Reconstrução paleoambiental de um depósito sedimentar em Turvo-Paraná, utilizando fitólitos, análises isotópicas (δ13C) e datações absolutas 14C

Abstract

The research is the analysis of a testimony sediment (44 cm), recovered close to the urban area of Turvo-Paraná, in a remnant of Araucaria Forest, analysis was performed of the assembly of phytoliths every 2 cm (22 samples), for both samples were subjected to heating with potassium hydroxide - KOH (10%) and was subsequently made by density separation using zinc chloride (2.2 g/cm³), were used 50 l of material for mounting the blades with Entellan ®. There quantification of 200 phytoliths identifiable by sequence, was also performed, to estimate concentrations of phytoliths. From the score, we calculated the rates of adaptation to aridity (Iph), climatic index (Ic) and moisture content (Iu), these indices are calculated based on the relationships of phytoliths from different subfamilies of Poaceae. 14C datings were performed at two different depths, to 44 cm dating reached 14,553 Cal yr BP and 22 cm 6090 Cal yr BP. The analyzes of the isotopic signals show that the testimony varies from -19.0‰ to -21 base 5 cm to 10‰ showing insignificant change in a gradual way and along the profile. It was possible to establish the presence of two phases as to changing climatic conditions for the sedimentary deposit, Phase I starts at 14,553 Cal yr BP (44 cm) up to 24 cm, prior to 6090 Cal. years BP, in an environment with predominance of drier climatic conditions, as evidenced by high rate of adaptation to aridity, low moisture content and low phytoliths indicative of water stress, Phase II is characterized by a gradual increase in humidity, low adaptation aridity index and a isotopic enrichment, featuring a wetter climate and/or high moisture available in the soil. Interpretations corroborate studies in the state of Paraná, Mato Grosso do Sul and Minas Gerais.