DEPOSITIONAL HISTORY OF THE EARLY
SYNRIFT SEQUENCE AT GABAL HADAHID,
SOUTHERN SINAI, EGYPT
AHMED A REFAAT
Geology Department, Faculty of Science, Cairo University, Giza, Egypt.
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The Early Miocene synrift sequence exposed at Gabal Hadahid, Southern Sinai, Egypt consists of two distinct rock units; the Rudeis Formation which conformably overlies the Nukhul Formation and is on-lapped onto the Middle Eocene Mokattam Formation. The Rudeis Formation is unconformably overlain by a continental sequence of red pebbly sandstones and polymictic conglomerates that belongs to the Sarbout El Gamal Formation.
Three major sedimentary cycles could be recognized within the studied Early Miocene sequence. The first cycle corresponds to the Nukhul Formation and is represented by littoral sedimentary facies while the second sedimentary cycle is represented by offshore marine to submarine fan sediments corresponding to the lower Rudeis Formation. The third sedimentary cycle is characterized by shallow marine environment that matches the upper part of the lower Rudeis Formation.
The clay mineralogy of the Nukhul and Rudeis formations is quite different. The Nukhul sediments are more enriched in illite and kaolinite together with smectite and less predominant illite/smectite mixed layer. Whereas the Rudeis sediments are more smectitic in composition accompanied with illite/smectite mixed layer and small proportions of illite and kaolinite.
The Nukhul Formation is made up of immature coarse elastic sediments of conglomerates and sandstones interbedded with sandy marls and fossiliferous limestone. The Nukhul Formation represents the first shallow marine transgressive deposits overlying the pre-Miocene sediments during transgressive systems tract (TST). The maximum flooding surface (MFS) is represented by fine-grained argillaceous sediments, rich in planktonic foraminifera, which dominate the lower part of the Rudeis Formation. They are composed of monotonous sequence of green gypsiferous fossiliferous marl, laminated siltstone and mudstone with thin interbeds of argillaceous limestone. These were deposited in a relatively deep marine environment with localized development of submarine fans during transgressive systems tract (TST). They are overlain by shallowing upward sequence of shallow marine yellowish brown cross-bedded and massive sandstone and yellow sandy fossiliferous and bioturbated limestone during highstand systems tract (HST).
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