Eerie shapes athwart microbial layer stacks  (6)
deutsche Version
eerie shapes and cracksAlthough the fossil shapes called "eerie" here are not a well-defined group, it is tried here to set them apart from the more conventional shapes encountered in cherts. 
The shapes considered here
  -  are of various appearance: red-stained bulky clouds, thin red sheets,
        or anything in between,
  -  had formed later than the conventional shapes in cherts,
  -  had formed mostly (but not always)
        in disregard of pre-existing structures,

Fig.1: Red chert (Permian) with features resulting from quite different processes: red cloud penetrating thin sheets from microbial layer growth, large early cracks in the layer stack below right. 

Like the conspicuous red shapes considered before ( Permian Chert News 18, 27, 28, 36, 37 ), the one in Fig.1 is enigmatic since it does not indicate a possible interpretation. Its outline is partially well-defined and smooth but fuzzy elsewhere. One part of the boundary on the left fits well to the stack of layers as if one of the layers or the space between them had acted as a diffusion barrier against the spreading red stain. An outgrowth emerging upwards from the big red shape might be analogous to a lateral outgrowth from a red front in 27 (there below in Fig.2). This possible analogy, however, does not provide an explanation for the spreading red stain.
Likewise unexplained remain the rug-like formations, seen in Fig.2 mostly as narrow sections. Possibly, some dissolved iron compound was guided by means unknown along curved sheets, oxidized, and precipitated as fine-particle hematite which makes a strong red colour even with tiny volume fraction. Since diffusion alone would make diffuse outlines, the sharp outlines seen here must be due to a quite different process which has not revealed itself. 
eerie shapes across sheets
Fig.2: Red chert (Permian) with a stack of stained microbial sheets traversed by apparently immaterial rug-like formations, 
(Image width 7mm, same scale as Fig.1.)

Apparently the formation of the red rugs was neither affected by pre-existing structures nor by mutual contact.
Either picture shows very narrow brittle cracks as late formations in the hard chert. Something else in Fig.1 is quite different. The stack of microbial layers had been fractured well before final silicification, as seen from the curvature of the layers in the fragment which must have been turned upside down. Obviously, the red outgrowth of the cloud grew later.
Other evidence of fracture at an early stage of silicification is provided by the wide cracks below right in Fig.1. By comparing the layer pattern on either side of the crack, the expected lateral displacement becomes evident. The absence of displacements on either side of large red stripes as in 36 shows that there were no wide cracks involved.
This contribution continues the series of eerie shapes without getting closer to an explanation.       
H/375.1 (1999) and  H3/102 (1995), old fragments of a Lower Permian chert layer, found among glacial river deposits at Hänichen,
    Döhlen basin, Freital near Dresden, Saxony.

H.-J. Weiss      2022

Scolecopteris pinnule cross-section, Sardinia Permian Chert News38
Site map
Permian Chert News
Permian chert