marine ichnofossils of middle-late eocene deposits in south of mashhad and their application in sedimentary environment interpretation

middle-late eocene deep marine deposits (483 m.) of the islam-ghaleh section, south mashhad, rich in ichnofossils in shale and sandstone layers. these flysch type sediments are composed of sandstone, shale and marl in gray to green in color and are divided into five subunits. the lower boundary of these successions is gradual with red conglomerate and sandstone and their upper boundary is gradual with gypsum and red gypsiferous marls of probably eocene age. the most important identified ichnofossils in these successions are bergaueria isp., gyrophillites isp., halopoa annulata, halopoa storeana, helmintopsis tenuis, ophiomorpha isp., paleodictyon (glendodictyon) goetzingeri, paleodictyon (glenododictyon) strozzi and thalassinoides isp. that are abundant in middle and upper parts of the section. increasing of bioturbations and ichnofossils accumulation in these relatively deep water sequences can be related to concentration of sparse marine nutrition and formation of oxic conditions in the deep environments that could be related to sea floor currents. so, presence of abundant and index ichnofossils can be used as an important indicator for identification and confirmation of turbidite systems in the middle – late eocene sequences of the studied area and their correlation with similar successions in other parts of iran and the world.