Depositional history and sequence stratigraphy of Tirgan Formation (Barremian - Aptian) in western and centeral Kopet Dagh area, NE Iran

The Tirgan Formation (Barremian - Aptian) is well exposed in the Kopet Dagh in northeast Iran. Three stratigraphic sections in Esfidan, Dadanlu and Radkan were measured and sampled. Their thicknesses are 207.8, 498.2 and 238 metres, respectively. Based on study of 260 thin sections, 17 carbonate and 4 clastic lithofacies have been identified. Carbonate lithfacies are deposited in a carbonate ramp in open marine, shoal, lagoon and tidal flat environments. Sea level changes during Barremian - Aptian time led to formation of two large scale depositional sequences in all sections. Base and top boundaries of the Tirgan supersequence are type Two. We believe that this study can help in reconstruction of tectonic history of the area during Lower Cretaceous time.