No abstract

This article presents a palynological study carried out on a sediment core from a peat deposit in Serra de Botucatu, in SÃo Paulo State, southeastern Brazilian Plateau. This region has been covered by grassland vegetation and forest patches throughout the recorded period. AMS radiocarbon dating plus palynological analysis of 27 samples from the sediment core allowed the recognition of several environmental changes that took place during the last 33,000 yr recorded in the core. The relationship between sedimentation rates and changes in the abundance of plants recognized through their pollen record, particularly a few important indicator species, provided the paleoenvironmental history for the Serra de Botucatu region, allowing the identification of changes in climate conditions and comparison with other regions in Brazil. One of the most remarkable features of this record is the cold and humid conditions during the Last Glacial Maximum, which diverges from previous interpretations for southeastern and southern Brazil but is in good agreement with paleoclimatic data from trace elements from cave stalagmites in SE Brazil. No indications of human impacts on the vegetation were found in this record.

Analysis of organic sediments from a swamp forest on the coastal plain of São Paulo State (southeastern Brazil) has been carried out. Diatom and pollen contents from the same samples were analysed. This study allowed reconstruction of the regional paleoenvironment during the Late Holocene. From at least 4400 to 3250 yr BP the site was a lagoon surrounded by a relatively open forest. At ca. 3250 yr BP, after the retreat of the sea, a swamp forest occupied the area. This swamp forest remains until the present day. It was locally altered during a short period between ca. 1400 and 775 yr BP when, due to a rise in groundwater, a fresh water lake or marsh was formed. The climate was similar to the present during the whole Late Holocene, except for three slightly more humid episodes: 3250-2600, around 2000, and 1400-775 yr BP. No human impact on the vegetation was recorded during the Late Holocene. Our results show that sea level was higher than the present zero level from 4400 to 3250 yr BP, contradicting a widely accepted relative sea level trend that suggests that at least two important negative sea level oscillations occurred during the Holocene (4100-3800 and 3000-2700 yr BP). Conversely, these results tend to confirm more recent studies that propose a continuously declining relative sea level trend. Comparison of our data with those from 24 sites situated in southeastern, southern and central Brazil show that the more humid episodes recorded at Cananéia-Iguape might be correlated with El Niño like events. Trends in climatic evolution during the Late Holocene are opposite at north and south of 20ºS latitude.

A análise palinológica e diatomológica do perfil sedimentar de uma turfeira da região do Baixo Ribeira de Iguape (estado de São Paulo, Brasil), mostrou mudanças significativas nas condições ambientais. Antes de 3.250 anos AP a região era recoberta por águas salobras em conexão com o mar, depois ela foi ocupada por uma floresta paludosa. A penetração do mar está relacionada à transgressão marinha que culminou há 5.100 anos AP. A descida do nível do mar foi progressiva de 5.100 anos AP até o presente, sem oscilações notáveis. Esta mudança radical das condições ambientais pode explicar a distribuição geográfica dos sítios arqueológicos da região, em particular a presença de sambaquis a 50 km da costa.

-SPONGE SPICULES AND CHANGES IN SEA LEVEL IN THE IGUAPE REGION, SOUTHEAST BRAZIL. Sponge spicules recorded in peaty sediments obtained by coring (520 cm depth) was analyzed in order to detail the paleoenvironmental changes in the lower course of the Ribeira de Iguape River (Iguape/SP -24º34'17"S/47º37'33"W) in southeast Brazil. The sediment core was dated at three horizons using radiocarbon dating as follows: (i) 6,240± 30 years BP at 430 cm; (ii) 4,500± 25 years BP at 225 cm and (iii) 2,920±25 years BP at 145 cm. Gemmoscleres of the continental sponge Oncosclera navicella (Carter) and microscleres of Corvoheteromeyenia sp. were identified, as were spicules of marine sponges, but these could not be determined to the species level. The variations in the content between of marine and continental sponge spicules indicated: (i) a phase with a predominance of freshwater flows when sea level was lower than at present prior to 6,240 years BP; (ii) a phase of marine transgression that started at least 6,240 years BP; (iii) a phase with large fluctuations in sea level between 6,240 and 4,500 years BP; and (iv) a phase with a predominance of freshwater flows between 4,500 and 2,920 years BP. The results also suggest a possible change in the direction of the channel of the Ribeira de Iguape River to the west of the study site during the Holocene.