Sedimentological and geochemical characterization of DF-2 well, Onshore Western Niger Delta: Implications for provenance, tectonic history and paleo depositional conditions

Abstract

The sedimentology and geochemistry of the major oxides and trace elements of DF-2 well, Onshore, Niger Delta, are presented in this study. The study is aimed at describing the sedimentological characteristics as well as using the major oxides and trace elements to investigate the provenance, tectonic history and palaeo-depositional conditions of the well. Selected samples were investigated with fused bead X-Ray Fluorescence (XRF) spectrometry to determine their major oxides and fused bead laser ablation inductively couple plasma mass spectroscopy (LA-ICP-MS) for  their trace elements. Sedimentological analysis from the well shows that the lithology ranged from shaly sand, sandy shale, sandstone and shale. The results show the dominance of silicon oxide (SiO2) contents which ranges from 81.1 to 91.4 wt. % (average of 87.1 wt. %). The low average concentration of Cr<150 ppm and Ni <100 ppm, the ratios of Th/Sc, Th/Co, Th/Cr, Cr/Th, La/Sc, as well as the plots of Th/Co versus La/Sc and TiO2 versus Zr, all infer a felsic source rock. The discrimination plots of ratioK2O/Na₂O against SiO₂ and Log K₂O/Na₂O against Log SiO₂/Al₂O₃ indicated passive continental margin. Various chemical classifications of the sediments show that the sandstone facies plotted mainly in quartzarenite, sublitharenite and Fe-rich sand domains. The samples were deposited under oxic environment based on the average values of U/Th (0.26 ppm), Ni/Co (2.79 ppm) and Cu/Zn (1.81ppm) and bivariate plot of Ni/Co versus V/Cr. However, the bivariate plot of Ni/Co versus V/ (V+Ni) specifies oxic to  anoxic conditions and V/Vi + Ni ratios indicate oxic, suboxic to euxinicpalaeode positional environments for the sediments. Geochemical characterization illustrates mixed marine and terrigenous source input, deposited mainly in semi humid/humid climate. The positive values attained from ratios of Al₂O₃/(CaO+MgO+Na₂O+K₂O) infers mineralogical maturity based on stable mobile oxides content in the studied samples.

Keywords: Felsic Rock, Quartzarenite, Litharenite, Passive Margin, Mobile Oxide, Mature Sediments.