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Sandstone Geochemistry And Provenance Of The Nsukka Formation, Southeastern Nigeria
X-ray fluorescence analysis of the sandstone component of the Nsukka Formation in the Inyi-Okigwe area of the Anambra Basin, was conducted to determine the mineralogical composition and interpret the depositional history. The results revealed that the sandstone has an average silica (SiO2), alumina (Al2O3), and iron oxide (Fe203) contents of 93.89%, 1.91%, and 1.28% respectively. Titanium oxide (TiO2) averages 0.55%, while other oxides occur in traces. The observed high percentage of quartz (SiO2) and low value/absence of Na2O and CaO in the samples reflect intensive chemical weathering and/or sediment recycling. The samples are classified as quartz arenite. Based on raw oxide discriminant function analyses the clastics are interpreted to be generated from a pre-existing sedimentary terrane. Plot of log SiO2 against log (K2O/Na2O) revealed that the clastics were derived from a passive to active continental margin setting. Evidence from chemical and the mineralogical indices of alteration (CIA and MIA) respectively show that the climate of the source region was semi-humid and characterized by intense chemical weathering.
Keywords: Nsukka Formation, X-ray fluorescence, alteration indices, silica oxide, provenance evaluation.