biostratigraphy, paleoecology, microfacies and depositional environment of the asmari formation (oligocene-early miocene) in karanj oil field, sw iran

Core data analysis of one well from the karanj oil field, southwestern iran, allowed us to precise the biostratigraphy, microfaciesand paleoecology of the asmari formation. analysis of thin section from this cored well permitted identification of 28 genera and 20species of benthic and planktic foraminifera respectively. subsequently four benthic foraminiferal assemblage biozones were identified,as follows: (1) lepidocyclina-operculina-ditrupa assemblage zone, (2) archaias asmaricus-archaias hensoni-miogypsinoidescomplanatus assemblage zone, (3) miogypsina-peneroplis farsensis–elphidium sp. 14 assemblage zone and (4) borelis melo curdica-borelis melo melo assemblage zone; indicating an oligocene (rupelian-chattian) to early miocene (aquitanian to early burdigalian)age for the asmari formation. microfacial study of depositional textures led to characterizing 12 microfacies types, indicatingenvironments in five different settings: restricted lagoon, open lagoon, shoal, slope, and basin mostly in the upper asmari formation.these sediments had been deposited under 3 different salinity levels (from 34 to more than 50 psu) in an environment ranging fromaphotic to oligophotic and to euphotic zones, and under oligotrophic to eutrophic conditions from the chattian to the burdigalian on acarbonate platform (homoclinal ramp). in the studied well, the asmari formation had been deposited in a marine environment withnormal salinity during the rupelian-chattian interval and in a marine environment with high salinity during the aquitanian to theburdigalian times.