Exploratory assessment of sedimentary provenance and pedogenesis: implications for sedimentary landscape

In humid tropical climates, the evolution of sedimentary landscapes is primarily controlled by intense chemical weathering and pedogenesis, often obscuring the boundary between sedimentary provenance and soil formation. A key question persists regarding the origin of sandy surface layers: is it a sedimentary cover from the Quaternary or an in-situ product of intense pedogenesis? To investigate this interplay, an integrated pedological and sedimentological assessment was conducted along a catena on the Rio Claro Planation Surface, where four soil profiles were sampled from a slope adjacent to an isolated topographic depression. The approach here proposed sought to elucidate the genesis of sandy material capping hilltops and conduct an exploratory assessment along a flattened sedimentary landscape. Analytical methods included soil macromorphology, X-ray diffraction (XRD), X-ray fluorescence (XRF), grain-size analysis, and quartz grain microtextural analysis. The profiles are dominated by kaolinite, gibbsite, and Fe-Al oxides, with quartz as the primary residual mineral. High chemical weathering indices (CIA, CIW > 97%) and a low Desilication Index (DI) attest to an advanced stage of chemical alteration. Quartz grains in the surficial sandy layer display microtextures indicative of both mechanical transport (impact, abrasion) and, more critically, intensive chemical dissolution, with the latter becoming more pronounced with depth and overprinting primary sedimentary features. These findings confirm that the sandy material capping the landscape is a pedogenetic residue from the prolonged and intense lateritic weathering of the Piramboia Formation sandstones. This autochthonous model of landscape evolution, driven by prolonged pedogenesis under tectonic stability and a humid tropical climate, best explains the thorough homogenization of the original sedimentary sequence.