Depositional Model of Maastrichtian Mamu and Ajali Formations in Auchi Area Western Anambra Basin, Southern Nigeria
Iloloh, O. J
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Sedimentological, palynological and sequence stratigraphic analyses were used to characterize and interpret the environment of deposition of Maastrichtian Mamu and Ajali Formations outcropping in Auchi area western Anambra Basin, Nigeria. Interpretation of depositional environment was done using lithofacies study, sedimentary structures, textural and biostratigraphic attributes. Five lithofacies were identified namely cross bedded sandstone, laminated sandstone, massive bedded sandstone, dark grey laminated shale and heterolithic facies. Identified facies from Mamu and Ajai Formations suggest deposition in a brackish to shallow marine environment and fluvial to tidally influenced shoreline environment respectively. The palynomorphs identified in the rocks include: Monocolpites marginatus, Longapertites sp., Proteacidite miniporetus and monocolpopollenites spheriodites. These forms indicate early Maastrichtian age for the Mamu. Petrographic study shows that sandstones found are averagely super mature with angular to sub angular grains. The high quartz content suggests recycling from older sediment sources. The high percentage of staurolite from the heavy mineral analysis suggests inputs from a metamorphic provenance. The provenance for the sediment therefore could possibly be the Abakaliki Anticlinorium and the Oban Massif.