FIELD CHARACTERISTICS AND ASPECTS OF THE SEDIMENTOLOGY OF THE LOKOJA BASAL SANDSTONE IN THE BIDA BASIN, NIGERIA: IMPLICATIONS FOR PALEODEPOSITIONAL ENVIRONMENT

The Lokoja Basal Sandstone, well - exposed in road cuts along the Okene Abuja highway, was examined to characterize its sedimentological attributes and depositional history.This Campanian to Maastrichtian unit consists of alternating sandy, clayey, and conglomeratic beds, reflecting shifts in depositional energy and sediment supply. The sandstone varies in grain size from very fine to coarse (0.0063 mm - 4 mm), with occasional pebble sized fractions, indicating periodic episodes of higher energy conditions. Pebbly horizons and conglomeratic interbeds further attest to the fluctuating hydrodynamic conditions during deposition.Sedimentary structures within the succession are dominated by bimodal cross-stratification with north and south azimuths. This bidirectional paleocurrent pattern suggests differing flow regimes. The cross-stratified sand bars are composed of angular to subangular grains. The presence of angular to subangular pebbles points to a short transport distance. Such textural immaturity, coupled with the dominance of high-angle cross-stratification, indicates deposition under a high-energy fluvial regime and short transport distance.