Re: Canadian Coal - depositional setting

From: Kevin Sharman <ksharman@pris.bc.ca>
Date: Fri Jan 16 2004 - 18:20:30 EST

----- Original Message -----
From: "Bill Payne" <bpayne15@juno.com>
To: <ksharman@pris.bc.ca>
Cc: <asa@calvin.edu>
Sent: Thursday, January 15, 2004 10:18 PM
Subject: Re: Canadian Coal - depositional setting

> 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.
Congrats again. I figured you were catching up from that.
> 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?
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.
You are
> making a good case here for transgression, but transgression will fit
> either model.
Bill, progradation is regression, not transgression. There is a relative
lowering of sea level as you go upsection. I would give you the benefit of
the doubt and call your comment a typo, but I see you've repeated it below.
> > 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.
The dating info was an aside, as I mentioned, and is not central to my
argument.
> 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;
It's a regressing shoreline; see above.
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.
 Coal does not occur in isolation. One must look at the coal itself AND the
context of it.
>
> > 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.
No, it's based on published alleged duration of the Flood, measured
thickness of sedimentary rocks, a reasonable estimate for peat to coal
compression (based on evidence from coal balls) and your floating mat
speculation.

> > 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.
Nope. Go to a modern beach and look at how long thin objects like sticks
are oriented - horizontally to sub-horizontally. Look at the post I made
quoting Carmichael about the horizontally oriented log impressions at the
top of D seam. Your explanation for vertically oriented roots in the photos
is that waterlogged roots hung vertically while sand settled around them.
(snip) Dec 1: "Rather, as the roots settle out the sand settles around the
roots." and (snip) Dec. 4: Tree trunks get waterlogged at the root end
first and rotate from a horizontal to vertical floating position, and then
with continued
waterlogging sink to the bottom, and maintain their vertical orientation
while being buried. I am suggesting that roots may do the same thing,
i.e., float vertically to the bottom and get buried."

 I contend that this would not happen in a high energy environment like a
beach sand. Roots would be expected to be oriented ~horizontally. So the
beach sand model has predictive power based on observed modern examples. The
> branching upward of some roots,
I thought you backed off on this line of argument on Jan. 2: (snip)
"Therefore, I'll back
off my statement that roots don't branch upward - they usually don't. I
suppose you and Glenn win that one. :-)"
the common plane of termination of some
> roots,
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.

>and the odd, isolated tree root (if it's in situ, where are the
> rest of the roots of the supposed root ball)
We discussed this as being due to roots moving in and out of the plane of
the rock face.
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.

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.

> > 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?

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?
> > 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.
Bill, I live in a small town of 3000 people, an 8-hour drive from the
nearest university library. Very few of the references that I have quoted I
had on the shelf. I got them the hard way - calling favors from friends in
the city, bugging the company librarian, etc. Some are online - try
http://www.em.gov.bc.ca/Mining/Geolsurv/Publications/default.htm for BC coal
info, especially in the "Geological Fieldwork" link. I will send you or
post the Carmichael thesis abstract, but the thesis itself is 300 dogeared
pages, and I'm not photocopying thatJ Try the University of British
Columbia.
>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.
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!
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.
>
> Do you have a photo of the "strong" root bioturbation?
There is a photo in the thesis captioned "root penetrated sandstone" - looks
about like my photos.

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

> > This depositional setting for the Gates coals (coal on shoreface
> > sand) is not unique.
> 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.
You bet. The Mist Mountain coals in SE BC are being mined at the rate of 25
million tones/year, but industry geologists have their hands full with day
to day stuff. Plenty of mine faces but little time.
>
> > 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?
See below on isoapachs of conglomerate and sand bodies. These thicken and
thin rapidly and are linear. Glenn has also posted examples on his site.
>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.
Bill, rocks don't talk. The evidence must be interpreted. How do we
geologists do this? We look for distinctive features in these rocks and see
if we can see them in other settings, both ancient and modern. Before you
start with the "dogmatic uniformitarianist assumptions" argument, let me say
this. The degree of objectivity one can bring to an interpretation depends
on the degree to which one can suspend one's pre-conceptions. So, let's
suspend away..

If we look at the Gates interseam sediments and recognize a pattern of
features like stacked sandstone bodies, linear patterns of conglomerates and
sandstones, fine grained mudstones with bivalves, etc. (the description),
AND we can find specific modern environments that show the same features,
the simplest explanation is that the ancient environment was similar to the
modern one (the interpretation). If we see that the features in Gates
interseams (description) do not match up with modern deposits from turbidity
flows (description), then the simplest interpretation is that they were not
formed by turbidity flows (interpretation). I think the above reasoning can
be independent of pre-conceptions.

 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!

Bye for now,

Kevin
Received on Fri Jan 16 18:21:36 2004

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