Sedimentary conditions of the Pabdeh-Asmari formations boundary in NW of the Ilam

Authors

1 Department of Geology, Faculty of Science, University of Zanjan, Zanjan, Iran

2 Department of geology - Faculty of science - University of Zanjan - Zanjan - Iran.

3 Associate professor, Department of Geology, Faculty of Sciences, University of Zanjan

Abstract

In order to investigate the biostratigraphic zones and depositional environment of the Pabdeh-Asmari formations boundary, one stratigraphic section (Shirah-Choqachalanchi) has been sampled in the northwest of Ilam. Twenty-five samples were collected from thirty-three meters carbonate layers. All samples have been analyzed for their fossil content and facies characteristics. The Pabdeh Formation in this area consists of thin-bedded limestone with interbedded thin layers of argillaceous limestone, thickening-upward to the Asmari Formation. Fossil studies lead to identification of 13 species belonging to 26 genera of foraminifera that two biozones can be differentiated based on fossil index (Globigerina spp. zone And Lepidocyclina-Operculina-Ditrupa assemblages zone). Rupelian-Chattian age can be proposed for the studied sequences based on biozonation. Facies studies show two facies (1- planktonic and benthic foraminifera wackestone to packstone, and 2- planktonic foraminifera wackestone) related to the outer ramp depositional environment. Facies studies, grain texture and comparing the data obtained from this research with other sections of the region show that sedimentation occurred in a calm outer ramp environment, away from storm wave influence.

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History

  • Receive Date: 30 April 2024
  • Revise Date: 20 July 2024
  • Accept Date: 21 August 2024

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