Paleoenvironmental evolution and sequence stratigraphic reconstruction during the Late Cretaceous in southern Egypt: Implications for palynological and geochemical proxy data

Abstract

During the Campanian-Maastrichtian, long-term cooling drove eustatic sea-level fall, promoting carbonate platform deposition at mid-to-high paleolatitudes. Here, 85 rock samples were collected from the Campanian-Maastrichtian uppermost Qusseir, Duwi, and lowermost Dakhla formations at three sections in the El-Sebaiya area of the Nile Valley (Egypt). A comprehensive approach, including palynological, whole rock geochemistry, and total organic carbon (TOC) analyses, was performed. Four palynofacies assemblages (PFA) were identified in the three sections. PFA-A shows high abundances of amorphous organic matter (AOM), suggesting deposition in a shallow marine environment, whereas PFA-B exhibits moderate abundances of phytoclasts and AOM, indicative of deposition in fluvio-deltaic to marginal shallow marine conditions. PFA-C is dominated by phytoclasts, mainly of opaque equidimensional particles, characterizing a fluvio-deltaic environment, while PFA-D is characterized by moderate levels of AOM and dinoflagellate cysts (dinocysts) with low phytoclasts, pointing to a shallow marine shelf environment. Dinocysts are dominated by peridinioid forms combined with the common distribution of phosphorite belts, reflecting that the southern Tethys was controlled by upwelling-driven elevated productivity settings under varying redox conditions. Data further allowed the reconstruction of three third-order transgressive-regressive sequences. The transgressive systems tract (TST) sediments are characterized by an increase in AOM, coincided with elevated carbonate content, Mn, and Mn/Al ratios, with maxima corresponding to the maximum flooding surface (MFS) within most sequences. Conversely, the regressive systems tract (RST) sediments show an increase in phytoclasts and elevated SiO₂, Zr, Zr/Al, Ti, Ti/Al, and Sr/Ca ratios, with their highest values corresponding to the maximum regressive surface (MRS).