Geochemistry of the middle-upper Miocene Bathan Formation, Al-Rehaili area, Jeddah, Saudi Arabia: provenance, tectonic s
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ORIGINAL PAPER
Geochemistry of the middle-upper Miocene Bathan Formation, Al-Rehaili area, Jeddah, Saudi Arabia: provenance, tectonic setting, and paleoweathering implications Ibrahim M. Ghandour 1,2 & Rabea A. Haredy 1 Received: 1 December 2018 / Accepted: 3 July 2019 # Saudi Society for Geosciences 2019
Abstract The present work investigates geochemical and mineralogical signatures preserved in the fluvio-lacustrine sediments of the middle-upper Miocene Bathan Formation at Al-Rehaili area, northern Jeddah, Saudi Arabia to constrain the composition and tectonic setting of the source area and to appraise the influence of weathering. Sixteen sediment samples were collected from the lacustrine delta plain and delta front sandstones (SS I), lacustrine offshore mudrocks, and the younger fluvial channel sandstones (SS II). The sandstones are compositionally immature first cycle. The sandstones (SS I) and the mudrocks of the first depositional stage were derived from an intermediate igneous source rock, whereas the sandstones (SS II) of the second depositional stage were derived mainly from a felsic igneous source rock with subordinate contribution from an intermediate igneous source rock. They indicate an active continental margin to oceanic arc tectonic setting. The values of the Chemical Index of Alteration (CIA) and the Plagioclase Index of Alteration (PIA) as well as the Al2O3/Na2O, Rb/Sr, and Al2O3/(CaO+Na2O) ratios indicate that the source rocks experienced low to moderate degree of weathering consistent with arid to semi-arid climate that prevailed during the Miocene. Subaerially exposed lacustrine offshore mudrocks displayed excessive depletion in the concentration of mobile elements comparing to the bedrock. The low values of the paleoweathering indices are further explained by the enhanced uplift of the Red Sea Escarpment after the cessation of the first stage of the Red Sea floor spreading at 14–15 m.y. ago. Keywords Bathan Formation geochemistry . Provenance . Tectonic setting . Paleoweathering . Red Sea syn-rift deposits
Introduction Tracing the provenance and identifying depositional control on sedimentation using proxies such as biogenic remains, textures and sedimentary structures, and paleocurrent data are significant goals in many studies (Pettijohn 1975; Zuffa 1985; Hernández-Hinojosa et al. 2018). However, variations in the mineralogical and geochemical composition of sedimentary rocks are still the most applicable approaches for interpreting the provenance, tectonic setting, and type and magnitude of Editorial handling: John S. Armstrong-Altrin * Ibrahim M. Ghandour [email protected] 1
Marine Geology Department, Faculty of Marine Science, King Abdulaziz University, P.O. Box 80207, Jeddah 21589, Saudi Arabia
2
Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt
weathering conditions in the hinterland, particularly for unfossiliferous sedimentary rocks. In addition, the chemical composition of sedimentary rocks is employed to interpret hydraulic sorting and mineral f
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