Document Type : Original Research Paper

Authors

1 Ph.D. Studentin, Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

2 Associate Professor, Department of Geology, Faculty of Sciences, Golestan University, Gorgan, Iran

3 Professor, Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract

The Cambrian- Ordovician boundary strata in the Kalat section, western Koppeh-Dagh, comprise continuous succession of fine clastic sediments, mostly argillites with some shell beds, accumulated offshore. This interval contains  analmost complete succession of conodont biozones, including the Cordylodus intermedius, Cordylodus lindstromi and Cordylodus angulatus biozones. The first appearance of the planktonic graptolite Rhabdinopora cf. Flabelliformis flabelliformis (Eichwald, 1840) in black argillite of the upper part of the Cordylodus lindstromi Biozone indicates relatively precise position of the Cambrian- Ordovician boundary in the section. Cambrian- Ordovician boundary beds in the eastern Alborz Region can be subdivided into three lithological units: Furongian bioclastic limestone mainly replaced by fine clastic sediments in the upper part, the terminal Cambrian Cruziana sandstone representing a shoal complex and the Tremadocian grey argillite accumulated offshore. In this area the position of Cambrian- Ordovician boundary is situated somewhat below the base of the Asaphellus inflatus- Dactylocephalus trilobite Biozone. 

Keywords

Buatois, L. A., Zeballo, F. J., Albanesi, G. L., Ortega, G., Vaccari, E. and Mangano, M. G., 2006- Depositional Environments and Stratigraphy of the Upper Cambrian-Lower Ordovician Santa Rosita Formation at the Alfarcito area, Cordillera Oriental, Argentina: Integration of biostratigraphic data within a sequence stratigraphic framework. Latin American Journal of Sedimentology and Basin Analysis, 13: 65-95.
Chen, J. and Gong, W., 1986- Conodonts. In Aspects of Cambrian–Ordovician Boundary in Dayangcha, China. (Chen, J., ed.), China Prospect Publishing House, Beijing, 93-223.
Cooper, R. A. and Sadler, P. M., 2012- The Ordovician Period. In The Geological Time Scale 2012 (Gradstein, F. M., Ogg, J. G., Schmitz, M. D. and Ogg,G. M., eds). Elsevier, Chapter 20, Amsterdam [ebook].
Cooper, R. A., Maletz, J., Wang, H. and Erdtmann, B. D., 1998- Taxonomy and evolution of earliest Ordovician graptolites: Norsk Geologisk Tiddskrift, 78:3-32.
Cooper, R. A., Nowlan, G. S. and Williams, S. H., 2001- Global stratotype section and point for base of the Ordovician system, Episodes 24: 19- 28.
Davidson, T., 1868- On the earliest forms of Brachiopoda hitherto discovered in the British Palaeozoic rocks. Geological Magazine, 5: 303-316.
Eichwald, E. 1840- Ueber das silurische Schichtensysstem in Esthland. Akademie der St. Petersburg, pp: 240.
Erdtmann, B. D., 1986- Early Ordovician eustatic cycles and their bearing on punctuations in early nematophorid (planktic) graptolite evolution. In Walliser, O.H., Ed., Lecture Notes in Earth Sciences, Global Bioevents, 8: 139-152.
Ghaderi, A., Aghanabatil, A., Hamdi, B. and Miller, J. F., 2009- Biostratigraphy of the first and second member of type section of the Shirgesht Formation in north of Tabas with special emphasis on conodonts. Journal of Earth Scinces Iran, 67: 150-163.
Ghavidel-Syooki, M., 2006- Palynostratigraphy and palaeogeography of the Cambro-Ordovician strata in southwest of Shahrud city (Kuh-e-Kharbash, near DehMolla), Central Alborz, Northern Iran. Review of Palaeobotany and Palynology, 139: 81-95.
Ghobadi Pour, M., 2006- Early Ordovician (Tremadocian) trilobites from Simeh-Kuh, Eastern Alborz, Iran. In Bassett, M.G. and Deisler, V.K. (eds): Studies in Palaeozoic palaeontology. National Museum of Wales Geological Series, 25: 93-118.
Ghobadi Pour, M., Mohibullah, M., Williams, M., Popov, L. E. and Tolmacheva, T. Yu., 2011- New, early ostracods from the Ordovician (Tremadocian) of Iran: systematic, biogeographical and palaeoecological significance. Alcheringa, 35: 517-529.
Ghobadi Pour, M., Popov, L. E., Amini, A., Ahmadi, M. A. and Tolmacheva, T. U., 2009- The Cambrian – Ordovician faunal transition in southern Kopet-Dagh, north-eastern Iran. 53th Palaeontological Association Annual Meeting, Birmingham University, England, p. 70.
Holmer, L. E., Popov, L. E., Koneva, S. P. and Bassett, M. G., 2001- Cambrian – early Ordovician brachiopods from MalyiKaratau, the western Balkhash Region, and northern Tien Shan, Central Asia. Special Papers in Palaeontology, 65:1-180.
Holmer, L. E., Popov, L. E., Streng, M. and Miller, J. F., 2005- Lower Ordovician (Tremadocian) lingulate brachiopods from the House and Fillmore Formations, Ibex Area, Western Utah, USA. Journal of Palaeontology, 79: 884-906.
Jahangir, H., Ghobadi Pour, M. and Ashouri, A. R., 2014- Palaeobiogeography of conodonts from the Alborz Mountains through Cambrian–Ordovician transition. Paleontology (Iran), 1 (2): 137-148. [In Persian.]
Jeong, H. and Lee, Y. I., 2000- Late Cambrian biogeography: conodont bioprovinces from Korea. Palaeogeography, Palaeoclimatology, Palaeoecology, 162: 119-136.
Kaljo, D., Borovko, N., Heinsalu, H., Khazanovich, K., Mens, K., Popov, L., Sergeyeva, S., Sobolevskaya, R. and Viira, V., 1986- The Cambrian-Ordovician boundary in the Baltic–Ladoga clint area. Eesti NSV Teaduste Akadeemia Toimetised. Geoloogia, 35: 97–108.
Kebria-eeZadeh, M. R., Ghobadi Pour, M., Popov, L. E., Baars, C. and Jahangir, H., 2015- First record of the Ordovician fauna in Mila-Kuh, eastern Alborz, northern Iran. Estonian Journal of Earth Sciences, 64. [In press.]
Koneva, S. P. and Popov, L. E., 1988- Acrotretides (inarticulate brachiopods) from the Cambrian–Ordovician boundary beds of the Malyi Karatau Range (south Kazakhstan). Ezhegodnik Vsesoiuznogo Paleontologicheskogo Obshchestva, 31: 52-72. [In Russian. ]
Kushan, B., 1973- Stratigraphy and trilobite fauna of the Mila Formation (Middle Cambrian-Tremadocian) of the Alborz Range, North Iran. Report Geological Survey of Iran, 46: 1-70.
Miller, J. F., 1969- Conodont fauna of the Notch Peak Limestone (Cambro-Ordovician) House Range, Utah. Journal of Paleontology, 43: 413-439.
Miller, J. F., Evans, K. R., Freeman, R. L., Ripperdan, R. L. and Taylor, J. F., 2011- Proposed stratotype for the base of the Lawsonian Stage (Cambrian Stage 10) at the First Appearance Datum of Eoconodontus notchpeakensis (Miller) in the House Range, Utah, USA. Bulletin of Geosciences, 86: 595-620.
Miller, J. F., Evans, K. R., Loch, J. D., Ethington, R. L., Stitt, J. H., Holmer, L. E. and Popov, L. E., 2003- Stratigraphy of the Sauk III interval (Cambrian-Ordovician) in the Ibex area, western Millard County, Utah and central Texas. Brigham Young University Geology Studies, 47: 23-118.
Muller, K., 1959- Kambrische Conodonten. Zeitschrift Deutschen Geologische Gesellschaft, 111: 434-485.
Nielsen, A. T., 2004- Ordovician sea level changes: A Baltoscandian Perspective, 84-93. In The Great Ordovician Biodiversification Event (Webby, B. D., Paris, F., Droser, M. L. and Percival, I. G., eds). Columbia University Press, New York. 484 pp.
Nõlvak, J., Hints, O. and Männik, P, 2006- Ordovician timescale in Estonia: recent developments. Proceedings of the Estonian Academy of Sciences, Geology, 55: 95-108.
Peng, S. C., Geyer, G. and Hamdi, B., 1999- Trilobites from the Shahmirzad section, Alborz Mountains, Iran: Their taxonomy, biostratigraphy and bearing for international correlation. Beringeria, 25: 3-66.
Popov, L. E. and Holmer, L. E., 1994- Cambrian-Ordovician lingulate brachiopods from Scandinavia, Kazakhstan, and South Ural Mountains. Fossils and Strata, 35: 1-156.
Popov, L. E., Ghobadi Pour, M., Kebria-eeZadeh, M. R. and Shahbeik, S., 2011- First record of silicified Cambrian (Furongian) rhynchonelliform brachiopods from the Mila Formation, Alborz Range, Iran. Memoirs of the Association of Australasian Palaeontologists, 42: 193-207.
Popov, L. E., Holmer, L. E. and Miller, J. F. 2002- Lingulate brachiopods from the Cambrian-Ordovician boundary beds of Utah. Journal of Paleontology, 76: 211-228.
Terfelt, F, Bagnoli, G. and Stouge, S., 2012- Re-evaluation of the conodont Iapetognathus and implications for the base of the Ordovician System GSSP. Lethaia,. 45: 227-237.
Viira, V. and Sergeeva, S., 1986- Razrez  ordovika  nar.  Kuluyme: in Materialy po geologii I poleznym iskopaemym Vostochnoi Sibiri. Nedra, Leningrad, 68–82.