Conodont biostratigraphy of late Devonian deposits in the Shirband section (Damghan, NE Iran)

Abstract

The Upper Devonian deposits are relatively thick and developed in eastern Alborz. These deposits are located in Shirband area which is attributed to Geirud Formation. Shirband Upper Devonian deposits are situated by a discontinuity with the same gradient on Mila Formation and also under Mobarak Formation. The thin limestone, shaly limestone, and shale layers of the Geirud Formation are gradually followed by thin limestone and shale layers of the Mobarak Formation. Study of conodont fossils in this section probably indicates continuity deposits between the Geirud and Mobarak Formations. On the basis of studying conodonts, seven standard biozones were determined with the Famennian age (arranged from oldest to youngest): 1—triangularis to linguiformis zone, 2—crepida zone, 3—rhomboidea zone, 4—trachytera to marginifera zone, 5—postera zone, 6—postera to expansa zone, and 7—praesulcata to sulcata zone.