Sedimentology and Geochemical Evaluation of Campano-Maastrichtian Sediments, Anambra Basin, Nigeria.
Uzoegbu MU and Okon OS
Department of Geology, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria.
Department of Geology, Federal University, Oye-Ekiti, Ekiti State, Nigeria.
Accepted 28 August, 2017
Citation: Uzoegbu MU and Okon OS (2017). Sedimentology and Geochemical Evaluation of Campano-Maastrichtian Sediments, Anambra Basin, Nigeria..International Journal Geology and Mining 3(2): 110-127.
Copyright: © 2017 Uzoegbu and Okon. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.
The Cretaceous sediments in the Anambra Basin (SE Nigeria) consist of a cyclic succession of coals, carbonaceous shales, silty shales, siltstones and sandstones interpreted as deltaic deposits. Statistics reveals a graphic mean range from 1.5 to 2.8, sorting range from 0.45 to 1.58, skewness range from -0.58 to 0.32 and kurtosis between 0.38 and 2 for the Ajali Sandstone. From these results, the sandstones in the area are dominated by medium to coarse grains, poorly to moderately sorted, coarse skewed and very platykurtic sediments. Further sedimentological evaluation in six localities indicates fluvial-flood plain-marginally marine facies for the Mamu and Nsukka Formations and marine for the Nkporo and Enugu Shales. The geochemical evaluations show that total organic carbon (TOC) (8.95wt%) of the samples constitutes that of good to excellent source rock with oil, oil/gas, gas prones for kerogen types I, II/III, III indicated by Rock-Eval S2/S3 (9.13). The high oxygen index (OI) (42.61 mgCO2g-1TOC) suggest deposition in a shallow marine environment. The Tmax (430oC), indicate the immaturity to onset of maturity of these source rocks. Potential reservoir units occur in the fluvial sandstones of the Ajali Formation and in the marginal marine and flood plain sandstones of the Mamu Formation. The shales and claystones of the Nsukka and Imo Formations may provide regional seals.
Key words: Sedimentology, Geochemistry, Kerogen, Petroleum system, Depositional environment, Cretaceous, Anambra Basin.