GeoArabia, 2012, v. 17, no. 1, p. 125-176 Gulf PetroLink, Bahrain Guadalupian (Permian) brachiopods from the Ruteh Limestone, North Iran Gaia Crippa and Lucia Angiolini ABSTRACT Thirty-three brachiopod species from the Guadalupian Ruteh Limestone of North Iran are here systematically described and illustrated. Brachiopods have been collected bed-by-bed along five stratigraphic sections and in one fossiliferous locality in the region between Dorud and Shirinibad in the Alborz Mountains. Four new species and one new genus are erected in the present paper: Haydenella eminens n. sp. Perigeyerella rutehiana n. sp., Martinia bassa n. sp. and Bisolcatelasma iraniana n. gen. n. sp. Quantitative biostratigraphic analysis of the brachiopod data based on the Unitary Association method (Guex, 1991) has lead to the construction of a local sequence of three discrete biozones: the Squamularia sp. B-M. bassa Biozone at the base of the formation, the H. kiangsiensis-N. (N.) asseretoi Biozone in its middle part and the R. exile-R. gemmellaroi Biozone at its top. The latter however has been recognized only in the Shirinabad section. As already envisaged for the Carboniferous and Lower Permian brachiopod faunas from North Iran, the Guadalupian fauna is comprised mostly of cosmopolitan taxa, confirming the role of the Iranian microplate as a staging-post for most of the late Palaeozoic. When compared to the younger Lopingian faunas collected in the same regions of North Iran, the Ruteh brachiopods appear significantly different, indicating a marked biotic change in the brachiopod communities across the end- Guadalupian biotic crisis. INTRODUCTION The aim of this paper is to systematically describe the brachiopod fauna of the Ruteh Limestone collected bed-by-bed along several stratigraphic sections in the Alborz mountain chain and to discuss their biostratigraphic implications. This study increases the knowledge of Guadalupian brachiopods from the Cimmerian blocks, which are important in understanding the complex pattern of the opening of the Neo-Tethys Ocean (Muttoni et al., 2009a, b). This allows a preliminary comment on the palaeobiogeographic affinity of the Ruteh brachiopods to be reported herein. The study of Guadalupian brachiopod distribution is also important for unraveling the pattern of the end-Guadalupian biotic crisis (i.e. Jin et al., 1994; Clapham et al., 2009; Isozaki and Aljinovich, 2009; Shen and Shi, 2009). The biotic crisis deeply affected several fossil groups, including fusulinids, bivalves, corals and brachiopods, and its causes are still not clear. This paper completes the revision and description of the Upper Palaeozoic brachiopod associations of North Iran, starting with the Cisuralian faunas (Angiolini and Stephenson, 2008) and continuing with the Lopingian (Angiolini and Carabelli, 2010) and Mississippian ones (Bahrammanesh et al., 2011). These systematic descriptions update the palaeontological works done in the sixties by Gaetani (1964, 1965, 1968), Fantini Sestini (1965a, b, c) and Fantini Sestini and Glaus (1966), which were based on smaller collections and provide a survey of the faunal succession and biotic events which characterized the Iranian microplate from the base of the Carboniferous to the Permian–Triassic event. 125 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/1/125/4568994/crippa.pdf by guest on 27 September 2021 Crippa and Angiolini GEOLOGICAL SETTING The brachiopods described in the present paper have been collected in the Alborz mountain range in North Iran, a 1,500 km long mountain system, flanking to the south of the Caspian Sea (Figure 1). The Alborz range is a seismically active belt resulting from Late Tertiary–Quaternary intracontinental transpression and structured above an ancient Eo-Cimmerian collisional orogen, which is still recorded at its core (Zanchi et al., 2006). The Palaeozoic–Mesozoic stratigraphic succession preserved in the Alborz (Assereto, 1966) was deposited along the passive margin of the Iranian microplate, which detached from the Gondwanan margin in the Early Permian and drifted northward to collide with the Eurasian margin in the Late Triassic (Muttoni et al., 2009a, b; Gaetani et al., 2009; Zanchi et al., 2009). The Pennsylvanian–Upper Permian succession of the Alborz mountain range has been recently revised by Gaetani et al. (2009); it starts with the Pennsylvanian–Sakmarian Dorud Group, which is unconformably capped by the Ruteh Limestone, a thick carbonate platform of Middle Permian age, from which the brachiopods described in the present paper have been sampled. The Ruteh Limestone is in turn overlain by a lateritic horizon with karst features indicating prolonged subaerial exposure under tropical climate conditions (Muttoni et al., 2009b). During the Late Permian the succession is transgressed by the marine limestone and marlstone of the Nesen Formation. The Ruteh Limestone was established by Assereto (1963), with its type-section designated north of Ruteh in the Jaj Valley. Gaetani et al. (2009) revised its upper boundary placing it at the base of the lateritic horizon, which corresponds to Assereto’s upper ironstone (1963, p. 537, fig. 11). The Ruteh Limestone is generally 150–250 m-thick reaching 600 metres along the Caspian side of the Alborz; it comprises dark grey marly bioclastic packstone at the base, followed by a succession of well-bedded bioclastic packstone and wackestone with local intercalations of marlstone and black cherty nodules and frequent Zoophycos trace fossils. Basaltic lava flows and tuffs occur in the upper part of the Ruteh Limestone in the area north of Elikah-Nesen (Gaetani et al., 2009). 38°N TURKEY Caspian 52°E 54° Sea N 38° SYRIA Figure 1 Med Sea 0 km300 IRAN IRAQ JORDAN TURKMENISTAN KUWAIT N 0 50 BAHRAIN QATAR EGYPT Arabian km Shield UAE OMAN SAUDI ARABIA Caspian Sea Gonbad-e-Qabus Red SUDAN Sea YEMEN Arabian Sea ERITREA Aliabad Fazelabad Chalus Gorgan Shirinabad Sari Amol Elikah Mangol Sharud Dasht-e-Nadir Emarat Kiyasar Hassanakdar 36° Khouban Pass Damghan Ruteh Dorud Talar Rud M. Damavand 36° Karaj Mobarakabad Shamirzad Firuzkuh TEHRAN Semnan 52° 54° Figure 1: Geographic sketch map of North Iran, showing the location of the Dorud, Ruteh (which indicatesFigure both 1 the Ruteh type section and the nearby Ruteh Valley section), Khouban Pass, Mangol Restaurant 1 and Shirinabad sections. 126 126 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/1/125/4568994/crippa.pdf by guest on 27 September 2021 Guadalupian (Permian) brachiopods, Ruteh Limestone, North Iran Brachiopods have been collected bed-by-bed along five stratigraphic sections: Dorud (36°00’18.3’’N, 51°29’01.6’’E), Ruteh (35°58’38.3’’N, 51°32’28.9’’E) and Ruteh Valley (35°58’35.2’’N, 51°31’59.0’’E), Mangol Restaurant 1 (36°14’58.2’’N, 52°22’05.1’’E), and Shirinabad (36°53’46’’N, 55°09’30’’E) (Figures 2–7) and in the fossiliferous locality of Khouban Pass (Figure 1; Table 1), where a section could not be measured due to the poor quality of the outcrop. THE BRACHIOPOD FAUNA The brachiopod fauna described in this study is based on 455 specimens and is comprised of 33 species belonging to 27 genera of which four species and one genus are new: Neochonetes (Nongtaia) asseretoi (Fantini Sestini, 1964), Haydenella kiangsiensis (Kayser, 1883), Haydenella aff. H. khasorensis (Reed, 1944), Haydenella eminens n. sp., Ogbinia sp. ind., ?Entacanthadus sp. ind., ?Otariella sp. ind., Spinomarginifera sp. ind., Tyloplecta n. sp. sp. ind. s cf. T. yangtzeensis (Chao, 1927), Reticulatia sp. ana B ind., Bilotina yanagidai Angiolini and Bucher, O. husseinii n. sp. 1999, Vediproductus vediensis Sarytcheva, 1965, DORUD SECTION aff. sp. Linoproductus aff. L. lineatus (Waagen, 1884), (36°00'18.3”N / 51°29'01.6"E) ?Linoproductus sp. ind., Magniplicatina sp. ind., ?Chonostegoides sp. ind., ?Urushtenoidea sp. Kotlaia bistriata Omanilasma Bilotina yanagidai Martinia bassa Perigeyerella rutehi Orthothetina vediensi ind., Orthothetina vediensis Sokolskaya, 1965, ?Permophricodothyris Squamularia Shemshak Orthothetina sp. ind., Perigeyerella rutehiana n. Formation 03IR 50 sp., Schuchertella semiplana (Waagen, 1883), 03IR 49 Kotlaia bistriata (Reed, 1944), ?Spirigerella sp. ind., Martinia bassa n. sp., Squamularia sp. A, Squamularia sp. B, ?Permophricodothyris sp. 03IR 47 ind., Reticulariina sp. ind., Rostranteris exile 03IR 48 Gemmellaro, 1899, Rostranteris gemmellaroi Smirnova and Grunt, 2002, Dielasma sp. ind., 2 m Omanilasma aff. O. husseinii Angiolini and Zarbo, 03IR 46 bis Ruteh 2006 and Bisolcatelasma iraniana n. sp. Limestone The brachiopod fauna of the lower and middle 03IR 46 part of the Ruteh Limestone was previously known through the works of Fantini Sestini Sandstone 03IR 45 Bioclastic (1965b) who described 41 species from Shah Zeid limestone eleven fossiliferous beds in the area between Formation Covered Hasanakdar and Ruteh (Table 2), so more to the west than the outcrops we studied Figure 2: Composite section showing the brachiopod (Figure 1). The assemblages described by range distribution in the Dorud section. Fantini Sestini (1965b) as having been collected at Khouban Pass and at Ruteh correspond to some of the beds collected by us in the same Table 1: Range chart showing the brachiopod localities. The material described by Fantini distribution at Khouban Pass. Sestini (1965b) generally consists of very few specimens for each taxon, some of which are n. sp. poorly preserved; however notable is her record of species of the genera Cleiothyridina,