Grain-Size Distribution and Paleohydrodynamic Analysis of the Maastrichtian Ajali Sandstone, Anambra Basin, Nigeria

Document Type : Original Research Article

Authors

Geology Department, School of Physical Sciences, Federal University of Technology, Owerri, Nigeria

Abstract

The Maastrichtian Ajali Sandstone of the Anambra Basin, southeastern Nigeria, was investigated to assess its grain-size distribution and paleohydrodynamic characteristics, to interpret its depositional environment and flow regime. Twenty representative samples were analyzed for statistical grain-size parameters, including mean grain size (1.29–2.10ϕ), standard deviation (0.41–1.13ϕ), skewness (−0.39 to 0.40ϕ), and kurtosis (0.64–1.50ϕ). These values indicate that the sandstones are coarse to medium-grained, moderately to moderately well sorted, and exhibit both positive and negative skewness, ranging from platykurtic to leptokurtic, indicating deposition under fluctuating high-energy conditions, including channel and possible beach environments. Bivariate and multivariate plots confirm a unidirectional, high-energy fluvial system, while the log-probability curves show mixed transport mechanisms (traction, saltation, and suspension). Paleohydraulic reconstructions suggest flow velocities of 0.5–1.2 m/s, consistent with braided river systems. Provenance analysis further indicates sediment derivation from the nearby Oban Massif and Basement Complex. Collectively, the data indicate that the Ajali Sandstone was deposited in a braided fluvial system influenced by episodic high-energy events in a semi-arid climatic setting, with minor tidal modifications in marginal zones.

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References

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