Palynological evidence of a Campanian-Maastrichtian age of the Northern Bida basin, Nigeria: Implications for paleoenvironment, paleoclimate and hydrocarbon prospectivity

Abstract

The result of this study hereby documented is probably the first of its kind in terms of the source of the samples (ditch cutting) used for palynological analysis. Studies related to ascertaining paleoenvironment, paleoclimate and hydrocarbon prospectivity status are yet to be conducted using subsurface samples within the Bida Basin. Consequently, ditch cuttings obtained from two pilot exploratory wells located at Kudu and Agaie (K and Y wells respectively) areas of the Northern Bida Basin were analysed for the purpose of studying the paleoenvironment, paleoclimate and hydrocarbon prospectivity status of the Basin. The K-well was drilled to a depth of 75 m and the Y-well to a depth of 70 m and the k well was sampled at 1 metre interval while well Y was sampled at 2 m interval, giving a total of 105 ditch cuttings. The studied samples are mainly sandstones, mudstones and shales, implying lithological samples from the Bida formation. The aim of the study is to use the results of the palynological analysis to infer the Palynostratigraphy, paleoenvironment, paleoclimate and possible hydrocarbon prospect within the Bida basin. Palynological analyses were performed on the 105 samples obtained from the two exploratory wells using the conventional acid method of palynological preparation technique and the microscopic analysis of the palynoslides. Well K is very rich in palynomorphs both in terms of taxonomical species and quantity and has afforded a clear interpretation of the paleoenvironment, paleoclimate and hydrocarbon prospectivity of the section of the basin penetrated. Palynomorphs identified include Monocolpites sp, Proteacidites sigalii, Psilatricolporites sp, Tricolporopollenites sp, Acrostichum aureum, Cyathidites sp, Laevigatosporites sp, Rugulatisporites caperatus, and Verrucatosporites sp. Two (2) palynostratigraphic zones from Late Campanian to Early Maastrichtian are proposed. The zones, in stratigraphically ascending order, are as follows: Selaginella myosus – Classopollis sp taxon range zone (late Campanian) and the Proteacidites sigalii – Psilotricolporites sp taxon range zone (Early Maastrichtian). The vertical distribution of the palynoforms and the few presence of dinoflagellates show only one major paleodepositional environment: the terrestrial to nearshore type characterized by dominant terrestrial spores and pollen that were occasionally inundated by marine incursion. The inferred paleoclimate ranges from savanna to rainforest as evidenced from the diagnostic palynoforms. In addition, the paleoclimate, paleoenvironment and age of the penetrated strata suggest a considerable potential for natural gas accumulation within the basin.