Trilobites du Dévonien des Ardennes (zone rhéno-hercynienne) : biostratigraphie, évolution et événements

Abstract

Trilobites make up a major component of the Devonian macrofauna in the Ardennes (Belgium, northern France). This has been properly described for the first time through a recently commenced revision. While the Lochkovian and early half Pragian were dominated by classic Rhenish Homalonotidae and Acastidae, the extensive offshore environments that developed in the upper Pragian and Emsian became important habitats to mixed Rhenish-Bohemian trilobite communities. The, at times, richly diversified trilobite assemblages of the early Middle Devonian homoclinal ramp show more gradual (in composition) differences with the exceptions of very littoral habitats and local carbonate build-ups which are each of distinct configurations. The significantly impoverished trilobite fauna of the late Middle Devonian carbonate platform remains poorly documented. A subsequent diversity upsurge is associated with eustatic sea level rises which enabled new immigrations in the basal Frasnian. Trilobites became rare towards the end of the Devonian. Two immigration waves are recognised during the Devonian in the Ardennes: one in the mid Pragian and a second in the lower Frasnian. A third wave in the upper Emsian, which was the only one described in the previous literature, cannot be readily confirmed. As a taxonomic addendum four new species are described from the Middle Devonian in the Couvin area, namely Goldius endelsi sp. nov., Gudralisium rossumi sp. nov., Phaetonellus lelubrei sp. nov. and Diademaproetus dianae sp. nov. Lastly, a list of available species names originally described from the Devonian in the Ardennes is provided.