Writers : Ghaderi,Abas؛ Aghanabati,seyed ali؛ Hamdi,bahaoddin
Refference : 1th symposium of Iranian paleontological society
Publishing Year : 2007

Abstract :

Shirgesht Formation is one of the fossiliferous units of Central Iran which in the type section is defined (informally) in the terms of 3 members. This formation is mainly composed of limestone, marl, siltstone, shale and dolomite with 1236 meter thickness. The Shirgesht Formation in type section area, conformably overlay on the upper part of Derenjal Formation with a gradual contact, composed of brachiopods limestone bearing (Billingsella limestone). The Shirgesht Formation is overlain by sandy limestone and volcanic rocks of Niur Formation. To do biostratigraphy studies on the second member of the Shirgesht Formation in the type section, totally 14 rock samples were selected. According to conodont content of the Shirgesht Formation second member, 2 conodont assemblage zones were determined which shows an age of Early Ordovician (Tremadocian – Arenigian). The recognized biozones are as followed:
1. (Drepanodus - Paltodus? deltifer? Assemblage zone)
2. (Paroistodus? proteus? Assemblage zone)

The mentioned conodont assemblage zones are equivalent with the upper part of Deltifer Global standard biozone and Proteus biozone. The Tremadocian – Arenigian boundary is located in the base of Paroistodus? proteus Assemblage Zone in middle part of second member of the Shirgesht Formation.

Subject List : Conodont, biostratigraphy