systematic description, paleoecology and paleobiogeography of khangiran formation oyster bivalves, in the chehelkaman synclinal, east of kopet-dagh basin

kopet-dagh basin is located in north and northeast of iran. khangiran formation is one of the most important formations of paleogene deposits. for study of khangiran formation bivalves, chehelkaman syncline section has been selected. this section located in west of sarakhs city, east of kopet-dagh basin. lithology of this formation in the sarakhs region composed of marl, marly limestone and siltstone. in addition lithology of deposits with oyster shells consists of 50m olive green monotonous marl with large shells of oysters that are very well preserved. based on this shells study, species of sokolowia beldersaiensis and sokolowia buhsii of ostreidae family have been recognized. these shells indicate sub-tidal to shallow marine environments and euhaline waters and proposed middle eocene age (bartonian stage) for these sediments. furthermore, paleobiogeography survey of this bivalves indicate dependency of khangiran formation to tethyan realm, that this realm limited to central asian region and located between transylvanian basin of romania, in the west and tarim basin of china in the east. retreat of this sea in the middle eocene cause of oyster shells composed in the bartonian stage. these shells indicate dependency of kopet-dagh basin to turan sea that this subject causes of strengthens of urasian theory of kopet-dagh basin.