Abstract
Soils in the Depressão Central and Campanha Gaúcha in Rio Grande do Sul State, Brazil, developed from sedimentary rocks are mainly Alfisols (Luvissolos, Planossolos and Plintossolos) and Ultisols (Argissolos) with high textural contrast between A and/or E horizons and clayey B horizons. Red Ultisols dominate in well-drained areas in the summit. But many soils present redoximorphic features on the backslope and footslope, with mottled and/or nodules similar to plinthite due to the oscillating of the water table above the [...]
Highlights
Gondwanic sedimentary rocks of the Pirambóia and Sanga-do-Cabral formations predominate in the Ibicui river - Negro river depression (CPRM, 2006) of Rio Grande do Sul State, Brazil, whose lithologies constitute the substrate of several soil types, among which Ultisols and Alfisols, with or without plinthite, and with high textural contrast stand out between horizons A and B
The soils with plinthite usually occur at the base of the steepest slopes, due to vertical drainage restrictions caused by poorly permeable siltstones and the accumulation of Fe compounds from the lateral subsurface transport (Brasil, 1973; IBGE, 1986; Streck et al, 2008)
This study aimed to evaluate the main process responsible for the high textural contrast in soils developed from different sedimentary lithologies and how the redoximorphic features observed in some soils may be related to genesis of plinthites and ferrolysis processes
Summary
Gondwanic sedimentary rocks of the Pirambóia and Sanga-do-Cabral formations predominate in the Ibicui river - Negro river depression (CPRM, 2006) of Rio Grande do Sul State, Brazil, whose lithologies constitute the substrate of several soil types, among which Ultisols and Alfisols, with or without plinthite, and with high textural contrast stand out between horizons A and B. There is a standard distribution for the soils in the landscape. It is relatively simple, with red Ultisols occupying the highest shares, where they develop on sandstones. The Alfisols and some Ultisols occupy the lower thirds of the slopes with long pendants and smooth undulating relief, usually originated from siltstones and mudstones with intense mottles and features similar to plinthite at the base of profiles. The soils with plinthite usually occur at the base of the steepest slopes, due to vertical drainage restrictions caused by poorly permeable siltstones and the accumulation of Fe compounds from the lateral subsurface transport (Brasil, 1973; IBGE, 1986; Streck et al, 2008). Many of these soils present morphological features and properties indicative of argilluviation processes (Kämpf and Curi, 2012), the hypothesis that high textural contrast can be formed by the contribution of processes such as ferrolysis (Brinkman, 1970, 1977, 1979; Jimenez-Rueda and Demattê, 1988; Andrade, 1990; Almeida et al, 1997; Oliveira Junior et al, 2017) is not discarded
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