SIGNIFICANCE OF OLEANANE OCCURRENCE IN SHALES OF OPUAMA CHANNEL COMPLEX, NIGER-DELTA

In the Opuama Clay Channel Complex situated in the northwestern Niger delta, the combined abundances in argillaceous elastics of 18α(H)- and 18β(H)-oleanane relative to 17α(H)-hopane, computed as oleanane parameter (OP), increases with burial depth, maximizing at an average 28% and 39%, respectively, for marine and nonmarine organofacies having corresponding maturities R0% 0.46-0.58. At higher maturities (R0% >0.6) OP rapidly decreases to lower values (≤10% approximately), making it difficult to infer, by the parameter alone, the different primary sources of organic matter. The oleanane threshold depth delimits the diagenesis/catagenesis boundary precisely and should correspond to the top of the oil-generative window (TOGW) in the area. The oleanane parameter can also be practically applied in distinguishing oils from different sources as well as oils formed from a common source, at different thermal maturities, e.g., early versus late generated oils. © 1990, American Chemical Society. All rights reserved.