Petrographic Studies, Heavy Mineral Analysis and Pebble Morphogenesis; Implications for Sedimentary Processes of Southern Bida Basin, Nigeria

The sandstone and conglomeratic sandstone facies of Lokoja and Patti Formation, Southern Bida Basin were analysed for their mineralogical compositions and pebble morphogenesis. The identified framework grains include the dominant quartz grains, feldspars, mica and rock fragments while heavy minerals include Zircon, Topaz, Tourmaline, Staurolite, Sphene, Rutile and Olivene. The heavy minerals were used as indicators of sources of sediments; Zircon and Tourmaline suggest igneous and low grade metamorphic rocks whereas Staurolite and Rutile show high grade metamorphic rocks. The angular to sub-angular shapes of the heavy minerals and sub-angular shapes of quartz grains respectively indicate textural immaturity of the sediments. This is associated with absence or low degree of physical weathering and abrasion due to short distance of sediment transport and it implies the prevalence of chemical weathering of the source rocks. The grain to grain contacts among quartz grains, the occurrence of overgrowths and iron oxide cements are consequences of post depositional changes of the sediments. Interpretation of pebble sizes, sphericity and oblate-prolate index provided information about the paleoenvironments.