Biostratigraphic and sequence stratigraphic study of the Late Cretaceous-Paleogene succession in the Anambra Basin, southeastern Nigeria: Insights from the Amama-1 and Bara-1 wells

This study presents an integrated biostratigraphic and sequence stratigraphic analysis of the Late Cretaceous–Paleogene succession in the Anambra Basin, southeastern Nigeria, based on data from the Amama-1 and Bara-1 exploration wells. The aim is to refine the chronostratigraphic framework and reconstruct the depositional history of the basin. Lithostratigraphic, palynological, foraminiferal, and wireline log datasets were combined to delineate major stratigraphic units, identify maximum flooding surfaces (MFS), sequence boundaries (SB), and establish systems tracts. Key formations encountered include the Nkporo, Mamu, Ajali, and Nsukka Formations, revealing varied depositional settings ranging from marginal marine to fluvial environments. Biostratigraphic zonations identified include the Globotruncanella havanensis, Bolivina afra/B. explicata, and Morozovella velascoensis foraminiferal zones, and palynological zones such as Ctenolophonidites costatus and Retidiporites miniporatus. Chronostratigraphic calibration and paleoenvironmental interpretations correlate closely with regional and global stratigraphic events. The findings affirm the Anambra Basin's significance in petroleum system evaluation and underscore the utility of integrated stratigraphic methods in subsurface reservoir characterization.