Combined Petrographic and Geochemical Studies of Maastrichtian Patti Formation Sandstone, Bida Basin, Nigeria: Implications for Provenance and Compositional Maturity

Abstract

Geochemical data on sandstone facies of the Maastrichtian Patti Formation in Bida Basin, Nigeria, is presented and interpreted in this paper with respect to its provenance and compositional maturity. Petrographic data from thin sections and X-Ray Diffractometry were also integrated. Petrographic data from the sandstones classified them mainly as quartz-arenites and minor sub-arkose while geochemical indices such as high average values of SiO₂/Al₂O₃, low Na₂O+K₂O and K₂O/Na₂O values also indicate the samples are sub-litharenite to quartz-arenite type. Relatively high average values of total REE (141.40 ppm), Th (7.59 ppm), Hf (6.82 ppm), and Zr (205.12 ppm) coupled with low concentrations of Ni (3.06 ppm), Co (1.66 ppm) and V (20.65 ppm) in the sandstones indicate felsic igneous provenance. The discrimination functions plot shows that the sandstones were sourced mainly from matured sedimentary provenance and a passive margin setting is deducted based on the plots of TiO₂ versus Fe₂O₃+MgO and  K₂O/Na₂O versus SiO₂. The sandstones show high average value of SiO₂ (86.8 %) and low values of Al₂O₃ (6.11 %), K₂O (0.12) and Na₂O (0.02 %), suggesting that the sediments are mature. Plot of SiO₂ versus (Al₂O₃+K₂O+Na₂O) further lend credence to chemical maturity and reveals semi-humid to humid paleoclimate. The Chemical Index of Alteration (CIA) value of 96.49 and the Plagioclase Index of Alteration (PIA) of 99.05 respectively are supportive of high weathering of the source area. The sands were most probably recycled from older Lokoja Formation during the late Maastrichtian Tethys inundation in the basin.