História paleoambiental neopleistocena-holocena, do médio Vale do Rio Paraíba do Sul, Estado de São Paulo: com base na análise da palinoflora.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

This paper is about palynological studies realized at Paraíba do Sul river floodplain, in São Paulo. The hole made by vibro-core reached 390 cm depth. The core showed two very similar sedimentation cycles represented by sand in the basis, followed by clay and peat on the top. Besides, the second sequence presents one clay layer on the peat. The first sequence, the clay was dated from 11400-11220 cal. years B.P. in the basis (interpolated age) and from 9435 years B.P. (interpolated age) on the top; the sapric peat revealed an age from 5907 years B.P. (interpolated age). In the other sequence, the sands top was dated in 900-860 years B.P., the clays top in 706 years B.P. (interpolated age) and the hemic peat in 490-290 cal. years B.P. These sequences were interpretated like fluvial deposits channel that pass by lacustrine from oxbow lake. The dates reveal a hiatus at about 5000 years in between the cycles. In each cycles course, the palynomorphs show that the vegetation follows the channel abandonment with flora gradual stabilization and the lake sedimentation; however, the channel resume evidenced by the second cycle, it shows the interruption about the occupation and the vegetation succession. Cold times are well documented by the arboreal montane elements Araucaria, Podocarpus, Drymis, Ericaceae and Myrtaceae. The succession elements such as Alchornea, Cassia, Cecropia, Croton and Didymopanax are in all ecozones and they always show oscilations. It suggests that in any moment the vegetation in this region hit and/or stayed in climax. According to the palinoflora, the climatic conditions would have been: from 11400-11220 cal. years B.P. warm and humid, relatively drier between 9000 and 8800 years B.P. and about 5907 years B.P. (interpolated ages); from 8601 to 8696 years B.P. (interpolated ages) much cold; in between 462 and 401 years (interpolated ages) very cold too that can be related to the Little Ice Age; from 452 years B.P. the climate starts to be as similar as todays climate. The isotopic results showed that the organic matters in the first cycle are result of plants mixture from C3, C4 and phytoplankton. The second cycle results initially in phytoplankton, changes to phytoplankton and cycle C3 plants and, on the top, happens a mixture of the plants from both cycles (C3 and C4) and phytoplankton.

ASSUNTO(S)

palynology, quaternary, paraíba do sul, peat. palinologia, quaternário, paraíba do sul, turfeira geologia ambiental

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