Calcareous nannofossils biostratigraphy and paleoecology of the Miocene Qom Formation (Burdigalian, Central Iran)

During the Early Miocene a global cooler interval was followed by warmer paleoclimate conditions. At the end of the Burdigalian, the Miocene Climatic Optimum (MCO) occurred and brought about global warming and resulting changes in paleoecology and paleoceanography. The Qom Basin (Iran) was situated between the Mediterranean Sea and Indian Ocean and is considered as part of the main Tethyan Seaway, established from Oligocene to Miocene times. In this study, two calcareous nannofossil biozones are recognized in the e-member of the Qom Formation (Burdigalian), the NN3 (zone Sphenolithus belemnos) and NN4 (zone Helicosphaera amplipareta) zones, respective. The modifications in paleoecology and climatic conditions played a vital function in the assemblage structure and the frequency of the calcareous nannofossils during the Burdigalian. From the early to the middle Burdigalian, paleoecologic conditions in the Qom Basin changed from oligotrophic with a warm climate to eutrophic, accompanied by an increase in productivity in the basin, coincided with a cooler climate and inferred upwelling conditions. In contrast, in the late Burdigalian, mesotrophic to oligotrophic conditions were dominant in the basin, affected by the predominance of the MCO and global warming. Warming impacted nutrient availability and salinity, and changes in circulation patterns in the Tethyan Seaway because of the stepwise tectonic closure of the Qom Basin. The paleoceanography and tectonic activity thanks to alteration in the connectivity between the Tethyan Seaway and other basins influenced the calcareous nannofossils assemblages.

Keywords: Miocene Climatic Optimum, Calcareous nannofossils, Qom Formation, Paleoecology, Burdigalian