The study of eight stratigraphic sections along Cairo–
Suez district, between Gebel Ataqa and Gebel Mokattam,
reveals a thick Lower Eocene Ypresian carbonate section,
approximately 210 m thick, at Gebel Abu Treifiya just to the
west of Gebel Ataqa. It is represented by the Minia Formation
rich in Nummulites praecursor, Orbitolites pharaonum
Schwager, Alveolina frumentiformis Schwager, and one of the
precursors of Nummulites gizehensis group. The Minia Formation
is a fairly clear, warm, and shallow marine facies. The
Middle Eocene Lutetian sediments are totally missing in all
studied sections probably reflecting instability in deposition
echoed in the active block movements the area witnessed since
the Paleozoic. The Bartonian sea transgressed over the area
depositing Gebel Hof Formation at the base, Observatory Formation
in themiddle, and Qurn Formation at the top. The Gebel
Hof Formation was deposited in an open-marine environment,
passed upward into shallow marine, neritic to reefal facies; for
the Observatory and Qurn formations, the former changed
laterally into a sheltered lagoon facies, Sannor Formation, rich
in Somalina stefaninii Silvestri, Dictyoconus aegyptiensis
Chapman, and Idalina cuvillieri Bignot and Strougo. The Upper
Eocene sediments,Maadi Formation, are mainly represented
by a carbonate–clastic section showing shallowing-upward
cycles resulted by the retreating of the sea shoreline northward
during the Late Eocene, with high supply of terrigenous sediments.
The lower carbonate cycle of the Maadi Formation was
deposited in a restricted platform and tidal flats, whereas the
upper siliciclastic cycle containing Carolia placunoides banks
was probably deposited in a winnowed platform edge. These
depositional environments were developed in grabens, ramps,
and footslopes of the down-faulted Middle Eocene blocks, i.e.,
syn-tectonic deposition. The fluviatile Oligocene sediments
were highly controlled by the structural and topographic lows,
where a substantial thickness was deposited, Gebel Ahmer
Formation, occupying several grabens and gently sloping areas
between many synthetic faults. |
