PALEOENVIRONMENTS AND PROVENANCE OF THE CLASTIC SEDIMENTS OF THE LOKOJA-BASANGE FORMATION, BENIN FLANK OF ANAMBRA BASIN, NIGERIA

Abstract

Paleoenvironmental and provenance study of outcropping sediments exposed at different locations within the Lokoja Basange Formation in the Anambra Basin were investigated to deduce the transportation history, provenance and paleoenvironments of the sediments. Successions of the sandstones, siltstones and shales observed along road cut and river channels were studied to establish their field relationship and characteristics. 11 sandstones samples were selected and subjected to grain size analyses to determine the graphic mean, sorting, skewness, and kurtosis while 10 sandstone samples were analyzed by heavy mineral. Field observation revealed three lithofacies mainly sandstones, siltstones, and shales in the studied sections. The mean, sorting, skewness, and kurtosis have the following ranges (0.07- 4.3, 0.78 - 2.20, -1.18 - 0.77, and 0.48 -4.92) respectively. The sandstones ranged from finemedium- coarse grained exhibiting poor sorting. The sandstones were characterized by angular to sub angular grains having low maturity reflecting short transportation history and fluvial depositional environments in a low energy setting. Most of the sandstones are finely skewed and leptokurtic while few samples exhibits very coarse skewed and platykurtic. The siltstones and shales suggest a coarsening upward progradational pattern and may indicate a deltaic sedimentation. Heavy mineral assemblages observed in the sandstones include zircon, rutile, magnetite, topaz, and tourmaline which suggests provenance from igneous and metamorphic sources from the Precambrian Basement Complex of Nigeria.