Lithology plays a fundamental role in rock weathering and erosion, and in landscape evolution. When weathering‐ and erosion‐prone lithologies are protected from erosion by more resilient rock types (e.g., quartzites and banded iron formations) unusual weathering products result. At the Southern Espinhaço Range, Minas Gerais, Brazil, bauxitic weathering profiles are found in a unique geomorphological–lithological–climatic setting. Resistant quartzites acted as a barrier against erosion of interbedded hematite‐phyllite lenses, channelling solution flows and facilitating the formation of deep weathering profiles. The long‐term exposure of the hematite‐phyllites under alternating wet and dry tropical climates favoured widespread bauxitization. Here we investigate the geochemical, mineralogical, geochronological and micromorphological signatures of scaffolded bauxites in order to reconstruct their evolutionary history. Our data suggest that recurrent aluminium and iron mobilization within the profiles were mainly driven by mineral dissolution‐reprecipitation mediated by bioturbation and the influx of vegetation‐derived organic species. (U–Th)/He geochronology of Al‐goethite reveals that bauxitization started at least since the Lower Miocene, with important intensification of weathering in the Upper Miocene and Lower Pleistocene. The adjacent resilient quartzites acted as scaffolds for bauxitization and supported the preservation of more erodible weathering profiles developed over phyllites. Surface waters that could not infiltrate into the impermeable adjacent quartzites preferentially infiltrated into the more weathereable phyllites, enhancing their porosity and permeability, further enhancing weathering. The evolutionary history of Southern Espinhaço Range bauxites suggests a new model of bauxitization in ancient land surfaces evolution underlain by quartzites, where erosion‐prone lithologies are scaffolded by resilient quartzites and survive long‐term weathering with minimum erosion, producing bauxites.

<p>Bauxites associated with quartzite karsts have not been previously reported.  In the Southern Espinhaço Range, Southeastern Brazil, bauxitic duricrusts reveal a unique geological-geomorphological setting. The spatial relationship between hematite-phyllites and quartzites and their different strengths play a key role in the development of thick bauxite profiles. The quartzites, resistant to physical and chemical denudation, scaffold the more easily eroded phyllites, protecting the later from physical erosion and allowing long-term – tens of millions of years – chemical weathering to transform phyllites into bauxites. We investigate the geochemical, mineralogical, geochronological and micromorphological signatures of bauxites in order to reconstruct their evolutionary history. Our data reveal periods of intense aluminum and iron dissolution-precipitation triggered by the strong bioturbation, revealing a crucial role for vegetation in bauxite evolution. (U–Th)/He geochronology of Al-goethite reveals bauxitization peaks in the Upper Miocene and Lower Pleistocene, during periods of higher rainfall. We identify a ferruginous duricrust that preceded bauxitization, suggesting perhaps an even more protracted history of weathering, now partially erased by the later-stage bauxitization. Our findings show that the elevated landscape positions and effective drainage into the exposed bedrock were crucial for ferruginous duricrusts to be chemically dismantled, leaving essentially a bauxitic duricrust residue. The chemically and mechanically resilient quartzites of the Southern Espinhaço Range were the main scaffolds that permitted bauxitization of the hematitic phyllites. A new model of bauxitization scaffolded by quartzites is revealed by this study.</p>