Some important pollen and spores of the upper miocene–pliocene sediments, Nzam-1 well, Anambra Basin, Southeastern Nigeria

Abstract

Palynological study of the uppermost section of Nzam-1 Well with interval 113-366 m in Anambra Basin, Nigeria was investigated to determine the geologic age based on the occurrences of pollens and spores, and to compare the result obtained with established ages from other biostratigraphic tool. The methodology of sample preparation involved the logging of the samples in order of depth, litho-description, and laboratory chemical processes. The chemical processes include initial acid decarbonisation of the samples, sample digestion with hydrofluoric acid, sieving of the samples with 10 μm mesh to remove clay particles; and then the oxidation of the organo-debris. The samples were later subjected to heavy liquid separation, using zinc bromide to separate the maceral from the organic debris. The maceral was rinsed with water and ethanol beforebeing mounted on the glass slide with DPX. The stratigraphic interval investigated revealed that it belonged to the Echitricolporites spinosus zone or Zone P800 and subzone P820-P880. It was characterized by the co-occurrences of marker forms such as Cyperaceaepollis sp., Nymphae lotus, Retistephanocolpites gracilis, Echiperiporites estalae, Arecipites sp., and Crototricolpites crotonoisculptus. The interval also contains stratigraphically important geologic age diagnostic pollen such as Podocarpus millanjianus, Multiareolites formosus, Zlivisporites neogenicus, and Zonocostites ramonae. The bio-assemblages were indicative of the Upper Miocene-Pliocene age of the Ogwashi-Asaba Formation. Older forms such as Crassoretitriletes vanraadshooveni, Striamonocolpites rectostriatus, Praedapollis sp., and Perfotricolpites digitatuswere derived fossils which suggested that Ogwashi Asaba Formation was reworked sediment.