BENTHIC FORAMINIFERAL BIOSTRATIGRAPHY OF THE OLIGOCENE SEQUENCE OF THE ASMARI FORMATION IN THE INTERIOR FARS SUB-ZONE, ZAGROS BELT, SW IRAN

The benthic foraminifera of Oligocene carbonate deposits of the Asmari Formation in the Hoz-e-Bidmeshk section in the Interior Fars Sub-zone, Zagros Belt, SW Iran, were studied for biostratigraphic zonation. The Asmari Formation in the studied section is 388 m thick, conformably overlies the Paleocene-Eocene deposits of the Pabdeh Formation and is conformably overlain by the Gachsaran Formation. Nineteen genera and 20 species of benthic foraminifera were recognized in the Asmari Formation. Miliolids were identified only at the order level. The benthic foraminifera are assigned to two assemblage biozones in the formation: the Lepidocyclina spp.-Nummulites fichteli-Nummulites intermedius-Nummulites vascus and Archaias kirkukensis-Archaias asmaricus-Archaias hensoni-Miogypsinoides spp. zones. The biozones show that the studied carbonate succession of the Asmari Formation was deposited during the Rupelian and Chattian. In the late Chattian and Miocene, sea level fall prevented deposition of the Asmari Formation in the Interior Fars Sub-zone and the evaporites and shallow-marine marls of the Gachsaran Formation were deposited during the Miocene.