In this study, the Paleocene-aged Chehel Kaman formation in Nizar village, located in the east of Kopet Dagh sedimentary basin, has been investigated. In terms of lithology, this formation includes limestone, marl limestone, marl and shale. In order to carry out paleoecological studies, determine the sedimentary environment and microscopic facies, 79 thin sections of the Chehel Kaman Formation have been prepared and studied in this section. 20 genera and 13 species of benthic foraminifera, 4 genera and 3 species of planktonic foraminifera, and 3 genera of calcareous algae have been identified in the micropaleontological investigations. Based on the identified genera and species, Paleocene age (Danian- Thanetian) was identified for this formation in Nizar section. The paleogeography of the ostracodes showed that this formation was deposited in a shallow and relatively energetic environment, and from the base to the top, the amount of oxygen in the environment decreases and the rate of sedimentation increases. Also, warm weather conditions prevailed during the deposition of this formation and the salinity of the environment was relatively high. The studies of the facies of this formation have led to the identification of four facies belts (open sea, dam, lagoon and intertidal zone) and 16 microscopic facies. The combination of sediment identification and paleontology data indicates that this formation was deposited in a hemoclinal carbonate ramp. From the base to the top of the section, the facies changes show deepening conditions, which is consistent with the results of biostratigraphy studies.