Petrography and geochemistry of the Jurassic siliciclastic rocks in the Khashm El-Galala area (NW Gulf of Suez, Egypt): Implication for provenance, tectonic setting and source area paleoweathering

Abstract

The petrography and geochemistry (major and trace elements) of the Jurassic sandstones from the Khashm El-Galala area (NW Gulf of Suez, Egypt) have been investigated to infer their provenance, tectonic setting, and degree of source rocks paleoweathering. The studied sedimentary succession is made up of two rock units, namely the Rieina Formation (Bajocian) and the Ras El-Abd Formation (Bathonian–Oxfordian). These formations consist mainly of sandstones, siltstones and claystones, with local interbeds of limestones. Petrographic, modal, and major elemental analyses demonstrate that the studied sandstones are texturally-matured quartz-arenites. The sediments were primarily derived from plutonic felsic igneous (granitic) rocks and recycled older quartzose sedimentary rocks, with a rare contribution from a metamorphic source. The detrital modes of sandstones suggest cratonic provenance. As indicated by Chemical Index of Alteration and Chemical Index of Weathering (averages values are 76.73 and 79.45, respectively), the source area of the studied sandstones was affected by a relatively high degree of chemical weathering and alteration under warm humid conditions. The trace element concentrations and their ratios (La/Th, Cr/Th, Th/Sc, Cr/V, and Y/Ni) suggest the predominant felsic character of source lithologies. Regarding the regional tectonic setting, discrimination diagrams based on major and trace elements indicate that the studied sandstones were deposited in a passive continental margin. In terms of palaeogeography, it can be suggested that the studied Jurassic sandstones were deposited on the margin of one of the rift basins existed in the northwestern part of the Arabo-Nubian Shield.