Geochemical characterization of a Cretaceous black shale from the Mamfe Basin, Cameroon

Abstract

Shale from Cretaceous strata of the Mamfe Basin has been characterized by petrological and geochemical techniques. The aims of this study were to assess the quality of its organic matter, evaluate its thermal evolution and highlight its potential as a source rock. The total organic carbon (TOC) (4.45 wt%) of the shale constitutes that of a good source rock with oil-prone kerogen indicated by Rock-Eval S2/S3 (26.1). The low oxygen index (OI) (8 mgCO 2 g −1 TOC), pr/ph (1.79) and high gammacerane index (22) suggest deposition in a highly saline reducing environment. The n -alkane distribution dominated by n -C 15 and infrared spectrum dominated by aliphatic and aromatic functional groups are considered to be indicators of Type II kerogen. The CPI (1.1), T max (441° C), C 31 (S/S+R) ratio (0.6), Rr (0.7%) and MPI-1 (0.6) all indicate the maturity of this rock. This thermal evolution is thought to account for its current hydrogen index (HI) (222 mgHC g −1 TOC). Expulsion may have occurred before uplift and erosion but a more elaborate study is required to evaluate the petroleum systems of the basin.