Age determination of base of Khangiran formation based on calcareous Nannoplanktons in Chehel Kaman syncline

   General:
     Khangiran formation crop out in Chehel kaman syncline at west of Sarakhs city about 60 Km away. This formation mainly is composed of grey-olive grey marl.
In this region the Khangiran formation is conformable with the Chehel kaman formation in the lower contact and the upper contact of Khangiran formation is disconlormahie with Quaternar deposits (bess). However, the main purpose of this research is age determination of base of Khangiran formation. From this investigation three characteristic species (Tribrachiatus orihostylus, Discoaster lodoensis & D. kuepperi). were identified and based on the first occurrence and fossil assemblage of these species, Ypresian stage (Early Eocene) is suggested for base of Khangiran formation that correspond to Trihrachialus orthostylus zone (NPl 2) of Martini standard zonation (1971).