The geological reseaches in the Alborz, Zagros and Central Iran Basins

Archive for January, 2021

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

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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

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