Abstract
Palynological analysis was carried out on Ten (10) samples from outcrops of the Campanian Enugu Formation, a component lithostratigraphic unit of the Anambra Basin, using the acid maceration techniques for recovering acidinsoluble organic-walled microfossils. Two main lithological units were encountered, which include: carbonaceous shale and siltstone. Result from kerogen laboratory examination reveals two (2) main groups of palynofacies association namely; palynofacies (A and B), based on the change in particulate organic matter constituents of organic residue extract. Palynofacies A is characterized by abundant opaques debris with common terrestrial phytoclasts, which occupy the southwestern and northwestern parts of the studied area, whereas palynofacies B dominates in the northeastern part, characterised by abundant phytoclasts followed by frequent opaques debris. Kerogen type III with gas-prone material is suggested for both palynofacies. The examined exine of spore/ pollen grain are pale yellow – yellow, with Thermal Alteration Index TAI of 1+ to 2- and Vitrinite Reflectane (R o) (0.3 % - 0.4 %) in palynofacies A, and yellow – yellow brown, with Thermal Alteration Index TAI of 2- to 2, and Vitrinite Reflectane (R o) of 0.3% - 0.5% in palynofacies B. These revealed source rock that is thermally immature to slightly mature but has potential to generate mainly gas. The kerogen data generated using transmitted light microscopy correlated well with geochemical data obtained using rock-eval pyrolysis method, and this shows the method a reliable tool for assessing petroleum potential in any given sedimentary basins.
Highlights
The Anambra Basin overlies Benue Trough in the northwestern and southern parts (Fig. 1 and Fig. 2)
The basin rests on the Awgu Formation in the southern Benue Trough, demonstrably over an angular unconformity
The stratigraphic package (Fig. 3) of the Anambra Basin is theorized to have originated as a result of the depression of the area around the southern Benue Trough contemporaneous with folding of the latter in the Santonian
Summary
The Anambra Basin overlies Benue Trough in the northwestern and southern parts (Fig. 1 and Fig. 2). CHIAGHANAM, OSITA IGWEBUIKE, IKEGWUONU, OKECHUKWU NICODEMUS, EKWEGBALU, CHIKODI JENNIFER, ANIWETALU, EMMANUEL UDE, AND CHIADIKOBI, KINGSLEY CHUKWUEBUKA forms the basal part of the Anambra Basin and consists of Nkporo Formation, Enugu Shale, Owelli/Otobi Sandstone, and Afikpo Sandstone. This lithological group reflects a funnel-shaped shallow marine shelf setting that graded into channeled low-energy marshes. OPTICAL (VISUAL) KEROGEN ASSESSMENT OF ENUGU SHALE, ANAMBRA BASIN, SOUTHEASTERN NIGERIA: Fig. 2: Regional stratigraphy of southeastern Nigeria showing the petroleum system elements of the Anambra Basin (modified after Nwajide, 2006) These studies were based on geochemical methods using rock-eval pyrolysis. Assess petroleum potential and source rock quality of the Enugu Shale
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