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<p>In this research, we investigated the environment of a carbonate ramp formation called Pabdeh from the Paleocene to the end of the Oligocene, a part of the carbonate reservoirs in the Zagros Basin. For this purpose, coring samples and cutting were employed at every two meters of the studied formation. Petrographical analysis of 159 thin sections derived from a 365-m core interval of well 12 and 29&#xa0;m from well 31 in the Karanj oil field identified four microfacies: (1) planktonic foraminifera packstone with phosphate and glauconite (Microfacies A1); (2) planktonic foraminifera wackestone lime-mudstone with phosphate and glauconite (Microfacies A2) (3) bioclast, ooid, intraclast packstone–wackestone (Microfacies A3), and (4) mudstone with interlayer wackestone–packstone with silt-sized fossils (Microfacies B). The petrographic investigation and depositional interpretation revealed numerous signs of a storm signal on the investigated site, such as: (1) the presence of packstone–wackestone bioclast layers with a sharp erosional contact. (2) The occurrence of packstone–wackestone bioclast layers with normally graded bedding. (3) The inclusion of lithoclast fragments from the Mutone facies within the wackestone–mudstone facies. (4) The parallel arrangement of bioclastic components. (5) The alternating pattern of thick and fine laminates on a millimeter scale. It is concluded that the sedimentation environment of the Pabdeh Formation was a deep outer-ramp environment that gradually changed to a middle ramp influenced by storms. More laboratory studies showed diagenetic processes, including: micritization, glauconite, phosphatization, pyritization, cementation, bioturbation, dolomitization, silicification, ironization, and physical compaction. The porosity observed in these samples was primary and secondary, and their types are intragranular, intergranular, and mold. Also, the predominant cement seen in this formation is equant calcite cement. Thoroughly comprehending the sedimentary environment allows us to pinpoint potential areas for organic matter accumulation. In the case of the Pabdeh Formation, which serves as a source rock in the Karaj oil field, this underscores the significance of sedimentological data as a critical factor in the exploration and discovery of hydrocarbon resources. Furthermore, the study shows that storm activity indicators are carefully examined, providing insight into the shift from a deep outer-ramp environment to a middle ramp impacted by storm events.</p>

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Sedimentary facies and depositional-diagenetic model of storm-influenced carbonate ramp system, Paleocene–Oligocene of Pabdeh Formation, Zagros, Iran

  • 期刊论文

  • 发表日期：

    2025年3月22日

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  • Fatemeh Saberi,
  • Mahboubeh Hosseini-Barzi,
  • Pourya Asoude,
  • Farhad Abdollahzadeh Bina,
  • Ahmed E. Radwan

摘要

In this research, we investigated the environment of a carbonate ramp formation called Pabdeh from the Paleocene to the end of the Oligocene, a part of the carbonate reservoirs in the Zagros Basin. For this purpose, coring samples and cutting were employed at every two meters of the studied formation. Petrographical analysis of 159 thin sections derived from a 365-m core interval of well 12 and 29 m from well 31 in the Karanj oil field identified four microfacies: (1) planktonic foraminifera packstone with phosphate and glauconite (Microfacies A1); (2) planktonic foraminifera wackestone lime-mudstone with phosphate and glauconite (Microfacies A2) (3) bioclast, ooid, intraclast packstone–wackestone (Microfacies A3), and (4) mudstone with interlayer wackestone–packstone with silt-sized fossils (Microfacies B). The petrographic investigation and depositional interpretation revealed numerous signs of a storm signal on the investigated site, such as: (1) the presence of packstone–wackestone bioclast layers with a sharp erosional contact. (2) The occurrence of packstone–wackestone bioclast layers with normally graded bedding. (3) The inclusion of lithoclast fragments from the Mutone facies within the wackestone–mudstone facies. (4) The parallel arrangement of bioclastic components. (5) The alternating pattern of thick and fine laminates on a millimeter scale. It is concluded that the sedimentation environment of the Pabdeh Formation was a deep outer-ramp environment that gradually changed to a middle ramp influenced by storms. More laboratory studies showed diagenetic processes, including: micritization, glauconite, phosphatization, pyritization, cementation, bioturbation, dolomitization, silicification, ironization, and physical compaction. The porosity observed in these samples was primary and secondary, and their types are intragranular, intergranular, and mold. Also, the predominant cement seen in this formation is equant calcite cement. Thoroughly comprehending the sedimentary environment allows us to pinpoint potential areas for organic matter accumulation. In the case of the Pabdeh Formation, which serves as a source rock in the Karaj oil field, this underscores the significance of sedimentological data as a critical factor in the exploration and discovery of hydrocarbon resources. Furthermore, the study shows that storm activity indicators are carefully examined, providing insight into the shift from a deep outer-ramp environment to a middle ramp impacted by storm events.