Response on coal

From: James Mahaffy (
Date: Thu Aug 15 2002 - 14:43:13 EDT

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    I don't really have time to do a lot. I do like the way you
    respond. You did better than I thought you could, but it is still to
    broad and I think fails when you try and apply the model to the

    > On Mon, 22 Jul 2002 17:59:50 -0500 James Mahaffy <>
    > writes:
    > > 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.
    Still think this is a bit of a problem. If you are going to make the
    organics coming from the floating mats, how come the Black shale (higher
    in organics) has generally no plant fossils while the gray shales that
    are usually immediately above the coal have a lot nice compressions.
    > > 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
    > some
    > > 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
    > than
    > > 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
    > in
    > > 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.

    Not bad (I really am impressed by the attempt), but still flawed -
    perhaps fatally. IF your model is right then it would appear as a down
    cutting channel. While they do exist this one ws not. You need to have
    your turbidity current to be present while the vegetation mat is being
    deposited. You also need to explain why the Herrin coal thickens to
    about 6-8 feet on the flanks of the channel while more distantly it is
    much thinner (about 4 feet). The data on this is excellent (ISGS coal
    section mapping).

    Also would a turbidity current cut down through coal. It is fairly

    > > 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.


    > 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.

    Your model forces you to something like this but often it is not the
    dominant spore that differs and I would think with different vegetation
    mats you would be more apt to get a lot of spores out of place and not
    found only lower or higher in the coal section.

    > 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;

    This is just not true. Yes historically at one time this was thought to
    be true and is still true of some coals or in some places. But their
    are clearly many that do have Stigmaria rootlets in the underclay. When
    I was at the University of Illinois I glanced at all the MS and Ph.D.
    theses and a number dealt with this problem. The lack of roots in many
    places may still be something not easily explained but it in a number of
    places their are rootlets penetrating the underclay. Bear in mind too
    that lycopod roots are different than angiosperm roots so they may have
    had difficulty penetrating some harder substrate. However they do a good
    job of penetrating rotting vegetation as is clearly demonstrated in
    preserved peat in coal balls where the vegetation where stems are often
    full of rootlets that have grown into them.

    > B) General lack of either tree stumps or roots in partings;

    In at least the "Blue Band" Not sure it is generally true.

    > C) General lack of vertical tree stumps/trunks in the sediment overlying
    > coal seams;

    Too broad a statement. I brought back a big stump from a coal (probably
    the Black Oak coal) near Pella. It was sitting right on top of the
    seam. There was a second one (obviously sigillaria) that also appeared
    to be sitting on the top of the coal and extending perhaps 20 feet up
    into the siltstone. I also believe both Bill DiMichele and Aureal Cross
    describe areas of coal seams where there are numerous upright casts
    right at the top of the coal.

    Remember in underground mines you would never see them.

    > D) General lack of change in total coal seam thickness between areas
    > containing splits and those that contain no splits;

    Not true at all of the Herrin. It is much thicker in the vicinity of the
    Washville channel.

    > E) Commonly extensive, continuous nature of thin partings;

    Grant you that one.

    > F) Generally consistent thickness of coal seams draped over
    > contemporaneous slopes.

    Only is some cases. Some coals in Illinois are widespread and fairly
    universal in their thickness but there are others that are restricted to
    topography. Only deposited in lows. The assumption is that the
    widespread coals were deposited on a flat floodplain. In other words
    sediments deposited before the coal flattened the topography. But I
    would have to refresh myself on the specific stratigraphy before I went

    James and Florence Mahaffy    712 722-0381 (Home)
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