Florissant Preservation, some original remains?

[Paleome]

As I slowly work through the paper shale ( diatomaceous tuffaceous shale) of the Florissant Formation, I wonder if some of the remains might be original, and not mineralized. 

 

As I understand, the original lake was full of diatoms, microscopic algae with siliceous shells (frustules).  There were numerous volcanic events in the area, contributing to the enrichment of this lake water with dissolved silica.  Diatom and bacterial activity are thought to be prime reasons for such magnificent preservation.  That is, stressed diatoms are known to secrete thin mucus mats composed of a polysaccharide slime, wherein insects and plant materials were trapped at or near the surface of the lake, and sealed into a protective coating, preventing rapid decay.  Bacterial colonies may have also contributed mucus to these mats, which eventually sank to the bottom of the lake and became buried by another layer of ash-clay.  This continued, over and over again, flattening remains and leaving two types of preservation.  Where there was significant decay, we find imprints.  Others compacted and decayed even more slowly to leave a residue of carbon behind; these are known as compression or carbonization fossils.

 

I see something more, however.  It looks like the original chitin of the insect and arachnid bodies, shiny and clear.  Also, in the twigs and fragments of wood preserved in the paper shale, I frequently see brown or black pieces of soft, spongy, cork-like woody material.  This does not appear to be mineral in nature, but decayed wood.  Is this actually what it is, or is it just a form of carbon?

 

Usually, many fossils have been completely mineralized and turned to stone, but these seem different.    Can anyone here explain to me what I am seeing, and why?

Thank you, Debra