Miniature fossil sewage tank
deutsche Version

Sewage treatment, of course, is not an invention of Man. So it should not be surprising to find some fossil evidence of this process but it would be difficult to recognize it as such. Hence, what may be regarded as a fossil model of a sewage treatment tank, nicely shaped as a tiny sphere as seen in this image, deserves closer inspection.
chlamydospore with microbial floccules
The spherical tank is a "chlamydospore" of one of several fungus species preserved in the Lower Devonian Rhynie chert. Chlamydospores are not analogous to the dust-like spores known from mushrooms. They grow on the filamentous fungus hyphae and are
filled with reserve stuff which enables them to outlive the hyphae in case the latter die and decay. In some samples the fossil chlamydospores are found in several sizes corresponding to the species, often not quite spherical, and occasionally numerous. Most often they are no more attached to a hypha. Hyphae without chlamydospores are a common sight in the Rhynie chert (see Rhynie Chert News 77, 78) but rare in other cherts. 
The chlamydospore seen here is an exceptionally big one, diameter
0.75mm. Possibly it died before new hyphae could grow from it, and the organic substance inside decayed and turned into "sewage". The overall aspect suggests that microbes had grown inside and clustered into floating floccules similar to those known from sewage treatment plants.
Apparently, iron ions from decay products formed oxides which settled on the floccules, thereby staining them yellow and red. The heavier floccules, preferably the red ones, sank to the bottom before all got fixed by the formation of silica gel. Gel formation was facilitated by diffusion of dissolved silica through the wall and favoured by the lower pH caused by the decay products inside.
The subsequent progress of silicification seems to have followed the usual path: more diffusion of dissolved silica into the gel making the gel stiffer and causing the water to diffuse outward until the present state of translucent bluish chalzedony had been reached.

Finally it be mentioned that the probabilty of finding 
a big fossil chlamydospore like this one, colourful and incidentally cut into halves, is extremely low.

Sample: 0.55kg, found by Sieglinde Weiss
in 2014.

H.-J. Weiss       2015

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