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In the Opuama Clay Channel Complex situated in the northwestern Niger delta, the combined abundances in argillaceous elastics of 18a{H)-and 18/3(H)-oleanane relative to 17a(if)-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 (f?0% >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.

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