Re: Canadian Coal - depositional setting

From: Bill Payne <bpayne15@juno.com>
Date: Mon Jan 26 2004 - 22:12:41 EST

On Sun, 25 Jan 2004 12:33:13 -0700 "Kevin Sharman" <ksharman@pris.bc.ca>
writes:

> As you say, this is speculative. Speculation is a good start, but by
itself
> can't form the basis of a scientific argument. My understanding is
that the
> pre-flood world described in the Bible is rather dry, and "rather large
land
> areas producing vast areas of peat" are not mentioned, to my
> knowledge.

No, but it does imply that "things were different then." "...., but
streams came up from the earth and watered the whole surface of the
ground." (Genesis 2:6)

> If you are not proposing picking up intact thick mats of peat, but
rather
> amalgamating loose collections and concentrating them into much smaller
> areas, how do you keep them concentrated in a turbulent flood? As an
> analogy, try dumping a bag of sawdust or peat moss on a lake or sea.
The
> material will spread out.

You're right, I hadn't thought that through. I guess the mats would have
to be bound together with roots until they started to settle out of
suspension. Then getting thin mats to become "hundreds of feet thick"
(my words) is problematic, as you pointed out.

> The rate does not need to be constant, it needs to be between the upper
rate
> (above which a lake would form) and the lower rate (below which the
peat
> emerges and growth stops).

If the rate is initially faster than the peat can form then it seems that
there would be no way for the peat to gain a foothold. I guess though
that at some point there is a shoreline, and that is where the swamp
begins.

> > I thought decomposition was retarded by submergence and the supposed
> > reducing environment of deposition. Glenn has said that tree trunks
are
> > preserved for at least, I think, hundreds of years when submerged.
If
> > so, the surface of the lake bottom would be populated with standing
trees
> > for centuries.

> In anoxic waters, such as at the bottom of deep lakes or the ocean,
there
> will be no aerobic decomposition, and organic material will be
preserved.
> At the top of the peat when it is submerged, there is oxygen.
Peatification
> proceeds until the oxygen is used up, then anaerobic decomposition
kicks in
> (deeper in the peat profile).

You didn't address my question. I am asking how you would prevent
partings from forming on lake bottoms with standing trees. Partings seem
to usually be thin (from millimeters in thickness on up) and laterally
extensive. You need to explain how you would smooth out the lake bottom
before any partings formed. I'm saying it would take centuries for
waterlogged tree trunks to decay, and during this time no partings formed
since partings don't contain standing tree trunks.
 
> > In the meantime, until all of the trees had decomposed
> > and the lake bottom was smooth, any partings would be interrupted by
> > standing tree trunks. Since I don't think your partings include
standing
> > trees, what mechanism do you offer to keep turbid water out of the
lakes
> > until after the lake bottom is smooth?
>
> As mentioned above, recharge of meteoric groundwater is the clean water
> source. Turbid, sediment laden water is brought in by storm processes
> breaking over river levees and introducing parting material into the
swamp.

I understand where parting material comes from. But if the swamp bottom
is covered with trees and/or grass, the vegetation will baffle the flow
of the turbid water, restricting the extent of the parting and
interrupting the parting with vertical stems/trunks. I see a parting as
a snapshot in time of the depositional surface, and that surface appears
to be free of standing vegetation. It doesn't look like a recently
flooded swamp or a swamp that received an overbank deposit of mud.
Partings in the Pennsylvanian can cover hundreds of square miles. Are
the partings in the Gates different?

> In the intensively explored and mined area (20 km X 10 km), there are
no
> river channels cutting the basal coal. There is an area I can think of
> where the basal coal thins to ~1 m, but I can't say if this is because
it's
> cut out by a channel. Outside of this, drillhole control is more
> sparse.

> See the block diagram I posted a link to. It's a cartoon, but shows
that
> there was an elevated source area, then a broad (75 km wide) flat
coastal
> plain. The source area was many hundreds of km long (the rising Rocky
> Mountains), and hundreds of km wide. The proximal deposits of the
material
> eroded from the source area were laid down at the foot of the
mountains,
> uphill from the coastal plain, because of the reduction of gradient.
The
> sediment that did make it over the swamps is represented by the
interseam
> strata.

This is something I didn't understand. I thought the shoreline was
prograding as the peat was being deposited, which is what I also gathered
from the block diagram. But you're telling me that the shoreline only
progrades when the interseam sediments bury the swamp, and a new swamp
then forms on top of the new sediment??? Doesn't the block diagram show
the peat riding up over the sand as they simultaneously transgress
seaward? How can this occur if there is no additional sediment being
introduced along the shoreline as the peat is being deposited?

> In the Gates, the proximal deposits have been removed by recent
> (post-orogeny) erosion. In the case of the Mist Mountain Fm. of SE BC,
the
> overlying Elk Formation is a series of alluvial fan conglomerates and
> sandstones with thin discontinuous coals. These represent proximal
> deposits. The Cadomin Fm. of NE BC is another example of a proximal
> alluvial fan deposit.

What do you propose as an energy source to transport these proximal
deposits over the swamp? Did the shoreline and swamp submerge and
thereby increase the gradient below the proximal deposits? Or did the
entire area subside? I assume that these interseam deposits are not
channeled, but are sheets of sediment that cover the entire area of the
swamp (20,700 km^2) and beyond?

> How's that for quick turnaround? :-)

Stinks. You're making me look even worse. :-(

Just kidding, but one of these days I'm going to make you think and that
may take you more than a few minutes. :-)

Bill

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Received on Mon Jan 26 22:27:53 2004

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