Wallonia as an international reference for the geological timeline
In 2016, researchers from the EDDyLab - Evolution & Diversity Dynamics Lab - at ULiège proposed a new definition of the boundary between the Devonian and Carboniferous geological periods (359 million years). This new definition has been tested by hundreds of researchers around the world and the results are now compiled in a special issue of the journal Palaeodiversity & Palaeoenvironments. The ULiège is a key contributor to the geological timeline.
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eological time is divided into periods (Cambrian, Carboniferous, Jurassic, etc.), together covering the 4.6 billion year history of the Earth. The many climatic, environmental, and biological changes that have punctuated this history are recorded in rock layers, forming an incredibly rich archive of the Earth's past. "By studying these successive layers, we are able recognise boundaries between the different periods, each boundary being defined by a specific event or 'marker', such as an extinction event or a change in the climate, explains Julien Denayer, a palaeontologist at the EDDyLab (Geology Research Unit/Faculty of Science) and first author of the article. A locality is then designated, making the rocky successions of this particular place the international reference for this transition." It was in Belgium, in the 19th century, that numerous divisions of the time scale were defined, such as the Frasnian, Tournaisian, Viséian, Namurian, etc... These names are still used today on an international scale.
The boundary between the so-called Devonian and Carboniferous geological periods (359 million years ago) was the first to be formally defined in 1927. The fossils marking the boundary were too rare, so this definition was of little use. A second attempt was proposed fifty years later, but was also invalidated by the International Commission of Stratigraphy, the scientific body that establishes and validates the subdivision of geological time, again because of the scarcity of the fossils supposed to mark the boundary.
“For the past ten years or so, palaeontologists and geologists specialising in the Devonian and Carboniferous periods have been working on redefining this boundary, says Cyrille Prestianni, palaeontologist at ULiège and co-author of the article. In 2016, we proposed a new definition, this time based on several contemporary phenomena, well recorded in the rocky successions of Wallonia." According to the ULiège researchers, the boundary between these two periods can be defined by the so-called Hangenberg Sandstone event - an episode of abrupt decrease of sea levels - which is also correlated to a major extinction that decimated typical Devonian ecosystems such as coastal marshes and reefs. In ecological terms, this extinction was more severe than the extinction of the dinosaurs at the end of the Cretaceous!
Since then, researchers around the world have tested the applicability of this criterion to define the boundary. The results of these years of research are now compiled in a special volume of the journal Palaeodiversity & Palaeoenvironments. The EDDy Lab researchers publish an exhaustive review of the geological and palaeontological knowledge of the Devonian-Carboniferous boundary in Wallonia and the surrounding regions. In this paper, the members of the EDDy Lab propose a scenario explaining the ecological and climatic crisis that caused the extinction of the Devonian fauna and flora. “Our work is not yet finished, says Julien Denayer, the next step is to select a new type locality. Several Walloon sites are now being studied using state-of-the-art techniques and will be proposed to become the world reference for the Devonian-Carboniferous boundary!”
Scientific references
- Denayer, J., Prestianni, C., Mottequin, B., Hance, L. & Poty, E., 2021. The Devonian-Carboniferous boundary in Belgium and surrounding areas. Palaeodiversity & Palaeoenvironments, https://doi.org/10.1007/s12549-020-00440-5
- Aretz, M., Corradini, C. & Denayer, J., 2021. The Devonian-Carboniferous Boundary around the globe: a complement. Palaeodiversity & Palaeoenvironments, https://doi.org/10.1007/ s12549-021-00495-y
- Prestianni, C., Sautois, M. & Denayer, J., 2016. Disrupted continental environments around the Devonian-Carboniferous Boundary: introduction of the tener event. Geologica Belgica, 19/1-2: 135-145. http://dx.doi.org/10.20341/gb.2016.013
