Sponge spicules in peaty sediments as paleoenvironmental indicators of the Holocene in the upper Paraná River, Brazil

Abstract

The presence of freshwater sponge spicules was analyzed in samples of peaty sediments obtained in two vibro-cores from the Taquarussu region (22º30'S, 52º20'W, Mato Grosso do Sul State, Brazil). Four samples were dated by 14C method as 11,570±80 years BP (depth 240 cm), 9,710 ± 80 years BP (depth 220 cm), 4,610 ± 70 years BP (depth 130 cm) and 4,010 ± 80 years BP (depth 29-35 cm). The freshwater sponges detected were Heterorotula fistula Volkmer-Ribeiro & Motta, 1995, Radiospongilla amazonensis Volkmer-Ribeiro & Maciel, 1983, Corvospongilla seckti Bonetto & Ezcurra de Drago, 1966 and Trochospongilla repens Hinde, 1888. The first two species are typical of lentic environments and the other two of lotic habitats. These two pairs of species are found in alternating throughout the length of core 2, indicating flooding pulses, which may be responsible for the peat formation and accumulation along the river Esperança marginal embayments during the Holocene. There is also evidence of a wetter period between 4,610 and 4,010 years BP. The results corroborate the palynological studies previously produced for the region. This is the first dated fossil record of Heterorotula fistula and Trochospongilla repens.