Biostratigraphy, sequence stratigraphy and paleoenvironment of Well A1, offshore Niger Delta Basin, Nigeria

Abstract This study establishes a stratigraphic framework for Well A1 in the offshore of the Niger Delta Basin, integrating foraminiferal biostratigraphy, gamma-ray log interpretation, and lithostratigraphic analysis. Seventy-seven (77) ditch-cutting samples (4300–9200 ft) were prepared using standard micropaleontological techniques, yielding diagnostic planktonic and benthic foraminiferal assemblages. First downhole occurrences constrain deposition to the Late Miocene–Early Pliocene (4.16–9.50 Ma), and four planktonic biozones (N19–N15) were delineated and correlated with maximum flooding surfaces at ca. 9.50 Ma, 6.00 Ma, 5.05 Ma, and 4.00 Ma. Two lithological units, Paralic (4300–8000 ft; sand/shale ≈ 40:60) and Marine (8000–9200 ft; sand/shale ≈ 10:90) record a transition from inner neritic to upper bathyal settings. Four depositional sequences, each comprising transgressive and highstand system tracts, were identified. These results refine Miocene–Pliocene chronostratigraphy in the offshore Agbada Formation and provide regional tie-horizons useful for well-to-well correlation and reservoir prediction across the offshore depobelt.