Taxonomy, biostratigraphy and biofacies of an Upper Ordovician (Katian) conodont fauna from the Casaio Formation, Northwest Spain

Although Katian conodont faunas from high-latitude Gondwanan to peri-Gondwanan regions are widely referred to in the literature, their taxonomy is not yet stabilised, which is critical to biostratigraphically constrain the climate and tectonic events preceding the Hirnantian mass-extinction. In the present contribution, 595 conodont elements and abundant fragmentary conodont material recovered from meta-limestones of the Casaio Formation, northern Central Iberian Zone, is taxonomically and biostratigraphically analysed. The conodont assemblage is characterised by the genera Amorphognathus, ?Baltoniodus, ?Drepanoistodus, "Drepanodus", Eocarniodus, Hamarodus, Icriodella, Istorinus, Panderodus, Sagittodontina, Scabbardella, and Walliserodus, and documents the lower Amorphognathus ordovicicus Zone (Ka3) in Northwest Spain. After the taxonomic analysis, Icriodella iberiensis sp. nov. is proposed, and the complexity of the balognathid genera Sagittodontina and Amorphognathus is further discussed. Based on the composition of the major components, a new Icriodella-Sagittodontina-Amorphognathus Biofacies is introduced. Conodont based correlations and cluster analysis verify the strong similarity of the conodont assemblage of the Casaio Formation with the Thuringian conodont faunas from the Upper Ordovician Mediterranean Province.