Palynological and foraminiferal records for palaeoenvironmental and palaeoclimatic reconstruction of the late Cretaceous–Early Paleogene transition in the Anambra Basin, Southeastern Nigeria

Abstract

The Late Cretaceous–Early Paleogene transition in the Anambra Basin, southeastern Nigeria, records a complete cycle of marine regression and transgression driven by the combined influence of global eustatic sea-level fluctuations and regional tectonics. This study integrates palynological and foraminiferal analyses of ditch-cutting samples from two exploration wells (Alpha-1 and Beta-1) to reconstruct the palaeoenvironmental and palaeoclimatic evolution across this critical interval. Biostratigraphic zonation based on the last appearance datums (LADs) of key taxa establishes a robust chronostratigraphic framework spanning the Late Campanian to the Early Paleocene (Danian). The succession is constrained by the occurrence of Globotruncanella havanensis in both wells, while Morozovella velascoensis is recorded exclusively in the Alpha-1 well, together with the palynological marker taxa Ctenolophonidites costatus and Retidiporites miniporatus . Hierarchical cluster analysis and principal component analysis of palynological data delineate three statistically significant assemblages corresponding to continental swamp-forest, transitional coastal plain, and mangrove–coastal swamp environments. The depositional history records a regressive–transgressive cycle from restricted marginal-marine conditions of the Nkporo Group through progradational deltaic systems of the Mamu and Ajali formations to renewed marine transgression represented by the Nsukka Formation and Imo Shale. Palynological climate proxies indicate three major phases: (i) warm but seasonally dry conditions during the Late Campanian–Maastrichtian; (ii) a transitional K–Pg interval marked by significant floral turnover; and (iii) peak warmth and humidity during the Early Paleocene, coinciding with maximum marine flooding. This integrated and quantitatively supported study refines the biostratigraphic framework of the Anambra Basin, provides new insights into tropical vegetation and climate dynamics across the K–Pg transition, and strengthens regional stratigraphic correlations and palaeoenvironmental interpretation for hydrocarbon exploration in West African marginal basins.