Re: Sulphur, Forams and Partings in Coal

From: Bill Payne <bpayne15@juno.com>
Date: Sat Jan 03 2004 - 11:39:34 EST

On Tue, 30 Dec 2003 21:21:24 -0700 "Kevin Sharman" <ksharman@pris.bc.ca>
writes:

[KS] Please describe a modern example of an ecosystem which, when ripped
up, could produce a peat mat hundreds of feet thick (actually you would
need one thicker than that to produce the thicker seams in the geologic
record). If you are claiming that "things were different back then",
please back this up with evidence.

[BP] The peat mat would have formed in situ first, accumulating thick
deposits of peat, which would be lifted into suspension as a unit by
flood water.

[KS] Please describe the mechanism for depositing this sediment beneath
the mat.

[BP] “…the Herren ‘blue band’… parting of blue gray clay…generally ranges
from 1 to 3 inches in thickness and lies a little below the middle of the
coal. In most parts of Illinois there is an additional parting averaging
inch thick 6 to 10 inches below the blue band, and at many places a
minute dark shale or clay parting averaging 1/8 inch is 1-1/2 to 2 feet
below the top of the coal. 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. A principal problem to
explain in any case is how the forest vegetation of a swamp could be so
completely levelled as to permit accumulation of a continuous layer of
clay averaging an inch or so in thickness. If one argued…for an
allochthonous origin for the coal, the vast known extent of these and
other coal beds would make such an interpretation impossible…for there
would be no available source for the vegetation whose detritus was to
cover such vast areas.” (Wanless, H.R.,1952. Studies of field
relationships of coal beds. In: Second Conference on the Origin and
Constitution of
Coal, 164-167, 172-173)

I think the general "in situ" consensus is that these partings in the
Herren coal of the Illinois basin are overbank deposits. Of course this
explanation doesn't address the lack of stumps, which Wanless
acknowledges, nor does it address the lack of roots from the overlying
coal. With the floating-mat model I would think the best explanation for
thin, widespread partings is a turbidity flow. I understand that the
Blue Band parting is thicker near a paleochannel and thins away from the
channel. So my explanation for the parting is that the turbidity-current
flow followed the paleochannel and overflowed the banks to spread out
from there.

This explanation is OK for waterborne clastics, but is a bit strained
when applied to volcanic-ash falls. I suppose the volcanic ash could
fall on adjacent open water and then drift with currents under the
floating mat.

[KS] Carmichael (1983) in his thesis on the Gates Fm. describes the
contact between the top of the D seam (the uppermost thick seam in the
Gates) and the overlying unit, which he calls facies 1A. “lithologies
consist of fine to granular sandstones and conglomerates…the base of
facies 1A is abrupt or erosional…the basal surface is planar and locally
channeled…groove marks and impressions of small wood fragments or large
logs are common near the base and along the basal surface…vertical log
impressions up to 2 meters high are present in coarse to granular
sandstones at the base of facies 1A…. their vertical orientation and
position directly above the D coal seam suggests that they represent tree
trunks in growth position.” (p. 136, 143). This facies is interpreted
as an estuarine channel fill with tidal influence.

This evidence supports the idea that most standing trees at the top of
the original peat were flattened due to a high energy transgression of
the sandstone/conflomerate of facies 1A, with some trees left standing.
This depositional evnirinment would not be conducive to vertical
emplacement of waterlogged transported tree trunks like the Me. St.
Helens analogue.

[BP] Based upon what you've presented, I'm inclined to agree. However,
I'd like to see some photos and more detail. This sounds like an
interval between the Mary Lee and Blue Creek coals in Walker County,
Alabama which has a number of vertical stumps and was described by Demko
and Gastaldo: "Sedimentological and biostratinomic features of the Mary
Lee coal to Blue Creek coal interval are used as the basis for the
interpretation that sediment loading and compaction of buried peat
controlled the alternation between peat mires and clastic swamps, and the
stacking of the clastic swamps." (Demko, Timothy M. and Gastaldo, Robert
A., 1992. Paludal environments of the Mary Lee coal zone, Pottsville
Formation, Alabama: stacked clastic swamps and peat mires, International
Journal of Coal Geology 20, abstract)

A later study showed that the tree trunks overlap, and one vertical trunk
spans several "stacked clastic swamps." Things aren't always what they
first appear to be.

[KS] See above. The trees can be flattened, and the peat surface
bevelled, by the influx of water and sediment. Also, as you mentioned,
the top of the peat may not have had trees growing on it. Succession of
the peat community from a forest swamp into open grass marshes has been
proposed in the literature, aided by wildfire.

[BP] This succession seems to put an undue strain on the data - partings
are common and the coals don't appear to change as a parting is
approached from below.

Bill

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Received on Sat Jan 3 00:09:09 2004

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