Beyond the control section: the hidden history of oxisols

Abstract

Although intensely studied by pedologists in the tropical region, several questions remain without consistent answers regarding the genesis and morphology of Oxisols. The excessive focus of the pedological investigations in the upper part of these soils, e.g. the control section (200 cm), has systematically left aside the records that may exist of different moments of pedogenesis in these soils and that are at greater depth, for times several meters from the surface. The term "polygenetic processes", "bioturbation throughout the profile", "complex pedogenesis" are the most frequent arguments used for features that are difficult to interpret and hierarchize in these soils. What can be generalized to the Oxisols in terms of pedogenesis? Oxisols under the Cerrado, the Atlantic forest and the Araucaria forest underwent similar pedogenetic processes? What is the influence of the parent material? What differs from pedogenesis in Oxisols of geomorphic surfaces of different ages? These are the general questions of this project and the main objective of this is firstly to revisit the studies carried out to understand the Oxisols genesis and their relationship with planing surfaces. After that, to choose, describe and collect samples of these soils until the saprolite, e.g. beyond the control section, in regions that represent different bioclimatic, geomorphology and geology conditions in Brazil. The selected areas include the Peripherical Depression of São Paulo, the West of Minas Gerais, and the Basaltic Province of Paraná, where some Oxisols profiles will be selected for high resolution description and sampling. In order to reconstruct paleoenvironmental changes in different temporal scale and to relate them to pedogenesis, dates (14C and U-Th/He), analysis of the isotopic composition (´13C) and of the phytolithic assemblage along the profiles will be performed. In the area on basalt, with clayey Oxisols derived from a single parent material and with well defined climatic variation, a study of soil organic matter chemistry will also be done by GC/MS pyrolysis for paleoenvironmental reconstitution of the Quaternary. Chemical, mineralogical and geochemical analyses, selective dissolution and granulometry will be carried out on selected samples of the soil profiles to evaluate the parent material and pedogenetic processes of the Oxisols. Micromorphological analysis will be carried out systematically and focused on description and quantification of the biological features to evaluate if the intensity and shape of the faune action is differentiated in depth, different parent material and environmental conditions. It is expected that from the results obtained in the three study areas it will be possible to improve the understanding of the genesis of these soils as a continuum from the surface to the contact with the saprolite and to clarify questions that are still little clarified of the most representative soils of the Brazilian territory. (AU)