TY - JOUR ID - 57826 TI - Biostratigraphy of the First and Second Members of Type Section of the Shirgesht Formation in North of Tabas with Special Emphasis on Conodonts JO - Scientific Quarterly Journal of Geosciences JA - GSJ LA - en SN - 1023-7429 AU - Ghaderi, A. AU - Aghanabati, A. AU - Hamdi, B. AU - Miller, J. F. AD - Center of Excellence for Paleontology, Ferdowsi University of Mashhad, Iran AD - Research Institute for Earth Sciences, Geological Survey of Iran, Teharan, Iran AD - Missuri University, USA Y1 - 2008 PY - 2008 VL - 17 IS - 67 SP - 150 EP - 163 KW - Shirgesht Formation KW - Tabas KW - Type section KW - First and second members KW - Biostratigraphy KW - Conodont KW - Early Ordovician KW - Tremadocian – Arenigian DO - 10.22071/gsj.2009.57826 N2 - The 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, conformably overlay on the upper part of the 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 the Niur Formation. To do biostratigraphy studies on the first and second members of Shirgesht Formation in the type section, totally 99 rock samples were selected. The conodont fauna of lower part of its first member contain some species of Westergaardodina, Furnishina and prooneotodus which show an age of late Cambrian. Several species of Cordylodus, Oistodus, Drepanodus, Proconodontus and Paroistodus in distance of middle part of the lower member to the end of the second member represent an age of Tremadocian – Arenigian. According to conodont content of the first and second members of Shirgesht Formation, 7 conodont assemblage zones were determined in the type section which show an age of Late Cambrian – Early Ordovician. The recognized biozones are as follow:   1. Furnishina - Westergaardodina Assemblage Zone. 2. Proconodontus - Oneotodus Assemblage Zone. 3. Cordylodus  proavus - Cordylodus  oklahomensis  Assemblage Zone. 4. Cordylodus  lindstromi  Assemblage Zone. 5. Cordylodus  angulatus  Assemblage Zone. 6. Drepanodus - Paltodus  deltifer  Assemblage Zone. 7.Paroistodus  proteus  Assemblage Zone. The mentioned conodont assemblage zones are equivalent to Cordylodus spp., Deltiferand Proteus global standard conodont biozone. In contrast with the previous reports, the Cambrian – Ordovician boundary is located in the first member of the Shirgesht Formation. Thus, the Shirgesht Formation in type section is diachronous formation.    UR - http://www.gsjournal.ir/article_57826.html L1 - http://www.gsjournal.ir/article_57826_12795aa55737b98cb5dc8d91e0cf9b7a.pdf ER -