Microfacies, sedimentary environment and sequence stratigraphy of the Qom Formation in East Siyah Kuh surface section (South of Garmsar)

This paper represents the sequence stratigraphic analysis of the Oligo-Miocene shallow water carbonate succession of the Qom Formation, east of Kuh Siah outcrop (South of Garmmsar). The study is based on the lithosratigraphy, biostratigraphic framework (in the context of European standard biozonation), microfacies, paleoenvironmental interpretation and sequence srtatgraphic concepts. In this section, only f to c1 members of the Qom Formation can be differentiated. The biostrtigraphic results revealed that the benthic foraminiferal composition of the studied section has close affinities with coeval assemblages in Western Tethys and the Middle East. The larger foraminifera associations in the Qom Formation mark the SBZ 23 to 25 zones, referring to a time span from the late Chattian to Burdigalian. Based on the micropaleontological studies, the age of late Chattian (SBZ 23) is ascribed to c1 member which previously considered as Aquitanian, in East of Siah Kuh surface section. Sedimentary environment of the Qom Formation is related to a carbonate ramp platform. Based on sedimentary texture and percentage of skeletal and non skeletal allochems, 1 lithofacies and 13 microfacies from inner to outer ramp were determined. The sequence stratigraphic studies led to the determination of four 3rd order sequences. The first sequence with the Chattian age includes c1 and c2 members. The second sequence with the Aquitanian age includes c3, c4 and d members. The e and f members belong to third and fourth sequences with the age of Burdigalian.