The bituminous source of Clermont-Ferrand, a unique site in France

Did you know that hydrocarbons erupt at Clermont-Ferrand? It has nothing to do with Texas, but south of the city there is a source of bitumen: the Puy de la Poix source. We tell you all about this unique curiosity in France.

It used to be a very popular site with tourists and curious people but is now a secret again. In Clermont-Ferrand, a few meters from the airport runways, is Puy de la Poix. Its peculiarity: a source of bitumen that comes out of the ground to form a dark and unattractive puddle. This mound, only a few meters high, corresponds to an ancient eroded volcanic chimney, crossing the Limani River. It was once considered one of the great tourist attractions in Auvergne, due to the presence of bitumen there. Geologist Charlie Mercieca highlights the exceptional nature of this bituminous resource: “ It is a natural curiosity that cannot be denied on an almost local, national and international level. There are not many bitumen elevators in the world The source produces about one liter of bitumen per day.

The geologist explains in detail how the phenomenon formed over the centuries: “ Puy de la Poix is ​​located to the west of the Limagne plain, between Riom and Vic-le-Comte. There are bitumen leaks everywhere, and Puy de la Poix is ​​just one example of them all. About 25 million years ago, organic matter was trapped in the sedimentary deposits of this large inland lake that was called Limani at the time. The temperature of this organic matter increased very slowly as the marl was buried in the sedimentary mound. Organic matter transforms when temperature increases and hydrocarbons are formed. At Limani, unlike other places where oil is found, these hydrocarbons were neither captured nor stored at depth: they permeated their entire environment. In this area of ​​the Limani Plain, bitumen is found in almost all sedimentary outcrops. At Puy de la Poix the tar rises very slowly. It rises through thermal water: it’s not just bitumen, it’s continental water, also laden with carbon dioxide, methane and sulfur. “.

Because of its low flow, the source did not arouse envy. Charlie Mercieca explains: “ The source is of no industrial importance. Between 1880 and 1980, approximately 50 soundings up to 1,500 meters deep were carried out in this sector, and not only in Puy de la Boa. All these surveys showed that there was no need for industrial production. At this site, it is bitumen, not oil. The bitumen, a hydrocarbon very rich in sulfur, has been oxidized: it has absolutely no industrial properties needed for energy production. “. Not far from Puy de la Poix, there was another site of industrial importance: “ There were near Dalits (Editor’s note, near Clermont-Ferrand) , in the Royce mine, more significant extraction of this bitumen in the underground galleries. Both bitumen and limestone were mined to make gravel. This was done until 1980 “.

The geologist regrets that we have forgotten the source of Puy de la Poix: “This site has become completely deserted, and everyone has forgotten about it for a hundred years. In the 18th and 19th centuries, all the great French naturalists, such as Buffon and Guittard, came to visit the Puy de la Bois. It was inevitable at that time. Naturalists came To try to understand the origin of this rising bitumen and interested in its chemical composition, while this was the beginning of the industrial revolution. Today, only students of geology come to see this site as well as a few enlightened amateurs. It is a site for curious naturalists. According to the geologist, the bitumen will continue and the source will not dry up.

the Conservatory of Natural Spaces (CEN) Auvergne She has been running this site since 2009. “ We have entered into an agreement with the owner, the city of Clermont-Ferrand. It’s a textbook site because we did everything from A to Z: it was an unruly dump so we cleaned up the entire site and restored it. We made a little discovery trail using a booklet. We have started working on private peripheral plots. Every month we have a volunteer custodian who will clean the place “. Lucie Lecorgellier specifies: “ This is part of the bitumen and oil indicators that gave indications of the presence of oil resources in Limani. In Puy de Crouel, we also have natural bitumen lifts. At Mezel-d’Allier, there was an old mine, the Rois mine, exploiting bitumen. There was research in the 1970s but it did not lead to exploitation “.

Puy de la Poix has a very rich microscopic life: “ When bitumen mixes with water we have very specific bacteria. They play a role in the sulfur cycle. We will have a very special microcosm developing in this gap. Chemists conducted research there. Studies have also been carried out on the source’s radioactivity, which is very weak. Wildlife escapes from the asphalt because it is dangerous. Sometimes we find the carcasses of small mammals trapped in tar. “. The site is also of artistic interest: “ Recently, artist Anne Goyer worked with researchers to develop a system for extracting bitumen to paint with a blue color she calls light blue. “.
An inspiration for artists, and an interesting place for the curious, Puy de la Poix deserves our attention, especially since it is so easily accessible.