Paleoenvironmental reconstitution of a coastal tropical peatland and its relationship with the Holocene sea level variation (SE Brazil)

Abstract

Peatland Histosols, due to their association with autochthonous, water-saturated environments, provide ideal conditions for preserving pollen and non-pollen palynomorphs, serving as records of paleoenvironmental changes. The vegetation and environmental dynamics of a peatland during the Middle Holocene were reconstructed through the analysis of microfossils from a 502 cm deep Histosol profile, collected in the Parque Estadual da Campina do Encantado (Campina do Encantado State Park) (PECE), on the southern coast of São Paulo, Brazil. The palynological analysis was supported by stratigraphy, elemental and isotopic geochemistry (δ¹³C, δ¹⁵N), radiocarbon dating, and multivariate statistics. Four environmental change zones were characterized over the last 7,886 cal years BP. The first stage (7,886–5,657 cal years BP) showed a high concentration of diatoms and other marine elements, indicating seawater influence and the formation of an estuarine-lagoon environment, where vegetation was submerged by paleolagoon sediments, corroborating a Holocene Marine Transgression event. The second stage (5,657–3,771 cal years BP) marked the maximum rise of relative sea level (RSL), with the highest concentration of marine diatoms, as well as freshwater algae and brackish water diatoms, revealing a mixohaline environment and the persistence of the estuarine-lagoon system. By the end of this stage, marine diatoms disappeared, suggesting the paleolagoon’s disconnection from the sea. The third stage (3,771–2,247 cal years BP) was marked by the transformation of the paleolagoon into a freshwater lagoon, its sedimentation, and the establishment of arboreal vegetation in a water-saturated environment, where organic matter deposition led to the paludification process and the formation of peatland (Permanently Flooded Restinga Forest). The final stage (2,247 cal years BP − present) saw a decrease in herb pollen and an increase in tree and shrub pollen, with taxa indicating the presence of Periodically Flooded Restinga Forest, the most representative vegetation physiognomy today.