Field and geochemical evidences presented in this study reports the occurrence of Cretaceous anoxic events in the Northern Benue Trough, Nigeria. Five Cretaceous formations (Bima, Yolde, Pindiga, Dukul and Fika Formations) within the Northern Benue Trough were investigated, and the field evidences reveal the occurrence of dark colored, finely laminated shale units lacking bioturbation which are mostly associated with coarsening upward sequences. This is typical of sediments deposited under transgressive waters with prevailing anoxic condition which was ubiquitous during the Cretaceous. Furthermore, TOC values obtained from the geochemical analyses of the dark shales were considerably high; ranging from 1.35% as the lowest value to 3.67% as the highest value, consistent with concentrations of organic matter preserved due to anoxic condition of deposition. While sulphur content of the studied samples were found to fall within ranges below 1% (the highest being just about 0.6%). Rock-eval pyrolysis data obtained for the studied samples suggests kerogen Type III and Type IV, implying organic materials derived from either continental or mixed continental and marine depositional environments. T-Max data obtained shows that most of the studied shales are thermally immature, implying a negligible to poor hydrocarbon generation potential.
Key words: Cretaceous anoxic events, Northern Benue Trough, Black shales, TOC, Organic sulphur, Hydrocarbon generation potential, geochemical evidences.
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