PALEONTOLOGICAL EVALUATION OF IMO SHALE AT UMUNAUMUAWO, EZEAGU, ANAMBRA BASIN, NIGERIA: AGE AND PALEOENVIRONMENTAL SIGNIFICANCE

Abstract

The lithofacies and foraminiferal assemblages of the Imo Formation exposed at Umuna-Umuawo, Ezeagu, Anambra Basin were evaluated for the purpose of environmental interpretation and age dating. Lithofacies were described based on lithology. The lithologic units of the succession are basically dark-grey to bluish-grey shales with presence of gastropod mineralized shells depicting a marine depositional environment. The shale is interbedded with patches of siltstone and clay beds. The method of study involved the collection of samples and subsequent laboratory analysis of collected sample to evaluate final observable features. A total of six (6) samples of shale were collected from the outcrops (Aguobu-Owa, Mgbagbu-Owa, Agba-Umuna, Awha-Ndiagu) in the study area. Samples of shales were
prepared for micropaleontological analysis using the standard methods of foraminiferal sample preparation which involved disaggregation and washing of sample through a 63 micron mesh sieve, drying and picking of the foraminifera and other accessories. The recovered fossils were then studied under paleontological microscope. From micropaleontological analysis made, benthic arenaceous and calcareous foraminiferal assemblages were recovered. They include; Textularia sp., Textularia earlandi, Anomalinoides dorri, Fursenkoina cylindrical. They are all benthic typically of Late Paleocene to Early Eocene which coincides with the marine incursion in the Anambra Basin. These foraminifera forms suggest an inner neritic/ estuarine environment of deposition.