On the main island of the Archipelago of Fernando de Noronha, the dry tropical climate with oceanic influence and the parent material of volcanic origin are responsible for low soil weathering. The peculiar conditions are of particular scientific interest with a view to the improvement of the Brazilian Soil Classification System (SiBCS). For this purpose, the morphological, physical, chemical and mineralogical attributes of seven representative soil profiles (two Lithic Neosols, one "Saprolithic" Neosol, three Regolithic Neosols and one Fluvic Neosol) were characterized and classified. The lithic contact (R) of the Lithic Neosol consisted of coarse fragments of less than 50 cm deep rocks. The Saprolithic Neosol shows lithic contact beneath 50 cm depth but is preceded by a layer of weathered soft rock with original structure. The Regolithic Neosols are related with marine sedimentary deposits of the coastal areas and formed by bioclastic carbonate material from reefs, algae and sea animals. The layers of the Fluvic Neosol, developed on colluvial- alluvial sediments, have alternating texture and mineralogy. The Lithic Neosols were adequately classified at the subgroup level according to the SiBCS, 2nd edition (Embrapa, 2006), proposed as a new subgroup "fragmentary", based on our study. The other Neosols were not adequately classified, either due to peculiar characteristics, or due to the lack of more specific terms that would describe the distinct characteristics more precisely. This study suggests the following adaptations of the SIBCS: inclusion of a new suborder of Saprolithic Neosols, of a new large group of Psamitic Regolithic Neosols and of new subgroups of bioclastic carbonate Psamitic Regolithic Neosols and bioclastic carbonate Ta Eutrophic Fluvic Neosols.
Brazilian oceanic islands; soil taxonomy; lithic contact; bioclastic sediment
