Palynological Studies of Upper Creataceous-Paleocene Rocks in Auchi Sheet 266, Benin Flank, Western Extension of the Anambra Basin, Southwestern Nigeria

Abstract

Out crop samples from Mamu and Nsuka Formation at different locations and ditch cutting samples gotten from a water borehole at Ugbekpe-Ekperi road at different intervals collected from Benin Flank, Western extension of the Anambra Basin, were used for sedimentologic and palynology studies with the aim of establishing palynological assemblage zones, age and paleoenvironments of the sediments. Out crops and Ditch cutting samples were lithologically described using a transmitted light microscope in order to obtain their lithofacies and latter subjected to palynological slides preparation to identify the presence of palynomorphs. Lithofacies units identified were clay, sandy clay, silt, sandstone, shale and sandy shale facies. From the analyzed palynological slides, ninety one (91) palynomorphs species were identified in the outcrop samples, eighty three (83) were Miospores (pollen and spores) and seven (7) were Dinocysts while the borehole samples recorded fifty five (55) palynomorph species, forty three (43) were Miospores while fifteen (15) were Dinocyst. Clusters analysis were used to establish four (4) Palynological Assemblage zones which are Palynological Assemblage zones 1, 2, 3 and 4. Late Maastrichtian to Early Paleocene age is suggested for Nsukka Formation because of the presence / abundance of Spinizonocolpites baculatus with admixture of Apectodinium homomorphum and Homotryblium tenuispinosum. The occurrence of Monocolpites marginatus, Retidiporites magdalenensis, and non-occurrence of Spinizonocolpites baculatus in the outcrop samples suggests that Mamu Formation did not penetrate Late Maastrichtian. Thus Early to Middle Maastrichtian is suggested for Mamu formation. The occurrence of mangrove palynomorphs Zonocostites ramonae, fresh water algae Botryococcus braunii and Concentricyst circulus indicates sedimentation in coastal to shallow marine environment close to mangrove vegetation.