From: Bill Payne (email@example.com)
Date: Mon Aug 12 2002 - 00:11:46 EDT
On Mon, 22 Jul 2002 17:59:50 -0500 James Mahaffy <firstname.lastname@example.org>
> In my first point of my last post, I asked, "Is the model of rafted
> any better for explaining a sharp contact between coal and the clastic
> layers?" And you responded with Steve Austin's model of vegetation
> raining down organics and then as the water rose and the organic mat
> moved landward getting clastic sedimentation from the open water.
> Thanks for explaining the model but I see a few problems. Why would
> this result in a sharp transition and not a gradual transition at the
> top of the coal?
Maybe I misunderstood what you were asking. I thought you said the
floating-mat model couldn't explain a gradual transition from coal to
black shale. I was trying to show that Austin had explained that with
> Mind you sometimes there are more clastics in the
> upper part of coal seams but not that much. Also this ought to
> generally result in a dark shale immediately above the coal. While it
> differs in different areas, both the Herrin and Springfield Coals and a
> number of others have a grey (low in organics) non-marine shale right
> above the coal and then a marine back shale above that. It seems that
> Austin's model should have these reversed.
Is the "grey (low in organics) non-marine shale right above the coal"
similar to the Blue Band? If so, the mechanism for placement of the grey
shale may be similar to what I describe below for the blue band.
> You are right that the widespread "blue-band", which is apparently NOT
> volcanic ash is quite an amazing feature. If you believe Wanless (and
> you should), you can trace it in the Herrin for maybe several hundred
> miles and it is usually the same thickness and at about the same
> position in the coal seam [I think it is in his 1961 reference below,
> but I would need to check to be sure]. And yes the contacts at the top
> and bottom are usually sharp and planar, but as Dave Campbell noted in
> recent post the compression associated with coalification should
> decrease the irregularity of the surfaces.
Compression during coalification only works on organics, not on clastics
after they become grain-supported. I have seen a vertical
sediment-filled tree trunk just below a coal seam subjected to the
horizontal compression that produced the Appalachians. It's
circumference was slightly elongated perpendicular to the axis of
compression (which came from the southeast) due to thrust-compaction of
the sediment. The coal bark of the trunk was much thinner on the sides
in line with the thrust, and thicker on the sides perpendicular to the
direction of thrust. My point is that there was much more change in
relative thickness in the organic bark as it became coal, as compared to
the change in thickness of the sediment during compaction from the
thrust. This would also imply that the sediment was still soft when the
Appalachian Orogeny occurred - the sediment had not yet lithified.
Incidentally, these vertical, elliptical trunks are neat to study, they
are in effect strain gauges in the rock.
Applying this differential compaction to supposed irregularities in the
original surface of the soil (that later became rock) beneath and above
the organics (that later became coal), the question is would compaction
from burial by perhaps several thousand feet of sediment result in an
irregular surface becoming flat? Based upon the observations of
paleochannels in coal seams, it is obvious that where there was a channel
it is preserved, not flattened by compression. I would think that
irregularities in the soil below a coal seam would be better preserved
than those on top of a coal seam, since the soil below the seam would be
compressed less. Peat being compresses 3 to 5 times would reduce the
irregularities above the peat by that same amount. But still,
irregularities above a coal seam would be preserved, just reduced by the
amount of compaction in the organics.
So where does this leave us in considering the blue band of the Herren
Coal seam? As I understand from James' description, and from that of
Wanless, the base of the Herren is flat and has a sharp contact, as do
the bottom and top of the blue band and as does the top of the Herren. I
see absolutely no way that these contacts were at one time irregular and
became plane for thousands of square miles as a result of compression.
Speaking of the blue band and a couple of other partings in the Herren
Coal, Wanless says: "At any rate these partings are traceable through a
belt ranging from 550 miles in linear distance northwest -southeast from
north central Iowa to western Kentucky and 430 miles northeast-southwest
from central western Indiana to eastern Kansas." (Wanless, 1952, p 167)
Regardless of how this parting was formed (aeolian or aquatic), it
captures the topography of the top of the organic surface at the moment
of deposition. If this was a swamp, where are all of the vertical trees
that were supposedly growing in the swamp? If there had been trees
growing in the swamp, they would have been preserved (at least the base
of the trunks) in the partings. The absence of the trunks in the blue
band and other partings is evidence that this was not a swamp in the
first place. So James, how do you explain the lack of trees in the swamp
> I am not sure how Austin's
> model explains this widespread clastic pulse. Can you explain it when
> you have a vegetation mat floating on top? Remember it is also low in
> organics (not that black), but you could always I suppose postulate
> oxidation of the organics. For what it is worth, I showed in my thesis
> that the miospores of this band are closer to the coal above rather
> below this "blue band" And then to complicate matters Johnson (1972)
> showed that it seems to thicken as you approach the contemporaneous
> Walshville Channel.
> Which brings me to another point. In the Herrin and in the Springfield
> there are large channel structures that have been mapped and studied
> well enough to be quite sure that they were active structures at the
> time of deposition of the coal. One article on them is by Deb Willard
> the GSA spec paper (#286) on coal forming environments that you have,
> although a latter paper of her's with others in 1995 is more
> comprehensive. How can the channel sediments and their associated
> vegetation be made to fit with the floating vegetation model? While
> obviously the authors did not consider the floating mat model, that
> model, if it is going to compete, must be able to give a reasonable
> explanation for the sedimentation and vegetation patterns. And just to
> complicate matters Peppers has looked at loads of channel samples (of
> the whole seam) and has shown (Peppers in Phillips et al., 1985) in the
> Herrin Lycospora (the spore of one of the dominant lycopods) increasing
> from 65% to 85% near the channel. The same paper shows that a similar
> but more pronounced difference is seem in the samples close to the
> channel in the Springfield Coal. So Bill I really need to know how the
> vegetation model would try (I would not expect it to have worked it out
> as well yet) to explain the features that are interpreted as a
> contemporaneous paleochannel and the associated change in spores in
> the coal.
I envision an organic mat which has settled to the bottom, making a
smooth blanket of organics across the bottom. Then a turbidity current
flows across the bottom, cutting a channel into the organics. Because
the channel flow encounters friction it meanders and overflows the banks
of the channel, spreading a layer of silt or clay laterally for the
distance that the blue band can be traced (thousands of square miles).
The blue band came from the channelized turbidity flow, so it naturally
is thicker near the paleochannel. Since the predominant spores change
from one type below the blue band to those in the blue band and in the
coal above the blue band, then I would assume that there was another
floating mat with a different species of plants, and the spores from this
mat were washed into the turbidity current and incorporated into the blue
band and into the organics which settled over the blue band.
> And then there are the nasty problems like how do you explain
> biostratigraphy to work with your model in the numerous coals in the
> Illinois Basin (Peppers, 1964 and 1970). Some miospores are only found
> in certain coals and their ranges can and are used for the
> biostratigraphy of the coal. That for me was one of the main reasons
> why I find the flood model just unusable. You could ask the same
> of course for invertebrates in the fossil record. I don't think
> differential settling can explain the differences in miospores all
> extracted from coals.
I agree that differential settling due to specific gravity or morphology
explains nothing. I think things were kept segregated as they were
ripped up by water. The waters were choked by debris and there was very
little mixing. Either the different spores came from different floating
mats, or one type of spore absorbed water faster than another and
therefore settled out of suspension sooner. I have either read in
Austin's "Catastro Ref" or heard him say that different species of trees
absorb water at different rates, and therefore settle at different times.
In this way a floating mat of mixed log could produce apparently
mono-species layers of buried trees, since the different species settle
out at different times. However, physical segregation seems more likely
than different settling times from a mat of mixed vegetation and spores.
> Also not all coals are wide and flat in the Illinois Basin. Some have
> patterns that look like they fill lows in the topography. So you have
> to be careful that your model is not formed just from one of these
> widespread coals (Austin studied one of the widespread ones).
I would expect debris to be thicker in the lows. However, I have seen
coal of a consistent thickness draped over what appeared to be a
contemporaneous slope. How do you explain that with your swamp model,
James? Let me give you a specific example to explain.
In A. T. Cross' "The Geology of the Pittsburg Coal" (Cross, 1952) on p
47, Figure 6 shows a sandstone lens in the upper part of the seam. On p
49 is a photograph of the upper split of coal over the sandstone lens.
The text says: "The roof coal is three feet thick and to the left the
upper 12 inches is seen to split off and pass over a sand lens, which at
its thickest is about 10 feet. The upper split can be traced for about
100 yards where it can be seen to rejoin the main roof coal below." How
does this fit in the swamp model?
> Bill, I am really not trying to be hard on you, but the model can not
> used to explain just one sedimentary feature. It has to work fairly
> well for explaining most of what you see in order to be useful. Even if
> you can explain how some of these could be explained in a broad way, it
> would help me appreciate the model. To overturn the paradigm, you
> not only show a few areas where current models lack some explanatory
> power, you must show that the new paradigm work preferably better in
> most areas.
Just to reveiw, I have collected a number of features which I feel are
better explained with the flood model than the swamp model:
A) General lack of stigmarian axial root systems beneath the coal seams;
B) General lack of either tree stumps or roots in partings;
C) General lack of vertical tree stumps/trunks in the sediment overlying
D) General lack of change in total coal seam thickness between areas
containing splits and those that contain no splits;
E) Commonly extensive, continuous nature of thin partings;
F) Generally consistent thickness of coal seams draped over
> And now I have spent most of the afternoon, in between running around
> working on this. But at least I think I showed that I have considered
> and will consider your model but currently do not see it having enough
> explanatory power.
I thiink I have offered reasonable explanations to your objections.
Let's see how you do with the objections I have raised.
Reference: Second Conference on the Origin and Constitution of Coal,
Crystal Cliffs, Nova Scotia, 1952.
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