Castro Darciléa F, De Oliveira Paulo E, Rossetti Dilce F, Pessenda Luiz C R
Universidade de São Paulo, Instituto de Geociências, 05508-080, São Paulo, SP, Brasil.
An Acad Bras Cienc. 2013 Mar;85(1):35-55. doi: 10.1590/s0001-37652013000100004.
The main goal of this study was to reconstruct the Late Pleistocene-Holocene floristic composition in an area of the northern Brazilian Amazonia, comparing the results with other Amazonian localities in order to discuss the factors that have influenced phytophysiognomic changes over this time period. The work in eastern Marajó Island at the mouth of the Amazonas River was approached based on analysis of 98 pollen and diatom samples from core data distributed along a proximal to distal transect of a paleoestuarine system. The results indicated high concentration of Rhizophora, associated with arboreal pollen grains typical of the modern Amazonian rainforest during the last 40,000 cal yrs BP. Pollen composition also included wetland herbs. Diatoms were dominated by marine and fresh water taxa. Wetland forest, mangrove and, subordinately herbs remained constant during most of the latest Pleistocene-early/middle Holocene. At 5,000 cal yrs BP, there was a distinguished change from forest and mangrove to wet grassland savanna due to sea level fluctuation. As marine influence decreased, the estuary gave rise to fresh water lacustrine and swamp environments, with establishment of herbaceous campos. A main conclusion from this study is that solely the occurrence of herbaceous savanna can not be used as a definitive indicator of past dry climates in Amazonian areas.
本研究的主要目标是重建巴西北部亚马逊地区晚更新世-全新世的植物区系组成，将结果与亚马逊其他地区进行比较，以探讨在此时间段内影响植物群落面貌变化的因素。基于对98个花粉和硅藻样本的分析开展了在亚马逊河口马拉若岛东部的研究工作，这些样本来自沿一个古河口系统从近端到远端样带分布的岩芯数据。结果表明，在过去40,000 cal yr BP期间，红树属植物高度富集，同时伴有现代亚马逊雨林典型的乔木花粉粒。花粉组成中还包括湿地草本植物。硅藻以海洋和淡水类群为主。在晚更新世晚期-全新世早期/中期的大部分时间里，湿地森林、红树林以及次要的草本植物保持稳定。在5,000 cal yr BP时，由于海平面波动，出现了从森林和红树林到湿草原稀树草原的显著变化。随着海洋影响减弱，河口形成了淡水湖泊和沼泽环境，草本草原得以建立。本研究的一个主要结论是，仅草本稀树草原的出现不能作为亚马逊地区过去干旱气候的决定性指标。
