Tournai: Classic Locality and Classic Fauna… but What Is New?

Tournai, the historical area of the Tournaisian Stage, is situated in the western part of Belgium and constitutes a peculiar sedimentation area with the Namur-Dinant Basin, along the southern margin of Laurussia. This area is known for its quarries (historically for ornamental and building stones, nowadays for concrete production) and renown for the fossils that were found when the extraction of stone was hand-made. Most of these old quarries, situated on the flanks of the Escaut River were opened in the lower part of the Tournaisian limestone. They yielded a rich assemblage of generally well-preserved invertebrates, including brachiopods, corals, echinoderms, mollusks, sponges, trilobites, etc. Their great abundance facilitated the establishment of an active fossil trade during the 19th century. As a result, Carboniferous fossils from the Tournai area are frequently represented in numerous old institutional collections. Yet illustrated in scientific treatises in the 18thcentury, they served as a basis for numerous monographies published in the 19th century, notably by de Koninck, and led to the definition of the Tournaisian Stage. Although they were collected in different quarries, where different lithostratigraphic units were exposed, the fossils deposited in historical collections were, in most cases, simply labelled ‘Tournai’. The typical Tournaisian limestone exposed in the quarries of the Tournai area corresponds only to a part of the Tournaisian Stage (mostly the lower part of the upper Tournaisian or Ivorian regional substage). The contact with the Upper Devonian Series is known from boreholes but the transition with the Visean is not exposed anywhere due to erosion. Over the last decades, fossil material has been gathered from the active quarries located SE of the town of Tournai. Although they expose a c. 300 m-thick sequence of Tournaisian strata, it was not possible to recover the same taxa than those of the famous ‘classic’ Tournai fossil fauna. Nowadays, fossils can be found free from the limestone matrix where the rock is weathered, i.e. in karstic pockets tens of metres wide and deep affecting the upper part of the Tournai Formation (Vaulx Member). The typical ‘historical’ Tournai fossils, however, seem to originate from older parts of the Tournai Formation (Providence Member and Pont-à-Rieu Member) as they are dominated by distinct taxa. Nevertheless, it is not excluded that some of the species described in the early Koninck’s monographs came from the lower part of the unit overlying the Tournai Formation, namely the Antoing Formation (Lower Calonne Member; e.g. Chonetes Bed). Besides the richness in fossil, both in terms of diversity and number of individuals, the precise age and correlation of the Tournai fossil fauna remains a complex issue, notably because of the lack of foraminifers and the scarcity of conodonts. The latter suggest that the Tournai Formation belongs to the P. communis carinaZone, and probably does not reach the S. anchoralis Zone, i.e. lower and middle parts of the upper Tournaisian. Stratigraphic correlations with other part of the Namur-Dinant Basin are made possible with macrofauna, notably the rugose corals and brachiopods. The rugose corals from Tournai were studied by de Koninck, McCoy, Thompson and Milne-Edwards & Haime in the 19th century, then punctually by coral researchers in the early 20th century (Hudson, Carruthers, Vaughan, etc.). We here propose a taxonomic and stratigraphic revision of some solitary rugose corals, based on both newly collected material and historical collections. The very rich brachiopod fauna was studied primarily by Léveillé, de Koninck, Vaughan and Demanet, but it remains only partly revised, as recent studies have focused mainly on spire-bearing taxa (e.g., Athyridida, Spiriferida). Despite its status of locus typicus for the Tournaisian Stage, the Tournai locality cannot be understood alone, as it is often the case with type-localities and type-sections. In this case, the knowledge of the Tournaisian is complemented by other historical localities of Belgium (e.g., Dinant, Yvoir, Waulsort), Germany and the British Isles which offer various depositional settings and facies.