Depositional environment and stratigraphic framework of the NS- 1 well, Coastal Swamp Depobelt, Niger Delta Basin: a foraminiferal perspective

Abstract

A comprehensive analysis of 102 ditch-cutting samples from the NS-1 well in Leuma Field, Coastal Swamp Depobelt, Niger Delta Basin, covering depths from 4730 ft to 7790 ft, is presented. Lithologic descriptions revealed eleven lithostratigraphic sub-units within the transitional-paralic sequence of the Agbada Formation, comprising alternating sandstone and shale. The foraminiferal analysis identified 58 species: 14 planktonic, 26 calcareous benthic and 18 agglutinated benthic. Key planktonic index species such as Globigerinoides sp. and Globorotaliacontinuosa indicates a Middle to Late Miocene age. The biozonation correlates with the Blow (1969) Scheme (N7- N9/N10/N11) placing the intervals within the Middle Miocene to Late Miocene epochs. The depositional environment transitioned from Coastal Deltaic to Inner Neritic and Middle Neritic, suggesting a shallow marine setting influenced by a warm, humid climate. The presence of calcareous foraminifera supports a shallow marine deposition above the carbonate compensation depth. This study provides valuable insights into the sedimentological, stratigraphic, and paleoenvironmental history of the NS-1 well during the Miocene.