ABSTRACT

A description of two important oolitic ironstones from central and northwestern Nigeria is used as the basis for a general discussion on oolitic texture in ironstones. The Nigerian ores are of late Senonian and Tertiary ages and their original oolitic texture has been extensively modified by the migration of iron during weathering. They are compared with oolitic and pisolitic laterites and with certain hitherto undescribed ferruginous pisolites in the basal Carboniferous Limestone of Skrinkle Haven, South Wales, Great Britain.

During deposition, ferruginous oolites may be either hard and brittle or soft and easily deformed. The diversity of textures observed can be explained by this fact and by phenomena associated with the diffusion of iron through the rock after consolidation. The diffusion phenomena can produce what appear to be fractured oolites and other features apparently indicative of abrasion prior to deposition and therefore such features must be treated with caution in the interpretation of oolitic textures.