A 5200-Year History of Amazon Rain Forest

Abstract

The explosion crater (maar) Lake Kumpaka in the western Amazon basin of Ecuador has yielded an 18.6 m sediment core spanning 5200 radiocarbon years. Sedimentary stratigraphy and pollen analysis provide the first record of rain forest climate and vegetation at a site undisturbed by riverine process. Deeper sediments were deposited very rapidly, apparently as a result of a 500-year episode of drier climate that led to massive slumping or rapid erosion about 4000 years ago. A complex history of local storms is preserved through the upper part of the record as textural banding. A three-zone pollen history is recognized, with bound- aries at 3300 and 900 years BP. All three pollen zones are taken to represent facies of intact tropical rain forest. A large influx of pollen of the colonizing trees is present at all intervals, but the remaining pollen is of a diverse array of rain forest trees. About 350 pollen taxa are recognized, but only about 100 can be named. Changes in the pollen diagram synchronous with the postulated flooding event of northern Ecuadorian Amazonia 1300-800 years ago are apparent, but the palaeoecological significance of the changes cannot be assessed satisfactorily with the present data. It is possi- ble that the regime of high precipitation in northern Ecuador was contem- poraneous with a drier climate at Kumpaka, suggesting that the two sites may be on opposite sides of a climatic divide. The pollen record demonstr- ates that a complex history of Amazonian rain forest is preserved in lake sediments, despite the prevailing animal pollination mechanisms.