Biostratigraphy, Paleoenvironments, and Paleobiogeography of the Middle–Upper Eocene Ostracods from Northwestern and Northeastern Banks of the Nile Valley, Egypt

The middle and upper Eocene sedimentary successions exposed along the northwestern and northeastern portions of the Nile Valley, Egypt, have been thoroughly examined for their ostracod assemblages. This study enhances the understanding of biostratigraphic zonations and evaluates the paleobiogeographic distribution and paleoenvironmental conditions that prevailed during the deposition of this sedimentary record. Lithostratigraphically, the studied successions are subdivided into four stratigraphic units, arranged in ascending order as follows: the Qarara, the El Fashn, the Gehannam, and the Beni Suef formations. A total of 125 rock samples were selected and well analyzed, resulting in the identification of sixty-five ostracod species and subspecies belonging to thirty-three genera, fifteen families, and three superfamilies. The stratigraphic distribution of the recorded ostracod taxa contributed to the construction of four local biozones, spanning the interval from the upper Lutetian to lower Priabonian: Schizocythere fadlensis Zone (upper Lutetian–lower Bartonian), Loxoconcha pseudopunctatella Zone, Dygmocythere ismaili Zone (Bartonian), and Asymmetricythere hiltermanni Zone (Bartonian–Priabonian). These biozones are well described, discussed, and correlated with those previously documented in different areas of Egypt and neighboring countries. The statistical analysis, supported by ternary plot diagrams, indicates that the depositional environments of the studied rock units fluctuated between shallow inner neritic and deeper outer neritic marine environments. The identified taxa display a wide geographic distribution and show a significant similarity with those identified in the southern, northern, and eastern Tethyan provinces, suggesting a direct marine connection during the Eocene.