analysis of carbonate association and palaeoecology of benthic foraminifera of the qom formation in the naragh area (northeast of delijan)

the qom formation in naragh area, with 185 meter thickness, is exposed about 25 km northeast of delijan. this formation in the studied area, lithologically, consists of shale, gravely limestone, and sandy limestone, with thin, medium to thick bedded and massive limestons. it disconformably covers the lower red formation and is covered by recent alluvium. in this research, the role of large foraminifera and also the influences of different environmental factors such as salinity, temperature, hydrodynamic energy, light and symbiosis processes that affect the distribution of foraminifers have been studied to evaluate the paleoecology during deposition of this formation. the presence of large benthic foraminifera with corallinacea red algae in deep parts of open marine sediments is indicative of normal marine salinity with less light and energy. the shell of benthic foraminifera (with hyaline wall) in sediments of shallow water open marine indicates an decrease in water depth and increase in light and energy; therefore they become small in size. in semi-restricted lagoon environment, benthic foraminifers with porcelaneous wall and foraminifers with hyaline wall are present together. the presence of foraminifers with porcelaneous wall in shallower water rather than semi-restricted lagoon (in restricted lagoon) indicates an decrease in depth, therefore an increases in light and salinity. therefore, the results indicate that the qom formation in the studied area is deposited in the tropical to subtropical water in lower latitudes in an oligotrophic to mesotrophic and almost eutrophic zone. the light conditions during deposition of this section was probably euphotic in the inner shelf and oligophotic to mesophotic in the middle shelf. also, it is mostly placed in a normal salinity environment. investigation of carbonate associations in the studied area led to identification of three grain associations including rhodalgal, foralgal and foramol or entirely heterozoan.