Re: Sulphur, Forams and Partings in Coal

From: Kevin Sharman <ksharman@pris.bc.ca>
Date: Mon Jan 05 2004 - 00:48:50 EST

Hi Bill,
  ----- Original Message -----
  From: Bill Payne
  To: ksharman@pris.bc.ca
  Cc: asa@calvin.edu
  Sent: Saturday, January 03, 2004 9:39 AM
  Subject: Re: Sulphur, Forams and Partings in Coal

  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 replies} Please describe a mechanism for accumulating mats of peat hundreds of feet thick in the pre-flood timeframe, which I understand to be a few thousand years, using modern rates of peat accumulation which you quoted on Nov. 28, 2003:

   

  (snip) "On your web site you mention the Supardi et al article, which states rapid peat accumulation was 4-5 mm/yr, and a lesser rate was 2 mm/yr in the
  Indonesian peat swamps. At the most rapid rate of 5 mm/yr, it would have
  taken 30 years to form six inches of peat.

   

  If you are contending that peat accumulated more rapidly in the pre-flood era, please support this with evidence.

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

  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.

  {KS replies} Bill, I asked you to explain the interseam sediments: (snip) A fresh
> water floating mat model would have to account for the lateral extent of
> these coals (230 km X 90 km = 20,700 km2), deposition of the interbedded
> sediments (65 m to 90 meters thick), and the multiple seams (8 seams, 0.5
> meters to 10 meters thick).

   

   Are you contending that the interseam sediments (up to 30 meters thick between seams) are turbidites?

   

  {KS replies} As I've said before, thin widespread partings are hard to explain with either model. I have pointed out that the top surface of a floating mat deposited peat would not be smooth. The top surface of the parting in your model would have soft sediment deformation features from the next layer of veg material landing on it, wouldn't it? As far as I know, we don't see these in partings. Or are you contending that the parting was lithified prior to depositing the next layer of veg material?

  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 replies} This supposition is unsupported and far-fetched. However, far-fetched explanations can be plausible if backed up with evidence.

  [KS] 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.

  {KS replies} Sorry, Bill, it's the best I have.

  I noticed that you have not answered my question about how you would dilute the seawater underneath a floating mat to produce a low sulphur coal. Are you still thinking about it?

  Kevin
Received on Mon Jan 5 00:49:45 2004

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