Biostratigraphic Age Revision of the Asmari Formation in One of the Oil Fields in Southwest of Iran

Present study revises the biostratigraphy age of the Asmari formation in Dezful embayment in the southwest of Iran. Asmari formation thickness reaches 417.5 meters and it mainly consists of dolomite, sandy dolomite, limestone, sandy limestone, sandstone, and shale. Carbonate units comprise wackestone, packstone, grainstone, and less boundstone facies. According to the recognized assemblage zones and the previous Sr isotope data, new biozonation are defined for the Asmari formation in this filed. As a result, the Asmari formation is subdivided into five bio zones as follows:1. Borelis melo melo-Borelis melo curdica Assemblage Zone, Early Miocene (Burdigalian);2. Indeterminate Zone, Early Miocene (Aquitanian-Burdigalian);3. Miogypsina - Elphidium sp14 - Peneroplis farsensis Assemblage Zone, Early Miocene (Aquitanian);4. Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus Assemblage Zone, Late Oligocene (Chattian);5. Lepidocyclina-Operculina-Ditrupa Assemblage Zone, Late Oligocene (Chattian).Due to non-accompanied Lepidocyclina microfossils with Nummulites microfossils in the bio zone five, the related age is considered to be Late Oligocene (Chattian). Nummulites microfossils relating to Rupelian were not distinguished in the studied section of this filed.