Eerie shapes athwart microbial layer stacks
deutsche Version
eerie fingers

The colour of the red and yellow 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  stain appears as clouds or as 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 while still in a fluid state, as observed occasionally. (See Permian Chert News 8.)

Fig.1: Mysterious finger-like structure penetrating a stack of thin microbial layers, picture width 7mm.

The crack on the right went straight through the stack as if it were an isotropic material until its tip reached a 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.
eerie claw
Fig.2 (left): Similar as Fig.1, evenly spaced "claws" seen as if grabbing a bent stack of layers. 
Picture width 7mm, (same scale for all pictures).

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 turning into chalzedony, hence the dark aspect. By that time, the mysterious sructure had not yet been there since it had not got split by the crack. It cannot be explained as late cracks filled with red substance since there are no displacements associated with wide cracks.

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 as in Figs.3,4 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 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. Their precipitation as red hematite in definite sheets, thick or thin, branching or not, athwart existing structures, must remain enigmatic here.
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, 1992 ?),  H/333.1 (4.65kg, 2001).  The weight refers to the undivided samples.

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

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