Saprolitos na região Sudeste do Brasil: morfologia, classificação e evolução física-geoquímica-mineralógica

Abstract

Saprolites in the southeast region of Brazil: morphology, classification and evolution physical-geochemistry-mineralogical The saprolite is a geological body constituted by the mixture of primary and secondary minerals resulting of physical and chemical weathering, which retains traces of the original rock structure. It differs from the soil by the evident litogenetic affiliation and insignificant biological activity. Although the definitions, however, the limit and the distinction between soil and saprolite are not always clear, because the continuity between these bodies in terms of hydrological and geochemical processes, as well as their physical and mineralogical compositions, which creates great confusion in morphological descriptions and information network. Due to the multidisciplinary nature of the sciences involved and the partial dedication of all of them in the saprolite investigations, there is a great lack of standardization of terms and procedures for characterization and analysis. The overall objective of this thesis is the characterization of saprolite developed from various lithologies in order to draw up procedures for the description, classification and saprolite analysis. Specifically aimed to evaluate in detail the patterns of physical, mineralogical and geochemical changes in some materials influenced by lithological attributes how the mineralogical and chemical composition, as well as the structure of parental material. For this were described and sampled 15 weathering profiles, composed of soil, saprolite and rock derived from sedimentary and metamorphic rocks in southeastern Brazil, in the states of São Paulo and Minas Gerais. The descriptions shown that saprolite evaluated can be grouped into four main morphological types, proposed the following structural categories: continuous, fractured, fragmented and earthy. Among all evaluated saprolite, those derived from metamorphic rocks showed higher morphological complexity. Thus, 9 affiliated profiles schists and gneisses to have been subjected to physical, geochemical and mineralogical analyzes to evaluate the change processes and to developing the classification system of saprolites. The mineralogical composition of soils and saprolite was similar, however, there were dissimilarities regard geochemical attributes between this bodies. Physical properties such as density and porosity showed no significant differences between soil and saprolite, however, when considered in isolation saprolite samples, there was a positive correlation between weight loss and total porosity, making this last attribute able to integrate the proposed saprolite classification.

Field Perception of the Boundary Between Soil and Saprolite by Pedologists and its Differentiation Using Mathematical Models

“…The data were collected from 25 regolith profiles (P1 to P25) described by Guerra (2015) and Santos (2015) in their thesis, summing up to 137 horizons and layers, developed from: granite, syenite, gneiss, schist, sandstone, and siltstone (Table 1).…”

“…The particle density (Pd) was determined in Santos (2015) by the alcohol volumetric method (Claessen, 1997) and in Guerra (2015) using the helium pycnometer method (Danielson and Sutherland, 1986). The total porosity (TP) was estimated from the values of the bulk density (soil or saprolite) and the particle density (Pd) by the equation 2:…”

“…The selective extractions of iron were done with the dithionite-citrate-bicarbonate (Fe DCB ) and the ammonium oxalate (Fe OA ) methods described in Mehra and Jackson (1960) and (1) P01-P12 (Guerra, 2015) and P13-P25 (Santos, 2015); the order of the profiles presented here is not the same as the theses. Match (paper/theses).…”

“…In Guerra (2015), P01 = P03, P02 = P02, P03 = P05, P04 = P06, P05 = P08, P06 = P09, P07 = P10, P08 = P11, P09 = P12, P10 = P13, P11 = P14, P12 = P15. In Santos (2015), P13 to P25 corresponds P01 to P13 in the thesis.…”

“…(4) Profile classification was corrected in relation to the thesis (Guerra, 2015). (Peel et al, 2007).…”