Foraminiferal biostratigraphy of the upper part of the type-section of Ekenkpon Formation, Calabar flank, southeastern Nigeria. – A. J. Ukpong, N. Olivier and M.A. Ushundebe
ABSTRACT
Foraminiferal biostratigraphic analysis was carried out on the recent landside section near Ekenkpon village in Cross River State of Nigeria, which exposed part of the type-section of the Ekenkpon Formation in the Calabar Flank sedimentary basin. The nine metre (9-m) high section consists of flaggy, dark gray, fissile shales frequently intercalated with marl beds. Though rare to moderately abundant, the foraminiferal assemblage recovered revealed a dominant occurrence of the planktonics (Heterohelix pulchra, Heterohelix moremani, Heterohelix globulosa, Hedbergella planispira and Hedbergella delrioensis) over the benthonic forms (Ammobaculite sp. and Praebulimina sp). The absence of typical Cenomanian index forms, like Rotalipora balernaensis and Globigerinoides caseyi from the planktonic foraminiferal recovery, is a clear indication that the recently exposed section represents only the upper part of the Ekenkpon Formation (Late Cenomanian to Early Turonian age). The scanty and dwarfed nature of the benthonic foraminiferal recovery, coupled with equally dwarfed pelecypods and abundant thalassinoides recorded within this study section, is an indication of the fluctuating oxygen concentration which characterized shallow aerated oxic and anoxic marine settings worldwide during this geologic period.