Middle Ordovician Conodonts from the Chingiz Ridge (Kazakhstan): Taxonomy of the Naiman Formation Assemblage and Its Biogeographic Affinity

Abstract

Abstract —Conodonts from carbonate rocks of the Naiman Formation (Chingiz Ridge, East Kazakhstan) have been studied in detail for the first time. The mixed conodont complex is characterized by a high taxonomic diversity and includes species belonging to the stratigraphic interval from the upper part of the Dapingian Stage to the middle of the Darriwilian Stage of the Middle Ordovician. The conodont assemblage includes oceanic/deep-sea species of a wide geographic distribution, in particular, abundant Periodon macrodentatus and P. zgierzensis, which are characteristic of siliceous deposits of Kazakhstan. For the first time, the occurrence of species Scolopodus? mufushanensis, Drepanoistodus latus and Anodontus longus is noted in Kazakhstan. This indicates the existence of the biogeographic zoning by climatic zones typical of pelagic biota. The species Protopanderodus? nogamii indicates that the Kazakhstan conodont fauna belongs to the Australasian biogeographic province of the Eastern Gondwana. The conodont assemblage includes a number of regionally endemic taxa that characterize the Kazakhstan fauna as an independent biogeographic unit and confirm the relative remoteness of water basins of Kazakhstan from the eastern margin of Gondwana and from other paleocontinents in the Ordovician.