More than 2,500 m of predominantly terrigenous Senonian sediments have been penetrated in the Anambra Syncline. These sediments define three cycles of fluviodeltaic and shelf units, namely the Awgu Shale-Agbani Sandstone cycle, the Ogugu Shale-Owelle Sandstone cycle and the Nkporo Shale-Mamu-Ajali-Nsukka cycle. This depositional mechanism has resulted in successive alternations of potential source, seal, and reservoir units propitious for petroleum generation and accumulation. Potential source and seal beds are better developed for the Agbani and Owelle sandstones.

Total organic content (TOC) ranges between 0.22 and 4.16%, soluble organic matter (SOM) between 84 and 1,850 ppm, and saturated hydrocarbon (SHC) between 9 and 240 ppm in the Senonian shale units. Awgu and Nkporo shales appear to have the better source-rock characteristics.

Senonian sandstones in the basin are predominantly mature quartzarenites but lose porosity drastically with depth due to cementation by calcite, chert, and quartz overgrowth. The coarser grained, probably fluviatile sandstone facies have a dominant quartz cement and are generally more porous than the finer grained, probably deltaic sandstones cemented predominantly by calcite and chert.

Both diastrophic and synsedimentary, non-diastrophic structures abound in the Senonian sections here. These and possible stratigraphic pinch-outs in the sandstone units constitute potential entrapment features. However, successful exploration in the hitherto unproductive Upper Cretaceous units here will require a careful integration of structural, stratigraphic, geochemical, and diagenetic analysis.

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