Middle/Late Givetian ostracod assemblages from the Aisne quarry (Durbuy area, Ardenne, Belgium). Biostratigraphic and palaeoecological implications

The ostracod fauna of the Aisne quarry section (south-eastern border of the Dinant Synclinorium, Ardenne, Belgium) is studied here in order to complete the Middle Devonian record of these micro-crustaceans on the Ardennean platform, allowing thus biostratigraphic correlations at regional scale. Sixty-four ostracod taxa are recognized throughout the Givetian carbonate sequence of Aisne; one new species (Cryptophyllus magnei Maillet and Casier n. sp.) is formally described. In the lower part of the section, assemblages contain numerous species that are known to occur as early as the Late Eifelian. The recognized ostracod assemblages and lithostratigraphic correlations with analogous sequences in the Givetian historical type-area (Givet, French Ardenne), which are dated by conodonts, suggest that the sequence of the Aisne quarry is much more expanded. Three acme biozones are established herein for the Givetian stage; they will be useful for both regional (Ardenne area) and supra-regional correlations between the Boulonnais, Ardenne and Eifel areas. The sedimentary palaeoenvironments recorded in the carbonate sequence of the Aisne quarry are reconstructed based on the ostracod faunas. Finally, the biotic response of ostracods to the Taghanic Biocrisis is discussed.