International Journal of Geology, Agriculture and Environmental Sciences Volume – 2 Issue – 3 June 2014 Website: www.woarjournals.org/IJGAES ISSN: 2348-0254 WOAR Journals Page 10 Geochemistry of Merkhiyat Sandstones, Omdurman Formation, Sudan: Implication of depositional environment, provenance and tectonic setting. Elzien, S.M.; Farah, A. A. Alhaj, A. B.; Mohamed, A.A.; Al-Imam, O.A.O.; Hussein, A. H.; Khalid, M.K., Hamed, B.O.; Alhaj, A.B. 1 Department of Geology / Faculty of Petroleum and Minerals, Al Neelain University, Al Mogran, Khartoum, Sudan 2 Department of Petroleum/ Faculty of Petroleum and Minerals, Al Neelain University, Al Neelain University, Faculty of Petroleum and Minerals, Al Mogran, Khartoum, Sudan. 3 Department of Geophysics /Faculty of Petroleum and Minerals, Al Neelain University, Al Mogran, Khartoum, Sudan. Abstract: Major oxides and selected trace elements geochemistry, their ratios and discriminated diagram of sandstones from Merkhiyat Member, Omdurman Formation have been investigated to determine their depositional environment, provenance and tectonic setting. Geochemistry of Merkhiyat sandstones indicate that they are sub arkose, lithic arenite, quartz arenite, Fe-sand, and varied in their maturity. The source area recognized by humid to semi humid condition resulted intermediate to strongly weathering affecting due to the CIA values, these conditions lead to form clay minerals (e.g. kaolinite). Merkhiyat sandstones derived from granitoid, gneissic supplemented by recycled sand with minor influence of mafic provenances. The clay minerals may response of the high value or concentration of ferromagnesian trace elements such as Cr, Ni and V. The source rocks of the sediments material tectonically may continental margins; passive and active, and very restricted to oceanic island arc settings, and deposited on the passive basin. Keywords: Merkhiyat member, Omdurman formation, depositional environment. 1. Introduction Sandstone of Merkhiyat Member of Omdurman Formation occurs in Omdurman area is a north western part of Khartoum basin of central Sudan. Merkhiyat Member in the study area is composed of coarse to medium grained sandstone, conglomerate and minor mudstone. They represent, fining upward cycle and each sequence (cycle) based on conglomerate facies represent fill of minor channel and/or sand body of channel fill (CH) facies to over bank deposits facies(OF) deposit in fluvial environment. Over the years, the use of trace and major elements geochemistry for discrimination of tectonic setting and provenance had been commonly applied to sedimentary rocks (Tijani et al., 2010). The tectonic setting of a depositional environment influences composition of sediment (Pettijohn et al., 1987; Bhatia, 1983). Transport mechanism and mixing of materials from diverse source area may obscure the original signatures and thus prevent reconstruction of the paleogeography from geochemical analysis (Pinto et al., 2004). The usefulness of major (Bhatia, 1983; Roser and Korsch, 1988; McLennan, 1989; Armstrong-Altrin and Verma, 2005; Al-Juboury,2007; Huntsman-Mapila et al.,2009;Zaid,2012) and trace (Bhatia and Crook, 1986; Etemad-Saeed et al.,2011) elements geochemistry discrimination diagrams to infer the tectonic setting of sedimentary rocks. Trace elements are defined as any element that is present in relatively small amounts in soil and rock (Albright, 2004). Some immobile trace elements as such Y, Sc, Th, Zr, Hf, Cr, Co and REE are believed to be useful to be indicator of geological processes, provenance and tectonic setting (Cullers 1994; Bhatia and Crook, 1986; Taylor and McLennan et al.,1985; Liu et al.,2007), because there are relatively low mobility during sedimentary processor , these elements probably are transferred quantitatively into clastic sediments during weathering and transportation, reflecting the signature of the parent materials, hence are expected to be more used (Armstrong-Altrin et al.,2004). In this chapter major oxides and selected trace elements used to get signature of depositional environment, provenance and tectonic setting of Merkhiyat sandstones in study area. 2. General Geology and tectonic setting The general geology in Omdurman area is Pre-Cambrian basement rocks (gneisses, marbles, foliated batholitic granite and sheared acidic dyke), Cretaceous Omdurman Formation (Merkhiyat Member), Tertiary volcanic rock (basic and acidic) and Quaternary deposits (Fig.1). The study area is northwestern part of Khartoum basin (KB) west the Nile, Omdurman area. The KB is a one of Sudanese rift basins, which are mainly intra-continental basins, they characterized by thick non-marine clastic sequence of Jurassic? Cretaceous and Tertiary age (Shull, 1988). KB is a NW-SE trending rift basin lies on the eastern side of CARS (Jorgensen &Bosworth, 1989). KB is a large elongated basin aligned NW-SE, boarded to North the Sabaloka basement complex and to the south by faulted basement blocks North of Sinnar and Elduaim (Omer, 1983).