The Lashkarak Formation (Lower–Middle Ordovician) in the Gerdkuh locality, 10 km west of Damghan city, northern Iran, has been found to contain acritarchs and chitinozoans. This study aimed to understand these chitinozoan and acritarch successions as well as brachiopods in this part of the Alborz Mountains, in a novel manner. Ninety-seven surface samples from this succession were collected and analysed. Thirty samples yielded well-preserved palynomorph taxa such as acritarchs, chitinozoans, and scolecodonts, as well as graptolite remains. In total, 53 taxa were identified among the acritarchs (38 species belonging to 21 genera) and chitinozoans (15 species belonging to 10 genera). Although scolecodonts and graptolite remains were also observed, they were not studied in detail. The palynological analyses revealed the presence of several diagnostic acritarchs in the Lashkarak Formation, including Vulcanisphaera simplex, Arbusculidium filamentosum, Coryphidium bohemicum, Dactylofusa velifera, Striatotheca mutua, Arkonia virgata, and Orthosphaeridium ternatum. These acritarchs allowed the recognition of five acritarch assemblage zones. Similarly, seven chitinozoan biozones were recognised: Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Cyathochitina protocalix, Cyathochitina calix, Siphonochitina formosa, and Laufeldochitina clavata. These findings confirm the inclusion of the Alborz Mountains in the peri-Gondwana palaeoprovince during the Early–Middle Ordovician. The co-occurrence of the acritarch and chitinozoan taxa with previously identified brachiopods allowed for the establishment of a more detailed Early–Middle Ordovician biozonation, demonstrating their potential usefulness for global chronostratigraphy. Based on palynological and brachiopod assemblages, a shallow marine inner shelf setting is suggested for the Early–Middle Ordovician at the Gerdkuh locality. Moreover, in this study, four new morphotype species were erected, consisting of one new chitinozoan (Cyathochitina gerdkuhensis sp. nov.) and three new acritarchs (Baltisphaeridium razii sp. nov., Navifusa alborzensis sp. nov., and Orthosphaeridium iranense sp.nov.). However, Othosphaeridium cf. ternatum was left in open nomenclature.
Mohammad Ghavidel-Syooki, Mohammad Hossein Piri-Kangarshahi
Keywords: Early Ordovician(Tremadocian–Floian); Peri-Gondwana; Lashkarak Formation; chitinozoan and acritarch biostratigraphy; Alborz Mountains; Middle Ordovician (Dapingian–Darriwilan); Northern Iran
A siliciclastic succession is exposed at the Faraghan mountain, northern Persian Gulf, southeastern Iran. A detailed, high-resolution palynological analysis was performed on the Zardkuh, Seyahou, Dargaz, and Sarchahan formations to verify the exact age and palaeogeographic position of the High Zagros Mountains. Two hundred surface samples from this succession were collected and analysed. Most samples yielded abundant and well-preserved chitinozoans, acritarchs, scolecodonts, and cryptospores. Fifty-three chitinozoan species (21 genera) were identified that permitted to establish the Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Siphonochitina formosa, Belonechitina robusta, Tanuchitina fistulosa, Acanthochitina barbata, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, Spinachitina oulebsiri, and Spinachitina fragilis biozones in ascending stratigraphic order as was previously established for the North Gondwana Domain. These results indicate that the Zagros Mountain Belt of Iran was part of the North Gondwana palaeo-province during the Ordovician-Silurian. On the other hand, these chitinozoan biozones and other associated fauna (e.g. graptolites, trilobites, brachiopods, and conodonts) suggest a late Early Ordovician (Floian) to Early Silurian (Rhuddanian) age range, with unconformities, for this succession. Based on chitinozoan biozones, a distinctive hiatus is present between the Zardkuh and Seyahou formations at Faraghan mountain, which corresponds to the absence of jenkinsi-tanvillensis chitinozoan biozones, encompassing the latest Middle Ordovician (latest Darriwilian: stage slice Dw3) and the early Late Ordovician (Sandbian: the stage slices Sa1 to Sa2 and time slices 5a to 5b). Two chitinozoan species were erected: Belonechitina bifurcaspina sp. nov., Angochitina persianense sp. nov., and Eremochitina cf. brevis was left in open nomenclature.
Mohammad Ghavidel-Syooki
Keywords: Biostratigraphy; palaeogeography; chitinozoan biozones; northern Gondwana landmass; northern Persian Gulf; Iran
The study area is located in Tang-e Bagh at Kuh-e Genu, approximately 69 km, northern Persian Gulf. The age relationships of Sarvak, Gurpi, and Pabdeh formations were unclear in the study area because of the low-resolution biostratigraphy. Therefore, 152 samples were collected. All samples contain well-preserved foraminifers that permit clarification of the age of these formations. Nine benthic species (5 genera) and sixty-eight planktonic foraminiferal species (29 genera) were identified that were arranged eleven biozones with high resolution of biostratigraphy. Biozone Ⅰ corresponds to the total range of Orbitolina qatarica in the Mauddud Member of Sarvak Formation, suggesting the Cenomanian (middle Cenomanian) age. The biozone Ⅱ is characterized by the total range of Dicarinella asymetrica in the basal part of Gurpi Formation, indicating the Santonian age. Therefore, there is a hiatus between the Sarvak and Gurpi formations that includes part of the Mauddud Member, the whole Ahmadi Member, and the Ilam Formation. This hiatus encompasses the late Cenomanian to Coniacian that is marked by a few meters of Fe-stained deposits in the Kuh-e Genu; the interval range zones Ⅲ to Ⅶ as well as Abathomphalus mayaroensis zone Ⅷ (TRZ) are present within the rest of Gurpi Formation and suggests the Campanian to Maastrichtian. The biozones IX-XI are present within the Pabdeh Formation that corresponds to a Not Zone and two interval range zones (P1b, P1c-P2), suggesting Danian. Based on microfacies, texture, and paleontological analysis, a deep-water environment suggests for Gurpi and Pabdeh formations and shallow marine conditions for Sarvak Formation.
N. Farsi, M. Ghavidel-Syooki, S. A. Babazadeh3, S. H. Vaziri1
Keywords: Biostratigraphy; Upper Cretaceous; Lower Paleogene; Kuh-e Genu; NW Persian Gulf.
A total of 1500 surface samples were collected from the Ordovician outcrops of the Alborz Mountains and treated for acritarch and chitinozoan taxa to determine the exact age of Ordovician rock units and paleogeographic position of these mountain ranges. The Alborz Mountains stretches from the border of Azerbaijan along the western and entire southern coast of the Caspian Sea and finally runs northeast and merges into the Aladagh Mountains in the northern parts of Khorasan province. The Alborz Mountains are divided into the Western, Central, and Eastern Alborz Mountains that the Ordovician rock units (e.g. Lashkarak, Abastu, Ghelli, and Abarsaj formations) extend throughout this mountain ranges. The Lashkarak Formation is well-developed in the whole Alborz Mountains, whereas Ghelli, Abastu, Abarsaj formations, and Gorgan Schists have exposure in the southern Caspian Sea and the northern parts of Khorasan province. The study localities consist of the Alam-Kuh, Hassanakdar, Simeh-Kuh, Gerd-Kuh, Deh-Molla, Kuh-e Saluk, Fazel Abad, and Deraznau areas. Except for the Gorgan Schists in the Deraznau area which has low metamorphic grade, the rest of Ordovician rock units are siliciclastic sediments. The study materials either metamorphic or non-metamorphic samples contain abundant and well-preserved palynomorph entities (e.g. acritarchs and chitinozoans), which permit the exact age of rock units and relationships of the Alborz Mountains to the paleocontinents (e.g., Gondwanan vs. Laurentia palaeo-provinces).
Based on palynological analyses, the Lashkarak and Abastu formations contain several diagnostic acritarchs, consisting of Arbusculidium filamentosum, Barakella felix, Coryphidium bohemicum, Dactylofusa velifera, Striatotheca principalis, Cymatiogalea messaoudensis var. messaoudensis, Aureotesta clathrata var. simplex, and Vavrdovella areniga var. areniga. On the other hand, the presence of Eremochitina brevis, Velatachitina veligera, Desmochitina ornensis, Belonechitina henryi, Siphonochitina formosa, Cyathochitina jenkinsi, and Armoricochitina armoricana chitinozoan Biozones confirm the inclusion of the Alborz Mountains in the peri-Gondwanan paleoprovince during the Lower-Middle Ordovician. The Ghelli Formation is well-developed in Kuh-Saluk at the northern parts of Khorasan province, whereas the Abarsaj Formation and the Gorgan Schists are present in the southeastern Caspian Sea. The Ghelli and Abarsaj formations are characterized by the presence of Late Ordovician diagnostic acritarch taxa, consisting of Acanthodiacrodium crassus, Villosacapsula setosapellicula, Multiplicisphaeridium irregulare, Multiplicisphaeridium bifurcatum, Orthosphaeridium insculptum, Orthosphaeridium bispinosum, Orthosphaeridium quadrinatum, Ordovicidium elegantulum, Dactylofusa cabottii, Baltisphaeridium oligopsakium, Baltisphaeridium perclarum, Dorsennidium hamii, Diexapllophasis denticulata, Neoveryhachium sp. cf. carminae, Veryhachium lairdii, Navifusa ancepsipuncta, Leiofusa litotes, Muzivum gradzinskii, and Veryhachium inflatum. The aforementioned acritarch taxa are associated with the Belonechitina robusta, Tanuchitina fistulosa, Acanthochina barbata, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, and Spinachitina oulebsiri chitinozoan Biozones, which have been previously established in the ‘northern’ Gondwanan Domain. Herein, it should be mentioned that the Tanuchitina elongata and Spinachitina oulebsiri Biozones are present in the glacial member of the Ghelli Formation in Kuh-e Saluk. Moreover, the treated samples of Gorgan Schists contain the same acritarch and chitinozoan taxa of the Ghelli and Abarsaj formations which reveal the Late Ordovician for the Gorgan Schists. Therefore, based on palynological data, not only the Zagros Mountains but also the Alborz Mountains were part of the peri-Gondwana/Gondwanan paleocontinent.
Mohammad Ghavidel-Syooki
Keywords: Ordovician, Alborz Mountains, chitinozoans, acritarchs, Peri-Gondwana.
Acritarchs and chitinozoans were documented from Ordovician strata and miospores from Lower Permian beds in the Zardkuh area. Ninety-one palynomorph species, comprising acritarchs (63 species of 31 genera), chitinozoans (16 species of 12 genera), and miospores (12 species of 10 genera) were recognized that form 10 local assemblage zones, comprising Zones A–F= acritarchs, G–I= chitinozoans, and J= miospores. Zone A occurs in the uppermost Ilebeyk Formation, indicating Late Cambrian; Zones B–E are present in the Zardkuh Formation, suggesting Early Ordovician (Tremadocian–Floian)–Middle Ordovician (Dapingian) and Zone F occurs in the Seyahou Formation, presenting Late Ordovician (Hirnantian). Likewise, three Gondwanan chitinozoan Zones G–I were established in this succession. Zones G–H occur in the Upper Shale Member of the Zardkuh Formation, supporting an Early-Middle Ordovician (Floian–Dapingian), and Zone I is restricted to the Seyahou Formation, suggesting Late Ordovician (Hirnantian) age. Finally, Zone J occurs in the Faraghan Formation, confirming Early Permian. Based on palynomorph zones, two hiatuses are present within the Paleozoic sequences of the study area. The first hiatus occurs between the Zardkuh and Seyahou formations, encompassing the Middle Ordovician (Dapingian) and much of the Late Ordovician (Sandbian and Katian). The second hiatus appears between the Seyahou and Faraghan formations, spanning the Silurian, Devonian, Carboniferous, and earliest Permian (Asselian). The palynomorph taxa, including Arbusculidium, Striatotheca, Coryphidium, Vavrdovella, Eremochitina, Velatachitina, and miospore taxa, confirm that the study area belongs to peri-Gondwana paleoprovince. Four new species are Vavrdovella mawlawii sp.nov., Vogtlandia zardkuhensis sp.nov, Pseudocoryphidium zagrosensis gen et sp.nov, and Pterospermella saadii sp.nov.
Mohammad Ghavidel-Syooki
A siliciclastic succession is well exposed at Kuh-e Boghou, located in eastern-central Iran. To verify the exact age and paleogeographic position of this section of the Iranian Platform, a detailed, high-resolution palynological analysis of the Ghelli Formation was performed. Sixty-nine surface samples of the sedimentary succession were collected and analyzed. Most samples yielded abundant and well-preserved acritarchs (34 species of 24 genera), euglenids (3 species of a single genus), chitinozoans (36 species of 19 genera), and cryptospores (25 species of 10 genera). Based on the presence of well known chitinozoan species, a Late Ordovician (Katian–Hirnantian) age was assigned to this succession. The identified chitinozoan fauna allowed recognition of the Belonechitina robusta, Tanuchitina fistulosa, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, and Spinachitina oulebsiri biozones in ascending stratigraphic order as was previously established for the northern Gondwanan Domain. These results indicate that eastern-central Iran was part of the peri-Gondwana domain during the Late Ordovician. Seven morphotypes were recorded for the first time, and five of them were established as new species, namely Abditusdyadus khayyammii, Alhajrichitina spinifera, Dyadospora ferdowsii, Lophosphaeridium bulbosumensis and Moyeria hafezii, and two were left in open nomenclature (e.g. Eisenackitina sp. and Moyeria sp. A). The abundant cryptospore taxa in the Late Ordovician might be related to land-derived sediments acquired during the global sea level fall in the Late Ordovician glaciation or to the adaptation of primitive land plants in a wide range of climatic conditions. The association of terrestrial miospores with marine palynomorphs suggests a nearshore marine environment.
Mohammad Ghavidel-Syooki , Mohammad Hossein Piri-Kangarshahi
A complete profile was measured and sampled in the study area to determine the age of the Shemshak Group. A total of 159 samples were collected from plant-fossiliferous horizons and subsequently investigated in the Geosciences Faculty of Shahid Beheshti University Laboratory. Fifteen identified plant macrofossil species (ten genera) were categorized into Osmundales, Dipteridales, Marattiales, and Peltaspermales. The species encountered are Korallipteris yipinglangensis, Cladophlebis nebbensis, Cladophlebis haiburnensis, Cladophlebis denticulata, Clathropteris meniscioides, Dictyophyllum exile, Thainguyenopteris parvipinnulata, Osmundopsis sturii, cf. Marattiopsis intermedia, Scytophyllum waehneri, and
Peltaspermum decipiense. In this study, 5 ferns and seed ferns species are reported for the first time in the northeastern Alborz Mountain. A Late Triassic (Rhaetian) age is assigned to the Shemshak Group based on ferns and seed ferns chronostratigraphy.
Also, a lowland deltaic environment, including wet and drier conditions, is suggested by ferns and seed ferns revealed in the studied area.
Mohammad Ghavidel-Syooki & Maryam Farahimanesh & Abbas Sadeghi
M. Ghavidel-Syooki
The excellent preservation of the acritarchs, their great abundance, diversity and good stratigraphic control permit establishment of a detailed Middle and Late Cambrian acritarch biozonation. A total of 56 palynomorph species form the basis of 10 local acritarch assemblage zones. Assemblage zones I-II occur in the lower and middle parts of the Member C of the Mila Formation and suggest Early-mid Middle Cambrian; assemblages zones III-IV appears in the upper part of the Member C of the Mila Formation and the lower part of Ilebeyk Formation and encompass latest Middle and earliest Late Cambrian; acritarch assemblage zones V-IX occur in the middle and upper parts of the Ilebeyk Formation and characterize Late Cambrian; finally, acritarch assemblage zone X appears in the basal part of the Zardkuh Formation and proves to have an early Tremadocian age. Amongst the Late Cambrian acritarch assemblages of Laurentia only the two cosmopolitan species of Timofeevia phosphoritica and Vulcanisphaera turbata are shared with coeval strata in the High Zagros Mountains.
Iranian acritarch assemblages show a marked Gondwanan paleobiogeographical affinity, share a high proportion of taxa with typical Baltican and North Africa–Gondwanan assemblages, and are different from known Laurentian microphytoplankton suites. These results are in general agreement with paleogeographical models that place Avalonia, Baltica, and the North African part of Gondwana, at relatively high southern paleolatitudes, whereas Laurentia occupies a sub-equatorial position.
Four new acritarch species, namely Leiosphaeridia iranense, Navifusa reticulata, Ooidium zagrosensis, and Veryhachium ilebeykensis are described.
Keywords: Acritarch biozonation; Middle-Late Cambrian; Mila Formation; Ilebeyk Formation; High Zagros Mountains.
• Reza Behbahani, Mohammad Ghavidel-syooki, Somayeh Borji, Mahmoud Reza Majidifard, Morteza Yousefi, June 2019.
• DOI: 10.22084/PSJ.2019.17996.1192
In present research, depositional environment of the Ghelli Formation (Late Ordovician) was investigated in NE Alborz Basin (Robat-e-Gharabil Area; Kuh-e-Kurkhud). This study was performed based on field observations, thin sections petrography, sedimentary structures and palynological studies. Utilizing this multidisciplinary approach, four litofacies assemblages were recognized. The Ghelli Formation in studied area comprises alternation of thick to thin shale beds, medium to thin bedded sandstones, sandy limestones, laminated siltstones and diabasic sill. These lithofacies assemblages consist of arkose-subarkose, sandy allochem limestone, siltstone and shale. According to the properties of lithofacies, sedimentary structures and vertical stacking of these lithofacies suggest a storm and wave dominated shelf, wherein the depositional setting evolved from lower shoreface with lower- middle lithofacies (with hummocky cross stratification, truncation surface, parallel lamination and cross lamination) that gradually changed into upper shoreface with upper lithofacies (with swaley cross stratification, wave ripple-mark, parallel lamination, normal grading, wedge-shaped and tabular cross-lamination) which storm and waves induced currents had important roles in sediment reworking and redeposition. Using the Tyson diagram, four palynological facies (III, IVa, V and VII) were identified. Meanwhile, statistical studies on the palynological parameters (percentage of phytoclast, amorphous organic matter and lability parameter) indicate a shallowing upward trend in Ghelli Formation. Comparison of the relative abundance of marine palynomorphs with terrestrial palynological elements indicate less abundance of acritarchs and chitinozoans in comparison with cryptospores and plant fragments which indicate that Ghelli Formation is deposited in shallow marine environment.
Keywords: Ghelli, Formation; Alborz Mountains; Depositional environment; Sedimentary structures; Lithofacies; Palynological facies.
Chronostratigrahy of Acritarchs and Chitinozoans from
upper Ordovician Strata from the Robat-e Gharabil
Area, NE Alborz Mountains, Northern Khorassan
Province: Stratigraphic and Paleogeographic
Implications
M. Ghavidel-Syooki, and S. Borji
