Abstract
Detailed characterization of the outcropping sediments in the Ikpankwu and Ihube axis was undertaken to validate lithostratigraphic boundaries and nomenclatures which had stirred up debates amongst scholars in recent times. Stochastic method established dominant facies associations and preferred stacking patterns, which were used to interpret environments of deposition (EODs), while foraminiferal and palynological analyses fingerprinted both paleo depths and age of the sediments. The results established the dominance of similar lithofacies at the basal parts of both sections indicating mappable geological units and members of the same lithostratigraphic unit. The basal lithofacies are succeeded up section, however, by different lithological units in both the KM 75 and Ikpankwu sections. Interpretations of EODs using lithofacies successions predicted fluvial to tidally-influenced shallow marine deposits, which are environments in close affinity with each other. Interpretations using abundance and diversity of micro fauna supported non-marine (coastal-deltaic) to middle neritic paleo-water depths also, typical of marginal to shallow marine EODs. Recovered foraminiferal assemblages in the shale samples from the upper parts of both sections, however, depicted deposits of Nsukka Formation despite variations observed in lithofacies assemblages because the identified Haplophragmoides species that populate the upper units had been used to define the Late Maastrichtian-Paleocene age. Sediments at the basal parts with mappable lithological units at both sections were rather populated by species that connote the Campanian-Maastrichtian age when the Mamu Formation sediments were deposited. Palynomorphs recovered from both the basal and upper sections also suggested Campanian-Maastrichtian and Late Maastrichtian-Paleocene age, indicative of Mamu and Nsukka Formation sediments, respectively.
Highlights
The Anambra Basin is a structural depression located southwest of the Benue Trough and the immediate precursor to the Niger Delta
Recovered foraminiferal assemblages in the shale samples from the upper parts of both sections, depicted deposits of Nsukka Formation despite variations observed in lithofacies assemblages because the identified Haplophragmoides species that populate the upper units had been used to define the Late Maastrichtian-Paleocene age
The result of units that were later grouped into lithofacies types delineated in this study are briefly summarised in the subsections below, while the lithologs and detailed descriptions of each of the units are shown in Figure 3 and Figure 4
Summary
The Anambra Basin is a structural depression located southwest of the Benue Trough and the immediate precursor to the Niger Delta. Its demarcation from the Bida Basin to the northwest is less clear and arbitrarily placed. The northeastern and southern boundaries of the basin bordering some parts of Benue Trough and the Niger Delta are still not very clear due to stacking of the basins [2]. The western, southwestern and southern boundaries of the Anambra Basin have been inferred to be around Adeigba, Umuezeanam-Nnewi and Akokwa areas respectively [5]; while its boundary in the northwestern region is placed to be around Ogurugu and in the southeastern side around Umulokpa community. The basin extended up to Orokam in Benue State
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