Original paper

Sedimentary facies and sequence stratigraphy of the Cambrian Araba Formation, Gebel Somr El-Qaa'a, North Wadi Qena, Egypt

Ghandour, Ibrahim M.; Tawfik, Hossam A.; Maejima, Wataru; Abdel-Hameed, Abdel-Monem T.

Abstract

The Cambrian siliciclastic-dominated Araba Formation crops out at Gebel Somr El-Qaa'a, North Wadi Qena, on the western side of the Gulf of Suez, Egypt. It rests unconformably on the Precambrian Basement Complex and attains a thickness of ~20 m. Field based sedimentological investigations of four sections allow identification of five facies associations stratigraphically arranged as follows: fluvial (FA A), deltaic (FA B), tidal flat (FA C), offshore-shoreface (FA D), and subtidal-intertidal (FA E). Facies characteristics, as well as their lateral and vertical distributions, vary considerably between the studied sections. Sequence stratigraphic interpretations allow the identification of three unconformity-bounded transgressive-regressive sequences, each corresponding to a relative sea-level rise-fall cycle. The first sequence consists of three systems tracts - lowstand, transgressive and highstand with the transgressive one (TST1) only well-developed in section two. The second sequence is separated from the first by a tidal ravinement surface. Sequence two consists of transgressive intertidal flat, normal regressive highstand offshore-shoreface and ends with forced regressive upper shoreface deposits. The third sequence is bounded below by a widespread subaerial unconformity and consists of lowstand paleosols (facies Ps), thin transgressive tidally-influenced fluvial deposits and normal regressive highstand subtidal-intertidal sand-flat deposits. Shallow-marine deposits exhibit pronounced upward changes in depositional processes through the Araba Formation. The flood-dominated delta front sandstones (B1 facies) record a mixed process regime, with units being deposited under fluvial-dominated and storm influenced conditions. Forced regressive upper shoreface sandstones (facies D3) were deposited under tidally-influenced conditions, whereas the subtidal intertidal sandstones (FA E) were formed under tide-dominated conditions. The sediments at section three are completely devoid of storm-induced sedimentary structures. The sedimentation of the Araba Formation and its facies and stacking pattern were mostly controlled by the paleotopography, lack of vegetation, subsidence rate, relative sea-level and shorezone morphology.

Keywords

araba formationsomr el-qaa'acambrianfluvio-marinewadi qenaforced and normal regression