The Exploratorium: all about this fossil forest hidden in the Gard

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Tronc fossilisé visible dans l'ancienne mine de charbon de Champclauson dans le Gard. © 2019, Pierre Thomas, https://planet-terre.ens-lyon.fr

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[EN VIDÉO] anthracology: the archaeological study of charcoal Anthracology is a discipline of archaeobotanical specialized in the study of charcoal. It provides a better understanding of the daily life of a historical site. In this video, Inrap tells us more about this original activity. The region of Alès has been known and exploited since the Middle Ages for its coal deposits. Carboniferous levels are found in sedimentary levels of higher Carboniferous age, that is, 300 million years old. As the name suggests, this geological period is known to have produced large amounts of coal, especially in Western Europe. At the origin of this specificity, a very high level of CO2, about 30 times higher than in the 19th century, a climate and temperatures favorable to the development of dense vegetation and in particular of large trees with bark. The sea level is then relatively low. , which favors the creation of epicontinental seas and small basins. You have to imagine large tropical swamps over which stand trees over 40 meters tall, such as lepidodendrons, as well as tree ferns. The amount of decaying organic matter (remains of leaves, logs, etc.) is then very high in these small flooded basins. As they are buried, these plant residues will slowly turn into coal Much of the energy resources used during the industrial revolution came from the Carboniferous coal deposits. In addition, they are still exploited today. 300-million-year-old fossilized logs in a vertical position This is how the Alès basin, in the Gard, was industrially exploited until 2002, with a peak of activity in 1958. Then about 20,000 miners worked in the region to extract them. several million tons of coal. By the early 1990s, however, mining was very limited and survived only in a few open pits, mostly north of the village of Champclauson. In this particular site, the working faces reveal remains of fossilized logs, intact and in an “upright” position, to allow us to contemplate what the Carboniferous environment was like. The site is already urbanized and allows a journey of 300 million years, first you can see large vertical tree trunks. The bark patterns are still clearly visible. These are seal trunks, trees that can reach 30 meters in height. However, these logs are not “petrified”, as can be seen in the famous silicified wood forest of the United States (see first photo). It is therefore not what is commonly called “fossil wood,” nor is it coal. The interior of the logs is actually sandstone, a sedimentary rock that has replaced organic matter. Only the crust is still partly made up of organic matter. A vast deltaic plain in an equatorial climate of millions of years. At the end of the Carboniferous, the region (then located at the level of the equator) was then occupied by a large deltaic flood plain, lodged in a depression at the heart of an immense mountain range known as the Hercynian range. . This plain was crossed by numerous rivers that transported pebbles and large amounts of sediment, in this swampy area a dense vegetation developed producing large amounts of organic matter. During periods of flooding, the rivers would deposit sand around the logs, burying them vertically as they went, until they died. This is how the buried part was preserved, from 1 to 3 meters. This exceptional place is already part of the Dinopedia park. Interested in what you just read?
#Exploratorium #fossil #forest #hidden #Gard

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