PALYNOSTRATIGRAPHY AND LITHOFACIES ASPECTS OF MAMU FORMATION IN SOME PARTS OF WESTERN FLANK OF ANAMBRA BASIN, NIGERIA

Abstract

Integration of palynological, lithofacies, petrographical and micropaleontological interpretations of Upper Cretaceous Mamu Formation has provided the basis for the age, zonation, the rock type names and composition of the aforementioned formation in the Anambra Basin. Palynological data shows that the shale samples yielded fairly common to abundant and diverse palynomorphs assemblage of Longapertites marginatus, Laevigatosporites ovatus, Monocolpites marginatus, Retidiporites magdalensis, Proxapertites cursus, Periretisyncolpites giganteus, Constructipollenites ineffectus, Distaverrusporites simplex, Spiniferites ramosus, Echritriporites trianguliformis and Monocolpopollenites sphaeroidites thereby enabled the assigning of Maastrichtian age (Upper Cretaceous period) and establishing Longapertites marginatus Acme Zone, Longapertites marginatus /Monocolpites marginatus Assemblage Zone and Retidiporites magdalensis/Proxapertites cursus Assemblage Zone respectively. The analyses of the stratigraphic sections distinguished four lithofacies of (i) fissile and laminated shales, (ii) ferruginised and indurated shales, (iii) medium grained sandstone and (iv) ferruginised medium grained sandstones while the petrographic analysis established that the lithology belongs to the quartz arenites classification. Micropaleontologically, the analysis showed the sediments were barren of microforaminifera, which indicate that the environment of deposition was a shallow nonmarine environment.