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>      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
> shale black (see any petrology textbook authored by Harvey Blatt).  A
> 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
>I hope it's informative. Dan Varner.

I've read that some black shales (eg Kimmeridge Clay Formation) are so
organic rich (up to 20%TOC in some places) due to terrigenic inputs and not
due to any kelp/seaweed. I believe this conclusion was reached by
correlating abundance of terrigenic palynomorphs with TOC.

In the case of the KCF I have only come across one (from the late 19th
century) reference to a plant fossil and that was an algae called _Caulerpa