Document Type : Original Research Paper


1 Center of Excellence for Paleontology, Ferdowsi University of Mashhad, Iran

2 Research Institute for Earth Sciences, Geological Survey of Iran, Teharan, Iran


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


Aghanabati,A.,1977- Etude geologique de la regon de Kalmard(W. Tabas).Geological Survey of Iran, Report No.35, (1 - 230).
An, T.X., Zhang, F., Xiang, W.D., Zhang, Y.Q., Xu W.H., Zhang H.J., Jiang D.B., Yang Ch.Sh., Lin L.D., Cui Z.T., & Yang X.Ch., 1983- The conodonts of North China and the adjacent regions: Beijing, P.R.C., Science Press, 223 p.
Apollonov, M.K., 1991- Cambrian-Ordovician boundary beds in the U.S.S.R., in Barnes, C.R., and Williams, S.H., (eds.), Advances in Ordovician geology: Geological Survey of Canada Paper 90-9, p. 33–45.
Druce, E.C. & Jones, P.J., 1971- Cambro-Ordovician conodonts from the Burke River structural belt, Queensland: Australian Bureau of Mineral Resources, Geology and Geophysics, Bulletin 110, 158 p.
Dubinina, S.V., 1991- Upper Cambrian and Lower Ordovician conodont associations from open ocean paleoenvironments, illustrated by Batyrbai and Sarykum sections in Kazakhstan, in Barnes, C.R., and Williams, S.H., (eds.), Advances in Ordovician geology: Geological Survey of Canada Paper 90-9, p. 107–124.
Ethington, R.L. & Clark, D.L., 1981- Lower and Middle Ordovician conodonts from the Ibex area, western illard County, Utah: Brigham Young University Geology Studies, v. 28, pt. 2, 155 p., 14 pls., 12 tables [range charts of taxa].
Henningsmoen, G., 1973- The Cambro-Ordovician boundary: Lethaia, v. 6, p. 423–439.
Howard, J.D., 1978- Sedimentology and Trace fossils, in Basan, P.B (ed) Trace fossil concepts. Society of Economic Paleontologists and Mineralogists, short course, No. 5, P 11-42.
Lindstrom, M., 1984- Baltoscandic Conodont life environments in the Ordovician: Sedimentologic and paleogeographic evidence. Geological society of America, Special paper 196, (33 - 42).
Lofgren, A., 1993- Conodont from the Lower Ordovician at Hunneberg, south-central Sweden. Geol. Mag. 130, (215 - 232).
Lofgren, A., 1994- Arenig (lower Ordovician) Conodonts and biozonation in the eastern Siljan District, central Sweden. J. Paleont. 68, (1350 - 1368).
Lofgren, A., 1996- Lower Ordovician Conodonts, reworking, and biostratigraphy of the Orreholmen quarry, Vastergotland, south-central Sweden. GFF 118, (169 - 183).
Lofgren, A., 1997- Conodont faunas from the upper Tremadoc at Brattefors, south – central Sweden, and reconstruction of the Paltodus apparatus. GFF 119, (257 - 266).
Lofgren, A., 1997- Reinterpreatation of the lower Ordovician Conodont Apparatus Paroistodus. Palaeontology 40, (913 - 929).
Miller, J.F., 1984- Cambrian and earliest Ordovician Conodont evolution, biofacies, and provincialism. Geological society of America, Special paper 196, (43 - 68).
Muller, K.J., 1973- Late Cambrian and early Ordovician Conodonts from northern Iran. Geological Survey of Iran, Report No. 30, (1 - 78).
Ross, R.J.Jr., Hintze, L.F., Ethington, R.L., Miller, J.F., Taylor, M.E., & Repetski, J.E., 1997- The Ibexian, Lowermost Series in the North American Ordovician, in Taylor, M.E., 1997. (eds.) Early Paleozoic Biochronology of the Great Basin, Western United States. U.S. Geological Survey professional paper 1579.
Ruttner, A., Nabavi, M.H., Hajian, J., Bozorgnia, F., Eftekharnezhad, J., Emami, K.S., Flugel, E., Flugel, H.W., Haghipour, A., Iwao, S., Kahler, F., Ruttner-Kolisko, A., Sartener, P., Stepanov, D.L., Valeh, N., Walliser, O.H., & Winsnes, T.S., 1968- Geology of the Shirgesht Area (Tabas area, East Iran). Geological Survey of Iran, Report No. 4, (1 - 140).
Shergold, J.H. & Nicoll, R.S., 1992- Revised Cambrian-Ordovician boundary biostratigraphy, Black Mountain, western Queensland, in Webby, B.D. and Laurie, J.R., 1992, Global perspectives on Ordovician geology: Rotterdam, Netherlands, A.A. Balkema, p. 81–92.