Depositional–diagenetic evolution of the Wadi Halfa Oolitic Ironstone Formation, northern Sudan: A multivariate statistical approach

The so-called "Nubian Sandstone" represents a significant siliciclastic rock sequence extending across northeastern Africa; however, the depositional architecture and diagenetic evolution of its northern Sudan section remain insufficiently characterized. This study applies detailed sedimentological logs, grain-size analyses of 22 representative samples, petrographic point counting of 31 thin sections, SEM–EDX, XRD, and multivariate statistical methods, including Principal Component Analysis (PCA) and Cluster Analysis (CA), to reconstruct the depositional and diagenetic history of the Wadi Halfa Oolitic Ironstone Formation (WHOI). Sixteen lithofacies delineate a fluvial, deltaic, and shallow marine depositional sequence comprising cross-bedded sandstones, heterolithic intervals, oolitic ironstone, and barite-bearing layers. Grain-size parameters, multivariate statistics, and a centered log-ratio (clr) sensitivity analysis indicate a distinct depositional-energy gradient that separates coarse-grained fluvial channel deposits from finer delta-front and shallow-marine facies. Cluster analysis and ANOVA identify three statistically robust depositional groups (η² = 0.74), confirming the reliability of the sediment classifications. Petrographic and multivariate analyses distinguish three principal diagenetic facies: quartz arenite, ferruginous sandstone, and a barite-rich facies. Barite predominantly occurs as pore-filling and replacement cement, forming a distinct petrographic group associated with significant porosity reduction, supporting its interpretation as a secondary diagenetic cement. However, isotopic and fluid-inclusion analyses are required to determine the timing and fluid source of barite precipitation. The integrated depositional–diagenetic model demonstrates that the original depositional texture established the initial framework structure, while subsequent cementation by hematite/goethite and barite controlled porosity evolution. This comprehensive approach offers a reproducible framework for distinguishing depositional features from diagenetic overprinting in complex siliciclastic successions.