Permian wood implications: no charcoal, no creatures
deutsche Version

This headline applies to one particular chert sample from the Lower Permian Döhlen basin which had given rise to doubts about details of established palaeobotany, for the following reason: Fragments of black wood in white chalzedony had been interpreted as silicified charcoal at first sight (Fig.1). Palaeobotanists had claimed that not wood but only charcoal would show brittle fracture with fragments as small as those seen here. Erroneous but seemingly reasonable argumentation can cause persistent irritation, hence it must be contradicted. This has been done with detailed discussion in [1].

holes in wood
Fig.1: Permian wood, silicified together with the water where it had lain and become degraded, torn and broken into fragments while soft, with enigmatic holes. Picture width 11mm.

The mistrust raised by the alleged charcoal had spread to the alleged frass galleries and coprolites ascribed to unseen oribatid mites, unknown creatures, or insects. There is a considerable amount of scientific work on the subject, part of which has been discussed and declared erroneous repeatedly until the mites craze apparently waned
Lately, "beetle borings in wood" [2], have newly aroused the curiosity about any holes and coprolites in silicified wood. The alleged coprolites of the (unseen) beetles in [2] look like degraded wood fragments of various sizes and shapes similar as in [1].
The ongoing dispute about damage in petrified wood suggests a closer inspection of this sample, [1].
Conspicuous in Fig.1 are the rough holes in the wood, apparently arranged in a row, incidentally or not. They resemble the orderly row of "beetle borings" in [2].

Fig.2 (below):
Holes of uncertain origin in Permian wood with big and tiny fragments, detail of Fig.1.    Picture width 2.8mm.  Same scale in Figs.2-5.
fossil wood with holes
What is seen here is incompatible with an interpretation as silicified charcoal. Contradicting the above-mentioned argument it can be stated that breaking charcoal would never release cells as a whole as seen in Figs.2,4. A charcoal interpretation is also precluded by the round contour of the big fragment in Fig.1. After lying in the water for some time, the wood had lost its strength so that it deformed easily when torn, and individual cells split off.
Permian wood with holes
Permian wood with holesWhile the charcoal idea is easily refuted here, an interpretation of the irregular-shaped holes seems more problematic. Luckily, a few of them provide indications concerning their nature.

Fig.3 (2nd left): Permian wood with white spot in the tissue, there cells not fused by silicification.


Fig.4 (above right): Permian wood fragments with irregular hole and regular voids in chalcedony from dissolved calcite crystals. 

Fig.5: Calcite crystal grown inside and outside Permian wood without pushing the tissue aside.

The white spot in Fig.3 offers a first clue: The cells with white fill are not fused but rather loose. (They could be mistaken for coprolites by those who would like to find any.) What remains to be done is to offer an explanation of the strange phenomenon of loose cell-size clots amidst solid petrified wood.
A second clue is provided by Fig.4 where one of the enigmatic holes is seen in a small wood fragment surrounded by voids shaped like calcite crystals. Voids left by dissolved crystals are also seen in Fig.1. These observations suggest the assumption that the irregular holes, too, may somehow be related to calcite. This seems to be supported by a third clue, the lucky incidence of one small calcite crystal cut such that it is seen inside and outside the wood on one of the cut faces of the sample: Fig.5.
The observations suggest a tentative explanation based on various steps:
(1) Calcite crystals may grow while Permian chert is forming from silica gel.

(2) Calcite may grow right through the tissue without pushing it aside, as in Fig.5. It can be assumed that the calcite suppresses silicification there.
(3) The affected wood cells become filled with calcite but their walls remain poorly or not mineralized so that the fills may appear as separate cell-size clots, as in Fig.3.

(4) The calcite may dissolve and vanish, as seen in Fig.4 where the crystals have left angular voids in the chalcedony.
(5) Calcite in the wood as in Figs.3,5 may leave a fragile network of cell walls when dissolving, which may collapse and leave big holes as in Figs.1-4.

This tentative explanation of the conspicuous holes in Figs.1-4 may be suitable for critical reconsiderations of wood damage ascribed to creatures. Suspicion concerning the beetle borings in [2] seems justified by the fact that the alleged frass galleries and coprolites ascribed to never seen oribatid mites in several publications by Feng and Rößler have turned out erroneous [3]. The alleged coprolites are mostly cell fills consisting of fungus matter.
By the way, the present contribution indicates another possibility for the formation of cell-size clots which could be mistaken for mite coprolites: It is the deposition of crystalline calcite along with silicification, which may produce an assemblage of more or less loose cells filled with the mineral, as in Fig.3.
As mentioned above, a hole remains when the calcite dissolves. The observed roughly cylindrical shape of the big holes would imply a corresponding arrangement of the deposited and later dissolved calcite. How a cylindrical configuration could be brought about remains an uncertain item in the logic of interpretation.
Despite of some uncertainty, an alternative interpretation of the beetle borings in [2] as a purely mineral phenomenon similar as with the holes in this sample of Permian wood should be considered.
Sample found in 1992 at Wilmsdorf golf course, Possendorf near Dresden; 
kept in the own collection, label W/55, Parts 3,4.

H.-J. Weiss      2020

[1] Fossil Wood News 9 : Permian wood misinterpreted as fossil charcoal.
[2] Z. Feng, ..., R. Rößler: Beetle borings in wood with host response in early Permian conifers from Germany, Paläontol. Z. (July 2019)
[3] Fossil Wood News 16 : Elusive creatures in fossil wood – Clean-up in the wake of a waning obsession.

[4] Fossil Wood News 29 : Alleged fossil wood burrows.

quartz crystal with wood inside
Fossil Wood News  38
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