Weathering and the formation of hillslope deposits in the tropical highlands of Itatiaia — southeastern Brazil

Deposits of cobbles and boulders found hanging on midslopes of the Itatiaia Plateau reflect tectonic reactivation and a large range of climate-controlled processes, probably including frost weathering. These processes, more efficient in detaching debris from freefaces, were replaced, at the end of the Pleistocene, by colluviation. On the lower slopes of the plateau, less coarse CI and CII colluvia evince the reworking of upslope materials freed in former phases of weathering or erosion. Interpretation of hillslope processes was based upon the sedimentological, mineralogical and micromorphological characteristics of colluvia. CI may have originated in mass movements reaching deep into the regolith. CII colluvia were probably deposited by shallow processes, which reworked initially highly evolved materials, including on the way downslope poorly weathered rock fragments. s in weathering characteristics and hillslope processes suggest variations in environmental conditions of the Itatiaia Plateau since the Late Pleistocene. Coarser deposits would be associated to the wet and cold conditions of the Last Glacial Maximum. In the end of the Pleistocene, warmer and still humid conditions would have favored weathering and mass movement processes triggering the first generation of colluvia (CI). Discontinuous stone-lines found on mid-slopes would represent a short return to colder and eventually drier conditions. In the last 8,000 years, prevailing humid climates, with temperature excursions larger than those observed at present, encompassing phases of more intense gelifraction, would explain the deposition of CII sequences. However, such variations were not sufficient to interrupt the geochemical weathering trend toward kaolinitic and gibbsitic materials that persisted after the Last Glacial Maximum. nmental fluctuations of small amplitude and a decrease in the intensity of slope denudation during the Holocene seem to follow the general trend previously recognized in the neighboring highlands of Campos do Jordمo.