Biomarkers, carbon isotopic composition and source rock potentials of Awgu coals, middle Benue trough, Nigeria

Coal and carbonaceous shale samples were collected from two boreholes (BH 94 and BH 120) in Awgu formation of Middle Benue Trough, Nigeria. Source rock potentials of the samples were studied using biomarkers and carbon isotopic composition. Biomarkers in the aliphatic fractions in the samples were studied using Gas Chromatography–Mass Spectrometry (GC–MS). The Carbon isotope analysis of individual n-alkanes in the aliphatic fraction was performed using Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometer (GC–IRMS). The abundance of hopanes, homohopanes (C31–C35), and C29 steranes in the samples indicate terrestrial plant, phytoplankton and cyanobacteria contributions to the organic matter that formed the coal. High (Pr/Ph) ratio (3.04–11.07) and isotopic distribution of individual alkanes showed that the samples consisted of mixed terrestrial/marine organic matter deposited under oxic condition in lacustrine–fluvial/deltaic depositional environment. The maturity parameters derived from biomarker distributions showed that the samples are in the main phase of oil window.

► Coal source rock potentials were studied using biomarkers and carbon isotope. ► Organic matter of the samples was deposited under oxic condition. ► The samples were formed from both marine and terrestrial organic matter. ► Biomarker maturity parameters distribution shows that the samples are mature.