this research concentrates on the lithostratigraphy, biostratigraphy, microfacies and sedimentary environment of the asmari and gachsaran formations at southwest firuzabad. the thickness of the studied section in all 608.95 meters that 220.8 meters belong to the asmari formation and 387.95 meters belong to the gachsaran formation (champe and mol members). in the study area, the asmari formation overlies the pabdeh formation and it covered by the gachsaran formation. in studied section the asmari formation basically comprises of thin to massive bedded limestone, marly and nodular limestone. the gachsaran formation in champe member comprises of thin to thick bedded limestone and some marly and nodular limestone. mol member basically comprises evaporate and marl and a little thin to massive bedded limestone with marl. in this area chehel member of the gachsaran formation has not outcrop. the thickness of the champe and mol members are respectively 208.5 and 179.45. based on field observation 6 lithostratigraphic units for the asmari formation and 9 units for the gachsaran formation distinguished. biostratigrphy studies lead to identifying totaly 18 genera and 17 species of foraminifera, 18 genera and 15 species for the asmari formation and 9 genera and 6 species for champe and mol members of the gachsaran formation. based on biozones introduted by adams and bourgeois (1967) the asmari formation equivalent to 2 biozones: eulepidina - nephrolepidina- nummulites assemblage zone and miogypsinoides-archaias-valvulinid assemblage zone (archaias asmaricus- archaias hensoni assemblage sub zone) (adams and bourgeois, 1967) refer oligocene (rupelian-chattian) to early miocene (aquitanian) ages. the gachsaran formation equivalent to archaias asmaricus- archaias hensoni assemblage sub zone refer aquitanian age. based on laursen et al., (2009) biozones the asmari formation equivalent to 2 biozones: nummulites vascus-nummulites fichteli assemblage zone and archaias asmaricus-archaias hensoni-miogypsinoides complanatus assemblage zone (laursen et al., 2009) indicate rupelian-chattian ages and the gachsaran formation equivalent to 2 biozones: archaias asmaricus-archaias hensoni-miogypsinoides complanatus assemblage zone and indeterminate zone (laursen et al., 2009) indicate chattian-aquitanian ages. field observation and microscopic analyses led to the recognition of 10 microfacies belong to open marine and lagoon (under the terms restricted and semirestricted) environments for the asmari formation and12 microfacies belong to tidal flat and lagoon (under the terms restricted and semirestricted) environments. according to the identification and distribution microfacies asmari formation in studied section open shelf model with two part inner and middle shelf and for the gachsaran formation shelf carbonate is considered that depositional environment gachsaran formation limited to inner shelf two with tidal flat and lagoon (restricted and semirestricted) environments.