Biostratigrapgy, biofacies, and paleoecology of the Late Devonian deposits (Khoshyeilagh Formation) based on conodonts in northeast of Iran (around Bojnord and Jajarm)

In this study, the paleoecology, biostratigrapgy, and biofacies of the Khoshyeilagh Formation has been evaluated based on the found conodont species. The Khoshyeilagh Formation includes terrigenous-carbonate sequences which contains conodonts of shallow environments (Icriodus Polygnathu). The identification of 7 conodont species and sub-species led to the identification of 2 conodont biozones which are Upper rhenana-linguiformis, Lower triangularis-Lower crepida, respectively and also a biofacies named as Icriodus-Polygnathus. The identified biozones prove Late Devonian (Frasnian-Fammenian) age for the studied parts of the Khoshyeilagh Formation. The determined biofacies and the recognized conodonts in the studied sections represent shallow marine environment and warm tropical climate during the deposition time. Considering to the obtained fossil assemblages and comparing with the other sedimentary basins, the studied sections belong to the northern parts of Gondwana land. The analysis of biofacies and lithofacies show a decrease of depth at the end of Frasnian which is followed by an intense sea level drop similar to global examples. After a period of time and during Fammenian, the environment became deeper and open marine sub-environments (bioclast specule wakstone-packstone) were deposited.