Quantitative analysis and palaeoecology of Eocene Ostracoda and benthonic foraminifera from Gebel Mokattam, Cairo, Egypt

Abstract

A detailed study of the ostracod and benthonic foraminiferal assemblages of two sections from Gebel Mokattam (east of Cairo) yielded ostracod species and benthonic foraminiferal species in 25 samples from the Mokattam Group of late middle Eocene age and the Maadi Group of late middle to late Eocene ages. The remaining five samples representing the Gebel Ahmar Formation of Oligocene age, at the top of the succession, are barren of fossils. Cluster analysis, using the Jaccard coefficient of similarity (the group average linkage method), helped distinguish four ecozones of late middle to late Eocene age. Principal coordinate analysis (PCO) applied to the same data led to the distinction of two important environmental factors affecting the distribution of these ostracod assemblages in the study area: turbidity currents–exposure to water depth and oxygenation of water. Analyses of the microfacies and microfaunas indicate deposition in a well-oxygenated, turbid, shallow marine environment except at the base of the sequence, which implies reduced oxygenation. Despite the lack of planktonic foraminifera in the studied sections, however, the identified benthonic foraminiferal assemblage affirms that the age of the Mokattam Group is Biarritzian, while that of the Maadi Group ranges from Biarritzian to Priabonian. The Gebel Ahmar Formation, covering the whole succession, is assigned to the Oligocene. A reduced ostracod migration activity was detected along the shores of Tethys during the middle to late Eocene times.