Palynofacies and Kerogen Analyses of Upper Cretaceous (Campanian-Danian) Shales of Ugwueme Section of Anambra Basin, Southeastern Nigeria

Author(s): Nwatarali N. Alex

Three samples of shale recovered from late Campanian to Danian sediments around Ugwueme area, Anambra Basin were studied for their particulate organic matter distribution and hydrocarbon potentials. Two major palynofacies were identified and designated palynofacies A and palynofacies B. Palynofacies A occupies the basal unit (Nkwe mudstone unit of Nkporo Shale) and the topmost unit; Umuaku shale unit of Nsukka Formation).Palynofacies A is dominated by abundant amorphous organic matter (AOM) and some phytoclastmaterials majorly of macerol marine exinite and some terrestrial influenced materials. Palynofacies B represents the middle unit bed (AcharaUgwueme shale unit of Mamu Formation) constitutes abundant phytoclasts with opaque debris of well-preserved terrestrial influenced plant fragments. The kerogen investigation result shows Nkwe mudstone unit of Nkporo Shale Formation and Umuaku shale unit of Nsukka Formation to be type II/III kerogens known to be oil-gas prone material. The study reveals that AcharaUgwueme shale unit of Mamu Formation is of type III kerogen known to be gas-prone. Estimation of the maturation stage of the samples using the exinecolours of pale-yellow to yellow, the sporomorphs shows (1+ to 2+)thermal alteration index(TAI) and reflectance values of 0.3% for both Nkwe mudstone and AcharaUgwume shale unit, thus are thermally immature to generate hydrocarbons while Umuaku shale unit with exinesporomorphscolour of yellow –light brown, (2to2+), thermal alteration index (TAI) and reflectance value of 0.5% to be thermally immature to early mature (early oil phase of hydrocarbon generation).

Macerol Marine Exinite, Palynofacies, Phytoclast and Kerogen

1. Adeigbe, O.C. and Salufu, A.E. (2010).Geology and Petroleum potential of Campaniian – Maaesstrichtian Sediments in Anambra Basin, Southern Nigeria. Nigeria Association of Pet. Exp. Bull.Vol.22,No.1. p.13-17.
2. Akaegbobi, I. M. (2005). Sequence Stratigraphy of AnambraBasin:Journal of African Earth Sciences,Vol.42.p 394-406.
3. Chiaghanam, O.I., Chiadikobi, K.C., Ikegwuonu, O.N., Omoboriowo, A.O., Onyemesili, O.C., Acra E.J. (2013). Palynofacies And KerogenAnalysis of Upper Cretaceous (Early Campanian to Maastrichtian) Enugu Shale And Mamu Formation In Anambra Basin, South-Eastern, Nigeria. Int’l Journal of Scientific & Technology Research, Volume 2, Issue 8, P225-229.
4. Ekweozor, C.M. (1982). Petroleum Geochemistry Applications to Petroleum Exploration in Nigeria’s Lower Benue Trough. 20thAnniversary Proceeding. Nigerian Mining and Geosciences Society, vol.19.1,p122-129.
5. Ekweozor,C.M. and Gormy,J.R. (1983).Petroleum Geochemistry of the Early Tertiary Shales Penetrated by the Akwakwa 2 well in the AnambraBasin, Southern Nigeria. Journal of Petroleum Geology. Vol.6. p.207-216.
6. Nwachukwu, J. (1985). Petroleum Prospects of Benue Trough, Nigeria, American Association of Petroleum Geologists Bull., vol.69.4 p.601-603.
7. Nwachukwu, J. (1988). Source and Reservoir Rocks Potential of Eze-Aku Shale and the associated Limestone.Nigeria Association of Pet. Exp.Bull.vol. 3.2.p.81-88.Great AP Express pub. Ltd.Nsukka. Pp3.
8. Nwajide, C .S. (2013). Geology of Nigeria’s Sedimentary basins. CSS press, Lagos Pp.565.
9. Ojoh, K. (1990). Cretaceous geodynamic evolution of the southern part of Benue Trough (Nigeria) in the equatorial domain of the south Atlantic:stratigraphy, basin analysis and paleogeography. Bull. CentresRech. Explor-prod.Elf- Aquitaine, v.14, p.419-442.
10. Olade, M.A. (1975).Evolution of Nigerian Benue Trough (Aulacogen): A tectonic model. In Nwachukwu, J.,(ed.) Petroleum of Benue Trough,Nigeria. American Association of Petroleum Geologists Bull., vol.69,4. P601.
11. Reijers, T.J.A. and Nwajide, C. S. (1998). Nigeria Association of Petroleum Expl. Bull.,11V. (01) :p 23-32
12. Reyment, R,A.( 1965). Aspects of Geology of Nigeria.University Press, Ibadan, Nigeria.pp. 145.
13. Traverse, A. (1988). In: Paleopalynology. Unwyn-Hyman, Boston, pp. 600.
14. Unomah, G.I. and Ekweozor, C.M. (1993). Petroleum Source Rock assessment of the Campanian Nkporo Shale, Lower Benue Trough, Nigeria Association of Nig. Pet. Exp. Bull.Vol.8.p.172-186.
15. Whiteman, A.J. (1982). Nigeria: Its Petroleum Geology, Resources and Potential. Graham and Trotman, London,39p
16. Wright, J.B. (1968), South Atlantic Continental Drift and the Benue Trough: Tectonophysics v.6, :p 301-310.