The Cambrian – Ordovician boundary beds in the Saluk Mountains (south Kopet-Dagh) deposited in the active continental rift, associated with extensive intraplate basaltic volcanism. They exhibit the only complete conodont biozonal succession so far documented from Iran. It is subdivided into 11 succeeding conodont biozones from the Proconodontus muelleri to Paltodus deltifer zones. Two graptolite bearing horizons with the early representative of Rhabdinopora have been documented from the Cordylodus lindstromi Zone close to the inferred position of the Cambrian – Ordovician boundary. Recently Iapetognathus conodont elements were recovered from several stratigraphical levels within the Cordylodus lindstromi and Cordylodus angulatus zones. The presence of the early Rhabdinopora and Iapetognathus conodonts in the lower Cordylodus lindstromi Zone of south Kopet-Dagh is of outstanding importance for high resolution correlation of the Cambrian – Ordovician boundary interval and more precise definition of the position of the system boundary.

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