Foraminiferal analysis and palaeoenvironmental interpretation of borehole ET (BH-ET) in the Calabar Flank, South-eastern Nigeria

Foraminiferal biostratigraphy and palaeoenvironmental interpretation was carried out on core samples (5 samples between intervals 5-55 m) recovered from borehole ET (BH-ET) located in Etankpini area of the Calabar Flank, south eastern Nigeria. Lithologic description of the borehole samples were carried out and the borehole was sampled at 5 m interval. The samples were later composited at 10 m interval and a total of six samples were subjected to standard micropaleontological preparation procedures. Results from the lithologic analysis show that the basal section of the well (55-60 m) was made up of granite gneiss; overlain by light grey, calcarenite, bioclastic, pisolitic and stylolitic limestones (30-55). Dark grey fissile shales directly overlie the limestone (5-30 m). The foraminiferal recovery was generally low and characterized by planktonic species (Guembelitria harrisi, Hedbergella crassa, Hedbergella delrioensis, Hedbergella simplicissima, Hedbergellid spp., Heterohelix globulosa, Heterohelix planata, Heterohelix reussi, Hedbergella planispira and Hedbergella sigali). The absence of benthonic forms may be an indication of anaerobic bottom conditions. An age of Cenomanian-Early Turonian was assigned to the studied well based on diagnostic foraminiferal species assemblages. The recovered foraminiferal assemblage points to deposition within the Inner Neritic to Middle Neritic depositional setting for the studied well.   Key words: Neritic, Calabar Flank, biostratigraphy, planktonic, anaerobic.