Paleoenvironmental characterization of the lower course of the Mourão River, Paraná – Brazil

Abstract

The study analyzed the formation process of an alluvial terrace in the lower course of the Mourão River (Engenheiro Beltrão/Paraná/Brazil) by identifying and quantifying phytoliths and freshwater sponge spicules from a 75 cm deep sediment core (¹⁴C dating = 2,770 cal BP). From 45 cm onwards, it was possible to establish phytolith indices (tree cover; adaptation to aridity and water stress). Three paleoenvironmental zones were identified: i) 75 to 65 cm - sand and clay (~ 40%), low preservation and diversification of phytoliths (< 100), no spicules - period without water/short water residence time;  ii) 65 to 15 cm - predominance of clay (max. 60%), increased diversification and concentration of phytoliths from the base to the top (max. 220), phytolith indices related to the higher proportion of dicotyledons (arboreal and shrubby), presence of mesophilic Poaceae,  phytoliths from Podostemaceae and sponge spicules (gemosclere from Oncosclera navicella) - formation of the alluvial plain; iii) 15 to 0 cm - predominance of clay (55%), concentration of phytoliths (> 250), absence of spicules and phytoliths from Podostemaceae, phytolith indices related to the presence of xerophytic Poaceae and reduction in tree cover - establishment of the terrace.