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Conodonts from the Niur Formation (Silurian) of the Derenjal Mountains, Central Iran

Article in Geological Magazine · July 2013 DOI: 10.1017/S001675681200088X

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Peep Mannik C. Giles Miller Tallinn University of Technology Natural History Museum, London

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The user has requested enhancement of the downloaded file. Geol. Mag. 150 (4), 2013, pp. 639–650. c Cambridge University Press 2013 639 doi:10.1017/S001675681200088X Conodonts from the Niur Formation (Silurian) of the Derenjal Mountains, Central Iran

∗ P. MÄNNIK †, C. G. MILLER‡ & V. HAIRAPETIAN§ ∗ Institute of Geology at Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia ‡Department of Palaeontology, Natural History Museum, London SW7 5BD, UK §Department of Geology, Khorasgan (Esfahan) Branch, Islamic Azad University, PO Box 81595−158, Esfahan, Iran

(Received 5 October 2011; accepted 25 September 2012; first published online 24 January 2013)

Abstract – A Llandovery to Ludlow age for the Niur Formation in the Derenjal Mountains (east-central Iran) is proposed based on new data and previous work on other fossils. The uppermost part of the studied section yielded no diagnostic conodonts but may be Pridoli in age. Some intervals can be dated more precisely: Unit 11 (at least its upper part) is middle Telychian in age and corresponds to the amorphognathoides lennarti Zone; the lowermost part of Unit 16 is earliest Ludlow in age and corresponds to the crassa Zone; the uppermost Unit 16 is late Ludlow (Ludfordian) in age and corresponds to the snajdri Interval Zone. The Llandovery–Wenlock boundary lies between units 12 and 13 based on sedimentological evidence. The precise location of the Wenlock– Ludlow boundary in the section is not clear but lies below Unit 16. Present-day Iran was located far away from Baltica and Laurentia, on the other side of the Rheic Ocean. This ocean does not seem to have been a major migration barrier for most organisms including the conodonts. Keywords: stratigraphy, palaeogeography, conodonts, Niur Formation, Silurian, Iran.

1. Introduction weight varied between 0.5 and 3 kg and the number of specimens per productive sample from 2 to 361. The Lower Palaeozoic of Iran including the Silurian, is All samples were dissolved in buffered 10 % acetic well exposed in several regions: in the north along the acid and the residues washed through a 15.6 μm sieve. southern coast of the Caspian Sea (Alborz Mountains All residues were picked completely; heavy liquid and the Kope Dagh zone), in east-central Iran (Kerman– separation techniques were not applied. Illustrated spe- Saghand and Tabas regions; Fig. 1) and in the Zagros cimens were gold-palladium coated and photographed Basin (Gahkum and Faraghan mountains). The section using a Phillips XL-30 scanning electron microscope at studied here is located about 65 km northwest of the Natural History Museum, London. All material is Tabas, on the eastern side of the Dahaneh-e-Kolut deposited at the Department of Palaeontology, Natural Gorge in the Derenjal Mountains (Figs 1, 2). Here, History Museum (prefix NHMUK PM X). Where approximately 551 m of the Silurian Niur Formation conodont apparatus structure and therefore biological is exposed (Fig. 3). Silurian conodonts have been positioning of elements at generic level is proven reported from the Derenjal Mountains by Ruttner, from natural assemblages, the P ,P,M,S notation Nabavi & Hajian (1968) and Hamedi et al. (1997). 1 2 0-X outlined by Purnell, Donoghue & Aldridge (2000) is However, both publications provide lists of taxa and followed. When there is no evidence for homology no illustrations. The only known illustrations of Niur between different element types, the traditional Pa, Pb, Formation conodonts are from the Huk section located M, Sa, Sb, Sc notation has been followed. in NE Iran (Weddige, 1984). New samples from a section in the Derenjal Mountains have been studied for conodonts. The aims of this paper are to give a brief lithological description of the section, to update 3. Geographical and geological setting conodont identifications and associated ages, and to The Niur Formation was formally established by briefly discuss the palaeogeographic affinities of the Ruttner, Nabavi & Hajian (1968). In the studied fauna. section, the Niur Formation is underlain by fossiliferous limestone of the Shirgesht Formation of Early to Middle 2. Materials and methods Ordovician age and overlain by the siliciclastic Padeha Formation of presumed Early Devonian age. The type Forty-two samples were collected by V. Hairapetian section of the Niur Formation is located in the vicinity during fieldwork in 2004 and 2007. Only calcareous of Niur village in the Ozbak-Kuh Mountains, c.90km intervals of the section were sampled and processed, northeast of the section discussed in this paper. The with 17 samples yielding conodonts (Fig. 3). Sample section studied here in the Derenjal Mountains was referred to as the ‘reference section’ of the Niur † Author for correspondence: [email protected] Formation by Ruttner, Nabavi & Hajian (1968). There

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3.a. Hill A (units 1–4: 135.70 m) Base of the section. Lowermost part of the northern slope of Hill A; co-ordinates: 34◦ 05 8.3 N and 56◦ 4814.0 E; altitude: 1072 m. Description of the section starts from the base of a bed of olivine basalt, from the level tentatively correlated with the Ordovician–Silurian boundary. Unit 1. 12.80 m. Altered dark green massive olivine basalt. Unit 2. 23.50 m. Brown to grey, medium- to thin- bedded bioclastic packstone and grainstone with a bed of brown re-crystallized limestone at the top. Corals, brachiopods, ostracods and trilobites occur. Conodont samples (all levels are measured from the base of Unit 2; Fig. 3): S1, 3.20 m; S2, 4.10 m; S3, 4.40 m; S4, 7.10 m; S5, 8.40 m; S6, 9.10 m; S7, 10.70 m; S8, 16.10 m; S9, 16.80 m; S10, 17.70 m; S11, 21.00 m. Unit 3. 56.40 m. Altered dark green massive olivine basalt. TopofUnit3. Co-ordinates 34◦ 05 07.0 N and 56◦ 48 13.9 E; altitude 1077 m. The measured section continues about 600 m to the east of Hill A. The upper boundary of Unit 3 was traced to this point. Location of the base of Unit 4.34◦ 05 12.4 N and 56◦ 48 39.6 E; altitude 1071 m. Unit 4. 43.00 m. Intercalation of siltstone and silty shale. The rock is reddish brown and yields brachiopods, corals and rare trilobite fragments. At the base of the unit lies a bed of sandy limestone. Sample S11/1 comes from a level 35.80 m above the base of the unit. The upper boundary of Unit 4 (the top of Hill A) is probably faulted.

3.b. Hill B (units 5–12: 219.30 m) Figure 1. Location of the study area (Derenjal Mountains) The section continues on Hill B, which is to the south of in east-central Iran (a), and of the sampled section of the Hill A. The valley separating these two hills is covered Niur Formation in the Derenjal Mountains (b). (Modified from Hairapetian et al. 2008 with permission from Acta by alluvium. Palaeontologica Polonica). Base of the strata exposed on Hill B. Co-ordinates 34◦ 5 2.9 N and 56◦ 48 14.0 E; altitude 1040 m. Top of the section. Co-ordinates 34◦ 04 56.1 N and 56◦ 48 14.8 E; altitude 1082 m. are considerable lithological differences between these Unit 5. 63.00 m. White medium- to thin-bedded two sections. The sandstone members (units 5, 8, 10, sandstone (quartz arenite) with cross-bedding and fine 14) recognized in the section in the Derenjal Mountains lamination in some intervals. An interval of brown (Fig. 3) are missing in the type section of the Niur sandstone occurs in the middle part of the unit. Formation in the Ozbak-Kuh Mountains. The faulted Unit 6. 6.70 m. Brown thin-bedded sandy limestone. Ordovician–Silurian contact is overlain by dolostones Silicified brachiopods (mostly unstudied spiriferids) followed mainly by coral-bearing limestones higher in are quite common. Conodont sample: S12, 6.50 m the type section (Ruttner, Nabavi & Hajian, 1968). above the base of the unit. However, contrary to the original description of the Unit 7. 33.80 m. Grey to brown, medium- to thin- section in the Derenjal Mountains by Ruttner, Nabavi & bedded bioclastic packstone and grainstone rich in Hajian (1968), the lower contact of the Niur Formation brachiopods, corals, bryozoans, orthoconic nautiloids is also faulted (Bruton, Wright & Hamedi, 2004; and tentaculites. The uppermost beds of the unit are Ghobadi Pour et al. 2006). represented by sandy limestone. Conodont samples In the Derenjal Mountains, the Silurian is exposed (all levels are measured from the base of Unit 7): S13, on three major hills: A, B and C (Figs 2, 3). A general 13.00 m; S14, 16.30 m; S15, 19.40 m; S16, 28.50 m; description of the section is provided below. S17, 31.00 m. Macrofossils Mesoleptostrophia

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Figure 2. (Colour online) Field photographs of the section of the Niur Formation, Derenjal Mountains, east-central Iran. (a) Upper part (units 19 and 20, Hill C) of the section and the boundary between the Niur (Silurian) and the overlying Padeha (Devonian) formations; dashed line indicates base of the lowermost white quartzitic bed of the Padeha Formation. (b) Upper part of Hill B (units 10 to 12) and lower part of Hill C (units 13 to 16), view from the north. (c) Hill B, units 5 to 10, view from the west. (d) General view of the basal part of the section (Hill A, units 2 and 3).

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Figure 3. Studied section and distribution of conodonts. From left to right: systems, formations; hills where a particular interval of the section was studied; described units; lithological log (arrows below and above the log indicate that the section continues in both directions); locations and numbers of samples processed for conodonts (numbers in bold – samples that yielded conodonts); number of specimens in a sample; distribution of conodonts; conodont zones (after Cramer et al. 2011b) and general stratigraphy (Stage, Series, System). Grey boxes in the column of conodont zonation indicate zones (part of) which were recognized in the studied section. Abbreviations: Pt.–Pterospathodus; a.–amorphognathoides; p. – pennatus; K.–Kockelella; Oz.–Ozarkodina; s.–sagitta; o.–ortus; v.–variabilis; Anc.–Ancoradella; Pol.–Polygnathoides; S. Z. – Superzone; I. Z. – Interval Zone; Gorst. – Gorstian.

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(Mesoleptostrophia) sp., Isorthis (Ovalella) inflata Unit 17. 1.50 m. Grey to yellow thin-bedded Popov, Modzalevskaya & Ghobadi Pour, Dalejina? fossiliferous marlstone. rashidii Popov, Modzalevskaya & Ghobadi Pour, Conodont sample S29 is from 0.15 m above the base Stegocornu denisae Popov, Modzalevskaya & Ghobadi of the unit. Pour, Rhyidorhachis? sp., Stegorhynchus? sp., Unit 18. 20.50 m. Grey thin- to medium-bedded Hercotrema sp. and Striispirifer? ocissimus Popov, dolomitic bioclastic packstone. The sample S30 comes Modzalevskaya & Ghobadi Pour were identified from from 12.10 m above the base of the unit. sample S14 (Hairapetian et al. 2012). Unit 19. 26.20 m. Grey thin- to medium-bedded Unit 8. 14.20 m. White medium- to thin-bedded limestone with crinoids, brachiopods and corals. allochemic sandstone. At some levels poorly preserved Conodont samples (all levels are measured from the brachiopods occur. base of Unit 19): S31, 1.30 m; S32, 8.80 m; S33, Unit 9. 7.80 m. Intercalation of brown medium- to 10.10 m; S34, 12.10 m; S35, 19.70 m. Sample S31 thin-bedded sandy limestone and dolomitic limestone. contains unidentified spiriferids and rhynchonellids; a Rare fragments of brachiopods have been found. bed 3 m above sample S31 yields some unidentified Unit 10. 77.70 m. White medium- to thin-bedded rhynchonellids, atrypids and spiriferids; in sample S35 allochemic sandstone. At some levels poorly preserved brachiopods Lyssatrypa sp. and also some athyridides brachiopods occur. were found. Unit 11. 11.70 m. Grey thin-bedded bioclastic mud- Unit 20. 35.10 m. Brown medium-bedded more stone, wackestone and grainstone with brachiopods and or less calcareous dolostone with some sand in the corals. At the top of the unit, a ∼ 0.15 m thick bed uppermost beds. Some poorly preserved brachiopods of yellow biodetrital limestone with relatively coarse and corals(?) occur at the base of the unit. Sample S36 lithoclasts occurs. Conodont samples (both levels are was taken at 13.10 m above the base of the unit. In measured from the base of Unit 11): S18, 7.80 m; S19, the upper part of the section, the boundary between the 10.70 m. Niur Formation and the overlying white quartzite of the Unit 12. 4.40 m. Brown to red sandy limestone. Padeha Formation is conformable and transitional.

3.c. Hill C (units 13–20: 196.30 m) 4. Age of the Niur Formation The section continues without a gap in the succession 4.a. Conodonts to Hill C. Base of the section on Hill C. Co-ordinates Based on conodonts (identified by O. H. Walliser), 34◦ 04 49.8 N and 56◦ 48 6.4 E; altitude 1078 m. but also on some other faunas from the Derenjal Top of section. Co-ordinates 34◦ 04 44.6 N and Mountains, a Llandovery to (probably) Pridoli age 56◦ 48 7.3 E; altitude 1069 m. was suggested for the Niur Formation by Ruttner, Unit 13. 34.20 m. Highly fossiliferous bioclastic Nabavi & Hajian (1968). These conclusions were dark grey thin-bedded argillaceous wackestone and later supported by R. J. Aldridge (in Hamedi et al. packstone. Conodont samples (all levels are measured 1997). Weddige (1984) discussed conodonts from the from the base of Unit 13): S20, 1.30 m; S21, 4.90 m; Niur Formation exposed in the Huk locality in the S22, 18.10 m. Ozbak-Kuh Mountains and in a section in the Binalud Unit 14. 7.00 m. Brown medium- to thin-bedded Mountains near Mashad in NE Iran. partly calcareous (dolomitic?) sandstone. Unit 15. 40.80 m. Grey medium- to thin-bedded 4.a.1. Llandovery–Wenlock argillaceous bioclastic limestone (mudstone, wacke- stone, packstone and grainstone) with brachiopods and One sample studied by Ruttner, Nabavi & Hajian (1968; corals. Conodont samples (all levels are measured from W1119 from bed no. 12, most probably equivalent to the base of Unit 15): S22/1, 4.15 m; S22/2, 8.20 m; our Unit 7) yielded Hadrognathus staurognathoides S22/3, 9.00 m; S23, 13.80 m; S23/1, 30.20 m; S23/2, s.f. Walliser. Other taxa identified were Lonchodina 34.90 m; S23/3, 36.70 m; S24, 40.80 m. Samples S22 sp. s.f., Neoprioniodus sp. s.f. and Ozarkodina sp. and S23 contain brachiopods Isorthis sp. sensu lato and s.f. Without restudying these specimens, no valuable some rhynchonellids. stratigraphical information can be obtained. However, a Unit 16. 31.00 m. Grey thin- to medium-bedded late Valentinian( = approximately Llandovery) to early bioclastic packstone with brachiopods and dolostone Wenlock age suggested by Ruttner, Nabavi & Hajian interbeds. Two beds rich in corals, possibly with algae (1968) for this level agrees, in general, with our data. and bryozoans, occur in intervals 6.00–6.20 m and The conodont assemblage from Unit 7 (our samples 11.30–11.45 m above the base of the unit. Additionally, S15–S17; Fig. 3) includes two undescribed taxa, a 0.20 m thick bed of coral limestone was observed Ozarkodina sp. nov. (aff. Ozarkodina sp. C Mabillard & in the interval 7.90–8.10 m above the base. Conodont Aldridge) (Fig. 4o) and Ozarkodina sp. nov. A (Fig. 4f), samples (all levels are measured from the base of Unit along with staurognathoides, Wurmiella 16): S25, 3.10 m; S26, 5.00 m; S27, 14.30 m; S28, ex gr. excavata and some poorly preserved elements 29.20 m. of Panderodus and ?. D. staurognathoides

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Figure 4. Selected conodonts from the Niur Formation. Scale bar corresponds to 0.1 mm. (a) Wurmiella ex. gr. excavata (Branson & Mehl); NHMUK PM X 3592, lateral view of P1 element, sample S15. (b–d) Wurmiella excavata; (b) NHMUK PM X 3591, lateral view of P1 element, sample S20; (c) NHMUK PM X 3593, posterior view of S1–2 element, sample S21; (d) NHMUK PM X 3594, lateral view of P2 element, sample S21. (e) Distomodus staurognathoides (Walliser); NHMUK PM X 3275, upper view of Pa element,

http://journals.cambridge.org Downloaded: 11 Jun 2013 Conodonts from the Niur Formation 645 indicates that the Unit 7 limestone cannot be older section should be placed between samples S19 and S20. than middle Aeronian and corresponds to the D. stauro- Lack of any other taxa in the lowermost part of Unit gnathoides Zone (Loydell, Nestor & Männik, 2010). W. 13 indicates that S20 comes from a level above the last ex gr. excavata in this unit (Fig. 4a) is morphologically datum of the Ireviken Event ( = the level of extinction quite similar to W. excavata puskuensis (Männik), an of D. staurognathoides; Jeppsson, 1998), i.e. well above older form of the W.excavata lineage. W.e. puskuensis the Llandovery–Wenlock boundary (Männik, 2007b). is known to occur in strata of late Rhuddanian In this paper, the Llandovery–Wenlock boundary is and Aeronian age (Männik, 1994). If the Wurmiella tentatively drawn at the boundary between units 12 specimens in samples S12 and S15 from Unit 7 are and 13, at a level where sandy limestone of Unit really W. e. puskuensis, the unit (at least the lower and 12 is replaced by argillaceous limestone of Unit 13. middle parts of it; Fig. 3) is middle to late Aeronian Conodonts currently available do not allow precise in age. Ozarkodina sp. C Mabillard & Aldridge has dating of the strata just above this level. As a result, been described from the Telychian of the Marloes the base of Unit 13 up to the upper part of Unit 15 is Bay section, SW Dyfed, Wales (Mabillard & Aldridge, tentatively correlated with the Wenlock in this paper 1983). However, our specimens of Ozarkodina sp. (Fig. 3). nov. (aff. Ozarkodina sp. C Mabillard & Aldridge), although in general morphologically similar to those 4.a.2. Wenlock–Ludlow of Ozarkodina sp. C Mabillard & Aldridge, evidently represent another taxon which could be an older The conodont sample studied by Ruttner, Nabavi & representative of the same lineage (see taxonomic Hajian (1968; W1155 from bed 28) probably corres- discussion in Section 7 below). Hence, the conodont ponds to a level within our Unit 19. data suggest that the Aeronian–Telychian boundary steinhornensis subsp. indet. s.f. Walliser, Ozarkod- most probably lies within Unit 7 (Fig. 3). ina denckmanni s.f. Ziegler, Lonchodina greilingi The next samples, S18 and S19, come from s.f. Walliser, Oz. media s.f. Walliser, Trichonodella the upper part of Unit 11. Sample S19 yields the inconstans s.f. Walliser, Neoprioniodus primus s.f. richest and most abundant fauna (361 specimens) (Branson & Mehl), S. primus s.f. (Branson & Mehl) and in the studied section (Fig. 3). The fauna recovered Lonchodina sp. A s.f. were identified in this sample by includes Pterospathodus amorphognathoides lennarti O. H. Walliser. Based on this assemblage, a late Ludlow (Fig. 4i–k), D. staurognathoides, Pseudooneotodus to earliest Devonian age was suggested, with a proviso tricornis (Fig. 4q), Ozarkodina aff. waugoolaensis that it was probably latest Ludlow (Ludfordian) in (Fig. 4l), Aspelundia? sp., Wurmiella? sp., Oulodus? age. In modern terminology, the assemblage probably spp. and some poorly known or undescribed taxa: included Oz. confluens (Branson & Mehl), W.excavata Ozarkodina sp. nov. (aff. Ozarkodina sp. A Mabillard and Oulodus? sp. Assignment of elements identified & Aldridge) (Fig. 4h) and gen. et sp. nov. A (aff. I.? as S. steinhornensis subsp. indet. s.f. to any known sandersi Mabillard & Aldridge) (Fig. 4r–s). Gen. et sp. apparatus is more complicated. It is most probably a nov. A (aff. I.? sandersi Mabillard & Aldridge) first representative of the Oz. steinhornensis s.l. ‘group’ appears in sample S18 (together with Ozarkodina aff. appearing in most known successions in the late waugoolaensis) but is particularly common in S19. The Ludfordian. More material needs to be found and occurrence of Pt. a. lennarti in S19 indicates that this studied to decide if it belongs to Zieglerodina or to sample comes from the Pt. a. lennarti Zone and is Genus W eosteinhornensis (Walliser) sensu Murphy, middle Telychian in age (Männik, 2007a; Fig. 3). Valenzuela-Ríos & Carls (2004). As the samples from just above Unit 12, from the All samples processed by us from Unit 19 were lowermost and middle parts of Unit 13, yield only W. barren. The uppermost conodont in our collection excavata excavata (Fig. 4b–d), a taxon characteristic Zieglerodina? sp. (Figs 3, 4p) comes from sample of Sheinwoodian and younger strata, it seems most probable that the Llandovery–Wenlock boundary in the

sample S12. (f) Ozarkodina sp. nov. A; NHMUK PM X 3595, lateral view of P1 element, sample S15. (g) Ozarkodina cf. roopaensis Viira; NHMUK PM X 3271 lateral view of P1 element, sample S26. (h) Ozarkodina sp. nov. (aff. Ozarkodina sp. A Mabillard & Aldridge); NHMUK PM X 3596, lateral view of P1 element, sample S19. (i–k) Pterospathodus amorphognathoides lennarti Männik; (i) NHMUK PM X 3597, lateral view of Pb2 element; (j) NHMUK PM X 3598, upper view of Pa element; (k) NHMUK PM X 3599, lateral view of Pb1 element. All specimens from sample S19. (l) Ozarkodina aff. waugoolaensis Bischoff; NHMUK PM X 3600, lateral view of P1 element, sample S19. (m) Ozarkodina ex gr. snajdri (Walliser); NHMUK PM X 3268, upper (m1) and lower (m2) views of P1 element, sample S28. (n) Ozarkodina bohemica bohemica (Walliser); NHMUK PM X 3273, lateral (n1) and lower (n2) views of P1 element, sample S24. (o) Ozarkodina sp. nov. (aff. Ozarkodina sp. C Mabillard & Aldridge); NHMUK PM X 3601, lateral view of P1 element, sample S12. (p) Zieglerodina? sp.; NHMUK PM X 3602, lateral (p1) and lower (p2) views of P1 element, sample S30. (q) Pseudooneotodus tricornis Drygant; NHMUK PM X 3277, upper view, sample S19. (r–s) gen. et sp. nov. A (aff. I.? sandersi Mabillard & Aldridge); (r) NHMUK PM X 3603, lateral (r1), lower (r2) and upper (r3) views of Pa element; (s) NHMUK PM X 3604, upper (s1) and lower (s2) views of ‘ambalodiform’ P? element. Both specimens from sample S19.

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S30, from the middle part of Unit 18. Zieglerodina, 4.b. Other faunas which first appears in the uppermost Ludlow, is more Dating of the Niur Formation based on other fossils characteristic of the Pridoli and particularly of the is consistent with the results of the conodont studies. lowermost Devonian (Carls, Slavik & Valenzuela-Ríos, Rugose and tabulate corals, stromatoporoids, brachio- 2007). As a result, our material does not allow improved pods and ostracods are common in the studied section. dating of the uppermost part of the studied section but it Flügel & Saleh (1970) studied the diverse but mostly does not contradict the conclusions of Ruttner, Nabavi endemic rugose faunas in detail. From the outcrops on & Hajian (1968). Hill A (units 2 and 4) and the middle part of Hill B Based on our collections, two other intervals (Unit 7), they identified Grewingkia alternata Saleh, in the studied section can be dated precisely. Oz. Paliphyllum (Paliphyllum) oblongaecystosum Saleh, bohemica (Figs 3, 4n) has been identified from the Schlotheimophyllum sp., Streptelasma shirgeshtensis lowermost part of Unit 16, and probably from the Saleh, S. ruttneri Saleh and Tryplasma sp., suggesting a uppermost beds of Unit 15. At least two chronological Llandovery age for these strata (Flügel & Saleh, 1970). subspecies are known in the Oz. bohemica lineage: Characteristic Ludlow taxa were reported on Hill C Oz. b. longa Jeppsson characteristic of the upper from Unit 19 (beds 27–30 in Ruttner, Nabavi & Hajian, Wenlock (Homerian) and Oz. b. bohemica occurring 1968), Cystiphyllum (Holmophyllum) pauciseptatum in the lowermost Ludlow (in the lowermost Gorstian; Flügel & Saleh, and from units 13 and 15 (beds 24 Jeppsson & Aldridge, 2000; Calner & Jeppsson, 2003; and 26), Gyalophyllum (Coronoruga) sp. Jeppsson, Eriksson & Calner, 2006). The P element 1 From Hill A, units 2 and 4, Hubmann (1991a) of Oz. b. longa is relatively long and low, whereas that described tabulate corals of Llandovery age, including of Oz. b. bohemica is shorter and higher. However, Eocatenipora nicholsoni Kiaer, Catenipora obliqua variation in these dimensions is only distinct in larger Fischer-Benzon, C. micropora Whitfield, C. gotlandica collections, particularly in those containing many Yabe, C.cf.louisvillensis Stumm, C.cf.jarviki specimens of Oz. b. longa. As a result, when only a Stasinska, C. khorasanensis Hubmann and Halysites small number of specimens are available, it is often labyrinthicus Goldfuss. The Llandovery stromato- difficult to tell which subspecies is present. Only two poroid Ecclimadictyon pseudofastigiatum (Riabinin) well-preserved P elements from samples S24 and S25 1 described by Flügel (1969) most probably comes from (Fig. 3) have been recovered from the Niur Formation. the lower part of Unit 4 exposed in an outcrop on the However, as only short and high specimens with large western side of the Dahaneh-e-Kolut Gorge. Another basal cavities (Fig. 4n) occur, it seems most probable stromatoporoid, Clathrodictyon pustulatum Yavorsky, that our specimens belong to Oz. b. bohemica. In this was identified by him from units 13 and 15 (beds case, the lowermost part of Unit 16 is earliest Ludlow 24 and 26). Ostracods Pachydomella wolfei Copeland, (earliest Gorstian) in age and correlates with a level in Steusloffina cuneata (Steusloff), Arcuaria? triangulata the Kockelella crassa Zone (Fig. 3). Specimens of Oz. Neckaja and Punctobeecherella punctata Copeland in bohemica from samples S23/1 and S23/2 are too poorly association with pentamerid brachiopods from Unit 2 preserved to allow subspecies identification. suggest a mid Aeronian age for this unit (Hairapetian In sample S26, in the next productive sample above et al. 2011). the level yielding the uppermost Oz. b. bohemica, six The Stegocornu brachiopod association including poorly preserved specimens of robust Ozarkodina were the key rhynchonellid taxon Stegocornu denisae Popov, found (Figs 3, 4g). Morphologically they seem to be Modzalevskaya & Ghobadi Pour was collected from closest to Oz. roopaensis, which occurs in the Paadla sample S14 (Unit 7) (Hairapetian et al. 2012). The Stage in the Baltic (Gorstian to lower Ludfordian) dispersion of Stegocornu association brachiopods in corresponding to an interval from the K. crassa Zone Central Iran, Kope-Dagh and Afghanistan represents a to the Oz. snajdri Interval Zone (Viira, 1994; Cramer significant Aeronian regional event (Hairapetian et al. et al. 2011a). Two samples (S28 and S29) from the 2012). topmost beds of Unit 19 yield 29 specimens of Oz. ex gr. snajdri (Figs 3, 4m), a taxon characteristic of the middle to late Ludlow (Corradini & Serpagli, 1999; 5. Palaeogeographic affinities of faunas Viira, 1999). From the data presented above, it is evident that Unit Based on the palaeogeographic reconstruction of 16 in the studied section corresponds to an interval from Cocks & Torsvik (2002, fig. 8) for the late-Early the lower(most) Gorstian to the middle Ludfordian. Silurian – Late Silurian, the Iranian terranes, includ- Tentatively, the Wenlock–Ludlow boundary in the ing Central Iran (Lut), Alborz, Sanand and Zagros section is placed at the boundary between units 15 and terranes, were located between palaeolatitudes 15◦ 16 (Fig. 3). However, as units 13, 14 and 15 cannot be and 30◦ S, and formed part of Middle Eastern peri- reliably dated, the boundary could be at a lower level in Gondwanan/Gondwanan terranes (Fig. 5). East of the section. Rugose corals from units 13 and 15 suggest modern Central Iran, a vast shallow-water shelf with a a Ludlow age for these strata (Section 4.b). Based on dominant carbonate-siliciclastic sedimentation regime currently available data, it is not possible to locate the developed in the Silurian. During the Llandovery, the Ludlow–Pridoli boundary in the section. Zagros and probably Sanand terranes (located SW

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geographical conclusions based on other fossil groups. Poorly known conodont taxa in the Llandovery part of the studied section means that limited conclusions can be drawn at these levels. Conodonts occurring in units 7 and 11, such as Ozarkodina sp. nov. (aff. Ozarkodina sp. C Mabillard & Aldridge) (Fig. 4o), Ozarkodina sp. nov. (aff. Ozarkodina sp. A Mabillard & Aldridge) (Fig. 4h) and gen. et sp. nov. A (aff. I.? sandersi Mabillard & Aldridge) (Fig. 4r–s) seem to be restricted to this geographical region. However, their possible closest relatives are known from Avalonia on the other side of the Rheic Ocean in the Marloes Bay section, SW Dyfed, Wales (Mabillard & Aldridge, 1983). Many of the other conodont taxa found in the Llandovery part of the studied section (e.g. D. staurognathoides, Pseudooneotodus tricornis)are cosmopolitan. The distribution of Pt. a. lennarti is less well known, but based on data available, this taxon (as Pt. amorphognathoides in general) is also cosmopolitan (Männik, 1998). Conodonts are rare in Figure 5. Palaeogeographic position of Iranian terranes during strata of Wenlock and younger age in the studied the Early Silurian (Llandovery). Base map from Cocks & Torsvik (2002), with modifications. Abbreviations: Al. – Alborz; Sa. – section, but all taxa recognized are known away from Sanand; Za. – Zagros. (Modified from Hairapetian et al. 2008 Gondwana (Fig. 3). with permission from Acta Palaeontologica Polonica). The data above suggest that for many taxa the Rheic Ocean separating Gondwana from Laurussia was not of the Central Iran terrane) were attached to the a major barrier. Conodonts from the Tafilalt region of northern margin of Gondwana. These regions have a Morocco have also supported this hypothesis (Männik, similar sedimentological and biological history to the Loydell & Lubeseder, 2011). Tafilalt conodonts from Arabian domain (Lüning et al. 2000; Rickards, Wright the lowermost Tamaghrout Formation (lowermost & Hamedi, 2000; Wendt et al. 2002, 2005; Ruban, Wenlock), from the strata corresponding to the Pt. Al-Husseini & Iwasaki, 2007; Ghavidel-Syooki & pennatus procerus Superzone sensu Jeppsson (1997) Winchester-Seeto, 2004; Ghavidel-Syooki et al. 2011). are identical to Baltica palaeocontinent conodonts from the same interval. The description of the typical Baltic Despite the peri-Gondwanan setting of Central Iran thelodont Loganellia cf. grossi Fredholm in units 16 (according to the palaeogeographic reconstructions and 19 in the studied Niur Formation section also of Cocks & Torsvik, 2002), and its considerable suggests that there were migration paths between distance from the low-latitude Laurentia and Baltica Gondwana and Laurussia (Hairapetian, Blom & Miller, in the Silurian (Fig. 5), ostracods from the lower 2008). Niur Formation (from Unit 2) have strong Lauren- tian affinities. Taxa include Pachydomella wolfei, Steusloffina cuneata, Arcuaria? triangulata, Punc- 6. Conclusions tobeecherella punctata and several species of the genera Elliptocyprites, Punctaparchites, Aechmina, (1) Conodonts and other fossil groups suggest a Dicranella, Lomatopisthia and Ovornina (Hairapetian Llandovery to Ludlow age for the Niur Formation. et al. 2011). The ostracod fauna has some similarities However, currently available faunas do not allow dating to Baltic Palaeocontinent Late Ordovician – Early of the strata above Unit 16. Silurian faunas. Common taxa include A.? triangulata, (2) Unit 7 is either of Aeronian or Telychian in age. S. cuneata and several species of Bairdiocypris, (3) Unit 11 (at least its upper part) is of middle Bulbosclerites and Aechmina (Neckaja, 1958; Meidla, Telychian in age and corresponds to the Pt. a. lennarti 1996). Some taxa (S. cuneata, Bairdiocypris attenuatus Zone. Melnikova & Michailova), characteristic of the lower (4) The Llandovery–Wenlock boundary lies between Niur Formation, have also been reported from Uzbek- samples S19 and S20 and is tentatively drawn as istan (Melnikova & Michailova, 1999). corresponding to the boundary between units 12 and Assemblages of halysitid corals, particularly rep- 13. resentatives of the genus Catenipora from the Niur (5) The lowermost part of Unit 16 is of earliest Formation, also suggest palaeobiogeographic affinities Ludlow in age and corresponds to the Kockelella crassa with faunas known from the Laurussian terranes Zone. (Hubmann, 1991a,b; Flügel & Hubmann, 1993). (6) The Wenlock–Ludlow boundary lies below Unit Palaeogeographical distribution data of Niur Form- 16 and is tentatively drawn at the boundary between ation conodonts do not contradict any of the palaeo- units 15 and 16. However, as units 13, 14 and 15

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cannot be reliably dated, it cannot be excluded that walled broad-based P element with icriodelliform the boundary lies at a lower level in the section. denticulation on its anterior process, an incurved M (7) The uppermost Unit 16 is of late Ludlow element with prominent anticusp and denticulated (Ludfordian) age and corresponds to the Oz. snajdri posterior process, a sagittodontiform ‘S’ element, and Interval Zone. symmetrical to asymmetrical delicate Sa–Sb elements (8) Although the latest palaeogeographical recon- (Mabillard & Aldridge, 1983, p. 33). A similar suite of struction shows that present-day Iran was located far elements can be recognized in our gen. et sp. nov. A away from Baltica and Laurentia, on the other side apparatus, along with an ‘ambalodiform’(?) element of of the Rheic Ocean, this seems not to have been a distinct morphology (Fig. 4s). This additional element major migration barrier for many different organisms has quite well-developed ‘icriodelliform’ denticulation including the conodonts. on its processes. This element is missing in the 247 specimen collection of I.? sandersi described by Mabillard & Aldridge (1983). The apparatus of I.? 7. Comments on some taxa sandersi is evidently icriodelliform whereas that of Brief comments on some taxa in open nomenclature are gen. et sp. nov. A (aff. I.? sandersi Mabillard & Ald- given. A description of conodonts from the Derenjal ridge) represents another, more complicated apparatus section will be presented in another paper; key taxa are type. illustrated in Figure 4. Acknowledgements. V. Hairapetian was assisted by Drs Genus Ozarkodina Branson & Mehl, 1933 Leonid E. Popov and Mansoureh Ghobadi Pour in the field. Ozarkodina sp. nov. (aff. Ozarkodina sp. C Mabillard Constructive reviews were provided by two anonymous & Aldridge) referees. The study of P. Männik was supported by the Estonian Science Foundation (grant no. 8907). His visit to Figure 4o the NHM in March 2010, and the use of the SEM to study conodonts, was financed by the SYNTHESYS Project GB- Remarks.P1 elements of the apparatus identified here as Ozarkodina sp. nov. (aff. Ozarkodina sp. C Mabillard TAF-294. & Aldridge) bear some similarity to those described by Mabillard & Aldridge (1983, pl. 3, figs 9, 10) as References Ozarkodina sp. C. However, our specimens differ by having shorter and higher blades and less prominent BRANSON,E.B.&MEHL, M. G. 1933. Conodonts from the cusps. Bainbridge Formation (Silurian) of Missouri. University of Missouri Studies 8, 39–52. Ozarkodina sp. nov. (aff. Ozarkodina sp. A Mabillard BRUTON,D.L.,WRIGHT,A.J.&HAMEDI, M. A. 2004. & Aldridge) Ordovician trilobites of Iran. Palaeontographica A 271, Figure 4h 111–49. CALNER,M.&JEPPSSON, L. 2003. Carbonate platform

Remarks.P1 elements of Ozarkodina sp. nov. (aff. evolution and conodont stratigraphy during the middle Ozarkodina sp. A Mabillard & Aldridge) resemble Silurian Mulde Event, Gotland, Sweden. Geological Ozarkodina sp. A of Mabillard & Aldridge (1983, Magazine 140, 173–203. CARLS,P.,SLAVÍK,L.&VALENZUELA-RÍOS, J. I. 2007. Re- pl. 3, figs 7, 8) in general configuration only. Both visions of conodont biostratigraphy across the Silurian– taxa have short P1 elements with a high ventral blade Devonian boundary. Bulletin of Geosciences 82, 145– and denticles on the dorsal blade that rapidly decrease 64. in height from the cusp. Morphological differences COCKS,L.R.M.&TORSVIK, T. H. 2002. Earth geography are evident between these two taxa. According to from 500 to 400 million years ago: a faunal and palaeomagnetic review. Journal of the Geological Mabillard & Aldridge (1983), the Pa ( = P1) element of Ozarkodina sp. A has 3–4 short, erect, broad denticles Society, London 159, 631–44. CORRADINI,C.&SERPAGLI, E. 1999. A Silurian conodont of subequal size on its ventral blade whereas our biozonation from late Llandovery to end Pridoliˇ in specimens have relatively small denticles with one Sardinia (Italy). Bollettino della Società Paleontologica considerably larger denticle in the ventralmost part of Italiana 37, 255–73. the blade. The cusp of Ozarkodina sp. A is broad and CRAMER,B.D.,DAV I E S ,J.R.,RAY ,D.C.,THOMAS,A.T.& distinct whereas our specimens have cusps that do not CHERNS, L. 2011a. Siluria revisited: an introduction. In Siluria Revisited: A Field Guide. International Subcom- differ in size from the other denticles. The P1 element basal cavity of Ozarkodina sp. nov. (aff. Ozarkodina sp. mission on Silurian Stratigraphy, Field Meeting 2011 (ed. D. C. Ray), pp. 7–28. International Subcommission A Mabillard & Aldridge) is shorter but more strongly on Silurian Stratigraphy. flared than in Ozarkodina sp. A. CRAMER,B.D.,BRETT,C.E.,MELCHIN,J.M.,MÄNNIK, P. , K LEFFNER,M.A.,MCLAUGHLIN,P.I.,LOYDELL, gen. et sp. nov. A (aff. I.? sandersi Mabillard & D. K., MUNNECKE,A.,JEPPSSON,L.,CORRADINI,C., Aldridge) BRUNTON,F.R.&SALTZMAN, M. R. 2011b.Revised Figure 4r–s correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic 13 Remarks. According to the original description, the units and δ Ccarb chemostratigraphy. Lethaia 44, 185– apparatus of I.? sandersi contains a straight thin- 202.

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