The Kerri-Kerri Formation is a Paleogene sediment deposited in the Kerri-Kerri sub-basin of the Northern Benue Trough, Nigeria. This paper discusses the results of sedimentological and petrographic studies to determine the depositional environments and to classify the sandstones of the formation. For convenience of this study, the sub-basin has been divided into northern, central and southern portions. Eleven ( 11) lithofacies namely: Lateritic (paleosol) facies; Whitish/grayish sandstone facies; Heterolithic sandstone facies; Claystone facies; siltstone facies; Sandstone facies (Fine-grained, medium-grained and coarse-grained sandstone units); Pebbly sandstone facies; Reddish/brownish sandstone facies; Cross-bedded sandstone facies; Clast-supported conglomeratic sandstone facies and Matrix-supported conglomeritic facies) were identified across the basin. Four (4) depositional environments ( alluvial fan, meandering river, floodplain deltaic and lacustrine deposits) were defined from the log motifs. Fourty-five (45) sandstone samples were thin sectioned for petrographic studies which classified the sandstones as quartz-arenite. The samples consist mainly of quartz as the framework elements (85 -98 %) with clays, iron oxides and calcites, filling the voids. Abundance of polycrystalline quartz with wavy extinctions suggests that the sediments are mineralogically unstable. There is more impact of mechanical compaction on the quartz grains than chemical in the northern portion which indicates less humid climatic conditions at the time of diagenetic processes. There are more pore spaces within the Claystone and Siltstone facies suggesting a quiet environment of deposition for these rock units.
Key words: Sedimentological, Petrographical, Depositional environments, Mineralogically unstable, Less humid climatic conditions.
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