Searching for clues in the chert

How Mother Nature preserves ecosystems for millions of years

Fernlättchen with underneath, empty spore containers. The water-clear chalcedony allows a good recognition of the three-dimensional, cell-preserved plant remains. (Gravel pit Nobitz, Thuringia) © Ralph Kretzschmar, Museum of Natural History Chemnitz
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Can a plant with its three-dimensional structure be preserved for several million years? That sounds relatively simple at first, but soon turns out to be a real challenge. Freeze? To scan? Burn a virtual 3D model to CD? Nature has long since solved what causes people a headache. And with fantastic results: Not only individual plants, but entire habitats has kept them in pebbles for millions of years for research by today's scientists.

"The most well-known example of such a pebbled, terrestrial ecosystem is the Rhynie chert in Scotland. Early land plants, along with their inhabitants such as spiders and mites, were miraculously preserved by the waters of hot springs about 400 million years ago, "says Ralph Kretzschmar of the Museum of Natural History in Chemnitz.

Researchers now know that the so-called "Rhynie Chert" is not an exception. Other geological epochs come up with similar formations. Especially the permocarbon about 300 million years ago, with its pronounced volcanism in today's Europe, was particularly productive. "Plant organs and their complete structure were preserved, which otherwise - if at all - we only know as fossil imprints, " explains Kretzschmar. These include, for example, roots, barks, twigs, cones and leaflets, including their "roommates" such as mushrooms, crabs or snails.

A catch on the matter

3D virtual model of a fern frill section. Below is a cross section through the structure. Similar, seemingly chaotic-looking figures can be found on the intersections of Rotliegendzeitlicher pebbles. © Ralph Kretzschmar, Museum of Natural History Chemnitz

But it is not always easy for paleontologists to track down the silica-rich rocks and their riddles. For example, fossils containing chert are often found rearranged, the prim re, softer surrounding rock was eroded. "The fossil content is preserved, sometimes even better recognizable, but the geological context is lost." Kretzschmar describes one of the scientists' core problems.

An example shows just how important the exact classification in a stratigraphy is: In view of the huge ember cloud eruption that preserved the fossilized forest of Chemnitz, it was natural to assume that the abundant plant fragments in the Hornstein plate were from Chemnitz-Altendorf to violently torn off leaves and branches. display

Very precise observations in the primary deposits showed that the hornstone lenses had formed within already relocated volcanic ash in the upper part of the layer sequence. The contained plants were therefore rather pioneers of repopulation as victims of a disaster! F, summarizes the Pal obotaniker together.

Evaluation of the stones often problematic

Another problem concerns the evaluation of the stones. Common practice is the dismantling and polishing of the finds. For Kieselh lzer defined views of the cell structure can be generated in this way, on the basis of which a determination is made. In Kieseltorf, on the other hand, only two-dimensional, indiscriminate sectional images of many three-dimensional structures can be seen on polished sections. For example, if we were to cut off a shrub and see only the two-dimensional image of the cut surface, would we recognize the growth? Hardly! says Kretzschmar.

Schr ger Cut through a branch with leaflets from the Donnersberg Formation (Rhineland-Palatinate). The structure of the individual organs is cell-exactly recognizable. Ralph Kretzschmar, Museum of Natural History Chemnitz

Correcting cuts and reconstructions using virtual 3D models can help. These methods of data collection are promising from the scientists' point of view, but they are also time-consuming and expensive. In addition, non-destructive procedures such as computed tomography or ultrasound diagnostics will soon be tested for their usability.

But also in the future cost-effective, simple methods are in demand. "An in-depth look at other areas of expertise certainly can not hurt that, " says Kretzschmar.

What the collector does not know

But how come scientists to the chert stones with their valuable fossils, which can lead to the study and reconstruction of former ecosystems? What the collector does not know, he does not pick up: at first there were agate and Kieselholzenthusiasten who made interesting finds in gravel pits and in fields, sometimes without recognizing them. In the last few years, a veritable Hornstein fan base was formed, which uses as a contact and information source.

The main concern of this non-commercial website is to promote fossil-bearing cherts. "Annual workshops at the Museum of Natural History Chemnitz show the great interest of a growing group of enthusiasts. The collection and scientific processing of fossil-bearing chert stones has been recognized in Chemnitz not only as a historical commitment but also as an extremely promising field of activity. "Concluded Kretzschmar.

(Ralph Kretzschmar, Museum of Natural History Chemnitz, 23.11.2007 - DLO)