Re: coal again!

Keith B Miller (
Sun, 18 Apr 1999 16:21:37 -0500

Bill wrote;

>I've never seen a stump sitting upright in the top of a coal seam; well,
>perhaps one which was actually in a ~10-inch clayey-shale split in a coal
>seam. But "the stumps and trunks" which you imagine extending "from the
>top of the coal seam into the sediments overlying the coal" are virtually
>nonexistent. And this is one of the points supporting an allocthtonous
>origin for coal. If these supposed coal swamps were buried by rising sea
>levels, we would indeed observe tree trunks penetrating into the
>overlying sediments. Instead, we commonly see a razor-sharp planar
>contact between coal and the overlying strata. The vertical stumps and
>trunks we do see are suspended in sediment, not connected to coal, and
>without roots in every case I have observed.

The only cases of preserved stumps and trees that I have seen (which are
few) have extended from the top of the coal into the overlying sediment.
In these cases the encasing sediment was of tidal origin.

>How tall are these trees, what is the maximum diameter of the trees at
>the base, and how thick is the vegetation mat?

The trunk diameters are up to a foot perhaps, and the mats are a few feet thick.

>I guess I'll have to remain in the dark for the time being as to what the
>soil microstructure you are referring to is, since you refused to
>enlighten me by answering my request for a description of "diagnostic
>microstructural features" in my previous post.

I have not refused to provide you information, you have declined to read
it. There is no need for you to remain in the dark, unless you choose to
do so. You need to find a basic text on soil science. There is a very
extensive terminology for describing soil microstructures. The basic
elements are cutans (which are various types of coatings on ped
boundaries), voids (which have various shapes, surface coatings and
fillings), nodules and concretions of various mineralogical composition,
mottling and other evidence of alternating oxidation and reduction, and
matrix fabrics (which involves among other things the manner in which clay
minerals are oriented within the matrix). The characteristic
microstructure of the various recognized soil types is illustrated in
Brewer's classic text "Fabric and Mineral Analysis of Soils."

>I do follow what you are saying here, and, as I suspected, you are at
>odds with Gastaldo. I think, maybe you can correct me if I am wrong,
>that it takes perhaps 100 years of swamp growth to supply enough
>vegetation to form one inch of coal. So for the first 100 years of the
>swamp, there is little or no vegetation mat to hold shallow roots, they
>have to root in the soil. I understand that organics compress 5 to 10
>times their volume to form coal, so after 100 years the organic mat is,
>say, 5 to 10 inches thick. Gastaldo says that Stigmarian axial root
>systems penetrate the soil at angles exceeding 30 degrees, so we should
>have at least 100 years of growth with axial root systems well into the
>substrate. And after 100 years of 50- to 75-foot or taller trees rooting
>into the saturated soil, and dead trees falling over and pulling up their
>root balls out of the saturated soil and creating "potholes" beneath the
>vegetation mat (which we also don't see), the soil would be intensely
>rooted and microfine laminations would, in my opinion, be destroyed. As
>I understand your argument, you say that the laminations are preserved
>because the roots never penetrate the soil to any great extent. It seems
>to me that your argument is inconsistent with Gastaldo and with rooting
>structures of trees in modern-day swamps.

Modern trees on saturated substrates do not send down penetrating roots.
There is no need to send down roots for water, and the roots need to have
access to oxygen to respire. Their roots are thus very shallow. It is
likely that the soil features and rooting observed in paleosols underlying
the coals is unrelated to the conditions (climatically, and ecologically)
that existed during peat formation. Coals show vertical patterns in plant
composition during the accumulation of the peat. Plants growing during the
early stages of swamp or marsh development are likely to be very different
from those growing on an accumulating peat. There has been much work on
the paleobotany of carboniferous coals that document the changing species
composition of these environments (again see previous reference list).

Regarding laminations - I have already stated that it takes more that roots
to destroy them. Depositional fabric is destroyed by the turbation of the
soil from both biological activity and the movement of material by wetting
and drying, groundwater fluctuation, and other physical processes. I have
seen many cases of highly rooted soils with preserved depositional fabric.
Furthermore the underclays you and Gastaldo describe are not "intensely"
rooted anyway.

I don't really have anything else to contribute to this discussion if the
only issue you are willing to discuss is stigmarian root systems. My
experience is in recognizing and interpreting paleosol profiles within
non-coal bearing cyclothems of the early Permian (with the much needed
assistance of a soil scientist colleague). To understand the genesis of
underclays (a soil type that I do not have personal research experience
with), will require you to do some extensive reading in the literature. If
you choose not to make that effort, then you will not receive a hearing
beyond this listserve.


Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506