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Chrono-and biostratigraphical chart of the uppermost Cambrian to Lower Ordovician (Tremadocian) strata of Eastern Alborz showing correlation with biostratigraphical trilobite succession of South China and North Atlantic conodont biozones. BRE, Black Mountain Regressive Event; CRE, Ceratopyge Regressive Event; HDE, Hagastrand Drowning Event; CDE, Copiosus Drowning Event; 1, peritidal zone; 2, inner shelf; 3, outer shelf.
Source publication
The Tremadocian of the East Alborz Region is dominated by condensed fine clastic
sediments. These beds have yielded low to medium diversity trilobite associations, which belong to the
olenid, nileid and raphiophorid biofacies, characteristic of an outer shelf environment. Five successive
trilobite biozones can be recognised in the Tremadocian su...
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Citations
... This is due mainly to the absence of carbonates in the Absharaf Member of the Furongian Mila Formation, which comprises quartzose sandstones with Cruziana and Skolithos trace fossils, and in overlying dark grey argillites and siltstones of the Simeh-Kuh Formation ( � Alvaro et al. 2022). The latter contains a moderately rich trilobite fauna of the Asaphellus inflatus-Dactylocephalus Biozone (Ghobadi Pour 2006, Ghobadi Pour et al. 2015, Ghobadi Pour 2019. Asaphellus inflatus, the eponymous species of this biozone and Conophrys cf. C. pentagonalis Lu, 1962 occur in the Kalat section within the stratigraphical interval that may represent the Cordylodus angulatus Biozone (Fig. 2). ...
... The Lower Palaeozoic successions of the eastern Alborz and South Kopet-Dagh regions have been the subject of intensive research based on extensive palaeontological, biostratigraphical and sedimentological studies in the field during the last decade. A detailed trilobitebased biostratigraphical subdivision of the Tremadocian was proposed by Ghobadi Pour (2006) and Ghobadi Pour et al. (2015b) (Fig. 16), which has been subsequently constrained by a conodontbased biostratigraphy esta b lished for the Furongian and Lower Ordovician ) and, to a lesser degree, for the Middle Ordovician. These data make possible a precise correlation of the Ordovician strata from the Alborz Mountains with the global chronostratigraphical standard. ...
... The trilobite fauna yielded by the SimehKuh For mation mainly belongs to the nileid and raphiophorid biofacies (Ghobadi Pour 2006, although the Asaphellus inflatus-Dactylocephalus trilobite Association, including the olenide Chungkingaspis sinensis (Sheng, 1958), proliferated in the lower part of the formation (Ghobadi Pour 2019). According to Ghobadi Pour et al. (2015b), this association is probably vicariant with the Early Ordovician olenid -Asaphellus biofacies from the Cordillera Oriental, Argentina, described by Balseiro et al. (2011). The sediments of the SimehKuh Formation predominantly represent upper offshore environments somewhat below seasonal storm wave base . ...
The Ordovician litho- and biostratigraphic framework of Alborz, Kopet-Dagh and the East-Central Iranian blocks is
outlined and significantly updated, and a broad summary of the current state of knowledge of the Ordovician deposits
and faunas across Iran is documented. Four tectono-stratigraphical units (including the Alestan, Damghan, Saluk and
Talesh domains) are distinguished in northern Iran. They differ considerably from one another in their lithology, facies,
fossil record and completeness of their sedimentary record. A comprehensive revision of the Ordovician stratigraphy
in the eastern Alborz and the Kopet-Dagh regions leads to the definition of the (i) Simeh-Kuh Formation (new),
(ii) the Qumes Formation (new) and its subdivision into the Gerd-Kuh (new) and Raziabad (new) members, (iii) the
Lashkarak Formation and its subdivision into the Cheshmeh-Ali (new) and Hajiabad (new) members, (iv) the Abarsaj
Formation (formalised) in the Alestan Domain, (v) the Qyzlar (new) and Pelmis formations in the Saluk Domain, and
(vi) the Tatavrud Formation (new) in the Talesh Domain. The Ordovician strata of the eastern Alborz and Kopet-Dagh
Mountains comprise a rifting volcanism emplaced within an active horst-and-graben palaeotopography. Despite
the strong Ordovician biogeographical affinities with South China and, to a lesser extent, with Mediterranean peri-
Gondwana, zircon populations analysed from Cambro–Ordovician sandstones in the area point to the Arabian-Nubian
Shield of the western Arabian Peninsula and northeastern Africa as the principal continental sources. Consequently,
an open oceanic communication between the Mediterranean and the northern (Alborz) margins of Gondwana
and the southern margin of South China favoured the establishment of strong biogeographical affinities between
these mid-latitude basins. • Key words: Ordovician, lithostratigraphy, biostratigraphy, paleobiogeography, Iran,
Gondwana.
... This formation consists mainly of argillites and siltstones with some centimetre-scale sandstone and limestone interbeds, in total up to 130 m thick. It contains trilobites of the Asaphellus inflatus-Dactylocephalus to Asaphellus fecundus-Taihungshania miqueli zones (Ghobadi Pour 2006, 2019Ghobadi Pour et al. 2015a) and conodonts of the Paltodus deltifer-Prioniodus elegans conodont zones , all suggesting a Tremadocian to early Floian age. Other components of the fauna include brachiopods, ostracodes, echinoderms and graptolites. ...
... The overlying Simeh-Kuh Formation contains trilobites of the Asaphellus inflatus-Dactylocephalus Zone (Fig. 5). Deposition of this unit coincides with a significant drowning of the area down to the upper offshore and offshoretransition environments (Ghobadi Pour et al. 2015a;Ghobadi Pour 2019). According to Ghobadi Pour (2019), the trilobite fauna of this zone with Asaphellus, Conophrys, agnostides and the locally abundant olenid Chungkingaspis can be linked with the Olenid-Asaphellus biofacies, as defined by Balseiro et al. (2011). ...
Ordovician studies in Iran show significant progress since the beginning of the century. A number of individual faunas have been documented and a biostratigraphical framework based on conodonts, chitinozoans, acritarchs and trilobites developed. Correlation of Ordovician successions with the International Chronostratigraphical Time Scale has been significantly improved, and the position of the series and stage boundaries can be recognised with greater precision. While geographical proximity to temperate latitude Gondwana is apparent for most Iranian terranes, biogeographical links of Alborz and Kopet-Dagh with South China prevailed through the Early – Middle Ordovician. In Pakistan, Ordovician deposits have a restricted distribution in the Karakorum block (Chitral). Here they are represented by the Yarkhun and Vrdiakot formations with Floian – Darriwilian acritarchs, chitinozoans and early Darriwilian conodonts. In Peshawar District of the North West Frontier Province, an Early – Middle Ordovician age is likely for the Misri Banda Quartzite with Cruziana rugosa trace fossils. It is overlain conformably by carbonates of the Panjpir Formation, which has an inferred Middle Ordovician – Silurian age. Presently available information on the Ordovician of Afghanistan is mostly based on reconnaissance studies performed almost half a century ago, and a few monographed Early and Late Ordovician faunas.
... After generalized erosion of uplifted areas (Fig. 17), return to marine conditions was diachronous and different lithostratigraphic units onlapped the inherited palaeorelief, ranging from the Tremadocian Simeh-Kuh Formation to the Tremadocian-Floian Avesta Beds and the Darriwilian Cheshmeh-Ali Member. The overlying Tremadocian-lowermost Dapingian succession mainly comprises condensed siliciclastic sediments (Simeh-Kuh, Qumes and Avesta units), with trilobite-dominant benthic assemblages representative of the nileid and raphiophorid biofacies characteristic of outer shelf environments (Popov et al., 2009b;Ghobadi Pour et al., 2015b). ...
Recent reconnaissance geological mapping, identification of unconformities and chronostratigraphic dating of Miaolingian to Ordovician strata in the eastern Alborz Mountains have led to recognition of synsedimentary uplift episodes associated with block tilting and partial erosion of the Cambrian Mila and Ordovician Simeh Kuh, Qumes and Lashkarak formations. A chronostratigraphic revision of the Miaolingian-Late Ordovician fossil content is presented, and the Steptoean Positive Carbon Isotope Excursion (SPICE) chemostratigraphic shift, marking the Miaolingian–Furongian boundary, is constrained close to the Members 2/3 contact in the Mila Formation. Upper Ordovician basaltic lava flows embedded in the Abarsaj Formation and Devonian sills and dykes intruded in the Mila and Simeh-Kuh formations were geochemically analysed and compared with the voluminous lava eruptions recognized in the Katian-Llandovery Soltan-Maidan and Gorgan Schists formations, and in the ?Emsian-Eifelian Mighan Formation. They represent successive magmatic pulses of alkaline to subalkaline activities, separated by background (quiescent) intervals of up to 35 m.y., characterizing an intraplate field (continental rift) affinity compatible with OIB-like (ΔNb>0) mantle sources. Successive Miaolingian-Mid Ordovician (volcanic-free) uplift episodes were related to lithospheric doming preceding the onset of stepwise plume-related rift pulses, which shaped a large igneous province with transects of about 600 km, linking the Damghan and Alestan domains of the eastern Alborz Mountains with South Kopet-Dagh and some blocks of Central Iran.
... After generalized erosion of uplifted areas (Fig. 17), return to marine conditions was diachronous and different lithostratigraphic units onlapped the inherited palaeorelief, ranging from the Tremadocian Simeh-Kuh Formation to the Tremadocian-Floian Avesta Beds and the Darriwilian Cheshmeh-Ali Member. The overlying Tremadocian-lowermost Dapingian succession mainly comprises condensed siliciclastic sediments (Simeh-Kuh, Qumes and Avesta units), with trilobite-dominant benthic assemblages representative of the nileid and raphiophorid biofacies characteristic of outer shelf environments (Popov et al., 2009b;Ghobadi Pour et al., 2015b). ...
New detrital U-Pb zircon ages from the Sanandaj-Sirjan metamorphic zone in the Zagros orogenic belt allow discussion of models of the late Neoproterozoic to early Palaeozoic plate tectonic evolution and position of the Iranian microcontinent within a global framework. A total of 194 valid age values from 362 zircon grains were obtained from three garnet-micaschist samples. The most abundant detrital zircon population included Ediacaran ages, with the main age peak at 0.60 Ga. Other significant age peaks are at c. 0.64-0.78 Ga, 0.80-0.91 Ga, 0.94-1.1 Ga, 1.8-2.0 Ga and 2.1-2.5 Ga. The various Palaeozoic zircon age peaks could be explained by sediment supply from sources within the Iranian microcontinent. However, Precambrian ages were found, implying a non-Iranian provenance or recycling of upper Ediacaran-Palaeozoic clastic rocks. Trace-element geochemical fingerprints show that most detrital zircons were sourced from continental magmatic settings. In this study, the late Grenvillian age population at c. 0.94-1.1 Ga is used to unravel the palaeogeographic origin of the Sanandaj-Sirjan metamorphic zone. This Grenvillian detrital age population relates to the 'Gondwana superfan' sediments, as found in many Gondwana-derived terranes within the European Variscides and Turkish terranes, but also to units further east, e.g. in the South China block. Biogeographic evidence proves that the Iranian microcontinent developed on the same North Gondwana margin extending from the South China block via Iran further to the west.
Graptolites have been collected from sections through Lower Ordovician strata in northern Iran. At the Saluk Mountains, in the Kopet–Dagh region, mudrocks yielded fragmentary tubaria of Rhabdinopora sp. cf. R. flabelliformis , indicating the presence of lower Tremadocian strata there; stratigraphically, they lie between two limestone beds with the euconodont Cordylodus lindstromi . At Simeh–Kuh in the eastern Alborz Mountains (Semnan Province), upper Tremadocian – lower Floian strata include laminated dark mudstones that contain restricted graptolite faunas, mainly of small declined didymograptids; these are thought to represent incursions of plankton during periods of marine highstands. The lower major flooding surface in Simeh–Kuh coincides with an invasion of the graptolite biofacies and an incursion of Hunnegraptus ? sp.; the second major flooding surface is associated with an incursion of Baltograptus geometricus . They were most probably synchronous with those in the lower part of the Hunnegraptus copiosus Biozone and at the base of the Cymatograptus protobalticus Biozone in the of the Tøyen Shale Formation succession of Västergötland, Scandinavia, suggesting that observed characters of sedimentation were eustatically controlled.
A small bivalve fauna is described from the late Tremadocian of Iran, adding to the very few localities in the world where bivalves of this age are known. In addition to indeterminate praenuculids, the fauna includes the praenuculid Pensarnia and the pteriomorphian genus Glyptarca. The former is otherwise known from South Wales and the latter, from South and Mid‐Wales and West Yunnan, China.
The early late Tremadocian (Tr2) interval is exceptionally well represented in eastern areas of the Argentine Cordillera Oriental. New field collections and detailed taxonomic reassessments, as well as a revaluation of regional data, permit the development of a highly resolved trilobite-based biostratigraphic framework. The concept of the traditional Bienvillia tetragonalis biozone is emended and the new Asaphellus nazarenensis biozone is proposed. Hence, the Tr2 interval encompasses a succession of four trilobite biozones including in ascending order the Kainella teiichii, the Bienvillia tetragonalis, the Asaphellus nazarenensis, and the Notopeltis orthometopa biozones. This resolution is notably higher than that provided by biostratigraphically significant groups such as graptolites and conodonts, and allows a detailed basinwide correlation. New taxonomic information on A. nazarenensis Tortello and Esteban, 2014, and N. orthometopa (Harrington, 1938), is provided and the new species Asaphellus albae sp. nov. is defined. Detailed correlation of the trilobite fauna from the Tr2 interval with that of other paleocontinents is difficult. Taxa are mostly endemic or display wide geographic distribution but with long stratigraphic ranges. Overall, both trilobite-based and indirect international correlations highlight that this interval is hardly recognized, incompletely preserved, or the trilobite fauna is poorly known in most areas of Gondwana. Consequently, due to the completeness of the stratigraphic and fossil records of the Tr2 in the Cordillera Oriental, this region represents a global reference site for the study of this interval.
