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Petrography and geochemistry of the Lower Miocene Moghra sandstones, Qattara Depression, north Western Desert, Egypt
Author(s) -
Tawfik Hossam A.,
Salah Mohamed K.,
Maejima Wataru,
ArmstrongAltrin John S.,
AbdelHameed AbdelMonem T.,
El Ghandour Mai M.
Publication year - 2017
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3025
Subject(s) - geology , petrography , diagenesis , provenance , geochemistry , illite , arenite , sedimentary rock , siliciclastic , lithic fragment , weathering , clastic rock , sedimentary depositional environment , clay minerals , geomorphology , structural basin
The petrographic and geochemical compositions of the Lower Miocene Moghra siliciclastic sediments in the Qattara Depression, north Western Desert, were investigated to infer their provenance, tectonic setting, palaeoweathering conditions, and diagenetic history. The Moghra Formation (~200 m thick) is dominated by sandstones intercalated with mudstone and carbonates. X‐ray diffraction analysis revealed that smectite, kaolinite, and illite are the dominant clay minerals found in mudstones. The sandstones are mainly subarkose, sublitharenite, and quartzarenite types with an average modal composition of Q 89 F 6 L 5 . The sandstones possess various diagenetic overprints including mechanical infiltration of clay, compaction, cementation, dissolution, and replacement. Major and trace element concentrations suggested that the parent rocks are intermediate to felsic in composition derived from the Neoproterozoic Arabian Nubian Shield. The weathering indices such as the chemical index of alteration and the plagioclase index of alteration implied that the intensity of chemical weathering in the source area was moderate under semi‐arid climatic conditions. On the other hand, the index of chemical variability indicates a low compositional maturity. The tectonic discrimination diagrams demonstrated a collision setting for the Arabian Nubian Shield, which represents the main supplier of sediments to the study area. Statistical parameters, sedimentary structures, and ichnofossil contents suggested that the Moghra sediments were deposited in a tidally‐influenced fluvial environment.