The Oligo-Miocene Asmari Formation (up to 500 meters) is the most prolific petroleum reservoir rock in southwest Iran. It unconformably overlies the basinal deposits of the Eocene-Oligocene Pabdeh Formation and unconformably underlies the continental deposits of the Middle Miocene Gachsaran Formation. Field and petrographic investigations of 10 outcrop and subsurface sections of the Asmari Formation in the northwest of the basin led to recognition of dominantly shallow marine carbonate, siliciclastic and evaporite facies. These are arranged into 7 depositional sequences that are correlated with the Oligo-Miocene eustaticl sea level cycles. In the southwest distal sections, the lower and middle Asmari sequences (Chattian-Aquitanian) consist of mixed carbonate and siliciclastic facies, which change laterally to pure carbonate or carbonate and evaporite facies in the proximal area to the northeast. These sequences are absent towards the Zagros thrust belt, where the dominantly carbonate facies of the upper Asmari (Burdigalian) unconformably overlies the Eocene Shahbazan Formation. The Asmari Formation was deposited in the Persian Gulf foreland basin related to NW-SE trending Zagros orogenic belt. Both eustatic sea level changes and regional tectonics were responsible in controlling lateral and vertical facies variations of the Asmari succession. The dominantly carbonate facies and correlation of Asmari sequences with global sea level cycles suggest a strong eustatic control during deposition.
