Interpretação paleoclimática com base na análise da fisionomia foliar de duas floras pleistocênicas, Formação Rio Claro, São Paulo, Brasil

Abstract

Paleoclimatic interpretation based on the analysis of the leaf physiognomy of two Pleistocene floras, Rio Claro Formation, São Paulo, Brazil. The Jaguariúna and Jazigo Vargem Grande do Sul fossil floras are well-preserved records of an ancestor of one of the phytophysiognomies of the Atlantic Forest, the oldest belt of tropical forest in the world. These fossil floras are associated with the Rio Claro Formation, one of the most important sedimentary records of the Pleistocene from the São Paulo State Peripheral Depression, Brazil. The main physiognomic characteristics–type of margins and leaf area – of the angiosperm leaves from these floras allowed us to carry out the reconstruction of the mean annual temperature (MAT) and the mean annual precipitation (MAP) for the moment of their deposition. The different equations used to reconstruct the MAT and the MAP are based on univariate methods known as Leaf Margin Analysis and Leaf Area Analysis. These equations indicated that the warm and humid subtropical/tropical climate under which the Jaguariúna fossil flora developed was characterized by a MAT of 22.1–22.8°C and a MAP of 566–831 mm, and also that the warm and humid subtropical climate under which the Jazigo Vargem Grande do Sul fossil flora developed was characterized by a MAT of 24.6–25.1°C and a MAP of 747–961 mm. These values indicate that, at the moment of deposition of the fossil floras of Jaguariúna and Jazigo Vargem Grande do Sul, conditions were warmer and less humid than the current ones. Therefore, it is possible to infer that these floras developed in a smaller climatic cycle, the interglacial period, during which the Rio Claro Formation was deposited. Keywords: Atlantic Forest, Pleistocene, physiognomic characteristics, angiosperm leaves, climatic cycle, interglacial period.