Reconstructing paleoenvironments of the late Cretaceous sequence in the Anambra Basin, Nigeria: New insights from grain texture and morphology

This study investigates Campano-Maastrichtian sediments from the northern Anambra Basin, Nigeria, to refine existing paleoenvironmental models through a multi-proxy integration of particle size analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and principal component analysis (PCA). While previous studies relied on first-order textural data, the current integrated approach provides new insight into the interplay of provenance, episodic energy fluctuations, and diagenetic overprinting. Seventeen samples of sandstone, siltstone, and ironstone were collected from the Ajali and Mamu formations at Odagbo, Egume, and Iyale. Granulometric analysis reveals predominantly fine to medium-grained, unimodal, and poorly to moderately sorted sediments. Linear discriminant functions suggest deposition in a mixed fluvial and shallow marine setting, with potential episodic influence of high-energy density flows or storm-induced turbulence. SEM imaging shows grain morphologies ranging from angular to rounded, with microtextures such as: conchoidal fractures, dissolution pits, and quartz overgrowth, reflecting variable transport distances and diagenetic modifications. EDX spectra confirm quartz-dominated mineralogy with variable aluminosilicate, iron oxide, and traces of heavy mineral contributions, while the PCA identified three compositional groups: (1) quartz-rich, texturally mature assemblages; (2) feldspathic and clay-rich sediments of proximal origin; and (3) organic and iron (Fe)-bearing sediment reflecting redox variations. These results demonstrate that sediment supply was derived from cratonic interior sources, modified by fluvial input and reworked under shallow marine conditions with subsequent diagenetic overprinting. By integrating textural and geochemical data, this study highlights the interplay of provenance, episodic hydrodynamic fluctuations, and diagenesis, providing new insight into the paleoenvironmental evolution of the Anambra Basin.