Organic geochemical and palynological studies of the Maastrichtian source rock intervals in Bida Basin, Nigeria: implica
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ORIGINAL PAPER-EXPLORATION GEOLOGY
Organic geochemical and palynological studies of the Maastrichtian source rock intervals in Bida Basin, Nigeria: implications for hydrocarbon prospectivity Olusola J. Ojo1 · Ayoola Y. Jimoh2 · Juliet C. Umelo3 · Samuel O. Akande3 Received: 15 May 2020 / Accepted: 24 August 2020 © The Author(s) 2020
Abstract The Patti Formation which consists of sandstone and shale offers the best potential source beds in the Bida Basin. This inland basin is one of the basins currently being tested for hydrocarbon prospectivity in Nigeria. Fresh samples of shale from Agbaja borehole, Ahoko quarry and Geheku road cut were analysed using organic geochemical and palynological techniques to unravel their age, paleoecology, palynofacies and source bed hydrocarbon potential. Palynological data suggest Maastrichtian age for the sediments based on the abundance of microfloral assemblage; Retidiporites magdalenensis, Echitriporites trianguliformis and Buttinia andreevi. Dinocysts belonging to the Spiniferites, Deflandrea and Dinogymnium genera from some of the analysed intervals are indicative of freshwater swamp and normal sea conditions. Palynological evidence further suggests mangrove paleovegetation and humid climate. Relatively high total organic carbon TOC (0.77–8.95 wt%) was obtained for the shales which implies substantial concentration of organic matter in the source beds. Hydrocarbon source rock potential ranges from 0.19 to 0.70 mgHC/g.rock except for a certain source rock interval in the Agbaja borehole with high yield of 25.18 mgHC/g.rock. This interval also presents exceptionally high HI of 274 mgHC/g.TOC and moderate amount of amorphous organic matter. The data suggests that in spite of the favourable organic matter quantity, the thermal maturity is low as indicated by vitrinite reflectance and Tmax (0.46 to 0.48 Ro% and 413 to 475 °C, respectively). The hydrocarbon extracts show abundance of odd number alkanes C27–C33, low sterane/hopane ratio and Pr/Ph > 2. We conclude that the source rocks were terrestrially derived under oxic condition and dominated by type III kerogen. Type II organic matter with oil and gas potential is a possibility in Agbaja area of Bida Basin. Thermal maturity is low and little, or no hydrocarbon has been generated from the source rocks. Keywords Sterane · Agbaja · Mangrove · Spiniferites · Kerogen
Introduction The present study is focused on the source rock intervals of Patti Formation in the inland Bida Basin of Nigeria (Fig. 1). Bida Basin is of rift origin and filled with about 3.5-kmthick, flat lying upper Cretaceous clastic sediments, and they * Olusola J. Ojo [email protected] 1
Department of Geology, Federal University Oye Ekiti, Oye‑Ekiti, Ekiti State, Nigeria
2
Department of Geology and Mineral Sciences, Kwara State University, Malete, Kwara State, Nigeria
3
Department of Geology and Mineral Sciences, University of Ilorin, Ilorin, Kwara State, Nigeria
are relatively unexplored in term of petroleum prospectivity (Udensi and Osazuw
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