NIGERIAN JOURNAL OF SCIENCE AND ENVIRONMENT
Journal of the Faculties of Science and Agriculture, Delta State University, Abraka, Nigeria

ISSN: 1119-9008
DOI: 10.5987/UJ-NJSE
Email: njse@universityjournals.org

THE MAASTRICHTIAN SEDIMENTARY SUCCESSIONS OF THE ANAMBRA BASIN RECENTLY EXPOSED AROUND OKPEKPE AND IMIEGBA: PART OF THE MAMU OR AJALI FORMATION?

DOI: 10.5987/UJ-NJSE.16.056.1   |   Article Number: 09F9887   |   Vol.14 (1) - July 2016

Author:  Ejeh, Innocent O.

Keywords: Sedimentary successions, thalassinoides, lithofacies, ichnofacies, lithofacies associations, mamu formation

ABSTRACT

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The sedimentary successions of the Anambra basin recently exposed around Okpekpe, Imiegba, and the surrounding areas offer a unique opportunity to describe, associate the lithofacies with their depositional environment(s), and assign them to the right stratigraphic unit (formation). A geological field mapping and facies analyses of the sedimentary rocks in the study area revealed the following facies: shales, sandstones, mudstones (siltstones and claystones), a localized coal seam, the ichnogenus Thalassinoides and burrows suspected to be that of Ophiomorpha. The lithofacies and ichnofacies observed in eight logged sections were classified into three lithofacies associations genetically related to their depositional environments namely: (i) shales with intercalated siltstones and sandstones of intertidal flat/lagoon lithofacies association, (ii) the coal swamp/marsh lithofacies association, and (iii) the heterolithic tidal lithofacies association. These lithofacies and ichnofacies are comparable with those of the Mamu formation, although earlier reports on this formation stated that it is restricted to the southeastern part of the basin and is terminated at Idah, East of the Niger River. This study therefore highlights the possibility of the Mamu Formation extending (both in terms of surface and subsurface geology) to the western flank (west of the Niger River) of the basin, not only in the southeastern part of the basin as was hitherto reported. The lithofacies indicates paralic conditions as their gross depositional environment. The presence of Thalassinoides and Ophiomorpha-like burrows revealed sediments deposited under a shallow water environment, upholding the interpretation of the lithofacies associations.

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