Sedimentary Facies and Sequence Stratigraphy of Qom Formation Deposits in NE Delijan, NW Central Iran

The Oligocene Qom Formation deposits in NW Central Iran (NE Delijan) are widespread in NE-SW trend.Four members of the QomFormation (unknown, a, b& c1) in the study area consist of mainly marly limestone, limestone, sandy limestone and a minor amounts of sandstone. It disconformablyoverliesthe Lower Red Formation and the upper boundary is covered by the recent alluvium. Based on the benthic foraminifers assemblage, these deposits are attributed to Oligocene (Rupelian- Chattian). Petrographic considerationled to identification of 12 carbonatemicrofacies and one sandstone facies that may have been deposited in a homoclinal ramp and in 4 sub environments including tidal flat, lagoon, bioclastic bar and open marine. Sequence stratigraphy analysis led to identification of 8 3rdordersdepositional sequences bounded by type I and type II sequence boundaries. Comparison between interpreted relative sea level curve with global sea level curve showsreasonable correlation with the lower and upper sequence boundaries of this formation and also Rupelian- Chattianboundary and the differences in other sequence boundaries can be related to local tectonic activity in the sedimentary basin of Qom Formation and the local sea level changes.