Palynology and biostratigraphy of the Maastrichtian Coal Measures in the Anambra Basin, Southeastern Nigeria.

Abstract

A total of sixty-eight (68) core samples retrieved from eleven wells penetrating the Mamu Formation in the Anambra Basin, Southeastern Nigeria were studied for their palynomorph content in order to determine the age and paleoenvironment of deposition of the Mamu Formation. The wells are characterized by intercalation of laminated fine grained sand and light-dark grey fissile shale with interbeds of coal seams. The lower part with dark grey shale is characterized by the maximum development of Longapertites marginatus Acme Zone, dated Middle Maastrichtian. The upper part defined by intercalation of sand and shale with coal seam layers interbedding belong to Spinizonocolpites baculatus Assemblage Zone. This zone is characterized by the occurrence of Spinizonocolpites baculatus, S.echinatus, Gemmazonocolpites sp, Constructipollenites ineffectus, Syncolporites marginatus, Periretisyncolpites gigantus, Zlivisporites blanensis, Retidiporites magdalenensis, Distaverrusporites simplex, Foveotriletes margaritae, L.vaneendenburgi, Proxapertites cursus, Proteacidites sp, Buttina andreevi, Periretisyncolpites sp and Monocolpites marginatus. All these forms characterize Upper Maastrichtian age on the basis of the recognized diagnostic forms in the wells. The palynomorph abundance and diversity peaks and fossil assemblage of Mamu Formation show similarity with South American forms characterized by colder and warmer climate. These are directly related to eustatic change in sea level resulting to transgression and regression phases. The marine incursion resulted in Mid-Maastrichtian leading to the deposition of basal shale sequence of Mamu Formation while the coal seams were deposited during the regressive phases in the Late Maastrichtian.