Weathering, bauxitisation and soil genesis from the Nakobalevu Basalt, South-East Viti Levu, Fiji

The augite-olivine flows (5.3 Ma) capping Mount Nakobalevu, a few kilometres north-west of Suva, Fiji, have been subjected to rapid and deep weathering. The Nakobalevu K1 and K2 weathering profiles (at approximately 454 m altitude) show features of strong bauxitisation, and the attributes of a "classical" lateritic profile. Aluminium and iron enrichment in the 2-3 m depth layers of the Nakobalevu weathering profiles is marked, with the presence of abundant gibbsite (as gravels and nodules, and in the silt and clay-sized fractions), goethite, kaolinite, haematite and magnetite (grains); the presence of fragmented (goethitic and gibbsitic) crustal materials in each of the studied horizons, and the distribution pattern of the Al2O3, Fe2O3 and SiO2, would infer the occurrence of several erosion and weathering cycles, some of which would have evolved under drier climatic regimes. Using Soil Taxonomy, the Nakobalevu Pedon (JBK-1) is a Typic Kandihumult, clayey, kaolinitic, isohyperthermic, which does not give any indication of the gibbsitic materials present.