Eerie shapes athwart microbial layer stacks  - (3)  
deutsche Version
eerie shapesA certain type of silicification phenomena in cherts from the Döhlen basin have been called "eerie shapes" for their puzzling appearance: Permian Chert News 18 and 27 . In view of the present lack of a reasonable explanation it is hoped that more pictures will lead the way to understanding. 

Fig.1: Stack of microbial sheets
stained with hematite deposited as a result of oxygen production of blue-green algae as known from the "banded iron formation", much later superposed by hematite of unknown origin and in enigmatic shapes. Image width 3.5mm.
From the obvious fact that the red shapes in Fig.1 are not affeced by the layered structure
of the stack of microbial sheets it can be concluded that they formed much later when the stack had become rather homogeneous by thorough silicification. Likewise it is obvious that the big enigmatic shapes did not at all interfere with the delicate sheets.
The red shapes must have emerged at a late stage of chert formation, judging from traversed brittle cracks.
Some of the enigmatic shapes may mislead the observer into the assumption that they had been cracks: The branching shape in Fig.1 looks like wide cracks in gel but this impression is immediately dispelled by the shapes seen above. eerie shapes
Occasionally the enigmatic red shapes are seen as closed loops on the cut planes which possibly indicates that they are really closed bags, like the small one in Fig.1 and the big one in Fig.2. The red circle in Fig.2 seems to be a different enigma, not found anywhere else.
Fig.2: Stack of microbial sheets apparently enclosed in a red bag;
        tree fern root wall tissue (above) superposed by an enigmatic red circle
        Image width 3.5mm.

Fig.3 (below): Microbial layer stacks, bent and deformed by lateral compression, superposed by enigmatic shapes with bulging bags and cut-off ends unrelated to the underlying structure.
Image width 4.3mm, same scale as above.
eerie shapes

A bag-like structure is also seen in Fig.3 at either end of the enigmatic red shape: a bulging one on the left and a narrow one on the right. The layers or sheets of stained microbes are not horizontal here because the stack had been deformed by
lateral compression so that it became bent upward and the individual sheets became wavy. The 3D-aspect offered by the clear chalcedony reveals another enigma: a wide gap in the red shape (below right). There is no indication that this gap has been brought about by a crack. It seems to be only a strip without stain, extending into the depth.
Still more enigmatic is the sudden end of the bright red streak above left.

It appears that also Part 3 of this series, instead of contributing to understanding, offers additional enigmatic features of the shapes that seem to be not related to underlying structures: closed bags in Figs.1-3, a circle in Fig.2, and cut-off ends in Fig.3.

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

Scolecopteris pinnule cross-section, Sardinia Permian Chert News28

Site map
Permian Chert News
Permian chert