Lower Devonian brachiopod stratigraphy in the Rhenish Massif (Germany): restrictions and potential

Rhenish Massif and Ardennes are the type regions of the classic Gedinnian, Siegenian, and Emsian stages (and subunits) of the Lower Devonian, which are mainly defined by brachiopods. In the course of the ongoing taxonomic revision of the Rhenish Lower Devonian representatives of the phylum, numerous new biostratigraphic data have been obtained. The revised biostratigraphy includes 25 taxon range and 20 assemblage zones from the Pridoli to the Eifelian, which can be further subdivided into subzones. Although Lochkovian, Pragian, and Emsian GSSPs have long been defined elsewhere on the basis of pelagic guide fossils, the classic Ardenno-Rhenish stratigraphy is still an important reference in the Lower Devonian, e.g., for the envisaged redefinition of the basal Emsian GSSP.

The biostratigraphic utility of brachiopods is restricted both by their limited palaeogeographic distribution and their dependence on the facies. In the case of the Rhenish Lower Devonian, specific subtypes of the rhenotypic facies have to be considered (e.g., eurhenotypic, allorhenotypic and pararhenotypic facies). Nevertheless, the Rhenish brachiopods are excellent guide fossils, and thanks to close palaeobiogeographic relationships the revised biostratigraphy can be used with reservations in Western Europe and North Africa, i.e., within the boundaries of a ‘Maghrebo-European’ palaeobiogeographic unit. Here, correlations of regional brachiopod and global pelagic biostratigraphies are possible. To conclude, it can be said that the revised Lower Devonian brachiopod stratigraphy has the potential of providing a fine-scaled biochronological framework for future stratigraphic, palaeoecological, and palaeobiogeographic studies.