Stratigraphic and Paleoenvironmental study of the Eocene rocks at Gebel Mokattam and its neighboring areas, Greater Cairo, Egypt

Abstract

The Middle-Upper Eocene succession exposed in the study area at Gebel Mokattam and Maadi is divisible from base to top into the Mokattam Group (Observatory Formation) and the Maadi Group (Qurn, Wadi Garawi and Wadi Hof formations). The Eocene rocks in the area yielded twenty six ostracode species from the Upper Eocene succession at the Duwaiqa area in Gebel Mokattam and at the Maadi. Among the recorded ostracode species, Triginglymus maadiensis is newly erected. The recorded ostracode fauna has been biostratigraphically evaluated. It was possible to recognize two ostracode zones, Paracosta humboldti Zone and Uromuellerina saidi Zone, which have been both recorded in the Priabonian. The microfacies investigation of the carbonate rocks represented in three stratigraphic sections revealed the recognition of seven microfacies types in the Duwaiqa section, two microfacies types in the New Duwaiqa section, and six microfacies types in the Maadi section. The recorded microfacies types are comparable to five Standard Microfacies Types (SMF 5, SMF 8, SMF 9, SMF 12, and SMF 14) and three "Standard Microfacies Belts" (FZ) of Wilson (1975) (FZ4, FZ6, and FZ7). These types implicate that the Observatory and Wadi Garawi formations were deposited in a foreslope environmental setting, the Qurn Formation in a setting ranging from foreslope to open platform (shelf lagoon), while the Wadi Hof Formation was deposited in a winnowed platform edge sands environment that changed into open marine platform facies (shelf lagoon) and foreslope. Generally, the Eocene sequence exposed in the area reflects shallow marine settings with relatively deeper conditions towards the southeast. Shelf settings are further supported for the ostracode yielding parts of Wadi Garawi and Wadi Hof formations as indicated by dominance of representatives of the Trachyleberididae and Hemicytheridae which are both represented by taxa possessing eye-spots, besides the Loxoconchidae and Xestoleberididae, which become more frequent in the shallow phytal