Provenance evolution and tectonic environments of Fika shales from Pindiga formation, Gongola Basin, Northern Benue Trough, Nigeria

Abstract

The provenance and tectonic settings of the Fika shales from the Pindiga formation were evaluated using major oxides by x-ray fluorescence spectrometry (XRF). Among the major oxides identified, the shales exhibit elevated levels of SiO₂, with Al₂O₃>Fe₂O₃>MgO>CaO> K₂O>TiO₂>MnO>SrO>BaO; whereas the remaining oxides demonstrate low concentrations. This suggests that the shales are predominantly constituted of quartz minerals and were formed in marine settings. The relatively elevated levels of Fe₂O₃ (with an average of 4.35 %) and MgO (with an average of 2.98 %) in the samples indicate that the source rocks are likely to be mafic to ultramafic. The plots of Al₂O₃ against selected major oxides in the samples show strong positive correlation against SiO₂ and weak positive correlations against CaO, K₂O, and MgO. In contrast, it showed negative correlations against other oxides, which probably imply that these major oxides are not only hosted by clay minerals. Also, K₂O, CaO, and MgO showed weak positive correlations on the plots of SiO₂ versus major elements while others are negative which further suggests that they are associated with micaceous and/or clay minerals in the sediments. The ratios of Al₂O₃/TiO₂ and SiO₂/Al₂O₃ in the shales indicated that the sediments were derived from a mixture of felsic igneous to mafic igneous rocks and mixed compositional maturity, respectively. The cross plots of TiO₂ and K₂O against Al₂O₃ show that the mudstones are composed of basalt, granite, and illite minerals. The shales were grouped near the active continental margin on the plots of Fe₂O₃+MgO vs TiO₂ and Fe₂O₃+MgO vs Al₂O₃/SiO₂. This study showed that major oxides were effective in evaluating the provenance and tectonic settings of Fika shales from Pindiga formation in Gongola Basin, Nigeria.