How is shale formed?

[dpear@xxxxxxxxxx (D A Pearson)]

I've been thinking about a problem and I think now I need some opinions
from the men who know.
HOW IS SHALE FORMED?
I realize that first quiet conditions must prevail for the clay and silt
particles to settle.  But if the particles settle and compact in salt
water, why is there no calcium carbonate? As the water is forced out by
compaction under the weight of overlying layers, shouldn't calcium
carbonate precipitate between the particles? What could prevent this?
Temperature, oxygen content, biologic activity (or lack of it), a massive
influx of freshwater, variations in water depth,  what is our best choice
as to how shale forms in the ocean?
For that matter, what causes calcium carbonate to crystallize in marine
water under normal conditions?
Any thoughts and/or references on this matter will be greatly appreciated.


D A Pearson
Omaha, NE

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"...but if many eggs or young are destroyed, many must be produced, or the
species will become extinct."
-Charles Darwin-