Eerie shapes athwart microbial layer stacks
 
eerte fingers
The colour of the red chert varieties from the Döhlen basin (Lower Permian) in Saxony is due to the oxygen production of blue-green algae and subsequent precipitation of iron oxides. Depending on the growth mode of the algae, the red stain appears as clouds or stacks of thin layers. Most often everything looks normal but there are rare cases of unexplained phenomena as in Fig.1 where a red hand with five fingers does not only make an eerie sight but also seems to defy any attempt at an explanation. The fingers are certainly not brought about by disintegration of the layer stack as it is observed sometimes in cases where the vicinity of the layer stack was still fluid. (Compare Permian Chert News 8.)
The crack on the right
went straight through the stack as if it were an isotropic material. The crack tip obviously came upon certain position where the mechanical anisotropy of the stack was dominating so that fracture mechanics caused the crack to make a sudden kink. Later on, the crack got a thin red lining and a fill of clear chalzedony which appears dark now. This crack is not helpful in connection with the mysterious structure.

Fig.1: Mysterious finger-like structure superimposed on a stack of thin microbial layers.
        Picture width 7mm, same scale for all pictures.
eerie claw

Fig.2 (left): Similar as Fig.1, evenly spaced "claws" seen as if grabbing a bent stack of layers. 
Picture width 7mm.

Fig.2 provides additional information. The path of the long crack in the middle, ending below, had not been influenced by the presence of layers, hence it must have propagated at an advanced stage of silicification when the silica gel had become rather stiff. Later the crack healed by getting filled with clear silica gel, hence the dark aspect. By that time, the mysterious sructure had not yet been there, otherwise it would have been parted by the crack. It cannot be explained as late cracks filled with red substance since there are no displacements.

Fig.3 (right): Mysterious thick-walled bowl, unaffected by the microbial layers,
with 3D-aspect.  Picture width 5.5mm. 
mysterious bowl
Not only branching structures as in Figs.1,2 but also simple ones may give rise to awe and wonder as they make an otherworldly sight. In Fig.3, "this world" is made up of the usual yellow-stained microbial formationes in clear chalcedony, floccules below and sheets in stacks seen as parallel lines in cross-section, partially crushed at some stage of silicification, while a bowl-shaped body seems to float there ghost-like, penetrating everything. Part of its wall is seen extending into the depth, which provides a 3D-aspect.eerie shell

Fig.4 (left): Thin red shell among yellow-stained microbial layers in clear chalcedony, with 3D-aspectPicture width 5.5mm.

Unlike the red formations in the above images, the shell in Fig.4 is thin, 30-50µm (not seen with this illumination). The edge seen here is not a cut edge all along. There is a definite natural edge
of the shell, seen here only below left where it dives down behind microbial layers. The visual 3D-impression is enhanced by several stained layers in clear chalcedony on the left touching the red shell behind.

The enigmatic structures of the types shown here seem to be rare phenomena in the red Permian cherts from Saxony. Only a few more have been observed and recorded, and not much can be said about their possible way of formation. Apparently, oxygen and dissolved iron had moved through the solid silica gel by diffusion. No explanation can be given here concerning their precipitation as red hematite in definite sheets, branching or not, athwart existing structures.
Samples:
Old fragments of chert layers found in glazial river deposits at Hänichen and Wilmsdorf, Döhlen basin, Freital near Dresden, Saxony.
Labels: H/248.2 (1.8kg, 1999), H/375.1 (12kg, 1999),
W/8.2 (1.1kg, 1990),  H/333.1 (4.65kg, 2001).

H.-J. Weiss      2018
Scolecopteris pinnule cross-section, Sardinia Permian Chert News 18

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