Paleoenvironmental dynamics of low-order paleovalleys in the Late Quaternary – Palmas/Caçador Summit Surface – Southern Brazil

Abstract

The Quaternary dynamics of landscapes in the subtropical continental region of Brazil is not still well understood. Pedostratigraphic records of low-order paleovalleys (paleovalley heads and 1st- and 2nd-order paleovalleys) of the Palmas/Caçador summit surface serve as important resources for the identification of landscape component responses (relief, soil, sediment, and vegetation) of plateau areas of southern Brazil in the light of environmental changes driven by climatic variations of the Late Quaternary. We integrated litho-, pedo-, allo- and chronostratigraphic descriptions with carbon stable isotope analysis, phytoliths indices, and 14C and OSL dating. We found that at >44.86 ky BP, there was a change in the hydrodynamics of 2nd-order perennial channels (humid climate) controlled possibly by tectonics. At ~28.35 to <44.86 ky BP, there was a predominance of progressive pedogenesis (Johnson's Model) in wet and cold climates with minimal erosion and stable landscape components. At >23.69 to ~28 ky BP, regressive pedogenesis in dry climate began with a predominance of erosion by overland flows. At >2.60 to ~23.69 ky BP, full regressive pedogenesis occurred under a continuous climate regime of drier characteristics punctuated by millenary climatic fluctuations to a wetter regime of between ≤4.60 and 19.77 ky BP, echoing the results postulated by the Knox's model. During this period, the most pronounced modifications to the landscape were made with a change in vegetation from Campo Cerrado to Campo Limpo; with changes in erosion patterns caused first by overland flows and then earthflows/debris flows; and with the gradual silting (filling and burying) of gullies, valley heads and 1st and 2nd order valley bases. Since 2.60 ky BP the area returned to a predominance of progressive pedogenesis in wet and cold climates. Finally, we found that at the local scale, low-order basins (<4th-order) quickly responded to climate changes and millenary fluctuations with changes in vegetation and changes in the course of pedogenesis and morphogenesis. These results suggest that the responses of low-order bases landscapes to regional climatic changes should be considered in the formulation of evolutionary models of subtropical landscapes.