LITHOFACIES, PEBBLE MORPHOGENESIS AND PROVENANCE OF THE BIDA FORMATION, NORTHERN BIDA SUB-BASIN, NORTH-CENTRAL NIGERIA

Abstract

The sedimentary provenance of Campanian Bida Formation sediments at Patigi and Baganko axis northern Basin Sub-Basin, North-central Nigeria were investigated using facies, pebble morphology, grain size and heavy mineral analyses. The goal is to contribute to a better understanding of regional tectonics and paleogeography of the Bida Basin. Lithofacies analysis revealed four basic sub-facies; clast-supported, massive conglomerate (Gcm), matrix-supported, massive conglomerate (Gmm), clast-supported, crudely bedded conglomerate (Gh), crudely stratified to massive sandstone (Se) that belongs to gravel bar (GB) fluvial architectural elements. The facies association is typical of Intraformational Conglomerate deposited in a shallow sandy and gravelly braided river system to a proximal alluvial plain. The similarity in average values of independent functions and dependent variables derived from pebble morphometric indices of Coefficient of Flatness (0.66; 0.65), Elongation Ratio (0.94; 0.95), Maximum Projection Sphericity (0.78; 0.76), Oblate-Prolate Index (-2.23; -2.17), Roundness (sub-angular to rounded) and Form (compact bladed, compact, very platy, very bladed, elongate and bladed) for sediments in Patigi and Baganko areas respectively suggest deposition of the sandstones in fluvial settings. The pebble imbrications paleo-flow indicator data ranges from 18 to 40°W in Patigi pointing to extensive low-sinuosity fluvial deposition towards western part of the Basin. The granulometric results of the interbedded sandstone samples vary from coarse to very coarse sand, poorly sorted to moderately sorted, coarse skewed to very fine skewed and mesokurtic to very platykurtic and thus classified texturally as gravelly sand to sandy gravel. The identifiable lithic clasts with tourmaline and zircon types in the sandstones within the study area point exclusively to derivation from a granitic and metamorphic origin. In conclusion, the lithofacies and architectural elements of the Bida Formation in the Patigi and Baganko are interpreted to represent channelized fluvial flow of gravel dominated braided rivers in proximal settings. The grain size and pebble morphology parameters with their scatter plots and paleoflow data show the sediments were deposited in a fluvial environment and sourced from eastern part of the Bida