Vireux

Introduction

VERSION FRANCAISE

The “Mur des douaniers” (Vireux-Molhain, France)

Situated near the northeastern French town of Vireux-Molhain (southern Ardennes) is a road cut known as the 'Mur des douaniers' which has become famous for the numerous articulated trilobite remains that it has yielded. For many years, the 'Mur des douaniers' attracted much attention from fossil collectors. Tons of rock were taken from the site until French authorities were "forced" to close it down in the 1990s. Fossil collecting has been prohibited ever since and the French police are still actively patrolling the area. The only way to acquire trilobites from this famous site is to purchase them. Material does sometimes appear on fossil markets, usually comprising frequently occurring taxa such as Geesops sparsinodosus gallicus. Among the rarer trilobites from Vireux-Molhain are lichids and odontopleurids; both are extremely hard to come by.

This is due to the fact that the Emsian-Eifelian boundary does not coincide with the Emsian-Couvinian boundary but lies within the overlying Eau Noire Formation. Assignment to the St. Joseph Formation conflicts with lithology at the site and with the occurrences of the trilobites Geesops and Septimopeltis, for instance, which strongly suggest an Eifelian age. Furthermore, after Schraut (2000) the outcrops are of early Eifelian age based on the occurrence of the goniatite Pinacites jugleri. Van Viersen (2006) assigned the outcrops to the lower part of the Jemelle Formation. In 2008, Dumoulin & Blockmans recognised a new member of the Jemelle Formation, the Vieux Moulin Member, to which the outcrops at the 'Mur des douaniers' were also assigned.

2. A large part of the various (literature and internet) sources provides wrong names that were adopted from other (similar) sources. The panel that is placed at the site mentions 10 names of trilobites, but only a few of these appear to be correct. - At this point, 5 of the at least 11 species at the 'Mur des douaniers' have formally been described, some of which in open nomenclature.

The most significant error that is made by many sources, is that the Vireux fauna is being compared to faunas from other regions of differing age. Species such as Phacops latifrons, Cyphaspis ceratophthalmus, Asteropyge punctata, Gerastos cuvieri and Ceratarges armatus, which are claimed to have been discovered in the lower Eifelian of Vireux-Molhain and Treignes (Belgium), are typically known from the middle and upper Eifelian of the Eifel region. Phacops latifrons is a species that is restricted to part of the upper Eifelian and is believed to have middle Eifelian predecessors; therefore it is highly unlikely that it also occurs in the lower Eifelian. During examination of about 3000 trilobites from Vireux-Molhain in museum and private collections, I have not been able to identify any other phacopine than Geesops or Pedinopariops.

A nomenclatoral revision of the trilobites from the lower Eifelian of Vireux-Molhain is currently underway. The first of these have now been described.

Despite their popularity scant literature is available about the trilobites of the Mur des douaniers. Most sources concern booklets (e.g. Gibout, 1991), websites, or brief sections in professional papers (e.g. Struve, 1982; Schraut, 2000). Two errors consistently occur in the first two categories:

1. Traditionally, the rocks that are exposed at the road cut were assigned to the "Assise de Couvin" [note that Co2a is type horizon of Septimopeltis magnispina (Maillieux, 1938)] or sometimes the underlying "Assise de Bure". The age is said to be Eifelian. According to the panel that is placed at the site, the outcrops belong to the St. Joseph Formation. This formation is the basal unit of the Couvinian as perceived in the old literature by Maillieux and others, but is actually of Early Devonian (Emsian) age.

Gerastos catervus, a common trilobite in Vireux-Molhain.

Records in scientific publications are:

- Septimopeltis magnispina (Maillieux, 1938)

- Geesops sparsinodosus gallicus Struve, 1982

- Ceratarges cognatus van Viersen, 2006

- Gerastos catervus (van Viersen, 2006) (= Rhenocynproetus)

- Cyphaspis n. sp. A (sensu van Viersen, 2006)

- Koneprusia sp. A (sensu van Viersen, 2008)

- Diademaproetus? sp. (sensu van Viersen & Prescher, 2008)

- Septimopeltis sp. [second species fide van Viersen (2006)]

- Pedinopariops sp.

- Scabriscutellum sp.

- Kettneraspis cf. bayarti van Viersen, 2007

- Asteropyginae gen. & sp. indet.

Ceratarges cognatus, one of the rarer trilobites in Vireux-Molhain.