Elemental Geochemistry of the Upper Cretaceous Rakb Formation in Well C3-65, Sarir Field, Sirte Basin, NE Libya

• Osama Rahil Shaltami Rahil Shaltami

  Department of Earth Sciences, Faculty of Science, Benghazi University, Libya

  Author

• Husam Uldin Hamid Alghamari

  Libyan Centre for Sustainable Development Researches

  Author

• Mustafa A. Ben Hkoma

  Libyan Centre for Studies and Researches of Sciences and Environment Technology, Middle Zone Branch, Zliten, Libya

  Author

Assessing the elemental geochemistry of the Rakb Formation in well C3-65, Sarir Field, Sirte Basin, was the goal of this work. The results demonstrated that the Rakb Formation is classified as silica-rich argillaceous shale as indicated by the content of quartz and clay minerals. Numerous sources contribute to the Rakb Formation, including igneous (mafic, intermediate, and felsic rocks) and sedimentary (quartzose rocks), as showed by the plots of Al₂O₃ versus TiO₂, SiO₂ versus FeO, CaO versus Na₂O, F1 versus F2, and SiO₂/10-CaO-MgO-Na₂O+K₂O. Several parameters, including Fe/Al, Mn*, and SO₃, suggested that the Rakb Formation's proven depositional setting is the shallow anoxic marine environment. The plots of MgO versus Fe₂O₃, Al₂O₃ versus P₂O₅, Ca versus Fe, and CaO versus MgO supported this assumption. There was clear terrestrial input during deposition as indicated by the Ti/Al and Al/(Al+Fe) ratios. The Rakb Formation is considered part of the coastal facies as presented by the plot of Al₂O₃/(Al₂O₃+Fe₂O₃) versus Fe₂O₃/TiO₂. The Rakb Formation is not significantly affected by severe diagenesis as confirmed by the plots of CaO/Al₂O₃ versus P₂O₅/Al₂O₃. According to the paleoweathering indices (RR, CIA, CIW, PIA, and CIW´), the source area experienced moderate to high levels of paleoweathering intensity. Conditions during deposition were mostly semi-arid to semi-humid, as verified by the CIA, K₂O/Al₂O₃, and T values. The studied sediments are obviously immature, based on the ICV values. Paleoproductivity fluctuated from low to high as displayed by the P/Al and P/Ti ratios. Th plots of Al₂O₃/(100-SiO₂) versus Fe₂O₃/(100-SiO₂), SiO₂ versus K₂O/Na₂O, and SiO₂/20-K₂O+Na₂O-TiO₂+Fe₂O₃+MgO confirmed that he paleotectonic environment of the Rakb Formation is the continental margin.

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