The geochemistry of the pedogenized coverings of the Dissected Plateau of the Uruguay River – States of Santa Catarina/Rio Grande do Sul, Brazil

Abstract

Superficial deposits constitute an important sedimentary record with data that may be indicative of current and past environmental conditions. With the aim of analyzing the degrees of weathering affecting pedogenic surface formations and establishing relationships between pedological and geomorphological factors in the genesis and transformation of natural landscapes, this study investigated physical and geochemical evidence of 22 weathering mantles (pedogenized coverings) in Volta Grande, an upper valley stretch of the Uruguay River on the border between the states of Santa Catarina and Rio Grande do Sul, Brazil. Sedimentary and pedogenic materials were sampled from lower and middle/upper slope positions. Morphological descriptions of pedological profiles, particle size analyses, and ¹⁴C and OSL dating analyses substantiated the analyses of these materials. The study also resorted to geochemical analyses (Ki and STI indices) of pedogenic horizons representative of the study area’s weathering mantles, geomorphologically represented by the Dissected Plateau of the Uruguay River. The results indicate that, regarding the context of active morphogenesis of the upper Uruguay river valley, the studied pedogenized coverings show a low degree of weathering in the soil profiles sited at lower and upper slope positions, including hilltops and alluvial plains. This situation is consistent with the context of pedological rejuvenation during the entire Holocene, without, however, significant morphological and textural differentiation from the predominantly silty clay deposits.