Paleosol marked by contrasting formation processes: a pilot study using digital morphometrics in Southeastern Brazil

Abstract

Although soil formation results from the interactions of five classical factors and various pedogenic processes, such interactions can drastically change over time, which may be recorded in the so-called Paleosols. These soils may be formed under contrasting environmental conditions. Given such soils are rare in Brazil, this pilot study aimed to detail the morphological, physical, chemical (including elemental content and magnetic susceptibility (MS)), and mineralogical properties of a Paleosol with contrasting paleo- and current-drainage conditions, derived from sandstone having pellitic (fine) sediments intermixed, with support via digital morphometrics. Samples were collected in a regular grid of 15x15 cm along the soil profile down to 1.8 m depth. The soil samples were analyzed via portable X-ray fluorescence (pXRF) spectrometry and for assessment of magnetic susceptibility (MS), texture, fertility, and organic matter content. The mineralogy of the clay, silt, and sand fractions were determined via X-ray diffraction analyses. The pXRF and MS results were spatialized to the Paleosol profile. The first 108 cm of the soil profile are well-drained having reddish colors, contrasting with the underlying poorly drained unity having greyish colors. The MS values were higher in the first 108 cm of the soil profile, reach ing the lowest values in the 2Cg horizon at 142–180 cm depth. Quartz was the main mineral in sand and silt fractions, while kaolinite largely dominates the clay fraction in association with hematite. In the 2Cg horizon, the absence of hematite is related with the paleoredoximorphic conditions there. The Ti/Zr ratio indicated differ ences in parent materials of the reddish and greyish units of the Paleosol. The midslope position of the Paleosol makes colluvial deposition unlikely. The combined use of pXRF, MS, morphological, physical, chemical, and mineralogical analyses provided valuable details on the variation of the contrasting formation processes of the Paleosol studied.