--> Abstract: Generation, Expulsion And Distribution Of Aromatic Hydrocarbon As Maturity-Dependent Process In Post-Santonian Shales And Coals Of The Cretaceous Anambra Basin, by I. M. Akaegbobi and M. A. Adeboye; #90928 (1999).

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AKAEGBOBI, I. M., and M. A. ADEBOYE
Department of Geology, University of Ibadan, Ibadan, Nigeria

Abstract: Generation, Expulsion and Distribution of Aromatic Hydrocarbon as Maturity-Dependent Process in Post-Santonian Shales and Coals of the Cretaceous Anambra Basin

The generation and distribution of the C11+ aromatic components has been investigated in a total of 18 rock and 2 crude oil samples having mean vitrinite reflectance (Rr) between 0.50 and 0.90% mainly derived from the CampanoMaastrichtian shales/ siltstones and coals in the Anambra basin. The study focuses on dicyclic and tricyclic aromatic hydrocarbons most of which were identified on fragmentograms from a combined high resolution GC-MS analysis. The distribution of these series are strongly controlled by thermal maturation of organic matter as reflected in the empirical relationships between vitrinite reflectance (%Rm) and a number of naphthalene, phenanthrene and diverse thiophene ratios. In contrast, compositional variation of the organic macerals as indicated by the optical observation seemed to be minor significance. Organic source may influence the generation of certain specific aromatic compounds; this -however, could not be related to maceral composition. Consequently, organic facies effects are taken into consideration by the interpretation of the relative distribution of the aromatics contained in the extracts and crude oils. A gradual depth trend was observed for the diverse compound ratios calculated from the relative variations of the methyl-aromatics in each family. Methylphenan- Index (MP) especially and other indicies derived from dicyclic aromatics demonstrated good maturity parameters. Theoretically calculated vitrinite reflectance (Rc) values from the MPI range from 0.52-0.85%.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas