SEDIMENTARY SEQUENCES AND STACKING PATTERNS OF SEDIMENTARY ROCKS AT OKIGWE AND ITS ENVIRONS, ANAMBRA BASIN
Abstract
Four outcrops at Okigwe and environs (Onyekaba mine, ihube roadcut, Uturu roadcut/mine and Lekwashi quarry) in the Anambra Basin southeastern Nigeria were evaluated for an integrated field, sedimentologic and petrographic method. This study was aimed at studying the Sedimentary sequence and stacking patterns of outcropping data in Okigwe and its Environs. This study investigates the depositional environments, sedimentary processes, and stacking patterns of sandstones and shales in Okigwe and its environs within the Anambra Basin. Through lithologic, geometric, and biogenic analyses, the examined lithofacies were subdivided into seven distinct categories: planar cross-bedded sandstone, massive sandstone, Ferruginized sandstone, herringbone cross-bedded sandstone, sandstone with Ophiomorpha burrows, and shale surfaces. These lithofacies, coupled with sedimentary structures, reveal a complex depositional history. Grain size analysis across multiple samples indicated predominantly unimodal distributions with variations in sorting, skewness, and kurtosis, suggesting fluctuating energy levels during deposition. Sorting ranged from poorly to very well sorted, while skewness spanned from strongly negative to strongly positive, and kurtosis from platykurtic to leptokurtic. The textural maturity, showing sub-mature characteristics with limited clay matrix and moderate sorting, alongside a mineralogical maturity index between 2–7.6, further suggests moderate transport and reworking of sediments. Stacking pattern analyses at three primary locations highlighted both fining-upward and coarsening-upward sequences, reflecting depositional trends driven by varying energy levels.
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