Sedimentology and Geochemistry of Campanian - Maastrichtian Sandstones of Enagi Formation, Bida Basin, Nigeria

Abstract The provenance, paleoenvironments, and mineralogy studies of the sandstones of the Enagi Formation at Gulu and Kandi in the Bida Basin were investigated for preliminary reservoir quality assessment. The Gulu and Kandi samples are dominantly medium-grained with moderate sorting and fine to coarse-grained with poor sorting respectively. The quartz, feldspar, and rock fragments plots with average values of 76.2%, 8.7%, and 15.1% at Gulu and 59.3%, 24.6%, and 16.2% at Kandi suggest they are litharenitic and arkosic sandstones respectively. Bivariate plots of standard deviation, skewness, and kurtosis indicate river sands with little input from tidal environments in the Gulu area. The Gulu samples are more of fluvial channel deposits and shoreface lithofacies while the Kandi samples resemble alluvial deposits of a high-energy system. Al2O3/ TiO2, Zr/ TiO2, and Y/Ni versus Cr/V of the samples suggest a felsic igneous origin with little contribution from a mafic source. K2O/Na2O against SiO2 and TiO2 against Fe2O3+MgO point to a passive margin continental environment for the sediment source. The cementation of moderately sorted, sub-mature texture and litharenitic sandstones in the Gulu area will be low compared with the Kandi poorly sorted and arkosic lithofacies at the deeper subsurface. This study for the first time reports the presence of favorable geological indices for good porosity and permeability development in the Campanian – Maastrichtian sandstone reservoir of Enagi Formation. These results will further drive exploration work in the Bida and other West African Cretaceous rift basins for prospective underground water and hydrocarbon reservoirs.