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In a message dated 99-03-03 09:14:50 EST, you write:

      Shale (mudstone or any other variant) is nothing more than an
 agglomeration of clay-sized particles of clay minerals (phyllosilicates).
 True, black shales are generally bear a certain percentage of organic
 residue.  But only a very small amount (less than 1%) is required to turn a
 shale black (see any petrology textbook authored by Harvey Blatt).  A qual.
 scheme of the Pierre Shale might look some like - 97% clay minerals, 1%
 silicate minerals, 1% calcareous nannofossils, and 1% organic hydrocarbon.
      Truly "organic-rich" shales are sometimes referred to as oil-shale,
 and contain perhaps 3-4% hydrocarbon.
      There is absolutely no evidence of which I am aware to support the
 notion of a kelp choked seaway.

   This is a reply I received from a friend deeply involved in seaway studies.
I hope it's informative. Dan Varner.