Investigation of Lower Cretaceous strata by Calcareous Nannofossils at the western Koppeh-Dagh Basin in North of Tethyan province (Agh-Band Section)

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College of Geology, Faculty of Sciences, University of Tehran, Tehran, Iran

Abstract

The Lower Cretaceous strata, upper Sarcheshmeh, and lower Sanghaneh formations in the western Koppeh-Dagh Basin, North of Gonbad-Kavoos, Aghband section were selected and studied based on calcareous nannofossils. A total of 53 samples of dark gray shale, marlstones, and argillaceous limestones of these rock units with a thickness of 138 meters were collected. The sixty calcareous nannofossil species belonging to 25 genera and 6 families were identified. According to the biozones of the Tethyan schemes, the NC5 (E, D) to NC9B biozones, and based on the global standard schemes, the CC6 to CC8 biozones were recognized. Based on the biozones detected in the uppermost Sarcheshmeh and Sanganeh formations, the late Barremian to middle-late Albian? age was proposed for the studied strata. These studies showed that the sea level of the Tethys Ocean (Koppeh-Dagh basin) increased, similar to other parts of the world in the Barremian and Aptian ages, and the global sea level of the oceans decreased in the Albian, based on lithostratigraphy. Also, the gray to yellow marlstone of the Agche Gil Formation with Neogene age has stayed on the Sanganeh Formation and shows a hiatus from the Late Albian to Neogene in the studied section. The assemblages of warm water species such as Rhagodiscus asper, Ragodiscus gallagheri, Rhagodiscus angustus, Rhagodiscus achylostaurion, and Tranolithus orionatus indicate these strata deposit in the low to the medium latitudes in the Tethyan province at the western Koppeh-Dagh Basin.

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History

  • Receive Date: 04 July 2023
  • Revise Date: 04 November 2023
  • Accept Date: 14 November 2023

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