Paleogeographic, paleoclimatic and sea-level implications of glauconite deposits in Egypt: A review

Abstract

Glauconite deposits are confined to the Western Desert in Egypt of four different sequences and ages from older to younger include, 1) Lower Cenomanian Bahariya Formation, 2) Lower-Middle Campanian Qusseir Formation, 3) Upper Campanian Duwi Formation, and 4) Lutetian-Bartonian Hamra Formation.Lower Cenomanian, Upper Campanian and Lutetian-Bartonian glauconites occur as pellets, while the Lower-Middle Campanian glauconite occurs as fine-grained particles of non-pelletal texture. Based on K2O contents, the Lower Cenomanian and Upper Campanian glauconites are classified as slightly evolved, while the Lower-Middle Campanian and Lutetian-Bartonian glauconite are categorized as evolved. Positive correlations between K2O and Fe2O3 in the Bahariya Formation, Qusseir Formation and Hamra Formation deposits suggest a layer lattice glauconitization mechanism for these deposits. On the other hand, the lack of correlation between Fe2O3 and K2O declines the layer lattice formational mechanism for the Duwi Formation glauconite. A neo-formation mechanism was suggested for this glauconite. Rare earth elements patterns are the same in the four deposits and resemble the shallow sweater pattern.The four glauconite deposits formed in shallow marine environments and might correspond to major eustatic transgressive and global warming events. Glauconite of the Bahariya Formation corresponds to the Early Cenomanian Tethys major transgression in Egypt and can be correlated to the Albian/Cenomanian global cycle boundary as well as the early Cenomanian “hot greenhouse”. The sequence boundary near the topmost part of the Qusseir Formation matches the global warming of the Middle Campanian Event (MCE). The upper Campanian glauconite of the Duwi Formation occurs as lowstand wedge and may correlate to the late Campanian climatic warm optimum. The stratigraphic position of the Hamra glauconite above the unconformity surface refers to transgressive phase that may match with latest Lutetian major sequence boundary (Lu4) and global warming event of the Middle Eocene Climatic Optimum (MECO).Paleogeographic maps show that the Western Desert of Egypt during Cenomanian and Lower Campanian covered by shallow marine setting, which match with the proposed setting for the glauconites in these ages. However, paleogeographic maps for the Upper Campanian and Middle Eocene were modified to fit with the suggested setting of glauconites of these epochs. The prevalence of shallow marine setting during these four ages interprets the restricted occurrences of glauconites at the Western Desert of Egypt during these epochs.