Biostratigraphy of the Shirgesht Formation in Kalmard Mountains in Southwest of Tabas with special Emphasis on Conodonts

To study the Shirgesht Formation biostratigraphy in Kalmard Horst in relation to its conodont content, the Miyugodar (Miangodar) stratigraphic section was selected which is located in southwest of Tabas city. The Shirgesht Formation in the mentioned section is mainly composed of siliciclastic rock units and overlay unconformably on Kalmard Formation (attributed to Pre-Cambrian) and is overlain by Gachal Formation (Carboniferous). Thirty five rock samples were selected from appropriate rock units (Shirgesht and Gachal Formation). Samples were studied in laboratory for more details. According to the extracted conodont from Shirgesht Formation in Miyugodar section, the age of this formation can be regarded as Early Ordovician (Tremadocian - Arenigian). Three conodont assemblage zones were recognized in Early Ordovician units. They are: Cordylodus spp., Deltifer and Proteus Global Standard Conodont biozones. The recognized biozones are as followed: 1- Oneotodus - Drepanodus Assemblage Zone 2- Acodus deltatus - Protopanderodus Assemblage Zone 3- Acodus - Oistodus Assemblage Zone