Organic geochemistry of Cretaceous Lamza and Chikila coals, upper Benue trough, Nigeria

Some biomarkers and other compounds in the aliphatic and aromatic fractions of the Lamza and the Chikila coals were characterized and used in assessing the source input, maturity, hence the hydrocarbon generative potentials of the coals. The samples exhibit a slight n-alkanes odd carbon preference (CPI similar to 1), high pristane/phytane ratios and a dominance of 20S epimer Of C-29 sterane. The ratio Of C-30 alpha beta/(alpha beta + beta alpha) sterane and 22S/(22S + 22R) C-31-homohopane gave values of 0.77-0.83 and 0.58-0.60, respectively. The low Ts/Tm ratios are in agreement with the calculated vitrinite reflectance, R-c (0.60-0.70%). The methylphananthrenes maturity derived parameters (1-MP/9-MP; MPR; MPI-1; R-c) revealed a very slight variation and a consistent order of samples maturity with the exception of the R-c values. All these together with some other hopanoid ratios, show that the organic matter is terrestrially derived, deposited in an oxic environment and at marginal maturity for hydrocarbon generation. (c) 2006 Elsevier Ltd. All rights reserved.