Permian cherts
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Fossils preserved in chert are less well known even to people interested in palaeontology. As an exception, the famous Rhynie chert fossils (Lower Devonian, Scotland) are pictured in every palaeontology monograph but are seldom seen as real samples. Fossiliferous Permian cherts can be found at several sites worldwide but have attracted less attention during 20th century. In early 19th century, however, a few pieces of Lower Permain chert called "maggot stones" contributed greatly to the rising interest in fossils and their interpretation. The "Permian Chert News" part of this website is meant to contribute to the renewed interest in the cherts from the classic "maggot stone" location and elsewhere as there are good reasons to assume that they will reveal lots of newsworthy facts.

maggot fern pinnule with sporangia, cross-section
For example, there are cross-sections of fern pinnules in chert samples from Sardinia (Fig.1) which look perfectly like those of the "maggot fern" from cherts of the Döhlen basin, Germany, while some other plant parts in the cherts from the two locations look much different. Observations of this kind contribute to the fascination emanating from fossiliferous cherts. 

While the big Palaeozoic ferns are usually known as two separately fossilized parts: the beautifully silicified trunks often shown as polished round cross-sections, and the often less well preserved compressed fronds on siltstone slabs, preservation in chert is different. Here, the parts can be found lying together and preserved within their habitat, a shallow swamp turned into chert by silicification. As a peculiar fact, the state of preservation of trunks and fronds in chert is usually the other way round: Trunks are more or less squeezed flat but the foliage is not.
A chert sample with fern pinnules from Döhlen basin, first described in 19th century, serves as the type specimen of
Scolecopteris (literally: maggot fern), a genus of which more than two dozen species are now distinguished worldwide.
Cross-section of squeezed Psaronius in chert, Döhlen basin

Fig.1 (above): Fern pinnule cross-section with sporangia seen on the natural smooth surface of an old chert layer fragment from Sardinia. Width of the pinnule 1.7mm.


Fig.2 (left): Chert layer fragment with stem cross-section of the tree fern Psaronius silicified while lying in a shallow swamp in a state of partial decay. Cut and polished, width 8cm.

Fig.3 (below): One of the various "unidentified lying objects" which are a common sight in the cherts of the Döhlen basin, and possibly represent early stages of Psaronius, collapsed but not compressed while lying in the mud. Cross-section, width 34mm.

Unidentified lying object in Permian chert

It has to be mentiond that Psaronius trunks much bigger and better preserved than the one in Fig.2 are known from tuffaceous strata, notably from those at Chemnitz, but not from chert. However, only preservation in chert can reveal delicate herbaceous structures as the one in Fig.3.

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