Paleogeografia e Paleoambientes do baixo curso do rio Ivaí-PR

Abstract

The paleoenvironmental studies constitute a challenge to the investigative capacity of man, as they seek to reconstruct the past environment. For this purpose, they primarily use proxies like phytoliths and isotopic signals left in the soil by plants. From this perspective, the research focused on the recovery, identification and quantification of phytoliths, and sponge spicules and diatoms, aiming to paleogeographic and paleoenvironmental reconstruction. The study focused on a soil profile in Formação Caiuá called Trench Reserve (TR), and sediments of Ivaí Terrace (TI), both in the region of Douradina - PR. Along with this identification / quantification, were determined in TR: a) δ13C of soil, averaging -25,2 (C3 plants) across profile, b) two intervals dated by 14C AMS (at the University of Georgia / USA ) in 10,195 years Cal. AP 2δ (210-220cm) and 5963 years Cal. AP 2δ (140-150cm). The method used to recover the phytoliths was based on treatment with HCl and suspension ZnCl2 (density 2.35 g/cm3). The analysis results in IT enabled reconstruct the environment in three phases, as follows: i) the presence of active channel, ii) abandonment of channel and floodplain formation, iii) formation of Terrace. In the point of TR, the environment was reconstructed in two phases: i) environmental conditions slightly drier than today, under the control of forest in 10,195 years AP Cal; ii) wetter conditions to at least 5963 years AP Cal. The interpretations in IT correlate with other studies conducted near the study area noting changes in the course of this river in the Pleistocene. In TR, the occurrence of forest in this area generate hypotheses about the presence of forest refuges in the lower Ivaí river valley in the transition from the Pleistocene to the Holocene, and throughout the Holocene.