Petrochemistry of the Lower Cambrian Araba Formation, Taba Area, East Sinai, Egypt

Petrographical and geochemical analyses of the siliciclastic succession of the Lower Cambrian Araba Formation, Taba area, East Sinai, Egypt have been carried out to infer their provenance, tectonic setting and paleoweathering conditions. The succession (~ 70 m thick) consists of basal conglomerate, very fine-grained to pebbly sandstone with carbonate, siltstone and mudstone intercalations. It rests nonconformably over the Precambrian basement complex and underlies the Upper Cambrian Naqus Formation. The Araba Formation comprises 6 facies assemblages of remarkable textural and compositional variations. They are braided fluvial, sheet flood-dominated alluvial fan, flood plain, intertidal, beachface/subtidal and offshore. The sandstones are essentially subarkose, with subordinate amounts of sublitharenite and litharenite. Monocrystalline quartz is the most abundant mineral phase compared with polycrystalline grains and followed by K-feldspar and rock fragments, respectively. Lithic grains include acidic granites, metavolcanics and rarely chert fragments. Accessories include micas, zircon, tourmaline, rutile, hornblende, apatite and Fe-Ti oxides. Cementing materials include clay minerals, hematitic Fe-oxide, apatite, non-ferron calcite and dolomite, quartz and feldspar overgrowths, as well as barite and halite. XRD analysis reveals that smectite, I/S mixed layer, illite and minor kaolinite are the principal clay minerals. Porosity is represented by intergranular, intragranular, fracture, moldic and micro-intergrangular variety. Geochemically, the Araba sandstones are characterized by higher values of SiO2, Al2O3, K2O, Ba, Rb, Sr, Zr, higher ratios of Al2O3/TiO2, K2O/Na2O>>1, Al2O3/(CaO+Na2O) and Th/Co, and lower values of Fe2O3*+MgO, TiO2, Ni, Cr and V. The data reveals that the source area was subjected to uplift of low to moderate relief continental block that eroded under the influence of semi-humid to semi-arid climatic regimes and indicated the deposition in a passive continental margin setting. The detritus are mainly derived from the nearby Precambrian granites and acidic metavolcanics, together with the surrounding metamorphic rocks and cherts. The moderate values of paleoweathering Indices (Chemical and Plagioclase Index of Alterations; CIA and PIA, respectively) suggest that these sediments were primarily exposed to mild chemical weathering at the source area and later subjected to slight diagenetic modifications.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California