Re: Canadian Coal - depositional setting

From: Bill Payne <bpayne15@juno.com>
Date: Fri Jan 16 2004 - 00:18:03 EST

Hey there, Kevin! Sorry to have been out-of-pocket, but my younger
daughter's wedding consumed our lives for the last couple of weeks. It
was absolutely beautiful though, and worth every bit of the effort and
money.

Thanks for setting your e-mail to the ">" for my replies. They should
outlaw the vertical lines which don't permit you to insert separated
replies.

On Tue, 13 Jan 2004 22:30:12 -0700 "Kevin Sharman" <ksharman@pris.bc.ca>
writes:

> Evidence for progradation is in the form of tonstein (volcanic ash
> bed) correlations (Kilby, 1984) which showed that the top of the Gates
> Formation is diachronous, with marine shales of the Hulcross Formation
being
> deposited in the north at the same time as Upper Gates non-marine
sediments to
> the south. As an aside, one of the bentonites in the Hulcross Fm. has
> been dated (Ar40/Ar39 date of 107.1 Ma) and is used by Obradovich
(1993)
> to calibrate his widely used Cretaceous time scale. Another bentonite
> in the Moosebar Formation below the Gates demonstrates that the lower
> contact is diachronous as well. (Fans of Berthault's work take note -
> diachronous lithostratigraphic contacts were not news even in 1984!)

Do any of the tonsteins or bentonites cut through the coal? You are
making a good case here for transgression, but transgression will fit
either model.
 
> Any floating mat hypothesis would have to explain how vegetation
> could be deposited on a sand body that is prograding northwards over
time.
> At any given time, the shoreface sand existed as the top layer over
only a
> small part of the area, yet coal occurs directly overlying the
shoreface
> sand over its extent (230 km X 90 km = 20,700 km^2). The rate of
progradation
> was estimated by Leckie (1986) as 218 m to 437 m per 1000 years.

Radioactive dating is, in my mind, a black box which I intuitively
question. I prefer to be able to actually look at the data and hold it
in my hands, beat on it with my hammer, or thin-section it and study
under a microscope. Whatever Leckie estimated was based upon
assumptions, and his estimates mean little or nothing to me. I don't see
a problem with a floating mat following a transgressing shoreline; this
is exactly what Steve Austin proposed for the Kentucky No. 12 coal.
These are all what I consider secondary lines of evidence; at this point
I would prefer to look at evidence directly associated with the coal. I
know I owe you a couple of responses from a few weeks ago and will
attempt to get to those soon.

> If you want to put the deposition of this sandstone into a biblical
> timeframe, it would need to occur in a short time. The Phanerozoic
> sedimentary sequence in this area is ~9000 m thick. Dividing this
> by 400 days (alleged duration of the Flood) gives an average rate of
> deposition of 22 meters/day. Using a thickness for the shoreface sand
of 50
> meters, this would have to be deposited in a little over two days. Not
a lot of
> time to rain down ~80 meters of veg material to make that 8 meter seam,
is
> it?

You're trying to imagine what would happen, based upon your experience.
I understand that there are megabreccias in the SW US, and some of the
breccia consists of clasts hundreds of feet long. I don't think we can
conceive of what produced that breccia; nor can we conceive of what the
subsequent conditions may have been like.

> The sandstones are "clean" and "very well sorted", according to
> Carmichael (p. 42). This kind of compositional and textural maturity
is not a
> feature of rapidly deposited sediment, but is found in modern shoreface

> sands, due to reworking by wave action. The rate of progradation would
have
> been 90 km in 2 days! Trying to settle out roots vertically in a unit
that is
> being deposited this fast is a non-starter. Even in an old earth time
> frame, settling roots out vertically in a shoreface sand environment
> doesn't work. It would be too high energy - see the above quote about
> wave-dominated deltas and strandplains.

You say vertical roots can't be explained, and Glenn says on his web site
that diagonal roots are hard to explain, and I suppose horizontal roots
would also be "hard to explain." I can imagine that you guys would say
any orientation of roots would not be explainable except as in situ. The
branching upward of some roots, the common plane of termination of some
roots, and the odd, isolated tree root (if it's in situ, where are the
rest of the roots of the supposed root ball) in this "beach" environment
are all difficult for you to explain with the in situ model. I don't
think either of us can make a persuasive case at this point based on
roots.

> There are also burrows in the sandstone facies, which could not have
> been made in the short timeframe discussed above.

Why not? How long does it take for an animal to make a burrow? The
clams I have seen at the beach can pull themselves under the sand faster
than you can reach down and grab them.

> He also notes that "the top 30 cm to 1 meter of facies B (the upper
portion of the shoreface
> sand) is often strongly bioturbated. In most cases the bioturbation is

> caused by roots."

Ah, here is something I was driving at earlier. You've got the advantage
in that you have all of the literature. Can you tell me how to order the
papers relative to the Gates fm., or would it be possible for you to copy
and send me the papers? If so, please let me know (offline) in advance
how much that would cost. I would try to get them through interlibrary
loan, but that takes forever and a day if I get anything at all, and
chances are that if I do get a publication it will not be the volume I
requested. Of course, if it's online like the Alaska paper, that's easy
to get.

Earlier I was saying that you should not have individual roots visible
beneath the coal, but, if this was a swamp, there should be an
intensely-rooted mat which makes a gradational contact with the
underlying rock. The floating-mat model can accept the complete range
from no roots to "intensely-rooted" strata immediately beneath coals, and
this is exactly what we see in Alabama. From your photos and what you
have now told us, the sand beneath the Gates can have roots from what
appears to be a single stand of shrubs, or it can be intensely rooted
("strongly bioturbated"). Given this range of variation in rooting, I
suspect that there are also areas where there are no roots at all beneath
the coal. But just looking again at the individual roots in your photos,
please explain why there is not a "30 cm to 1 meter of facies B (the
upper portion of the shoreface sand) that is strongly bioturbated. 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?

Do you have a photo of the "strong" root bioturbation?

> Arguing that this sandstone was deposited more slowly than the
> average used above doesn't help, either. The Cretaceous succession has
repeated
> shoreline progradations, so slowing down this one just means you
> must speed up the rest to get the total amount of sediment allegedly
deposited
> in the Flood timeframe.

Again, I'm not so concerned about the Flood timeframe at this point. I
would rather concentrate on whether the coal is in situ or not.

> This depositional setting for the Gates coals (coal on shoreface
> sand) is not unique. The coal-bearing Jurassic/Cretaceous Mist
Mountain
> Formation of southeastern BC also rests conformably on the Morrissey
Formation,
> a shoreface sand, as do the coals of the Cretaceous Mannville
> Formation of central Alberta.

Then there should be plenty of outcrops where we could check for roots at
the coal-sandstone contact, and plenty of partings which should be
penetrated by stems.

> The interseam sediments consist of conglomerates, sandstones, and
> siltstones. None of these units can be interpreted as turbidites,
> as has been suggested for interseam sediments below floating mats.

Are you talking about what I said? I think I was referring mainly to
intraseam partings, although if the partings get thick enough then the
coals are usually considered separate seams - making the partings
interseam. I don't understand why you say "None of these units can be
interpreted as turbidites." When a turbidite slid off the continental
shelf near the St Lawrence seaway and off to the east, cutting the
trans-Alantic telephone cables, it was traveling at about 60 mph, as I
recall. I would think a 60 mph flow could move pebbles, sand and silt.
Is the conglomerate widespread and planar, or confined to channels? If
it is planar, then how do you propose to move and spread the pebbles?

> Carmichael (1983) recognized a variety of fresh water depositional
> environments, including stacked channel fills, proximal and distal
splays,
> lagoonal facies, lake deposits, etc. Channels and crevasse splays can
be
> recognized from isopachs of the conglomerate and sandstone bodies.
Lake
> deposits contain non-marine Unionid bivalves. None of the above rocks
could
> be deposited beneath an extensive marine floating mat, could they?

The rocks are, from what you said, conglomerate, sandstone and I guess
siltstone. Carmichael then interpreted the rocks to be fills, splays
lagoons and lakes, etc. Now you take Carmichael's interpretation and ask
me if, e.g., a lake deposit could be deposited beneath a floating mat.
The lake deposit - no, but a silt deposit - yes. I am attempting to make
my own interpretation of the data, which is often at odds with the
conventional wisdom. I'm sure we both have seen instances in the
literature where a particular interpretation was hotly debated. I always
try to separate the interpretation from the data, and I usually assume
that there is an alternate interpretation to what may seem quite obvious.

Bill

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Received on Fri Jan 16 00:32:47 2004

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