Paleocene and Lower Eocene deposits in SW Iran are known as Pabdeh formation.Pabdeh formation is one of the most important lithostratigraphy unit as source rock has been deposited in Zagros basin over an extremely long period in time. The area under research is the Ghachsaran 55 subsurface Section located from the Ghachsaran oil field in Dezful embeyment in zagros fold zone. The Lower boundry of this formation around Ghachsaran basin is identified by Gurpi formation. Study on lithostratigraphy of Paleocene and lower Eocene deposits have been led to the separation following units: clay limestone section in gray colour,11m in thickness, clay limestone section 18m in thickness containing chert inter layers, silt clay limestone section 3m in thickness, The clay limestone section 3m in thickness containing chert interlayers, clay limestone section 4m in thickness . biostratigraphy investigation of Pabdeh formation have been led to the identification of 39 species and 9 genera of foraminifers.In addition , basis of Paleocene- Early Eocene planktonicforamimnifers bioevent in Wade biozonation such as Morozovella velascoensis, Globanomalina pseudomenardii, Psudohastigerina wilcoxensis, Acarinina soldadoensis , Morozovella subbotinae , Morozovella formosa , 9 biozones and 4 subzones are recogenized and these correlated with oldest biozones of (Wynd 1965) Beside,the bio-boundary of Paleocene and early Eocene is identified based on (Wade et al. 2011).