Dry and cold climatic conditions in the formation of the present landscapein Southeastern Brazil - An interdisciplinary approach to a controversially discussed topic

New evidence on the paleoclimatic history of Southeastern Brazil is being f ound and analyzed in mostly interdisciplinary geoscientific collaboration. Specific information on the paleoclimate can be correlated with the Quatern ary processes that formed the modern landscape, which consists of a level o f stoneline-covered isolated hills and slopes leaning to the level of the S ulamericana index plain. Usually we find crystalline bedrock. The stoneline in its turn is covered by a fine sediment. In the headwater areas of the p resent river level deposits of black organic rich material are found that y ield abundant material for the analysis of fossil pollen. Pollen deposits from two regions of Southeastern Brazil, dated between 18.0 00 and > 48.000 14C yr B. P., prove clearly that the last-glacial landscape was covered by extensive areas of subtropical grasslands and small areas o f gallery forests along the rivers. The vegetation as seen from the pollen infers temperatures of 5 degrees to 7 degrees C below the present mean annu al temperatures as well as dry conditions. This evidence is supported by Th ermoluminescence dating of quartzes from clay samples that were taken from the hill tops and prove that the sediment was exposed to daylight about 20. 000 yrs B. P., thus indicating transport by wind. There is a clear mineralogical and granulometrical contrast between bedrock and the sediment cover on top of the stonelines, and finally the position of the stonelines between the weathered bedrock and the sediment on the top of isolated hills proves as definitely as all the other aspects that the s ediment cover consists of largely windtransported material. Thus the modern landscape presents forms influenced by the dry and cold cli matic conditions that all the evidence has proved. The work for this paper was done on several occasions with partners from di fferent disciplines.