SEDIMENTATION PATTERN OF SOUTHERN BIDA BASIN CENTRAL NIGERIA

Abstract

The determination of sedimentation pattern with which geologic factors were interplayed to establishthe paleoenvironment of deposition of sediments in the southern Bida Basin forms the focus of this study. This was established by detailed field mapping and laboratory techniques. The study area lies within latitude 7o 30’N and 8o30’N, longitude 6o15’E and 7o15’E. The southern Bida Basin stratigraphic succession comprises of Lokoja Sandstone, Patti Formation and Agbaja Ironstone. Field observation shows that Lokoja Sandstone consists of conglome conglomerate, sandstone and claystone facies. The result of the grain size analyses show that Lokoja Sandstones are generally poorly sorted, medium to coarse grained in texture. The morphometric analyses of the pebbles with the mean MPSI value of 80 indicates fluvial environment probably the alluvial fan. The result of the thin section shows that occurrence of monocrystalline quartz, polycrystalline quartz and feldspar may suggest input mainly from alkaline igneous or metamorphic rock. The Patti Formation in the study area consists of sandstone, silt-claystone and shale subfacies. With the cross-stratification on some of the ledges of sandstones beds, the Patti Formation indicates the shallow marine environment. The result of grain size analysis of the poorly sorted sandstones from the Formation shows that it is medium but the fine grains predominant. The Agbaja Ironstone consists of oolitic and concretional ironstone bed which are interbedded with sandstone and claystone. XRD analysis of the ironstones of Agbaja and claystones of the Patti reveal the following dominant minerals: quartz, kaolinite, goethite, illite, siderite, rutile with traces of microcline. The dominance of goethite in the Agbaja shows its deposition in the shallow marine environment. The sedimentation pattern in the southern Bida Basin therefore evolved from Fluvial settings to shallow marine