Formation of Upper Cretaceous bedded and nodular cherts in Egypt
Baioumy, Hassan M.; Abu El-Hassan, Mohamed M.
published: Aug 27, 2004
ArtNo. ESP155023302004, Price: 29.00 €
In addition to phosphorites, the Upper Cretaceous Duwi Formation contains abundant cherts that occur as lenses or beds. The cherts are dull, brittle, very dense rocks, black to dark brown in color, and massive to weakly laminated. They are composed of fine-grained, microcrystalline quartz with minor amounts of clays, organic matter and iron oxides. Neither radiolaria nor sponges spicules were observed in the studied cherts. Cherts are formed due to diagenesis of pre-existing biogenic silica. Silica was supplied along with phosphorus by upwelling currents prevailing during the Late Campanian in Egypt and the North African continental margin. Absence of biogenic relics can be attributed to the complete dissolution of these relics during diagenesis. Low MnO/TiO2 values, plot of Al2O3 against Fe2O3 normalized to SiO2, and plot of Al2O3/ (Al2O3 + Fe2O3) against Fe2O3/TiO2 indicate the formation of the Duwi cherts in an oxic continental margin environment.