Study of the Oligocene depositional sequences in the northwest of Hamedan

In order to study of the Oligocene depositional sequences, a stratigraphic section of the equivalent deposits of the Qom Formation (for convenience in the continuation of the article, Qom Formation is mentioned) which is 330 meters in thickness has been nominated in northwest of the Hamedan. Facies analysis has produced eight microfacies related to the four facies belts of tidal flat, reef, slope and open marine. Base on lacking the sediment gravity flows, turbidity facies, and abundance in reef facies deposits, a carbonate shelf is proposed for Qom formation. In this research, two depositional sequences and three-sequence surfaces have been separated based on sequence stratigraphic studies (the first and third sequence surfaces being of the first type). A comparison of the relative sea-level change curve in the study area with the Oligocene-Miocene global sea-level change curve shows that sequences of the Qom Formation have acceptable compatibility with global changes in seawater level. Also, the comparison of the sequence boundaries of this study with the Zagros and European basins indicates that the Oligocene sequence levels of the Qom Formation which are identified in the Zagros basin, are well corresponded with the results of this study compare to the European one.