Re: US Pennsylvanian Coal - depositional setting

----- Original Message -----
From: "Bill Payne" <bpayne15@juno.com>
To: <ksharman@pris.bc.ca>
Cc: <asa@calvin.edu>
Sent: Monday, March 15, 2004 10:17 PM
Subject: US Pennsylvanian Coal - depositional setting

HI Bill,

> On Wed, 25 Feb 2004 17:51:58 -0700 "Kevin Sharman" <ksharman@pris.bc.ca>
> writes:
>
> > Bill, Where is your explanation for beds of sporinite? You have not
> > answered my previous question about it in my post on Stokes Law. I
> don't
> > think you have a legitimate right to criticize an interpretation until
> you
> > come up with a better one yourself.
>
> I have a question about these sporinite beds. Would you please describe
> how you envision that these beds are formed? I understand that sporinite
> beds contain only plant spores, correct?
It would be helpful in this debate if you answered my direct questions, or
said you didn't know or needed more time. Let me state mine again - where
is your explanation for beds of sporinite, given that the particle size of
small spores dictates extremely slow settling through a water column?

Sporinite is a coal containing more than 50% spores. These are rich in
spores, but not exclusively spores. Spores are a major component of most
cannel coals, which accumulate sub-aqueously under reducing conditions.
This indicates flooding of the mire. The spore content can also be enriched
when peat is oxidized above the water table, because of the resistant nature
of the spores.

> And where is your explanation for the preservation of the thin, delicate
> beds of sporinite? How do you drain the lake, establish a meter-thick
> layer of pioneering vegetation at the rate of 0.2 to two mm per year,
> which will then compress as trees start to grow (meaning that the
> pioneering
> vegetation had to be even thicker than a meter to avoid bioturbation by
> tree roots), all without eroding or bioturbationg the sporinite bed.
Bill, you must not have read or understood my post of March 10th showing how
thin tephra layers in Recent peats were undisturbed, despite
re-establishment of peat growth above them. This directly refutes your
long-standing insistence that bioturbation by roots would destroy a thin
layer.

> How do you explain the origin of thin, widespread clastic mudstones? I
> think you said tonsteins are from an air fall; what about mudstone
> partings? Are you proposing that all partings are tonsteins, that none
> are overbank deposits?
No, most partings are from an introduction of clastic sediment by river
flooding, by a gradual rise in base level which permits introduction of
clastics from fluvial sources, or by a marine transgression. With flat
topography, flooding/rise in base level events can cover thousands of square
kilometers with a thin layer of sediment.

> > Let's start with a quote that you had in a post (Dec 25): "Trees in the
> > mixed peat-swamp forest and pole forest...have spreading, buttressed,
> and
> > prop roots, which are generally confined to a root mat 50-80 cm thick
> at the
> > top of the peat and do not penetrate to the deeper peat or mineral
> sediments below thick peat."
>
> > Read this again, Bill: "roots.. do not penetrate to the deeper peat or
> > mineral sediments below thick peat". Sounds pretty clear to me.
>
> You read it again, Kevin: "roots... are confined to a root mat 50-80 cm
> thick..." The roots penetrate almost a meter, and form a mat of roots
> which will bioturbate and destroy any bedding or parting which is within
> that root mat.
The example shows that the substrate doesn't have roots when they looked at
it. The real question is "Did the substrate ever have roots?" In other
words, did the substrate have roots when the peat was being established, the
roots bioturbated the substrate, and now they are not visible, or did the
peat establish without rooting of the substrate? If you say that the roots
were there, and now they're not, I will use this to explain ancient examples
of substrates with no roots. If you say the roots were never there, I will
use this to back up my contention that the roots didn't need to penetrate
the substrate. Your modern example isn't helping you.

> I visited a real swamp, located in Moundville, Alabama, today. I'll
> e-mail a couple of photos to you. (snip) I pulled up a small cypress tree
> (snip) I pulled up a small clump of grass growing in the water; the grass
had a
> very thickly-matted mass of roots (snip) These grass
> roots bear little resemblance to Glenn's photos of ancient roots, which
> are sparse, do not radiate, and are relatively short.
I will hold off commenting until I see your close up photos.
>
> > No, because the coal immediately above a parting is from the main swamp
> > forming plants. The pioneering plants do not contribute much
> >vegetation to
> > the coal.
>
> Now wait a minute. Are you saying that the pioneering plants don't
> contribute much vegetation to the coal, yet they contribute enough
> vegetation to support the succeeding trees so that the tree roots do not
> penetrate the mineral substrate or parting below?
No, they don't support the vegetation, the substrate does.
>You can't have it both
> ways, Kevin. If tree roots penetrate up to a meter, and if we don't see
> tree roots in partings, then there must have been something holding the
> trees above the parting (and above the sand underlying the Gates) while
> they grew.
As I've said, the tree roots grew horizontally in the plane of the top of
the substrate. This is a common sight on Cretaceous footwalls, as the link
to dino tracks in the Gates shows: http://members.shaw.ca/dinotracker/
(click on the "E2-Pit" link). To explain this by settling stumps from a
floating mat on the footwall, you need to have the substrate hold up the
stumps too. The odd tree root penetrates into the substrate, as I've shown
in pictures.

> Are you proposing that the pioneering vegetation was
> sufficient to support the weight of the forest, but then disintegrated
> without a trace during coalification?
The substrate (footwall or parting) holds the weight of the forest.
>
> The floors of many seams contain only clastics - no roots or anything
> else organic. Look at slide 25 on the ppt CD I sent you. This coal seam
> looks like any other from this area, yet there is no underclay (seat
> earth or paleosol) and no roots. Would you agree that these rootless
> coal seams are allochthonous?
In a word, no. See my discussion above about lack of roots below seams.
The seams with no roots could be hypautochthonous, with peat transported
within the swamp. If this is the case, they should be high in mineral
matter and inertodetrinite. Or they could be from the attached floating
mats Glenn mentioned. These appear to be of limited extent, as they
normally fringe the edge of lakes and abandoned channels, and they can be
considered in situ (not transported).

> Again, what mechanism do you propose to spread the clastics over wide
> areas? I think the literature will show that not all partings are
> tonsteins.
As above, rise in base level and introduction of clastics by fluvial or
marine
processes.

> > Since the presence of shorelines (dry land) seems to be your mechanism
> >for
> > bunching up plant material, explain whether or not dry land was present
> > during the deposition of all the Devonian to Recent coal measures.
>
> You're getting ahead of me; I'm still considering the details at this
> time, not the big picture.
I'm refuting your global flood/floating mat scenario, and you don't want to
deal with it.
>
> If a turbidity current won't work, then muddy water with the mud settling
> out of suspension will. And the roots resting on the bottom will get
> encased in the sediment as if they had grown in situ.
Now you are really grasping at straws. Settling out of suspension won't
work fast enough, for the Stokes Law reasons I outlined a month ago.
Settling velocity for a 4 micron silt particle is 1.2 meters per day. You
will want to invoke flocculation by low pH waters, but the ocean water you
are settling through would not be acidified by a mat. Salt water marshes
have shallow sea water in direct contact with the marsh peat, and the water
is not low pH. You need to settle particles through a deep water column
(the water column would have to start at 80 meters deep to settle out enough
peat to make an 8 meter seam at 10:1 compression ratio), so most of the
water would not even be in contact with peat.

Pure claystone partings are rare anyways; there is normally a lot of silt.
Silt particles don't flocculate to any great extent, because they don't
carry surface electrical charges like clays.

> > I quoted Grieve (1984) describing organic stringers in the tonsteins he
> > studied. This is evidence for roots; not conclusive, but evidence
> > nonetheless.
>
> It's evidence for organic stringers, not roots. Roots is an
> interpretation, not data. As we both know, roots bioturbate sediment
> layers; organic stringers which settle with the ash do not bioturbate.
> This is evidence supporting transported organics.
The presence of organic stringers is data. It is evidence for both in situ
roots and transported organics; it does not preclude either interpretation.
>
> > > (Creech, Michael, 2002. Tuffaceous deposition in the Newcastle Coal
> Measures:
> > > challenging existing concepts of peat formation in the Sydney Basin,
> >>New
> > > South Wales, Australia. International Journal of Coal Geology 5,
> >>185-214)
>
> > From the abstract of the paper referenced above: "It is proposed that
> the
> > peat surface was predominantly below the water table, and the term
> >"lowered
> > mire" is proposed to describe this environment. A subaqueous peat
> >surface
> > would protect thin volcanic ash deposits from subsequent redistribution
> >by
> > rainfall and surface runoff, and is consistent with a lack of tree
> > preservation within the intraseam tonsteins. It is envisaged that trees
> >were
> > generally restricted to the peat margins, and to specific horizons
> >where the
> > peat surface was exposed by a fall in the water table."
> I don't think Creech has the answers, just some guesses, and he is
> refreshingly honest enough to admit such. Of course, I may have missed
> the obvious, and you are welcome and encouraged to point out oversights I
> may make.
Is there a part in the body of the paper where he proposes the term "lowered
mire" as the environment of deposition, as he states in the abstract? If
there is, it might be valuable to quote it. It sounds like he is proposing
a reasonable interpretation for the data he see, even if he can't find a
perfect modern analogue.

> > > Ash falls on open water, goes into suspension and disperses over a
> >>wide
> > > area, including the areas beneath floating mats, as it settles to the
> > > bottom.
>
> > You still haven't shown how an ash fall can escape obliteration by
> >being
> > carried under a mat by currents. You say that it does, without giving
> > evidence to support your statement. As I explained above, the ash is
> >light
> > and is also very fine, and is extremely susceptible to mixing.
>
> Maybe a better word than "currents" would be "drift." This would move
> the ash without disturbing the bottom or obliterating any settled ash.
Your "drift" would have to transport sediment laterally 10's of kilometers
under the mat in a short time frame, then settle out tiny particles. Glass
shards in volcanic ash are commonly 20 to 60 microns - same problem as
settling clays and silts. You simply don't have enough time in a year-long
global flood to accomplish this over and over again to account for the
world's tonsteins.
>
Thanks Bill,

Kevin
Received on Wed Mar 17 09:02:54 2004