Paleovegetation and paleoclimate of "Vereda de Aguas Emendadas", central Brazil

The palynological analysis from an extensive palm swamp on top of a plateau, close to the city of Brasilia (15 degrees 34'S and 47 degrees 35'W), has shown a sequence of vegetational and climatic changes in the last 30,500 years. The area is the headwater of tributaries of the main Brazilian hydrographic basins: Amazonian (north), Parana (south), and Sao Francisco (east). At the base of the analysed core there is a clay deposit devoid of palynomorphs. At 30,480 +/- 100 yr BP, peal started to form in the area. Between 25,790 +/- 70 and ca. 24,200 yr BP, pollen grains and algal remains are abundant, indicating a marsh surrounded by open cerrado and patches of gallery forest on top of the plateau. Between ca. 24,000 and 21,450 +/- 100 yr BP, vegetation was denser than at present, with abundant marsh plants and the occurrence of some trees of a cooler climate, suggesting a climate more humid than at present and probably cooler. The absence of Mauritia pollen during that time indicates the palm swamp ("vereda") characteristic of the present-day area did not occur. The drastic decrease in concentration and diversity of palynomorphs from ca. 21,000 yr BP until 7,220 +/- 50 yr BP suggests a dry climatic phase that resulted in drier, more seasonal climate and the desertification on top of the plateau. Shortly after 7,000 yr BP, the abundance of pollen grains and spores increased and Mauritia pollen occurred in the sediments, suggesting increased humidity and the beginning of the palm swamp; from ca. 5,600 yr BP onwards, the present types of vegetation grew on top of the plateau: arboreal cerrado, gallery forest, and palm swamp. The climate of this phase was similar to that of the present. Charcoal particles are found throughout the record but they increase mainly after 2,600 yr BP, suggesting at least three extensive episodes when the local vegetation was burned. The sequence of events found here follows, in general, the same pattern described for other areas in central Brazil. However, the dry climatic phase is more strongly marked in Vereda de Aguas Emendadas, probably due to its location on top of a plateau. (C) 2000 Elsevier Science Ltd. All rights reserved.