Petrography,
mineralogy and geochemistry of sandstones of Gebel Gunna,
Central Sinai, Egypt
Hafez Sh. Abd EIWahab
Dept. Geology, Fac. Sciences, Ain Shams Univ., Cairo, Egypt |
The sandstones of "Nubia" (Nubian)
facies between the Precambrian rocks and
the marine Cenomanian in Gebel Gunna, central Sinai are generally submature
sublitharenites. These sandstones contain in the lower horizons rock fragments of granite,
granodiorite, gneissose granite, siltstone, chert and quartzite of various shapes and
sizes. and occasionally present as lenticular bodies.
The clay mineral assemblage is made up largely of kaolinite, and smaller
concentrations of illite, while interstratified illite - smectite and chlorite are the
least
abundant. Most of these minerals are detrital. The sandstones were affected
diagenetically in sequence with: silica over-growths, and authigenesis of K-feldspar,
clay minerals, calcite and dolomite. Chemically, the variation in major element contents
of these sandstones is attributed to the nature of parent rocks, the physicochemical
conditions during weathering, transportation and deposition, and to the effect of
diagenesis. The majority of trace elements entered the basin of deposition with the
clay minerals. Their contents reflect the clay assemblage and type and nature of
weathering processes that affected the parent rocks.
The textural maturity, mineralogy and the elemental grouping suggest that these
sandstones were inherited from more than one source not distant from the site of
deposition.
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