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Arabian Journal of Geosciences
Saudi Society for Geosciences
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Abstract: |
The mineralogy and geochemistry of the Upper Cretaceous Duwi black shales of Nile Valley district, Aswan Governorate, Egypt,
have been investigated to identify the source rock characteristics, paleoweathering, and paleoenvironment of the source area. The
Duwi Formation consists mainly of phosphorite and black shales and is subdivided into three members. The lower and upper
members composed mainly of phosphorite beds intercalated with thin lenses of gray shales, while the middle member is mainly
composed of gray shale, cracked, and filled with gypsum. Mineralogically, the Duwi black shales consist mainly of smectite and
kaolinite. The non-clay minerals are dominated by quartz, calcite, phosphate, dolomite, feldspar, with little gypsum, anhydrite,
iron oxides, and pyrite. Based on the CIA, PIA, and CIW values (average = 84, 94, 95, respectively), it can be concluded that the
litho-components of the studied shales were subjected to intense chemical weathering and reflect warm/humid climatic conditions in the depositional basin. The provenance discrimination diagram indicates that the nature of the source rocks probably was
mainly intermediate and mafic igneous sources with subordinate recycled sedimentary rocks (Nubia Formation). Geochemical
characteristics indicate that the Duwi black shales in Nile Valley district were deposited under anoxic reducing marine
environments.
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