Vireux-Molhain National Nature Reserve

The Vireux-Molhain national nature reserve (RNN104) is a national nature reserve of geological and paleontological interest. It is located in the Pointe de Givet, department of Ardennes, on the border between France and Belgium. It covers an area of 1.82 ha.[1] The site is known as Customs Wall (Mur des Douaniers) as it is near an old customs post. This outcrop of Middle Devonian shale (Eifelian: ± 397 million years) is notable for the quantity and good state of preservation of its fossils. Trilobites are well-represented.

Vireux-Molhain National Nature Reserve
LocationArdennes, France
Nearest cityGivet
Coordinates50°05′39″N 4°42′26″E
Area1.82 ha
EstablishedMarch 14, 1991
Governing bodyONF Ardennes

History

The discovery of the site is attributed to geologist Jules Gosselet at the end of the 19th century.[2][3][4] The deposit was frequently visited by paleontologists due to the profusion of fossils, the diversity of species, plus the quality of their preservation. It was subjected to intensive extraction by amateurs and professionals.[5]

The nature reserve was created in 1991 to regulate uncontrolled exploitation of the site and to allow conservation and study of fossils. Initially entrusted to the Ardennes Natural History Society. In 1996 responsibility moved to the National Forests Office.[2] It is accessible to everyone, with a strict ban on extracting and collecting fossils and minerals. Today, the main threats are intrusion of shrub vegetation and water infiltration as shale is very brittle.

Fossil collections

These protection measures have been seen as controversial:[6][7] banning collecting prevents new scientific study, despite the site's potential.[2] Natural erosion will ultimately destroy outcropping fossils, which could be exploited without degrading the site. Few studies are funded and this "set-aside" deprives the scientific community of discoveries and collection of information that competent amateur paleontologists could make.

Part of the collections are kept at the Bogny-sur-meuse Museum of fossils and minerals (Musée des fossiles et minéraux de Bogny-Sur-Meuse) with the help of the Mineralogical and Paleontological Association of Bogny-sur-Meuse (Association Minéralogique et Paléontologique de Bogny-Sur-Meuse) who have assembled the collections allowing researchers to study these fossils today.[2]

Despite the large quantity of fossils extracted from the site, knowledge of the fauna of middle Devonian remains incomplete.[2] Many species are not yet listed or have been incorrectly named.[8] Most has not yet been the subject of in-depth scientific study. Scientists exploit museum and other collections to better understand this fauna and more particularly the trilobites.[8][9]

Geography
Perimeter of the Vireux-Molhain National Nature Preserve

The reserve is located in Vireux-Molhain in the Ardennes (Pointe de Givet), on the northern slope of the Viroin valley, a few kilometers from its junction with the Meuse, in the Calestienne narrow limestone strip. It marks the transition from the Ardennes to the Fagne and the Famenne. It is accessed by an embankment on the edge of “Najauge road” between Vireux-Molhain and Treignes (departmental road 47 between Vireux-Molhain and Couvin). Collection of fossils and minerals is prohibited there.[2]

Geology
Outcropping shale.

Customs Wall (Mur des Douaniers) is an outcrop of rocks, formation of which began in Lower Eifelian, a period of Middle Devonian (Primary or Paleozoic era). These sediments formed 397 million years ago. The sedimentary layers were subsequently folded and subjected to temperature and pressure constraints during the orogeny of the Ardennes massif (Hercynian cycle). In more modern times, the Meuse and its tributaries have dug deep valleys in the plateau, revealing this outcrop of shales.[10]

Until the beginning of the century, the layers of Customs Wall were considered to belong to Assise de Bure and date from Lower Couvinian (Emsian). The revision of the geological map of Givet[11][12] and recent studies have shown that they belong to the Jemelle formation (Member of the Vieux Moulin) of Lower Eifelian.[8][2]

Fossil fauna

During Lower Eifelian, about 393 million years ago,[13] the region was submerged by a shallow sea. Life developed there in calm and warm waters. Corpses of dead animals were covered with sediment, initiating fossilization. The most abundant fossils are trilobites, but along with reef organisms and cnidarians.[14]

Identified trilobites (classified by orders):[8][9][15][16][17]

  • Proetida
    • Family Proetidae
      • Gerastos catervus (van Viersen, 2006) (previous names: Rhenocynproetus catervus,[18] Gerastos cuvieri (Steininger, 1831))
      • Diademaproetux cf. pertinax van Viersen, Taghon & Magrean, 2019
    • Family Aulacopleuridae
      • Cyphaspis cf. iuxta van Viersen, Taghon & Magrean, 2019
  • Phacopida
    • Family Acastidae
      • Asteropyge eonia van Viersen, Taghon & Magrean, 2019
    • Family Phacopidae
      • Pedinopariops ceuthonymus van Viersen, Taghon & Magrean, 2019
      • Geesops sparsinodosus gallicus (Struve, 1982). It is the most common species on the site. It has often been confused with Phacops latifrons.
  • Odontopleurida
    • Family Odontopleuridae
      • Kettneraspis eftychia van Viersen, Taghon & Magrean, 2019
      • Koneprusia sp. A (sensu van Viersen, 2008)
  • Lichida
    • Family Lichidae
      • Ceratarges cognatus van Viersen, 2006
  • Corynexochida
    • Family Scutelluidae
      • Septimopeltis magnispina (Maillieux, 1938) (previous name: Thysanopeltella magnispina)
      • Septimopeltis cf. akatastasia van Viersen, Taghon & Magrean, 2019
      • Scabriscutellum sp.

Administration, Management plan, regulations

The reserve is managed by the Ardennes National Forest Office.

The nature reserve was created by a decree of March 14, 1991.[19]

Further reading
  • Géologie de la France, vol. 1-2, Paris, BRGM et SGF, 2006 (ISSN 1638-5977)
  • Lettre d'information des réserves naturelles des Ardennes n°5, Office national des forêts - Conservatoire du patrimoine naturel de Champagne-Ardenne, décembre 2007, 4 p. (ISSN 1777-8913)
  • Lettre d'information des réserves naturelles des Ardennes n°6, Office national des forêts - Conservatoire du patrimoine naturel de Champagne-Ardenne, juin 2008, 4 p. (ISSN 1777-8913)

References
  1. "Vireux-Molhain | RESERVES NATURELLES DE FRANCE". www.reserves-naturelles.org. Retrieved 2020-01-24.
  2. ONF (2018). "Réserve Naturelle Nationale Vireux-Molhain - Plan de Gestion 2019 - 2028" (PDF). DREAL Grand Est (in French). Retrieved 24 January 2020.
  3. Jules Gosselet devoted most of his activity to the geological study of northern France and Belgium, dedicating two major works to it: Esquisse géologique du Nord de la France et des contrées voisines (1880-1903) and L'Ardenne(1888). He collected countless mineralogical and fossil samples which made it possible to open in Lille a museum of geology and mineralogy in 1902. He is the "father" of the Givetian stratotype.
  4. A.P. van Viersen & G. Daumeries (2012). "Les trilobites du Dévonien ardennais du "Mur des douaniers" à Vireux-Molhain". Fossiles, Revue française de Paléontologie. 8: 5–15.
  5. ONF. "Réserve Naturelle Vireux-Molhain - Plaquette" (PDF). DREAL Grand Est (in French). Retrieved 24 January 2020.
  6. Qu’est devenu le « Mur des Douaniers », haut lieu du trilobite ardennais et réserve géologique ? Géopolis
  7. Essai sur la protection des fossiles, minéraux et sites, Cercle minéralogique et paléontologique de Belgique
  8. van Viersen, A.P. (2006). "New Middle Devonian trilobites from the Mur des douaniers (Vireux-Molhain, northern France)". Senckenbergiana Lethaea. 86: 63–75. doi:10.1007/BF03043635. ISSN 0037-2110. S2CID 129836161.
  9. Crônier, C.; Van Viersen, A.P. (2008). "The Mur des douaniers, an exceptionally well-preserved early Eifelian fossil site". Bulletin de la Société Géologique de France. 179: 89–95. doi:10.2113/gssgfbull.179.1.89. ISSN 0037-9409.
  10. Jonin, Max (2006). Mémoire de la Terre: Patrimoine géologique français. Delachaux et Niestlé. ISBN 2-603-01383-1.
  11. J.-L. Mansy (2006). Carte géologique de la France (1/50 000) feuille Givet (40) (2nd ed.). Orléans: BRGM. ISBN 978-2-7159-1040-9.
  12. F. Lacquement et al., Notice explicative de la carte géol. France (1/50 000) feuille Givet (40), Orléans, BRGM, 2006, 108 p. (ISBN 978-2-7159-1040-9)
  13. International chronostratigraphic chart 2016
  14. Bliek, Alain (2006). "La Vie en Ardenne occidentale au Paléozoïque supérieur (Dévonien-Carbonifère, - 416 à - 299 Ma)". Géologie de la France. 1–2: 21–27. ISSN 1638-5977.
  15. van Viersen, Allart P. (2008). "First record of the odontopleurid trilobite Koneprusia from the lower Eifelian of Vireux-Molhain (northern France), with remarks on the associated trilobite fauna". Geologica Belgica. 11: 83–91. ISSN 1374-8505.
  16. van Viersen, Allart P.; Prescher, Harald (2011). "New species of the Lichid trilobite Ceratarges from the middle Devonian in Morocco". Geologica Belgica. 14: 193–202.
  17. Viersen, Allart P. VAN; Taghon, Peter; Magrean, Benedikt (2019-02-26). "Early Middle Devonian trilobites and events in the Nismes – Vireux-Molhain area, southern border of the Dinant Synclinorium (Belgium, northern France)". Geologica Belgica. 22 (1–2): 7–33. doi:10.20341/gb.2019.001. ISSN 1374-8505.
  18. van Viersen, A.P.; Prescher, H. (2008). "Devonian Proetidae (Trilobita) from the Ardennes Massif (Belgium, N France) and the Eifel Hills (W Germany)". Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre. 78: 9–29. ISSN 0374-6291.
  19. "Décret n°91-279 du 14 mars 1991 portant création de la réserve naturelle de Vireux-Molhain (Ardennes)". Legifrance.
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