Late Darriwilian (Middle Ordovician) conodonts from eastern and southeastern Ireland

The Middle Ordovician (upper Darriwilian) marine deposits of the Bellewstown Limestone Member and Tramore Limestone Formation in eastern and southeastern Ireland, respectively, yield a diverse conodont assemblage of 21 taxa. The sedimentary rocks deposited on the Bellewstown Terrane represent an intra-Iapetus island arc setting. The Tramore Limestone was deposited in a back-arc setting at the eastern margin of the Leinster-Lakesman Terrane that is considered part of the peri-Gondwanan Ganderia Terrane. The conodont assemblage, including species of Baltoniodus, Eoplacognathus, Plectodina and Pygodus is assigned to the Pygodus serra Conodont Zone (upper Darriwilian, Middle Ordovician). The genera Drepanodus, Drepanoistodus, Gothodus, Panderodus, Periodon, Protopanderodus, Sagittodontus and Triangulodus and are also represented. The Darriwilian conodont assemblages from Bellewstown and Tramore in Ireland are characteristic of the 'eastern' Iapetus Ocean with a southern mid latitudinal position. The fauna resembles the San Rafael (Mendoza Province, Argentina) conodont fauna of the Cuyania Composite Terrane. Baltoniodus, Eoplacognathus and Sagittodontina are shared with faunas in Baltica, whereas Baltoniodus and Sagittodontina together with Yangtzeplacognathu s occur in South China and Plectodina and Yangtzeplacognathus are recorded from Gondwana. An important factor influencing the distribution of conodont taxa is the siliciclastic-dominated sedimentation, interpreted to reflect cool to temperate water conditions. The Bellewstown and Tramore conodont fauna is in marked contrast to other deposits on island arcs and back-arc terranes within the Iapetus. These are interpreted to represent low latitudinal, warmer, oceanic water conditions with Laurentian faunal affinity. Some potential new species are introduced in open nomenclature.