Biostratigraphy and depositional characteristics of the northern part of the Tethyan Seaway (Burdigalian, Central Iran) in a sequence stratigraphic framework

This study examines the paleoenvironmental evolution of the Qom Formation using biostratigraphy and petrography within a sequence stratigraphic framework to figure out spatial and temporal distribution of the depositional characteristics. The upper part of the Qom Formation (members e and f) was deposited in the northern branch of the Tethyan Seaway in the Central Iran Basin, and investigated along the Dochah and Jujukzar sections. Calcareous nannofossils and large benthic foraminifera indicate the succession was deposited during the early to middle Burdigalian in the Central Iran Basin. According to nannofossil assemblages two biozones NN2 (Discoaster Druggii zone) and lower part of NN4 (Sphenolithus heteromorphus zone) of Burdigalian age are identified in both members of the Qom succession. With respect to nannofossil zones, a hiatus (NN3, ca. 19-18 Ma) is recognized, related to erosion. Based on large benthic foraminifera, SBZ25 biozone including Borelis melo curdica (Burdigalian) is recognized in the member f of the Qom Formation. Based on petrography, ten depositional facies were deposited in four facies belts including lagoon, shoal, mid ramp, and basin, propagated in a ramp-type platform in the Qom Basin. Regarding stacking pattern of facies, three 3^rd-orderdepositional sequences were formed at the time, driven by relative sea-level changes. Regarding the sequence stratigraphic context, the upper part of the member e and member f are stratigraphically equivalent as evident by biostratigraphic and sedimentary evidence, which has not been investigated in previous studies. This study underscores and evaluates the sequence stratigraphy and sedimentary model of the Qom Basin in a high-resolution scale.

Key words: Qom Formation, Biostratigraphy, Sequence stratigraphy, Tethyan Seaway