Re: Canadian Coal - depositional setting

From: Kevin Sharman <ksharman@pris.bc.ca>
Date: Tue Jan 20 2004 - 00:16:06 EST

----- Original Message -----
From: "Bill Payne" <bpayne15@juno.com>
To: <ksharman@pris.bc.ca>
Cc: <glennmorton@entouch.net>; <asa@calvin.edu>
Sent: Sunday, January 18, 2004 10:41 PM
Subject: Re: Canadian Coal - depositional setting

Hi Bill,

> On Fri, 16 Jan 2004 16:20:30 -0700 "Kevin Sharman" <ksharman@pris.bc.ca>
> writes:
>
> > > Do any of the tonsteins or bentonites cut through the coal?
>
> > No, Kilby commented in another paper that following the tonsteins
> > landward was hard because the fresh water depositional environment
> reworked
> > them (sorry, no reference at hand). There are no tonsteins that I
> know
> > of directly in the Gates seams.
>
> Well Kevin, you say [above] that "There are no tonsteins that I know of
> directly in the Gates seams", but you have said that there are other
> partings, presumably in the Gates seams. Tonsteins (thin layers of
> volcanic-ash) are a special class of partings, or layered impurities, in
> this case within a coal seam. On Dec 30, 2003, you wrote:
>
> {KS replies} As I've said before, thin widespread partings are hard to
> explain with either model. I have pointed out that the top surface of a
> floating mat deposited peat would not be smooth. The top surface of the
> parting in your model would have soft sediment deformation features from
> the next layer of veg material landing on it, wouldn't it? As far as I
> know, we don't see these in partings. Or are you contending that the
> parting was lithified prior to depositing the next layer of veg material?
>
> I would say that the top surface of a floating-mat-deposited peat would
> be relatively smooth, at least smooth enough to allow a layer of clastics
> or dust to settle out of water and form a blanket of impurities over the
> peat deposit.

You have not provided a realistic mechanism for ash falls to be deposited
below a floating mat, remember?

>With subsequent 10x + compaction as the peat is coalified,
> the surface would ultimately be much flatter than it was when the parting
> material settled over the peat.

Interesting. I proposed compaction on Dec 22 as a method of smoothing out
the top surface of the peat, then you disagreed with it on Dec
27th: http://www.calvin.edu/archive/asa/200312/0375.html Now you're using
my
argument. It must've been a good one!

>As to the lack of soft-sediment
> deformation features, this is indirect evidence for a smooth depositional
> surface on the peat - which fits the floating-mat model but works against
> the swamp model with it's standing trees, shrubs and grasses.
>
> Now, if the Gates coals were formed in a fresh-water swamp depositional
> environment, and if the tonsteins were reworked and therefore not
> preserved, how is it that you do have partings other than tonsteins
> present in these coals? Why were not all of the partings reworked and
> therefore not preserved?

Tonsteins have not been found in these seams. If the ash fell when the
interseam sediments were being deposited instead of peat, it would be
reworked by currents. Land an ash layer in a river and it will be reworked.

I am advancing the following explanation for partings: Partings are made
when clastic material is introduced into a swamp which is already below the
water level due to the rate of subsidence being greater than the rate of
peat growth. The standing vegetation has toppled , and the vegetation has
begun to decompose. The top surface of the peat is relatively flat
because of this.

The partings are not reworked by currents, as the clastic input occurs
infrequently. Peat development begins anew on top of the parting material.

If clastics or an ash fall are introduced into a swamp which is still
actively growing, they will be bioturbated and mixed. A parting will not be
formed, and the clastics or ash will be incorporated into the coal as a
higher ash zone of mineral matter.

This explanation works for partings formed by waterborne clastic influx and
for the preservation of airfall ash layers falling into the water above the
swamp. It explains the presence of high mineral matter zones in seams that
don't form discrete partings as well.

> But in
> a prograding environment where the land is emerging as the shoreline
> retreats, the swamp model will have to explain how you can accumulate and
> preserve 80 feet of peat above the base level of erosion.

In a word, subsidence. (80 feet above should read 80 METERS to get an 8
meter seam with 10X compaction) Kalkreuth et al (1989) has a model: "Coal
seams formed on Lower Cretaceous wave-dominated strandplain sediments in
Western Canada are characterized by great lateral continuity, substantial
thicknesses, and relatively low ash and sulphur contents. The coals formed
behind an active shoreline in areas undergoing subsidence due to shale
compaction and dewatering." and "The shoreface sandstones of the
strandplain began to subside almost immediately after their deposition and,
as a result, it is only the immediate coastal sands which are at sea level.
The marine muds in front of the wave-dominated delta were initially
deposited with high porosity, typically exceeding 50%."

Bill, if you choose to answer my question from Jan. 4th :

"Please describe a
mechanism for accumulating mats of peat hundreds of feet thick in the
pre-flood timeframe, which I understand to be a few thousand years, using
modern rates of peat accumulation which you quoted on Nov. 28, 2003"

you will need to invoke subsidence. You're welcome for the tip :-).

> Also, when the tree roots can no longer draw nutrients from the mineral
> substrate (due to the thickness of the peat), the growth of vegetation is
> stunted. How big were the trees at the top of the coal?

You are arguing against yourself again, because YOU need to accumulate great
thicknesses of peat in the pre-flood time.

> > This is explainable as a layer of finer material which acted as a
> > micro-perched water table, so the roots didn't need to grow any
> > further down. Seizing on this when dozens to hundreds of roots around
> it
> > don't terminate at a common plane sounds like selective use of data.
>
> I didn't notice a common plane for them to terminate in.

I'm puzzled. Why did you say this: (Dec. 3) "Based upon the observations of
dissociated, inverted and horizontally terminated roots"

And this: (Dec 4) "This interpretation is supported by the common
root-termination plane of the thin, dark bed"

And this: (Dec. 15) "and the common plane of termination of
several roots."

>If sedimentation is relatively continuous and roots are being brought in
> with the sand, then there wouldn't be a planar surface for the roots to
> settle on, they would be continuously be incorporated into the sand,
> i.e., they would overlap rather than having a common plane of
> termination. If the plane of termination was the bottom of a
> micro-perched water table, then the top of the micro-pearched would have
> been above the bottom by the thickness of the perched water. Therefore,
> why did the roots go all the way to the bottom of the perched zone, why
> didn't they stop in the saturated zone above the aquitard?

We're talking about a perched water table of perhaps millimeters in
thickness.

> If
> we take the root ball of a tree and slice down through it, the slice
> should cut more than one root longitudinally, and even if it didn't we
> should see the cross-section of many more roots that were cut. I think
> your best option here is to agree that this root floated in and was
> buried vertically. You could agree that the tree root floated in and
> still maintain that the other roots are in situ.

Thanks for the suggestion, but I'l stick with my contention that it's in
situ, based on the argument below (high energy beach sand) especially
considering the length of ~ 1 meter. Since we don't see this root
immediately below the seam, I agree that it is harder to call it in situ.
If we isolate the argument to only this one root, I don't think either of us
can make a case.

> > I disagree. I contend that your vertically settling roots would not
> happen
> > in a high energy environment like a beach sand. Roots would be
> expected to
> > be oriented ~horizontally, not like those in the photos. You have
> already
> > said that the roots in the photos look identical to modern roots.
>
> You seem to be hanging your hat on the vertical roots. For the sake of
> argument I'll admit that I don't have a ready answer to explain vertical
> roots in a high-energy sand environment. But, given the things that you
> don't have a ready answer for, I'm not ready to concede this point.
>
> > There is a 50 meter thick sandstone with burrows at most levels. You
> tell
> > me - can these animals burrow 50 meters upward in two days?
>
> That would be 25 meters/day, or about 1 meter/hour, or less than 2
> cm/minute. What's the problem?

When and where did they start burrowing from? Well, in the classic flood
geology scenario, they would start at the bottom of the flood deposited
sediments (since people supporting this view can't seem to agree on where
this boundary is, maybe you would like to pitch in?). For the sake of
argument, let's use the bottom of the Phanerozoic, 8000 meters below the
coal in question. Distance ~8 km vertically, timeframe, less than one year.
Pretty tough animals..Or, if you don't subscribe to the classic flood
geology scenario, feel free to give another one.

Bill, there was a question in my last post that you didn't answer. I have
copied it below for your convenience:

"Are you proposing a single global flood (small "f" if you like) deposited
most or all of the coal in the world?"

Any answer this time?

> > You answered it above - some areas below the seam have lots of roots,
> some
> > fewer. Carmichael's judgement was that there were strongly bioturbated
> > zones. We can't argue with him, since we've mined out most of what
> > he saw!
>
> Carmichael's judgement was influenced by what he believed, and he
> obviously believed that these deposits were in situ, hence his use of the
> term "bioturbation".

No. Bioturbation means "churned up by living organisms". There is no
genetic implication. The judgement is in the use of the word "strongly", as
opposed to "moderately" or some other term with no precise definition.

 And yes we can argue with his interpretation of
> bioturbation.

What I meant was that we can't visit exactly the same outcrops he did. Are
you offering an alternative interpretation which fits the observed data of
disrupted bedding planes that are identical to modern examples of burrowed
and/or root penetrated sand?

> > > Are you proposing that after a single stand of shrubs, there was
> enough
> > > vegetation collected on the surface to prevent penetration of roots
> into
> > > the sand substrate?
>
> > Yes.
>
> Yes? You show us a photo of roots radiating from a shrub, which appear
> to reach about 10 to 12 inches into the substrate. I find it difficult
> to believe

argument from incredulity

that a single stand of shrubs will provide a continuous mat of
> peat at least a foot thick. Modern swamps accumulate only about 1 mm of
> peat per year, yet you are proposing to accumulate 300 mm of peat in just
> a few years. And you must accumulate a meter of shrub peat before the
> trees begin to grow and sink their roots down as much as 1 meter.

Once the water table rises due to subsidence, the shrubs and trees don't
need to send their roots downward for water. It is only the pioneering
shrubs which need to do this, before the water table rises.

> > Back in March 1999 you and Jonathan Clarke discussed turbidites on
> > ASA. See: http://www.calvin.edu/archive/asa/199903/0174.html in which
> he defines the
> > Bouma sequence (diagnostic criteria for turbidites), which, from the
> post,
> > you seemed to be unaware of at the time. This lack of knowledge of
> criteria
> > for turbidites did not prevent you from proposing them as a mechanism
> for
> > partings, however: (snip) Mar. 30, 1999) "I do see impurities in
> coals. Because
> > they are generally thin and widespread, I think they are the
> > result of turbidity currents rather than traction currents."
> >
> > That was then and this is now, though. Do you see Bouma sequences
> > (description) in the partings you are currently ascribing to turbidity
> > currents (interpretation)? I asked you what mechanism you proposed
> > to deposit the interseam sediment underneath a floating mat, and you
> > have not had time to respond yet. Fair enough, but any response MUST
> satisfy
> > the descriptive data!
>
> Turbidites can only transport the material available to them, and I still
> say that turbidites can deposit interseam sediment beneath a floating
> mat.

Then please substantiate your claim. I can propose that the interseam
sediments are deposited by lightning, aliens, or anything else I want, but
until I advance some data to support my position, no one should be expected
to accept it. Same as your contention above. You have not shown that
features in the interseam sediments match the criteria for turbidites.

>If the available material is of a single size, then the turbidite
> deposit will only contain material of that single size. My "lack of
> knowledge of criteria for turbidites" does not invalidate the mechanism
> as a possible explanation for the feature.

Now that you have the criteria, apply them to the data.

Instead of trying to trip me,

Easy, Bill. Asking you to substantiate your position is not trying to trip
you, in my opinion. If you feel I'm being too harsh, please let me know.

> let's see you explain partings within your swamp (with standing trees) or
> marsh (with standing shrubs and grasses) models. Remember, any vertical
> obstruction such as trees or shrubs, or even grasses, will act as a
> baffle and rapidly slow the flow of turbid water.

See the explanation near the start of the post.

>And also remember, in
> a freshwater environment "that following the tonsteins landward was hard
> because the fresh water depositional environment reworked them." That
> same freshwater environment will also rework your partings.

Not if the swamp area is protected from further influxes. See above.

Kevin

Kalkreuth, W., D.A. Leckie, and Labonte, M. (1989): Gates Formation (Lower
Cretaceous) Coals in Western Canada, A Sedimentological and Petrographic
Study. Contributions to Canadian Coal Geoscience, GSC Paper 89-8.
Received on Tue Jan 20 00:17:29 2004

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