Ordovician conodonts of the Katkoyeh formation in the Kuh-e-Bonorg section, Kalmard Horst (west of Tabas)

In this research, Ordovician conodonts obtained from the sedimentary succession of the informal Katkoyeh formation is studied in a stratigraphic section at the south of Kuh-e-Bonorg, eastern flank of Kalmard Anticline in the west of Tabas (Central Iran). The formation which is partly equivalent to the succession of the Shirgesht Formation in Tabas Block is unconformably overlaid the Kalmard Formation (attributed to the Neoproterozoic) and disconformably overlain by the Carboniferous Gachal formation. The Katkoyeh formation with 214.8 meter thickness is divided into three lithostratigraphic members including the Lower Sandstone (mostly quartzarenite to litharenite), Middle Shale (red to green shales interbedded with some dolomitic and calcareous sandstones, in laminated wavy stromatolite structure at the base) and Upper Carbonate (limestones, dolostones and marls). The section was sampled bed by bed for conodont studies so that 80 samples have been selected, however only seven of them were productive. Within the selected samples, six genera and 14 species of coniform and ramiform conodont elements are determined, a few of them are reporting for the first time from Iran. The obtained conodonts demonstrate the faunal assemblages equal to the proteus, elegans-evae and diprion Zones which confirm the age of Early Ordovician (late Tremadocian–Floian) for the studied section. The whole conodont material display a faunal affinity with the Baltoscandic and Argentina paleobiogeographic provinces.