Late quaternary landscape evolution in the Atlantic Plateau (Brazilian highlands): Tectonic and climatic implications of fluvial archives

Abstract

This paper identifies and discusses the major phases of relief evolution resulting from fluvial processes during the Late Quaternary in the Quadrilátero Ferrífero (QF) region (Atlantic Plateau) and contextualises them as strong indicators of the past tectonic and climatic influences on landscape evolution in the Brazilian highlands. Seven regional phases of fluvial level development (terraces and modern floodplains) were identified based on geomorphological and stratigraphic aspects and dated between 83 ka and the present. Although older records occur in some valleys (up to ~140 ka), they are poorly preserved and, therefore, ambiguous in interpretation. River valleys in the QF are generally narrow and deeply dissected, favouring intense erosion processes, thus inhibiting the preservation of Early and Middle Quaternary fluvial archives. Most of the seven phases identified were followed by periods of river downcutting into bedrock. However, river incision rates vary significantly and indicate that the Paraopeba River catchment belongs to a more active tectonic block. There was an association of the regional phases with climatic oscillations that may have influenced the rhythms of the fluvial incision. Driest/coldest periods were marked by the formation of fluvial depositional successions with duricrusts. Repeated formation of terraces with conglomeratic duricrusts may be related to lower rates of river incision in some valleys. Some other factors, such as the existence of knickpoints, the size of each river catchment and its position in the regional river system (trunk river or tributary), as well as in the regional tectonic arrangement, may have influenced the capacity of the rivers to respond differently to the same climatic and tectonic regional events.