ABSTRACT

The studied area lies between Latitude 5o30´ to 8o00´N and Longitude 6o00´ to 8o30´E. The sedimentary succession in the Anambra basin, southeast Nigeria is a potential active petroleum system with the generation, migration and accumulation of hydrocarbons in commercial quantities. The Cretaceous sediments in the Anambra Basin (SE Nigeria) consist of a cyclic succession of coals, carbonaceous shales, silty shales and siltstones interpreted as deltaic deposits. This research aims in determining the origin and depositional environment of organic matter from coals of the Mamu Formation in the Anambra Basin. Biomarkers in the aliphatic and polar fractions and aromatic hydrocarbon distributions 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 vitrinite reflectance measurements of the samples were taken using Zeiss standard universal reflected microscope. The δ13C isotopic values for n-alkanes range from –31.7 to –29.2 δ13‰PDB and –30.1 to –28.2 δ13‰PDB in Enugu and Okaba samples respectively. High (Pr/Ph) ratio (1.73-12.47) and isotopic distribution of individual alkanes showed that Mamu coal samples consisted of terrestrial organic matter with marine incursion deposited under oxic/suboxic-oxic in lacustrine-fluvial/deltaic environment.