Sequence stratigraphy of Qom Formation in South of Tehran

This paper represents the sequence stratigraphic analysis of the Oligo-Miocene shallow water carbonate succession of the Qom Formation, in kuh siah, Yort -e Shah no.1 well and Morreh Kuh outcrop (South of Tehran). The study was done, based on the lithosratigraphy, biostratigraphic framework (in the context of European standard biozonation), microfacies, and pale environmental interpretation and sequence stratigraphic concepts. The Qom Formation as an active petroleum system in the type locality was divided into a-g members but in study area, c1-f members in kuh siah, c4- f members in Yort e shah-1 and f members in Morreh kuh section can be determined. However, these studies could be carried out in the light of having detailed biostratigraphic data for time line determinations. The results showed that the benthic foraminiferal composition of the study area has close affinities with the coeval assemblages in Western Tethys and the Middle East. The assemblage is characterized by both hyaline and porcellaneous taxa including Borelis, Pseudotaberina, Meandropsina, Dendritina, Miogypsina, Miogypsinoides, Spiroclypeus, Heterostegina, Neorotalia, and Ammonia. The large foraminifera associations mark the SBZ 23 to 25 zones, referring to a time span from late Chattian to Burdigalian. Based on the discovery of late Chattian (SBZ23) deposits (previously supposed to be of early Miocene age), the Oligo-Miocene stratigraphy of the southeastern Tehran was also revised. The biostratigraphic results were also supplemented with the Paleo environmental interpretation of the microfossil assemblages. This study shows that sedimentary environment of the Qom Formation is related to Carbonate Ramp Platform. Based on sedimentary texture and percentage of skeletal and non-skeletal allochems, 13 microfacies from outer to inner ramp were determined. One of the main points for petroleum exploration is having a detailed stratigraphic data in context of sequence stratigraphy. In fact sequence stratigraphy helps to determine the elements constituting petroleum systems which are great importance in mapping the source, reservoir and cap rocks distribution. As the Oligo-Miocene deposits of Qom Formation are known as an active petroleum system in Central Iran. The recognition of sedimentary facies, transgressive system tracts (TST), and high stand system tracts (HST) of these deposits are necessary to find the high potential areas for hydrocarbon accumulations. The sequence stratigraphic studies lead 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 make third and froth sequences with the age of Burdigalian. The correlation of sequences showed toward North West the older sequences get disappeared and the age of Qom Formation get younger.