This
was verified by the mine superintendent. The other geologist and I
begged them to call us next time they see this.

The general lack of stems/trunks extending up from the top of seams, and
the general lack of roots from above, are probably the strongest points
in favor of the floating mat model. These same observations have been
made by many other geologists in the US and Australia. I have made the
same observation for every coal parting I have seen in Alabama and
Kentucky.
In his class notes, Steve Austin (geologist, Institute for Creation
Research) writes: "The coal [Kentucky No. 12] contains numerous shale
partings; six can be traced over an area of 1,500 square kilometers;
average parting thickness is 1.5 cm (0.6 inch). They are continuous
across short exposures in coal mines. Shale partings occasionally
contain marine fossils and were deposited in sea water. Shale partings
are not preserved in modern swamp deposits -- they are homogenized with
the peat by roots. If partings were deposited as mud over a swamp the
original continuity would have been disrupted by vertically standing
stems and trunks. After trees re-inhabited the surface following mud
deposition, the parting would be penetrated by roots. This penetration
has not been observed in any of the partings!"
"...the 'blue band'... parting of blue gray clay...generally ranges from
1 to 3 inches in thickness and lies a little below the middle of the
coal. In most parts of Illinois there i an additional parting averaging
1/2 inch thick 6 to 10 inches below the blue band, and at many places a
minute dark shale or clay parting averaging 1/8 inch is 1-1/2 to 2 feet
below the top of the coal. These parting are traceable through a belt
ranging from 550 miles in linear distance northeast-southwest from
central western Indiana to eastern Kansas. A principal problem to
explain in any case is how the forest vegetation of a swamp could be so
completely levelled as to permit accumulation of a continuous layer of
clay averaging an inch or so in thickness." (Wanless, H.R., 1952. studies
of field relationships of coal beds. In: Second Conference of the Origin
and Constitution of Coal, 164-167)
"One of the more enigmatic features revealed by the intraseam tonsteins
[volcanic-ash deposits] is an almost complete absence of tree
preservation, either as tree trunks extending from the coal ply below or
as Vertebraria (root structures) extending from the coal ply above...
The observations of this group, representing over 400 man-years,
confirmed the almost complete absence of tree preservation in intraseam
tonsteins within local seams." (Creech, M, 2002. Tuffaceous deposition in
the Newcastle Coal Measures: challenging existing concept of peat
formation in the Sydney Basin, New South Wales, Australia. International
Journal of Coal Geology 5, 190-191)
> (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).

Same dog bit me. I spent 15 years working for a consultant, mainly
drilling and mapping coal seams in the Warrior Basin in Alabama. It
never occurred to me until maybe 10 years later that coal was anything
but a swamp deposit.

> 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).

Are these "shrub" roots? Are you proposing coal-forming shrubs? If not,
where are the big tree roots?

> 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.

If the influx of water knocked the trees down, the tree roots should have
been pulled up, destroying the flat top of the peat and resulting in pot
holes filled with sediment. Since the partings are generally of a
consistent thickness, it is more likely that the surface topography of
the peat was preserved by the parting, i.e., there were no trees growing
there.

> 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).

Compaction, I understand, is generally though to be on the order of 10x
from peat to coal. The author of a paper told me, in defense of rooted
mats becoming banded coal, that compaction can reach as much as 25:1
going from loose peat to coal. But there is a problem with accommodation
space for shale and sandstone laid on an uneven surface. If a tree stump
is standing 25 inches and gets compressed to 1 inch, the sediment must
flow into the resulting void. If a 2-foot deep pot hole is filled with
sediment and flattened to 1 inch, what do you do with the 2 feet of
sediment that filled the hole? Sand compacts very little; clay compacts
only about 2:1. This "pot" of sediment would either push into the soft
peat below, cause the sediments above to drape over the "pot", or the
"pot" would have to be squeezed out laterally during compaction. It
seems more logical to say that the surface was planar to begin with, and
stayed that way during compaction.

> 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.

In the floating mat model, stumps and roots may or may not settle out
with the other peat materials. In the in situ model, standing
stems/trunks should always be preserved from the coal below, along with
root mats from above. I disagree that this is "inconclusive".

> 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.

Are you willing to follow the evidence where it leads? Of course, that's
a two-edged sword that will cut me just as quickly as you. :-)

> 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?

If you accept YEC literature (which I know isn't always reliable), there
is a marine tubeworm in the coal at Joggins, Nova Scotia named Spirorbis
(see www.icr.org/pub/imp/imp-316.htm). According to Harold Coffin
(www.grisda.org/origin/02051.htm) Spirorbis is associated with many coals
around the world. I suppose coals with high sulphur (marine influenced)
might be expected to be associated with Spirorbis, whereas low-sulfur
coals (freshwater in the floating-mat model) may not be expected to
contain Spirorbis. If we find Spirorbis and no forams in coal, we would
have to find an explanation - I can't think of one at the moment, but I
guess the first step is to get into the literature and see what is there.

The only reference to forams I have found so far is from Calder et al,
1996, The Westphalian D fossil lepidodendrid forest at Table Head, Sydney
Basin, Nova Scotia: Sedimentology, paleoecology and floral response to
changing edaphic conditions. Int'l Journal of Coal Geology 31, p 288:
"Six shale samples were disaggregated and examined for fossil protists...
Agglutinated foraminifera were found in four samples from the roof of
both the No. 3 and No. 4 coal bed, and from the parting within the No. 4,
with probable specimens in the other two beds... Sample yields are sparse
in comparison with yields from many other samples from the Sydney Mines
Formation."

Sample preparation for spore analysis included maceration with
concentrated HNO3 for 6 days. I suppose this aggressive acid would have
destroyed any foram tests that may have been in the coal, so I don't
think we can say that there are no forams in these coals. Do you agree?
If so, is there another method of sample prep or sample analysis that
would preserve the forams?

I've found a couple of references to coal intertonguing with marine
limestone, but I'll save that for another post.

Incidentally, Kevin, I ordered a copy of Stach. I look forward to
reading it, and thank you for the reference.

Bill

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Received on Sat Dec 27 22:50:08 2003