Facies Analysis and Grain Size Distribution of the Bima Formation: Insights into the Depositional Environment in Yarandua and Dadinkowa, Gongola Sub-Basin, Northern Benue Trough
Abstract
This study provides a comprehensive facies and granulometric analysis of the Cretaceous Bima Formation in the Yarandua and Dadinkowa areas of the Gongola Sub-Basin in Northeastern Nigeria. The study aimed at interpreting the depositional environments and enhance our understanding of the sedimentary processes that influenced this stratigraphic unit. Three lithostratigraphic sections, the Yarandua Quarry, Eastern Yarandua, and Dadin Kowa sections— were analyzed. Fieldwork involved sedimentary logging, describing lithofacies, measuring paleocurrent, and collecting twenty-nine sandstone samples for laboratory analysis. Grain size distribution was determined using dry mechanical sieving, and statistical parameters were calculated using the Folk and Ward graphical method. These parameters included mean grain size, sorting, skewness, and kurtosis, which helped interpret the energy conditions and transport mechanisms of the depositional system. The identified facies include matrix-supported conglomerates, cross-bedded coarse to very coarse sandstones, as well as interbedded fine- grained mudstone and siltstone units. These facies indicate deposition within a progradational alluvial fan transitioning to a braided river system. Vertical facies transitions suggest a gradual decrease in depositional energy from the base to the top of the formation. The grain size results reveal a predominance of coarse-grained, poorly sorted, and positively skewed sediments, indicating deposition under fluctuating, high-energy flow conditions. The combined findings from fieldwork and laboratory analysis suggest that the Bima Formation was deposited in a high-energy fluvial environment, characterized by sediment gravity flows and braided channel processes.
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