In this research, to identify microfacies, depositional environments, and to investigate and characterize carbonate assemblages, a total of 40 samples were collected from the Qom Formation in the Gonjan stratigraphic section. The thickness of the Qom Formation in this section is 100 meters. It unconformably overlies Eocene volcanic sequences with an igneous unconformity and is overlain by the Lower Red Formation with an erosional unconformity. The dominant lithology of this formation in this section consists of medium to thick-bedded limestone and marly sequences. The age of the Qom Formation in this section has been determined as Rupelian–Chattian based on previous studies. Based on the study of microscopic thin sections prepared from the Qom Formation sequences in the studied section, eight microfacies belonging to outer ramp and mid-ramp (distal and proximal parts) environments were identified. In this section, the gradual transition of these facies, along with the absence of debris-flow deposits, continuous barrier reefs, and coated grains (ooids), supports deposition on a gently sloping homoclinal carbonate ramp platform during the Oligocene. Based on the microfacies, the identified depositional environments, and their skeletal elements, three carbonate associations were identified: nannofor, Foralgal ( LB Foralgal) and Rhodalgal.