The biostratigraphy of the Upper Devonian of the Khoshyeilagh area, northeastern Alborz, Iran

Diverse and well preserved marine palynomorphs occur in the Padeha, Khoshyeilagh, and Mobarak formations in the Khoshyeilagh, central Alborz, north of Iran. The marine palynomorph assemblages consist of acritarchs, prasinophytes, and chitinozoans, comprises 27 genera and 46 species. In addition, the studied sediments contain 20 species of algae, foraminifera, and corals allocated in 11 genera. Vertical distribution of acritarchs and chitinozoans allows erection within these sediments of three local assemblage zones. Biozone I occurs in the upper part of Padeha Formation and basal part of the Khoshyeilagh Formation suggests Frasnian-early Famennian age and Biozone II is present in the Khoshyeilagh Formation and indicates Famennian age. Biozone III, which occurs in the basal part of Mobarak Formation, suggests a Tournaisian age for this interval. Many of the palynomorph groups such as, <i>Crassiangulina tessellita</i>, <i>Deltotosoma intonsum, Daillydium pentaster, Gorgonisphaeridium discissum, Helosphaeridium microclavatum, Horologinella horologia, Papulogabata annulata, Somphophragma miscellum,</i> and <i>Veryhachium downiei</i> are closely comparable with coeval assemblages recorded from the Australia, Ireland, Portugal, Saudi Arabia, North Africa, South America, and North America. This indicates the close relationship of the Iranian Platform to other parts of the northern Gondwana and southern Laurentian Domain during the Late Devonian-Early Carboniferous. Moreover, results of similarity indices of marine microphytoplankton indicate relatively high degree of similarity between the assemblages of Khoshyeilagh area and elsewhere in Alborz Mountains and Kerman Basin. Palaeontological evidences indicate that the Khoshyeilagh formation was deposited in a low energy, somewhat offshore, normal marine environment within the Alborz Basin, along the Palaeo-Tethys Ocean during this time interval. Furthermore, based on palynology data gathered from Iran, it can be concluded that Iran was an island during this interval of time.