Use of spongofacies as a proxy for river-lake paleohydrology in Quaternary deposits of central-western Brazil

Abstract

Sediments obtained by vibrocoring from Samambaia Lake (22º36’S / 53º23’W) in Taquarussu, Mato Grosso do Sul State, Brazil, were dated using thermoluminescence. Grain size and organic content analysis were performed, and the freshwater sponge spicules present in the sediments were identified. The age of sediments ranged between TL 4,350 ± 210 and TL 32,740 ± 163 years BP. Spicules of the sponges Dosilia pydanieli, Metania spinata, Radiospongila amazonensis, Corvospongilla sp. and Oncosclera sp. were found. Analyses suggest an alternation of lotic and lentic phases, in agreement with earlier lines of evidence regarding the existence of paleodrainage in the region during the Late Pleistocene to the Mid- Holocene, as well as previously described paleoclimatic conditions. This work reinforces the reliability of the use of freshwater sponge spicules as proxy data in the proposition of paleoenvironmental reconstructions. The term spongofacies is introduced for the sedimentary sequences in which spicules of freshwater sponge species predominate and indicate specific paleoenvironmental conditions.