Palynological analysis of a palm swamp in Central Brazil

Abstract

A 281 cm core collected in a palm swamp in Central Brazil yielded ages from more than 32,400 radiocarbon years B.P. to about 3,500 B.P. The palynological analysis indicates changes and oscillations in the climate during this time. At more than 32,400 years B.P. a palm swamp ( Mauritia) and a gallery forest occupied the coring site and an arboreal cerrado (savannalike vegetation) occurred in the region around the studied area. This indicates a vegetation similar to the present, suggesting a warm semi-humid climate with four to five months dry season as at present. At the end of the Middle Pleniglacial (32,400 to ca. 28,300) trees and shrubs started to decline in the region. From ca. 27,000 to ca. 20,000 B.P. the palm swamp was replaced by a shallow lake and a grassland occupied the region. This phase was humid and probably colder than the preceding two phases and the present climate. The decrease of pollen, spores and algae concentration from ca. 18,500 to ca. 11,300 suggests a dry and perhaps cold phase at the end of the Pleistocene. The dryness (but not the cold) continued from ca. 10,500 until ca. 7,700 and the site was burned during this phase, suggesting the dry season was longer than at present. From 6,680 to ca. 3,500 B.P. the Mauritia swamp, the gallery forest and the arboreal cerrado started to return to the region indicating an increase in humidity. There is no record from there to the present because of present human disturbance. The occurrence of abundant charcoal particles in the older sediments suggest that natural fires burned the cerrado several times during the Pleniglacial time, although the palm swamp was not directly burned. The presence of charcoal particles in the beginning of the Holocene could be in part produced by human occupation of the land. Comparison is made with results of other palynological analyses from cerrados and savannas of northern South America.