Abstract The Kopet Dagh Basin is located in north-east Iran where sedimentation continued throughout the Jurassic–Tertiary. The area studied is in the easternmost part of the basin. Two stratigraphic sections representing mainly the Lower Aptian Sarcheshmeh Formation have been measured. The Sarcheshmeh Formation in one of these sections (Mozduran) is about 200 m thick. It thins towards the other section (Baghak) in easternmost part of the basin where it about 150 m thick. It is conformably overlain by the Sanganeh Formation and underlain by the Tirgan Formation. Four different facies have been recognized; pelmicrite, mudstone–micritic limestone, biomicrite–bio-oomicrite and biosparite–oosparite. They reflect deposition on a carbonate ramp. Many small-scale shallowing-upward cycles (parasequences) have also been identified within transgressive and high stand system tracts. The cyclicity was probably related to subsidence, which in turn was related to both sediment loading and tectonics.