Reconstruction of the primary organic productivity of Campano-Maastrichtian shales of Nkporo and Aptian-Albian Awi Formations, Calabar Flank using pigment yield index

Purpose. To derive the paleo organic productivity exemplified by the pigment yield index in order to resolve the controversy on the petroleum potentials of Nkporo and Awi Formations in Calabar Flank, Southeastern Nigeria. Methods. Twenty outcrop samples each from Nkporo and Awi Formations in Calabar Flank, Southeastern Nigeria were analysed for total organic carbon, soluble organic matter and pigment richness by Walkley Black method, soxhlet extraction and column chromatography in order to derive the pigment yield index associated with paleo organic productivity which is needed to assess the petroleum potential. Findings. The geochemical analysis results of the total organic carbon, soluble organic matter, pigment richness showed that the outcrop samples had organic matter and hydrocarbon above the threshold required for petroleum generation and that the samples were deposited in predominantly anoxic setting. Originality. The results of the organic carbon (TOC) for Nkporo Formation – 1.51 to 4.30%; Awi Formation – 0.75 – 6.40%; soluble organic matter (SOM) Nkporo Formation – 110.5 to 4550.0 ppm and Awi Formation – 288.50 – 2664.25 ppm attest to the above threshold petroleum potential. Ni/Ni + VoP ratios for both Nkporo and Awi Formations < 0.5 to > 0.6 showed anoxic, paralic and oxic settings, though predominantly anoxic, excellent for organic matter preservation. Pigment yield indices of 5.88 and 5.58 equally depicts high petroleum potentials for the two Formations. Practical implications. These results can be used to assess the paleo bioproductivity which is primary in petroleum generation, and in the resolution of controversies in the comparative assessment of two or more basins or formations.