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

Archive for December, 2022

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 OrdovicianSilurian. 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.