Sedimentology and Palynostratigraphy of a Section Penetrated by Ane-1 Well, Niger Delta, Nigeria: Implications for Palaeoenvironmental Interpretation

Norbert E. Ajaegwu¹, Benard I. Odoh², Emmanuel K. Anakwuba¹, and Okey E. Akpunonu^1
1Geological Sciences, Nnamdi Azikiwe University, Awka, Nigeria
²Department of Geology and Exploration Geophysics, Ebonyi State University, Abakaliki, Nigeria

Fifty ditch cutting samples composited at 60ft intervals between depth 6,990ft and 9,930ft of Ane-1 well were processed for sedimentological and palynological analyses. The results from these analyses were used for the characterization of the studied section. The sedimentological study shows that analysed section belongs to paralic Agbada Formation. This section is subdivided into three lithofacies subunits based on their shale/sand ratios. The subunits are: Lower Biafra (9,930-8,035ft), Middle Biafra (8,035-7,115ft), and Upper Biafra (7,115-6,990ft). A total of 632 palynomorphs were identified from which some were selected for microphotography. The diagnostic palynomorphs recovered permitted the zonation and dating of the analysed section. The reference scales used in the zonation are those of Evamy et al and Morley. One zone and five subzones of Evamy et al and eight subzones of Morley were established in this work. The subzones of these two authors were correlated in both space and time. Late Miocene to Early Pliocene age was assigned to the studied section with Miocene/Pliocene boundary marked by quantitative base occurrence of Nymphaeapollis clarus and increase in Monoporites annulatus at 8150ft. This section belongs to Echitricolporites spinosus Zone of Germeraad et al. Palaeoenvironmental interpretation of the studied section was conducted by combining four elements namely: association of environmentally restricted marker species, percentage of Zonocostites ramonae in the total palynomorphs sum, nature of organic matter in the sediment, and lithological characters of the strata. The result shows that the overall environment ranges from coastal to marginal marine. Foram test linings as a good indicator of marine environment was used to subdivide the macro environments into coastal deltaic, coastal deltaic - inner neritic, and inner neritic.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas