عنوان مقاله [English]
IntroductionIn order to study the biostratigraphy, paleoecology and paleogeography of Qom formation ostracods, the Gonjan stratigraphical section was sampled and studied. 36 species and 23 genera of ostracods from Gonjan stratigraphical section have been studied and identified, which belong to two podocopid and platycopid orders. Based on the diversity of the identified foraminifera in this section and abundance of lepidocyclinids, the suggested age of Qom Formation deposits in Gonjan section are Rupelian?-Chattian. The presence and abundance of ostracoda with larger benthic foraminifera, Coralline red algae and Corals indicates the oligotrophic to mesotrophic conditions in the tropical to subtropical environments, with normal salinity and oxygen richness during the deposition of the Qom Formation.The Qom Formation consisting of limestones, marine marls, gypsum and siliciclastics was deposited at the last sea transgression in the Oligo-miocene age, with northwest-southeast trending in three basins of Sanandaj-Sirjan fore arc, Urumieh-Dokhtar intra arc and Central Iran back arc.Materials and MethodsIn order to conduct this research, based on lithology of layers, 45 marly and calcareous samples were collected.Results and discussionQom Formation in the study area consists of five limestone and marl informal members. These informal members are lower limestone, lower marl, middle limestone, upper marl, and upper limestone. 36 species and 23 genera of ostracoda from Gonjan stratigraphical section have been studied and identified:Cytherella sp., Cytherella dissimilis, Cytherella strangulat, Cytherelloidea sp., Paracypris sp.A, Paracypris sp.B, Krithe sp.A, Krithe sp.B, Trachyleberis sp., Ambostracon sp., Xestoleberis sp., Dentokrithe comma, Krithe trinidadensis, Loxocorniculum sp., Acanthocythereis sp., Buntonia sp., Loxoconcha ? sp., Cyprideis sp.A, Cyprideis sp.B, Actinocythereis sp., Actinocythereis iragensis, Legitimocythere sp., Parakrithe sp.A, Parakrithe sp.B, Cytheridea josephina, Cytheridea eggenburgensis, Ruggieria sp., Bairdia sp.A, Bairdia sp.B, Bairdia rafidainensis, Loxoconcha psedohamrinensis, Loxoconcha hamrinensis, Aurila sp., Costa tricostata, Mutilus sp., Ambocytherea sp.ConclusionThe presence and abundance of ostracoda with larger benthic foraminifera, Coralline red algae and Corals indicates the oligotrophic to mesotrophic conditions in the tropical to subtropical environments with normal salinity and oxygen richness during the deposition of the Qom Formation. Studies on the Qom Formation ostracoda in Gonjan section, indicate the similarity of these samples with other areas of Iran, India, north and north-east of Iraq, Turkey, eastern Mediterranean and North Africa. Thus it represents a seaway connection between these areas during Oligo-Miocene, which is considered as the Tethyan Seaway. The Qom Formation had a communicative role between Eastern Tethys and the Western Tethys region in the Iranian Plate.