[Rockhounds] salmon creek WA

[Thomas Yancey]

That is a key question and is the reason that the debate continues.

  In a sediment containing carbonate shell, siderite cements the 
sediment like any other cementing material, but in sediments with 
large amounts of organic plant debris, siderite acts as a replacement 
mineral instead of a cementing mineral. The Salmon Creek strata 
contain large amounts of wood and there are many layer of 
peat/lignite in the section.

There has to be a series steps in the siderite replacement process, 
between the complete replacement reaction to the simple cementing 
action. The famous Mazon Creek concretions are formed of siderite. In 
those nodules the siderite retains a good outline of the external 
form of the fossil and sometimes retains phosphatic skeletal 
material, but not calcium carbonate.

All that is needed to preserve the perfect shape and form is very 
rapid mineralization of the surface of the feces.  This is possible. 
The great fish concretions from Brazil formed very rapidly and in 
some cases the mineral replacement was so fast the soft tissue of 
arthropods and fish was replaced with mineral. There are well 
documented instances in those concretions of muscle fibers in the 
bodies of fish being replaced by minerals. (phosphatic mineral, not 
siderite)

Tom Yancey



>If really coprolite (feces), under what circumstances would they  be remain
>in such perfect shape and form as they became siderite concretions, 
>but at the
>very same time no fossil bones, turtle shells, fish, etc. are  found
>associated with these?
>
>Rich.
>

-- 
Thomas Yancey