Eerie shapes athwart microbial layer stacks  - (2)  
deutsche Version
red streak defying explanationThe eerie shapes presented in Permian Chert News 18  seem to defy any explanation, hence they may give rise to awe and wonder. More of such are shown here. One of them is the red streak in Fig.1. Obviously it had not been a wide crack since the horizontal microbial layers are seen to go right through, without being disrupted. The read streak does not only cross the layer stack but an old crack, too. Its sharp tip and smooth flanks indicate that it propagated when the layer stack was an elastic homogeneous body since its propagation was not affected by the layered structure. It seems to have been silica gel with a crack filled with water enriched with dissolved silica which enabled the crack to "heal". Later, the layer stack and the healed crack became traversed by the mysterious red streak.
Obviously, the crack and the red streak behaved quite differently with respect to the layer stack. The layered structure appears mechanically irrelevant but important for diffusion: The bright red had spread for a short distance along the layers on either side of the streak.
It is well known that stains may diffuse through hard chalcedony but possibly
the aspect of  Fig.1 had formed at an earlier stage while everything was still gel-like. It appears that Fig.1 has not brought us nearer to an explanation of the eerie shapes, and this may also apply to Fig.2 and Fig.3.
eerie shapes

Fig.1 (above): Microbial deposits
traversed by crack and mysterious streak.
        Image width 3.5mm.

Microbial layer stack interfered with enigmatic phenomena
        apparently mediated by diffusion.
Image width 8mm.

Fig.3 (below): Indistinct layer stack with early and late cracks and with diffusion effects.

        Image width 8mm.

microbial layers

It is hard to imagine how the wondrous aspect could be brought about by diffusion. Among the confusing 
structures, small details are clearly due to diffusion: the bleaching along the late cracks in Fig.2, and the bleaching and colouring around the crack tip in Fig.3 below right. Hence, one can assume that everything except the microbial structures and the cracks is mediated by diffusion but one cannot tell how diffusion could have produced what is seen here.
The layer stack in Fig.3 seems to be inclined agains the cut plane so that the layers appear indistinct and far apart. It had been broken off on the left while still soft. Another early crack, with wide opening and filled with bluish chalcedony,
runs across the stack but not farther, which shows that the stack had been elastic
while the surroundings had been fluid. Two late cracks with very small openings in Fig.3 run beyond for a short distance, which shows that the stack and the surroundings had been solid and hard when they formed.
Also it can be asssumed that the cracks are due to shrinkage stress arising when the stack hardens and shrinks faster that the surroundings. Several other cracks of finite length but short compared to the height of this chert sample of 24cm are due to inhomogeneous stress of unknown cause, like the crack of 6cm length whose tip is seen in Fig.3 below right and has been mentioned above.
Sample: H/375.1, old fragment (12kg) of a Lower Permian chert layer, found in 1999 among glacial river deposits at Hänichen, Döhlen basin, Freital near Dresden, Saxony.

H.-J. Weiss      2020

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