Paleo-environmental reconstructions of the Upper Cretaceous-Paleogene successions, Safaga, Egypt

摘要

The Late Cretaceous-Early Eocene sedimentary sequences in the Central Eastern Desert of Egypt were studied in three shallow boreholes (Wassief, Urn El-Huaitat, and Mohamed Rabah). This study focuses on an integrated investigation of biostratigraphy, lithostratigraphy and some geochemical parameters, to provide important clues to the relative sea-level changes and to interpret the prevailed depositional conditions.Micropaleontological study on planktonic foraminifera allows to identify eight zones, ranging in age from Late Cretaceous to Early Eocene. Three hiatal surfaces have been recognized as evidenced by missing formaniniferal zones: The first spans the Late Maastrichtian-Danian regional unconformity. The second one is recorded in the Late Paleocene. The third one is located at the Late Paleocene-Early Eocene (Thanetian-Ypresian) boundary. The environments of the study foraminiferal parameters range from the non-marine to outer neriticupper bathyal.Petrographically, thirteen Microfacies Types (MFT) have been recorded. Three MFTs constitute the siliciclastic facies; MFT-1; silty to sandy mudstone, MFT-2; organic-rich silty mudstone, and MFT-3; fine-grained sandstone/glauconite intercalations. Two MFTs represent a phosphorite facies which are MFT-4; phosclast packstone to phosclast grainstone and MFT-5; phosooid packstone to phosooid grainstone. Eight MFTs characterize the carbonate facies; MFT-6; non-fossiliferous lime-mudstone, MFT-7; phosphatic foraminiferal pack/grainstone, MFT-8; bioclastic foraminiferal packstone, MFT-9; bioclastic foraminiferal wackestone, MFT-10; glauconitic phosphatic foraminiferal Wack-Packstone, MFT-11; non-fossiliferous dolomitic mudstone, MFT-12; dolomitic glauconitic lime-mudstone, and MFT-13; dolomitic bioclastic wackestone. The depositional environments of the study microfacies range from the terrestrial to open marine outer neritic-upper bathyal.Geochemical parameters have been used to improve the litho- and biostratigraphic framework: the major oxides, TOC wt.% and the Chondrite-normalized REE. Based on the vertical distribution of CaO/P2Os, TiO2/CaO and cerium (Ce)-anomaly, changes in paleo-bottom water redox conditions were reconstructed and correlated with relative sea level changes. Prior to the major transgression during deposition of the Duwi Formation under reducing marine conditions, the prevailing oxic to sub-mdc bottom water terrestrial conditions during deposition of the Quseir Formation.