A field
appraisal of sedimentary facies and environment of the
Pre-Carboniferous, SW Sinai, Egypt
Sayed M. Ahmed and Rifaat A. Osman
Dept. Geolog., Fac. Sciences, Banha, Egypt |
In the Abu Durba area, the pre-Carboniferous
sequence is differentiated into:
Cambrian Araba Formation, Ordovician-Lower Silurian Naqus Fm, and topped by the Devonian
Wadi Malik Fm. Northwards at Wadi Sidri, the Naqus Fm is missing and the Wadi Malik Fm
unconformably overlies the Araba Fm. Farther northward, the Araba FM is reduced in
thickness and is unconformably overlain by the Carboniferous Um Bogma Fm or Abu
Thora Fm.
The Araba Fm is subdivided into 4 rock units of 5 clear sedimentary facies, starting from
base to top:
1) Conglomerates, cross-bedded and laminated sandstones, deposited in fluvial channel
system;
2) Laminated siltstones to claystones, laminated and cross-bedded sandstones, paleosols
and ferricrete bands, representing inter-channel fluvial deposits formed during flood
stages and modified by post depositional in situ processes of pedogenesis;
3) Siltstones and claystones, and thin to thick bedded, very fine-grained cross-stratified
and laminated sandstones, bioturbation is moderate to very high with Scolithos and
Cruziana tracks. These rocks were deposited in a low-energy marine offshore environment;
4) Fine sandstoe passing upward into very fine sandstone interbedded with siltstone and
claystone. The sequence contains numerous Trilobite tracks, Scolithos and small to large
tubes of sponge-like organisms (Archaeocyathus). This facies was deposited in lower
shoreface to offshore transition environment;
5) Medium to coarse, large- scale cross-bedded sandstones and laminated sandstones
deposited in the upper shoreface and tidal inlet.
The facies association forming the Naqus Fm indicates that it was deposited in
fluvio-glacial system. The vertical sequence of strata and sedimentary structures of the
Wadi Malik Fm reflects its alluvial environment.
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