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

Abstract

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.