Naqus Formation Research Articles

Paleozoic Lithofacies in Southwestern Sinai and Their Depositional Environments: ABSTRACT

Major breaks in sedimentation, accompanied by well-developed paleosols, have been successfully used to subdivide the 600 m (1,968 ft) of Paleozoic sandstone and shale sequence of southwestern Sinai, Egypt, into five smaller facies association units (i.e., formations). The lowest unit (the Araba Formation) is dominated by 1 to 10 m (3 to 32 ft) thick coarsening-up sequences of parallel-bedded, varicolored, fine-grained arkosic sandstone and muddy sandstone with abundant Skolithos burrows and in places Cruziana traces. This is the deposit of a low-energy prograding sandy coastal plain complex that grades upward into a thin, fining-up channel-overbank deposits with poorly developed paleosols. The overlying Naqus Formation scours deep into the Araba, and is characterized by l nticular, coarse to medium-grained, cross-bedded quartz sandstone with only a few clayey intervals. Well-rounded vein quartz and quartzite pebbles are scattered in the lower half, but form lenses in upper half. Crossbeds are common. The Naqus is interpreted as alluvial fan-braided stream deposits. A 15 to 20 m (49 to 66 ft) thick, conspicuous dark brown, ferruginous shale, ochre-yellow dolomitic sandstone and fossiliferous gray siltstone sequence, persistent all along the Qabeliat valley, overlies the Naqus and represent lagoonal deposits laterally equivalent to the shallow marine shale-dolomite sequence of the Um Bogma Formation farther north. The upper few meters of this unit developed into a paleosol. Basal fluvial channel sands of the succeeding Ataqa Formation cut into the Um Bogma aleosol, and grade upward into the fossiliferous green-red marine shales and subordinate sandstones in shoaling-upward sequences. Laterally, these shallow marine beds grade into coastal swamp deposits of carbonaceous shale and coal. Excellent paleosols developed at the top of the Ataqa Formation which in turn is deeply channeled by a thick succession of fining-upward, lenticular fluvial channel-sand-overbank paleosol facies of the Budra Formation. Southward in the Qabeliat valley, a parallel-bedded sequence of thick green shales and thin brown sandstones, both nonfossiliferous, intervenes in the middle of the Budra Formation and represents ephemeral lake deposits related to the fluvial system. Although the repetition of facies associations in the Paleozoic sequence of southwestern Sinai oints to the repetition of events, each lithofacies shows characters of its own sufficient to assign it to a specific environment. Marked asymmetry in the facies sequences suggests spasmodic character of the events. End_of_Article - Last_Page 423------------