Abstract
The Cretaceous sediments in Ikono-1 well, Calabar Flank, consist of a sequence about 1,878 m thick of calcareous sandy shale (Uppermost Mfamosing limestone Formation) at the base, overlain by continuous alternating sequence of black to dark and light grey shales with sandstone (Nkalagu Formation) and calcareous black fissile shale (Nkporo Shale) at the top. The sediments are fossiliferous and were deposited in a shallow inner neritic environment of less than 50 m. depth. Two marine transgressions were recognized, the Cenomanian-Turonian and Early Senonian transgressions. The Cenomanian is recognized by the presence of Hedbergella delrioensis, Hedbergella planispira, Rotalipora balernaensis, Trochammina sp. and Dorothia oxycona, while the Turonian-Santonian stage is characterized by the abundance of Heterohelix reussi, Heterohelix ultimatumida, Praebulimina fang, Gavelinella guineana, Nonionella robusta and Whiteinella baltica. Foraminifera indicative of Late Santonian-Early Campanian were not recovered, thus a period of erosion and/or non-deposition is suggested. Diagnostic species of Campanian-Maestrichtian age (Nkporo shale) are Globotruncana gansseri, Afrobolivina afra, Buliminella brevispira, and Globigerinelloides multispinatus.
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