Good evening Kevin,
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?
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.
> A series of vertical roots which look identical to modern roots, which
> crosscut bedding and which are connected to the overlying coal is
enough
> proof for you to accept an in situ origin for roots in sandstone; why
not
> mudstone? Because you think you can explain the mudstones as
turbidites,
> you think you are justified in using a different mechanism (turbidite
> emplacement vs. in situ growth) to explain the same data (vertical
roots).
> Trouble is, just saying that the mudstones are turbidites isn't enough.
You
> have to present evidence.
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?
> > You need to have a modern analog that shows pioneering vegetation was
> > established on layered soil, and trees growing above the pioneering
> > vegetation, with the layers of soil still intact, i.e., not
bioturbated.
> > If you can come up with such a modern analog, one which I can see in
> > photographs or drive to and study for myself, then you will have
undercut
> > one of the primary supports of the flood model. I don't believe such
a
> > modern analog exists. You will also need to show that the weight of
the
> > trees doesn't compress the underlying organic mat, which would give
the
> > tree roots access to the mineral substrate.
> 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.
I visited a real swamp, located in Moundville, Alabama, today. I'll
e-mail a couple of photos to you. You will be able to see trees and
grass growing together in the swamp. I pulled up a small cypress tree
growing in several inches of water to see if the roots were horizontal at
the top of the mineral substrate or if they went down even though they
didn't have to for water, since the tree was growing in water. The tree
is about 1/2 inch in diameter and measures 2 ft 2 inches tall above the
water. The roots went down to 2 ft 2 inches below the water surface, and
branched out several inches from the central tap root. These trees are
growing in a swamp without much in the way of "pioneering" vegetation. I
pulled up a small clump of grass growing in the water; the grass had a
very thickly-matted mass of roots which extended about 5 inches below the
water surface, and radiated out from the clump of grass. These grass
roots bear little resemblance to Glenn's photos of ancient roots, which
are sparse, do not radiate, and are relatively short.
> 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? 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. Are you proposing that the pioneering vegetation was
sufficient to support the weight of the forest, but then disintegrated
without a trace during coalification?
> Why do you think that all the plants would sink whole and be oriented
in
> growth position? All the floors of seams I've seen and read about
contain
> roots only, not roots, stems, bark, etc. If the source of your
vegetation
> is a ripped up mat of plant debris, it would be a mixture of all plant
> parts, and as these waterlog they would sink, and be in all
orientations,
> but mostly horizontal. This is not what the data shows, is it? We see
> vertical roots, not randomly oriented mixtures of all plant parts.
Stokes
> Law shows us that smaller bits would sink first, but you would have
whole
> plants sinking first. [I think you made a correction to that about
smaller bits sinking first]
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?
I'll try to get some decent photos of the coal seam near my office which
has the best Stigmarian axial roots I've ever seen. These roots are
mainly near horizontal, although I think at least one is about 10 degrees
below horizontal.
> The turbidity currents you propose must be gentle.
> What happens if they're not? You will get a churned up mass of mud and
> plant parts, which will lithify to shale with randomly oriented coaly
bits.
> We don't see this in partings. It just doesn't add up, Bill.
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.
> 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.
> > > Turbidity currents have a velocity. This would churn up your
waterlogged
> > > floating plants which are resting on the bottom and make it very
unlikely
> > > that they would all remain vertical.
> > If the plants were suspended in turbid water and plants settled as
the
> > sediment did, then the roots would be buried in growth patterns.
> So you are saying that all the roots would be buried in growth
position, and
> none of them would be horizontal or sub-horizontal. This doesn't work.
A
> current, which you need to deposit the mud, even a gentle current,
would
> push over the waterlogged roots. You have said they are suspended
> vertically in the water at the bottom. This means their density is
very
> nearly the same as the water, and they would be extremely susceptible
to
> stirring up.
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.
> > Slide 48: ".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 is an additional parting
averaging
> > ½ 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.
> > Here are three very thin partings covering roughly a quarter-million
> > square miles. Your explanation within the swamp model?
> You have done exactly what you objected to above: You are assuming the
> partings to be turbidites, and using that assumption to prove your
point.
> You have not shown that these are turbidites at all. The literature
> suggests quite a different origin:
[snip]
> This is evidence that the blue band may be volcanic (i.e. a tonstein),
but
> you use it as an example of a turbidite. As for the other partings
> described, I would not be surprised if they were found to be
> tonsteins too.
I think someone who would know told me several years ago that the blue
band got thicker near a paleochannel, and therefore was believed to be an
overbank deposit. I'll try to follow up on this and see if I can get a
reference.
> 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.
> > (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."
>
> Since you have the entire paper, please quote those parts which present
the
> author's comments that explain the data with an in situ model, then try
to
> explain why those conclusions are invalid. I can't help thinking you
left
> those parts out on purpose.
Leaving out critical parts is always a concern, even if it's not on
purpose. I'll be happy to copy and send the paper to you if you can't
get it. In fact, I will send you a copy of any or all of the papers I
have that you need. Let me know offline and we'll work it out.
From Section 8. Discussion and conclusions (Creech, p 212):
"The environment of peat formation included aspects of various
modern-day environments. Similarities with the broad braided river
channels in New Zealand can be invoked, including extensive grass swamps
such as those reported between large rivers in the Assam valley of
northern India (Bocking et al., 1988). The Dismal Swamp of North
Carolina and Virginia, USA incorporates large internal lakes, where peat
is accumulating in a largely forest setting. There is, however, no
contemporary analogue of a peat-forming environment that would preserve
the features outlined in this paper.
The findings of this work may have implications for other coal
basins around the world that display similar features, preserved by
volcanic ash falls. The work challenges the presumption that the
presence of preserved trees in strata associated with coal seams is, in
itself, evidence for a forested peat-forming environment."
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.
> > 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.
Bill
________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!
Received on Mon, 15 Mar 2004 23:17:08 -0600
This archive was generated by hypermail 2.1.8 : Tue Mar 16 2004 - 00:40:21 EST