The Lower-Middle Ordovician sediments exposed in the Faraghan Mountains, south-eastern Zagros Ranges, represent a condensed succession of siliciclastic-dominated rocks rich in palynomorph assemblages (acritarchs and subsidiary chitinozoans) and sparse shelly concentrations bearing biostratigraphically significant brachiopods and conodonts.The Lower Ordovician Zard-Kuh Formation comprises coarse-grained siliciclastic deposits rich in Cruziana ichnofossils.The lower 80 m of the overlying Seyahou Formation, late Floian to Katian in age, form a heterolithic succession composed of black and green shales, subarkoses and silty limestones.Its lower part is punctuated by a centimetric phosphoarenite that contains lingulate brachiopods (Atansoria yaseri sp.nov.) and conodonts (Baltoniodus aff.B. triangularis Lindström and Drepanoistodus sp.) that suggest a latest Floian age.The top of the condensed phosphoarenite is marked by a considerable hiatus that ranges the Dapingian and early Darriwilian interval.Overlying the hiatus, the Seyahou Formation comprises two fossiliferous levels, the oldest dated as mid-Darriwilian with chitinozoans characteristic of the Siphonochitina formosa Zone, and the youngest of the Katian Acanthochitina barbata Zone.Mid Ordovician phosphogenesis associated with starvation, reworking, resedimentation, and the onset of distinct stratigraphic gaps was a complex process recorded throughout the Arabian margin of Gondwana.In the Zagros Ranges, maximum flooding and phosphate precipitation are suggested as the counterpart of the Helskjer Drowning Event of Baltoscandia and the third-order maximum flooding surface that punctuates the Siphonochitina formosa Zone in North Africa.
Ghavidel-Syooki, M., Evans, D.H., Ghobadi Pour, M., Popov, L.E., Álvaro, J.J., Rakhmonov, U., Klishevich, I.A. & Ehsani, M.D., 15.5.2015. Late Ordovician cephalopods, tentaculitides, machaeridians and echinoderm columnals from Kuh-e Faraghun, High Zagros, Iran. Alcheringa 39, 530–549. ISSN 0311-5518.Late Ordovician (Katian, uppermost Acanthochitina barbata to Armoricochitina nigerica chitinozoan zones) cephalopods, tentaculitides, machaeridians and echinoderms are documented for the first time from the southern Zagros Ranges. A low-diversity cephalopod fauna includes Geisonocerina dargazense sp. nov., Isorthoceras sp. cf. I. bisignatum (Barrande) and other undetermined orthoceratides. The presence of Late Ordovician tentaculitides in the high- to mid-latitude margins of Gondwana has been documented previously, but no examples have been described in detail. Thus, Costatulites kimi sp. nov., which currently occurs associated with brachiopods characteristic of the Svobodaina havliceki (brachiopod) Association, represents the earliest undoubted record of tentaculitides in Gondwana. Machaeridians constitute a relatively common component of the Late Ordovician benthic faunas from the Mediterranean margin of Gondwana, but no previous records on the Gondwanan Iranian-Arabian segment have been reported. Three echinoderm taxa based on dissociated columnals are documented from the Armoricochitina nigerica chitinozoan Zone, including Sumsaricystis radiatus Stukalina, Ristnacrinus sp. and Rosulicrinus rosulus Stukalina.Mohammad Ghavidel-Syooki [m_ghavidelsyooki@yahoo.com] Institute of Petroleum Engineering, Technical Faculty of Tehran University, PO Box 11365-4563, Tehran, Iran; David H. Evans [david.evans@naturalengland.org.uk], Natural England, Suite D, Unex House, Bourges Boulevard, Peterborough PE1 1NG, UK; Mansoureh Ghobadi Pour* [mghobadipour@yahoo.co.uk], Department of Geology, Faculty of Sciences, Golestan University, Gorgan, Iran; Leonid E. Popov [leonid.popov@museumwales.ac.uk], Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, UK; J. Javier Álvaro [jj.alvaro@csic.es], Instituto de Geociencias (CSIC-UCM), c/ José Antonio Novais 2, 28040 Madrid, Spain; Utkyr Rakhmonov, Kitab State Geological Reserve, 9 Ipak Yuli Street, Sakhrisabz, Uzbekistan; Inna A. Klishevich, Department of Historical Geology, Geological Faculty, St Petersburg State University, Universitetskaya Naberezhnaya 7/9, 199034 St Petersburg, Russia [inna@IK4848.spb.edu]; Mohammad H. Ehsani [mh_ehsani@hotmail.com], Institute of Petroleum Engineering, Technical Faculty of Tehran University, PO Box 11365-4563, Tehran, Iran. *Also affiliated with Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, UK.
ABSTRACT Brachiopods are among the most common components of the Late Ordovician benthic faunal assemblages recorded in the Faraghan Mountains, Zagros Ranges, Iran. A total of 19 species referable to 16 genera are identified, including seven new species; namely Drabovia elegans , Hibernodonta bonehensis , Hedstroemina zakeenensis , Jezercia faraghani , Protomendacella multicostata , Tafilaltia dargazensis and Tafilaltia seyahouensis . Reported brachiopod assemblages are oligotaxic (2–3 species per assemblage) to monotaxic. The only exception is the medium diversity Aegiromena - Hedstroemina Association, with up to ten species, which occurs at the lower part of the A . nigerica Zone. Low diversity patterns were probably controlled by the palaeogeographical position of the region in high southern latitudes throughout the Ordovician. Paterula sp. and Iranospirifer sp. are the only brachiopods documented from the Silurian (Llandovery) Sarchahan Formation. This paper gives the first detailed report of shelly fossils from the Llandovery ‘hot shale’ of the Arabian margin of Gondwana. Most of the Katian genera, and many of their species, are shared with neighbouring high- to mid-latitude peri-Gondwanan margins, including Morocco, Spain, France, Sardinia and Bohemia.
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