Palynology and Stratigraphy Relationship of the Facies Intertongueing between the Afikpo Sandstone and Nkporo Shale in the Cretaceous Anambara Basin, Southeastern Nigeria
Palynological research on ditch cutting samples from the upper part of the Ubiaja- 1 well (40-1425ft) located in the western flank of the Anambra Basin Nigeria shows that sandstone of the Campanian to Early Maastrichtian age in Afikpo Basin has lateral extension into the Anambra Basin. Lithological description of the stratigraphic sequence indicates that the interval is characterized by nine different lithofacies units. These include granulestone, conglomeratic sandstone which are poorly sorted, thickly bedded and deposited in continental setting; pebble sandstone, coarse sandstone are also poorly sorted, with more pebble grains, deposited under high energy current in continental environment. Other lithofacies include claystone, mudstone, deposited in fluviatile environment; heterolith facies of various proportions of sand and shale comprising of shaly sand and sandy shale deposited in deltaic setting; followed by dark grey shale, deposited in the marginal marine environment. The sandstone facies is dated Campanian to Early Maastrichtian; equivalent to Afikpo Sandstone in the adjacent Afikpo Basin. Two palynological zones: Milfordia spp acme zone I characterized by relative high abundance of Milfordia spp. such as Milfordia sp. and Milfordia jardinei, dated Campanian and the overlying Foveotriletes margaritae zone II characterized by paucity of Milfordia spp. and co-occurrence of Monocolpopollenites sphaeroidites, Syncolporites sp., Ephedripites sp., and Monosulcites sp.; dated Early Maastrichtian age. The age dating and the stratigraphic lithofacies is equivalent to Nkporo Shale/Afikpo Sandstone known for Afikpo Basin stratigraphy but here reported newly in the Anambra Basin. This suggests lateral facies intertongueing of Afikpo Sandstone characterized by erosional surfaces, unconformable with Nkporo Shale, extended into Anambra Basin. The result reveals a new sandstone member in the Nkporo Formation or in another way makes Nkporo Formation to become Nkporo Group comprising of Nkporo Shale and Afikpo Sandstone.
