Paleoenvironmental Considerations of the Middle Holocene With Phytoliths in Serra do Cadeado, Paraná

Abstract

This study analyzed a sedimentary core of 130 cm depth containing about 30 cm of peaty bulk at its top, obtained from an unnamed pond located at Morro da Pedra Branca, in the municipality of Ortigueira, Paraná. The phytoliths present in the peaty sediment were identified and quantified. Three transects on three different microscopy slides were analyzed using an optical microscope with 40x zoom in each sample, totaling 13 samples.  At 30 cm depth, the sedimentary bulk was dated at 5,372 years cal. BP using 14C.. The following phytolith indexes were calculated: Tree Cover Density, Water Stress and Humidity. The results enabled us to conclude that the pond had a slow sedimentation rate (~ 1 cm/179 years). The most frequent morphotypes were from the Poaceae family (Rondel, Saddle, Bilobate), inferring predominantly grassland vegetation, with absence of the Arecaceae family (palm trees), a high producer of phytoliths of the Globular echinate morphotype. The phytolith assemblages found in the area indicate drier conditions in the Middle Holocene, moving toward to more humid climate conditions today. The interpretations corroborate other paleoenvironmental studies already carried out in the states of Paraná and Mato Grosso do Sul, where the existence of a drier period in the Middle Holocene has been demonstrated.