Global regression evidence in the Middle Miocene strata in the Zanjan area

• Main Authors: Javad Rabbani, Afshin Zohdi
• Format: Article in Journal/Newspaper
• Language: Persian
• Published: University of Isfahan 2022
• Subjects: regression; miocene; microfacies; zanjan; Stratigraphy; QE640-699; South Pole; South pole
• Online Access: https://doi.org/10.22108/jssr.2022.132732.1225; https://doaj.org/article/d67f886f27fe444082c1b431d29ac261

AbstractThe study of the effect of global regression on the Middle Miocene (upper parts of the Qom Formation and Lower parts of the Upper Red Formation) strata has been carried out on two stratigraphic sections in the Zanjan area, northwest Iran. Lithological and microfacies analysis shows that these carbonate strata gradually turn to clastic (sandstone and conglomerate) and, in some regions, turn to evaporate deposits. Microfacies studies also confirm this sedimentary facies changes. Thus, the pelagic wack/packstone microfacies gradually change to sandy bioclast pelagic wack/packstone and finally, at the top of the section changes to the continental sandstone. Facies and lithological changes confirm the shoreline regression that can be correlated with the eustatic sea-level curve. Evaporitic strata in some parts of this area show small restricted basins because of this event. The eustatic sea-level curve in the Langhian and Serravallian ages shows global sea-level fall that can be correlated with the global oxygen isotope changes and glaciation events at this time. Therefore, we can conclude that the Middle Miocene strata have been affected by this global regression in the Zanjan area. Keywords: Regression, Miocene, Microfacies, Zanjan. IntroductionThe Qom Formation is cropped out in central, north and northwest Iran (Daneshain and Dana 2019). The Burdigalian (Daneshian and Saiedi Mehr 2005; Daneshian et al. 2009; Noroozpour 2020; Rabbani and Zohdi 2021) and the Aquitanian–Burdigalian (Daneshian et al. 2010) ages have been proposed for these successions from northwest of Iran. The extinction of Borelis melo curdica confirms a the Burdigalian age in this formation (Rabbani et al. 2022). The Middle Miocene regression is one of the most important global sea-level fluctuations in the world (Haq et al. 1987; Thomas 2008). Some glaciation evidence in the South pole at this time can confirm this global regression (Lewis et al. 2014; Halberstadt et al. 2021). This study tries to find the effect of this global ...