JOURNALS

ABSTRACT

Shale from basal Campanian to Maastrichtian strata of the Anambra Basin has been characterized by pyrolytical and spectroscopical techniques. The aims of this study were to assess the quality of its organic matter, evaluate its thermal evolution, highlight its potential as a source rock the source input and paleodepositional conditions of the organic matter. The TOC (1.18 wt. %) of the shale constitutes that of a good source rock with gas-prone kerogen indicated by Rock-Eval S2/S3 (4.16). The high OI (136.00 mgCO2g-1TOC) and Pr/Ph (1.53) suggest deposition in a shallow marine environment. The n-alkane distribution dominated by n-C24 – n-C31 and infrared spectrum dominated by aliphatic and aromatic functional groups are considered to be indicators of Type III kerogen. The CPI (1.49), Tmax (430oC), C31(S/S+R) ratio (0.76) and Ro (0.56%) all indicate the onset maturity of this rock. This thermal evolution is thought to account for its current hydrogen index (174.00mgHCg-1TOC). The n-alkane distribution and predominance of low to medium molecular weight compounds (n-C10 - n-C20) with the significant waxy alkanes (+n-C25), suggesting a significant high contribution of marine organic matter with minor terrigenous organic matter contribution. The kerogen is predominantly mixed Type II/III and Type III organic matter in all analyzed samples. This indicate that majority of the analyzed sediments are oil/gas prone and gas prone. The Tmax value 430 ?C indicates that the organic matter is thermally immature to early mature for hydrocarbon generation. The Pr/Ph ratios of 1.53 suggest organic matter to be derived from source rock contains mixed organic facies and suboxic depositional conditions. The TS, Pr/n-C17 and Ph/n-C18 ratios systematically suggest the organic matter in all the analyzed samples fall within mixed algal/aquatic and terrestrially derived and deposited under suboxic paleoenvironmental conditions.