Provenance Interpretation and Depositional Environment of Sandstones of the Ajali Formation, South of Ifon, Western Flank of Anambra Basin, Southwestern Nigeria

Abstract

Grain size analysis, heavy mineral analysis, and petrographic studies of sandstones of the Ajali Formation near Imoru (south of the Ifon), the western flank of the Anambra Basin, were conducted to determine the provenance and depositional environment. The textural attributes of the Ajali Sandstone were inferred from the statistical variables namely graphic mean, graphic kurtosis, inclusive graphic standard deviation (sorting), inclusive graphic skewness with values of 0.37 - 1.17 (average 0.55Ø), -9.84 - 3.07 (average 0.09Ø), 0.05 - 1.02 (average 0.75Ø), and -0.03 - 1.00 (average 0.35Ø) respectively. Bivariate plots, such as simple skewness measure versus standard deviation (sorting) and mean versus sorting, suggest that the Ajali Sandstone is mainly a fluvial environment. The petrographic result indicates that quartz is the dominant detrital component with iron oxide, and hematite and goethite are the major cement in the analyzed sandstone sample. The zircon–tourmaline–rutile (ZTR) indices range from 67.65% to 73.17%, indicating that the sandstones are sub-mature to mature. Provenance indicators support igneous rocks of acidic compositions (e.g., granite) and high-grade metamorphic rocks (e.g., granite gneiss) of the Basement Complex of Southwestern Nigeria.