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<p>The marine outcrops of the Rashrashiyah Formation in the Sirhan-Turayf Basin at northern Saudi Arabia was previously assigned to the late Eocene and no detailed marine microfossils have been reported from them. Thus, the lithostratigraphy and planktonic foraminifera of this formation were examined in four lithologic sections: Rash-D1, Rash-D2, Rash-D3 and Section 2. The planktonic foraminifera indicated that the upper part of this formation is early Oligocene in age, which is a new (discovery) record in northern Saudi Arabia, and conformably overlies the upper Eocene deposits without interruption. Therefore, this study primarily aims to establish a time-stratigraphic framework for the studied sections using planktonic foraminiferal biostratigraphy and modify the lithostratigraphy of Rashrashiyah Formation. This formation was divided into lower and upper members, occupying a continental shelf-upper slope and inner neritic environments, respectively. We identified Ninety species of planktonic foraminifera, belonging to twenty one genera, allowing division of successions into five biozones of late middle Eocene-early Oligocene age. They are arranged from older to younger as follows: <i>Morozovelloides crassatus</i> Zone (E13), <i>Globigerinatheka semiinvoluta</i> Zone (E14), <i>Globigerinatheka index</i> Zone (E15), <i>Hantkenina alabamensis</i> Zone (E16), <i>Pseudohastigerina naguewichiensis</i> Zone (O1). These biozones represent the Eocene–Oligocene sequence with several steps of bioevents. Regional correlation of the sections using lithology and foraminiferal assemblages indicated that the region underwent to a major tectonism such as block-faulting after the deposition of lower Oligocene marine sediments. Subsequently, intensive erosion and weathering resulted in deposition of Miocene siliciclastics of the Sirhan Formation unconformably above a peneplained to irregular surface of unequal ages similar or probably synchronous to the syn-rift Miocene sediments in the Red Sea region. These results were correlated with their equivalents worldwide and in the neighbouring countries such as Jordan, Syria, Turkey, and Egypt, which could provide new information about the Eocene–Oligocene transition (EOT), the paleogeography of northern Arabian Plate as well as on paleoceanography of the Neo-Tethys.</p>

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Revised lithostratigraphy and planktonic foraminiferal biostratigraphy of upper middle Eocene-lower Oligocene successions from Northern Saudi Arabia

  • 期刊论文

  • 发表日期：

    2025年11月26日

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  • Ramadan H. Abu-Zied,
  • Mohammed H. Aljahdali,
  • Ibrahim M. Ghandour,
  • Abdulrahman A. Al-Malki,
  • Rashad A. Bantan

摘要

The marine outcrops of the Rashrashiyah Formation in the Sirhan-Turayf Basin at northern Saudi Arabia was previously assigned to the late Eocene and no detailed marine microfossils have been reported from them. Thus, the lithostratigraphy and planktonic foraminifera of this formation were examined in four lithologic sections: Rash-D1, Rash-D2, Rash-D3 and Section 2. The planktonic foraminifera indicated that the upper part of this formation is early Oligocene in age, which is a new (discovery) record in northern Saudi Arabia, and conformably overlies the upper Eocene deposits without interruption. Therefore, this study primarily aims to establish a time-stratigraphic framework for the studied sections using planktonic foraminiferal biostratigraphy and modify the lithostratigraphy of Rashrashiyah Formation. This formation was divided into lower and upper members, occupying a continental shelf-upper slope and inner neritic environments, respectively. We identified Ninety species of planktonic foraminifera, belonging to twenty one genera, allowing division of successions into five biozones of late middle Eocene-early Oligocene age. They are arranged from older to younger as follows: Morozovelloides crassatus Zone (E13), Globigerinatheka semiinvoluta Zone (E14), Globigerinatheka index Zone (E15), Hantkenina alabamensis Zone (E16), Pseudohastigerina naguewichiensis Zone (O1). These biozones represent the Eocene–Oligocene sequence with several steps of bioevents. Regional correlation of the sections using lithology and foraminiferal assemblages indicated that the region underwent to a major tectonism such as block-faulting after the deposition of lower Oligocene marine sediments. Subsequently, intensive erosion and weathering resulted in deposition of Miocene siliciclastics of the Sirhan Formation unconformably above a peneplained to irregular surface of unequal ages similar or probably synchronous to the syn-rift Miocene sediments in the Red Sea region. These results were correlated with their equivalents worldwide and in the neighbouring countries such as Jordan, Syria, Turkey, and Egypt, which could provide new information about the Eocene–Oligocene transition (EOT), the paleogeography of northern Arabian Plate as well as on paleoceanography of the Neo-Tethys.