Abstract

The oolitic texture of ironstones associated with laterites capping erosion surfaces at various localities in Nigeria has generally been considered secondary in origin and to have developed during formation of the surface laterite. Study of two major occurrences associated with upper Senonian (Cretaceous) deposits near Lokoja and comparison with oolitic and pisolitic laterites and with ferruginous pisolites in basal Carboniferous limestone deposits of Skrinkle Haven, Wales, lead to the conclusion that oolitic textures can develop in ironstones by two entirely different processes. One process involves accretionary growth around separate nuclei in a high-energy environment prior to deposition; the other involves diffusion and oxidation of iron in the solid rock during weathering.

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