AMAZONIA DURING THE LAST GLACIAL

New data on the vegetational history and Quaternary geology of Amazonia permit an improved reconstruction of past environments in Amazonia during the last glacial period. Although limited, data from Rondonia, Carajas and Guyana show that, in certain areas, savanna-type vegetation and savanna forest had replaced the rain forest during the late Pleniglacial (ca. 22,000-13,000 yr B.P.). The Amazonian forest may have been split up into one major west Amazonian and several other medium-size forest areas. This suggests a decline in rainfall of 500 to 1000 mm (a reduction of 25 to 40%). Temperatures may also have been 2-degrees to 6-degrees-C (4 + 2-degrees-C) lower than today, possibly substancially influencing Amazonian vegetation. During the humid middle Pleniglacial (55,000-26,000 yr B.P.), rivers carried a lot of water and sediment, resulting in the deposition of lower terrace sediments with one dry interruption around 40,000 yr B.P. (Carajas and Katira). In Carajas, there is evidence of dry periods ocurring at about 40,000 yr B.P., and during the early Pleniglacial (ca. 60,000 yr B.P.). Rivers carried little water and incised into the low terrace sediments during the dry late Pleniglacial. Water levels rose during the late glacial (13,000-10,000 yr B.P.) or at the beginning of the Holocene (10,000 yr B.P.). Sedimentation in (and of) the present inundation valleys commenced after that.