Eerie shapes athwart microbial layer
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
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
Fig.1: Mysterious finger-like structure superimposed on a stack of thin
width 7mm, same scale for all pictures.
Fig.2 (left): Similar as Fig.1, evenly spaced "claws" seen as if
grabbing a bent stack of layers. Picture
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
Fig.3 (right): Mysterious thick-walled bowl, unaffected by the
microbial layers, with 3D-aspect.
Picture width 5.5mm.
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.
Fig.4 (left): Thin red shell among yellow-stained
microbial layers in clear chalcedony,
with 3D-aspect. Picture
the red formations in the above images, the shell in Fig.4 is thin,
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.
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
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).